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Text

Table of Contents

Praise

Dedication

Title Page

Contents

Acknowledgments

1. What to Do Next

2. Evolving a Good Guess

3. The Janitor’s Dream

4. Evolving Intelligent Animals

5. Syntax as a Foundation of Intelligence

6. Evolution on-the-Fly

7. Shaping Up an Intelligent Act from Humble Origins

8. Prospects for a Superhuman Intelligence

Recommended Reading

Notes

Index

About the Author

ACKNOWLEDGMENTS

Helpful discussions with Derek Bickerton, Iain Davidson, Daniel C. Dennett, Stephen Jay Gould, Katherine Graubard (who suggested the book’s title), Marcel Kinsbourne, Elizabeth Loftus, Jennifer Lund, Don Michael, George Ojemann, Duanne Rumbaugh, Sue Savage-Rumbaugh, Mark Sullivan, and the late Jan Wind are reflected at multiple places in this book. Bonnie Hurren kindly pointed me to the Piagetian definition of intelligence.

The editors at Scientific American, John Rennie, Jonathan Piel, and Michelle Press, were very helpful (a short version of my intelligence argument appeared in their ‘Life in the Universe’ special issue of October 1994; well-tuned paragraphs from it are scattered throughout this book), as was Howard Rheingold at Whole Earth Review (the last part of the last chapter appeared in their Winter 1993 issue).

Among the others I must thank for their editorial suggestions are Lynn Basa, Hoover Chan, Lena Diethelm, Dan Downs, Seymour Graubard, the late Kathleen Johnston of San Francisco, Fritz Newmeyer, Paolo Pignatelli, Doug vanderHoof, Doug Yanega, and The WELL’s writers conference.

Blanche Graubard, as usual, edited the book before it was inflicted on the publisher, and I have again profited from her good sense and style. Jeremiah Lyons and Sara Lippincott edited the book for the Science Masters series and made many excellent suggestions for revision.

CHAPTER 1

WHAT TO DO NEXT

It is perfectly true, as philosophers say, that life must be understood backwards. But they forget the other proposition, that it must be lived forwards.

Sören Kierkegaard, 1843

All organisms with complex nervous systems are faced with the moment-by-moment question that is posed by life: What shall I do next?

Sue Savage-Rumbaugh and Roger Lewin, 1994

Piaget used to say that intelligence is what you use when you don’t know what to do (an apt description of my present predicament as I attempt to write about intelligence). If you’re good at finding the one right answer to life’s multiple-choice questions, you’re smart. But there’s more to being intelligent – a creative aspect, whereby you invent something new ‘on the fly.’ Indeed, various answers occur to your brain, some better than others.

Every time we contemplate the leftovers in the refrigerator, trying to figure out what else needs to be fetched from the grocery store before fixing dinner, we’re exercising an aspect of intelligence not seen in even the smartest ape. The best chefs surprise us with interesting combinations of ingredients, things we would ordinarily never think ‘went together.’ Poets are particularly good at arranging words in ways that overwhelm us with intense meaning. Yet we’re all constructing brand-new utterances hundreds of times every day, recombining words and gestures to get across a novel message. Whenever you set out to speak a sentence that you’ve never spoken before, you have the same creativity problem as the chefs and poets – furthermore, you do all your trial and error inside your brain, in the last second before speaking aloud.

We’ve lately made a lot of progress in locating some aspects of semantics in the brain. Frequently we find verbs in the frontal lobe. Proper names, for some reason, seem to prefer the temporal lobe (its front end; color and tool concepts tend to be found toward the rear of the left temporal lobe). But intelligence is a process, not a place. It’s about improvization, where the ‘sweet spot’ is a moving target. It’s a way, involving many brain regions, by which we grope for new meanings, often ‘consciously.’

The more experienced writers about intelligence, such as IQ researchers, steer clear of the C word. Many of my fellow neuroscientists avoid consciousness as well (some physicists, alas, have been all too happy to fill the vacuum with beginner’s mistakes). Some clinicians unintentionally trivialize consciousness by redefining it as mere arousability (though to talk of the brain stem as the seat of consciousness is to thereby confuse the light switch with the light!). Or we redefine consciousness as mere awareness, or the ‘searchlight’ of selective attention.

They’re all useful lines of inquiry but they leave out that activism of your mental life by which you create – and edit and re-create – yourself. Your intelligent mental life is a fluctuating view of your inner and outer worlds. It’s partly under your control, partly hidden from your introspection, even capricious (every night, during your four or five episodes of dreaming sleep, it is almost totally out of control). This book tries to fathom how this inner life evolves from one second to the next, as you steer yourself from one topic to another, as you create and reject alternatives. It draws from studies of intelligence by psychologists, but even more from ethology, evolutionary biology, linguistics, and the neurosciences.

There used to be some good reasons for avoiding a comprehensive discussion of consciousness and the intellect. A good tactic in science, especially when mechanistic-level explanations don’t help structure your approach to a fuzzy subject, is to fragment the problem into bite-sized pieces – and that is, in some sense, what’s been going on.

A second reason was to avoid trouble by camouflaging the real issues to all but insiders (maintaining deniability, in the modern idiom). Whenever I see words that have everyday meanings but also far more specific connotations used only by insider groups, I am reminded of code names. Several centuries ago, an uncamouflaged mechanistic analogy to mind could get you into big trouble, even in relatively tolerant Western Europe. Admittedly, Julien Offroy de La Mettrie didn’t merely say the wrong thing in casual conversation: this French physician (1709–1751) published a pamphlet in which he wrote of human motivations as if they were analogous to energy-releasing springs inside machines.

That was in 1747; the year before, La Mettrie had fled to Amsterdam from France. He had written a book, it seems, entitled The Natural History of the Soul. The Paris Parliament disliked it to the point of ordering all copies burned.

This time, La Mettrie took the precaution of publishing his pamphlet, entitled Man à Machine, anonymously. The Dutch, considered the most tolerant people in Europe, were scandalized and tried with a vengeance to discover who the pamphlet’s author was. They nearly found out, and so La Mettrie was forced to flee once more – this time to Berlin, where he died four years later, at the age of forty-two.

Though he was clearly ahead of his time, La Mettrie didn’t invent the machine metaphor. That’s usually ascribed to René Descartes (1596–1650), writing a century earlier, in his De Homine. He too had moved to Amsterdam from his native France, at about the same time that Galileo was getting into trouble with the Vatican over the scientific method itself. Descartes didn’t have to flee Holland, as did La Mettrie; he took the precaution, one might say, of publishing his book a dozen years after he was safely dead.

Descartes and his followers weren’t trying to banish all talk of spirits; indeed, one of their characteristic concerns was to identify exactly where in the brain lay the ‘seat of the soul.’ This endeavor was a continuation of a scholastic tradition that focused on the big reservoirs of cerebrospinal fluid inside the brain called the ventricles. Religious scholars of five hundred years ago thought that the subdivisions of the soul were housed in these cavities: memory in one; fantasy, common sense, and imagination in another; rational thought and judgment in a third. Like the bottle with the genie inside, the ventricles were supposedly containers for spirits. Descartes thought that the pineal gland was a better locale for the seat of government, on the grounds that it was one of the few brain structures that didn’t come in pairs.

Here at the fin de millennium, though there are theocratic countries where using code words would still be a good idea, we are generally more at ease when it comes to machine metaphors for mind. We can even discuss principled grounds for disputing any analogy of mind to machine. Minds, the argument goes, are creative and unpredictable; the machines we know are unimaginative but reliable – so machines such as digital computers initially seem like an unreasonable analogy.

Fair enough. But what Descartes established was that it was useful to talk of the brain as if it were a machine. You tend to make progress that way, peeling away the layers of the onion. Even if there is ‘something else’ hidden beneath the obscuring layers, the scientist tentatively assumes that there isn’t anything fundamentally unknowable, in order to test the alternative explanations. This scientific tactic – not to be confused with a scientific conclusion – has produced a revolution in how we see ourselves.

Mechanistic approaches to mind were, for a long time, missing an essential ingredient: a bootstrap mechanism. We’re used to the idea that a fancy artifact such as a watch requires an even fancier watch designer. It’s common sense – just as Aristotle’s physics still is (despite being wrong).

But, ever since Darwin, we’ve known that fancy things can also emerge (indeed, self-organize) from simpler beginnings. Even highly educated people, as the philosopher Daniel Dennett notes in the preface to Darwin’s Dangerous Idea, can be uncomfortable with such bootstrapping notions:

Darwin’s theory of evolution by natural selection has always fascinated me, but over the years I have found a surprising variety of thinkers who cannot conceal their discomfort with his great idea, ranging from nagging skepticism to outright hostility. I have found not just lay people and religious thinkers, but secular philosophers, psychologists, physicists, and even biologists who would prefer, it seems, that Darwin were wrong.

But not all. Only a dozen years after the 1859 publication of On the Origin of Species, the psychologist William James was writing letters to friends about his notion that thought involved a darwinian process in the mind. More than a century later, we are only beginning to flesh out this idea with appropriate brain mechanisms for darwinism. For several decades, we have been talking about the selective survival of overproduced synapses. And that’s only the cardboard version of darwinism, analogous to carving a pattern into a wood block. Now we’re also seeing brain wiring that could operate the full-fledged darwinian process, and probably on the milliseconds-to-minutes timescale of consciousness.

This shaping-up-the-improbable version of darwinism involves generating lots of copies of certain cerebral firing patterns, letting the copies vary somewhat, and then letting those variants compete for dominance over a work space (rather as those variants called bluegrass and crabgrass compete for my backyard). The competition is biased by how well those spatiotemporal firing patterns resonate with the ‘bumps and ruts in the road’ – the memorized patterns stored in the synaptic strengths. Such Darwin Machines are a favorite topic of mine, as you will see, but let us first get some idea of what intelligence is – and isn’t.

A useful tactic for exploring intelligence, one that avoids premature definitions, is the journalist’s who-what-where-when-why-how checklist. I’ll start with what constitutes intelligence and when intelligence is needed, simply because the term is used in so many ways that it is easy to talk at cross-purposes, just as in the case of consciousness. Narrowing intelligence down a little, without throwing out the baby with the bathwater, is the task of the next chapter, after which I’ll tackle levels of explanation and the ‘consciousness’ confusions.

A little ice-age perspective turns out to be important when exploring the evolutionary why aspects of intelligence, particularly in discussing our hominid ancestors. Alaska’s coastline is the best place to see the ice age still in action; Glacier Bay, some fifty miles long, was totally filled with ice only two hundred years ago. Now it’s populated with enough harbor seals, kayaks, and cruise ships to cause traffic jams. In the context of Glacier Bay, I’ll raise the question of how jack-of-all-trades abilities could possibly evolve, when efficiency arguments tell us that a streamlined specialist (the lean, mean machine beloved of economists) always does better in any one climate. The short answer? Just keep changing the climate, abruptly and unpredictably, so that efficiency doesn’t remain the name of the game.

In the fifth chapter, I’ll discuss the mental machinery needed for parsing sentences complicated enough to require syntax. Many observers, myself included, suspect that the big boost in intelligence during hominid evolution was provided by those logical structures needed for a grammatical language (and also useful for other tasks). Chimpanzees and bonobos (these ‘chimpanzees of the pygmies’ are a distinctly different ape, now called by the name that the natives were once said to use) provide some essential perspective for judging the role of language in intelligence and consciousness. Stones and bones are all that’s left of our actual ancestors, but our distant cousins show us what ancestral behaviors might have been like.

The sixth chapter takes up the problems of convergent and divergent thinking in the darwinian context. Small neurobiology meetings, such as one I recently attended down on Monterey Bay, certainly illustrate convergent thinking – all those specialists trying to find the one right answer, as the search for memory mechanisms narrows down. But divergent thinking is what creative people need to discover a scientific theory, or write a poem, or (at a more mundane level) dream up all those wrong answers to use in multiple-choice exams for testing convergent thinking. Whenever a neuroscientist proposes an explanation for a memory storage mechanism, questioners from the audience promptly suggest several alternative explanations – ones they’ve dreamed up on the spot with divergent thinking. So, how do we shape up a novel thought into something of quality, without the equivalent of the guiding hand that shapes up a lump of clay into a pot? The answer may be in the title of chapter 6. ‘Evolution on-the-Fly.’ The same darwinian process that shapes up a new species in millennia – or a new antibody during the several weeks of an immune response – may also shape up ideas on the timescale of thought and action.

In the penultimate chapter, I’m going to venture past the analogy of mental processes to other known darwinian processes and propose how (the mechanistic how of the physiologist) our brains can manipulate representations in such a way as to cause a copying competition, one that can be darwinian and so shape up randomness into a good guess. This descent into cerebral codes (which, like the bar codes in supermarkets, are abstract patterns that stand in for the real thing) and cerebral circuitry (particularly the circuitry of the superficial cortical layers responsible for the brain’s inter-office mail) has provided me with my best glimpse so far of mechanisms for higher intellectual function: how we can guess, speak sentences we’ve never spoken before, and even operate on a metaphorical plane. It even provides some insight into the big step up from proto-language to Universal Grammar.

This cerebral version of a Darwin Machine is what, in my opinion, will most fundamentally change our concept of what a person is. Like the Dodo in Alice in Wonderland, who said it was better to demonstrate the game than to explain it, I will walk you through the darwinian process in some detail, as it shapes up a thought and makes a decision. Trying to describe intelligence is not, I am happy to report, as difficult as describing how to ride a bicycle; still, you will understand the description a lot better if you develop a feel for the process rather than being satisfied with an abstract appreciation (what you’ll get from chapters 6 and 8, if you skip over my favorite chapter).

In the final chapter, I will come back up for air and summarize the crucial elements of higher intelligence described in earlier chapters, focusing on those mechanisms that an exotic or an artificial intelligence would require in order to operate in the range spanning clever chimps to human musical genius. I will conclude with some cautions about any transition to superhuman intelligence, those aspects of arms races that the Red Queen cautioned Alice about – why you have to keep running to stay in the same place.

[One doctrine] depicts man as an induction machine nudged along by external pressures, and deprived of all initiative and spontaneity. The second gives him the Spielraum [room to play] to originate ideas and try them out. Learning about the world means, on the first view, being conditioned by it; on the second view, it means adventuring within it.

J. W. N. Watkins, 1974

CHAPTER 2

EVOLVING A GOOD GUESS

While innate processing, instinctive behavior, internally orchestrated motivation and drive, and innately guided learning are all essential and important elements of an animal’s cognitive repertoire, they are not likely to be part of that more esoteric realm of mental activity that we associate with thinking, judgment, and decision making. But what is thought, and how are we to recognize its operation in other creatures within that most private of organs, the brain? What behavioral criteria can permit us to distinguish between the true thought that we are wont to believe goes into our aesthetic, moral, and practical decision making on one hand, and the intricate programming that can create the illusion of thought in at least certain other animals? Or could it be, as advocates of artificial intelligence suspect, that all thought, including ours, is just the consequence of clever programming?

James L. Gould and Carol Grant Gould, The Animal Mind, 1994

Intelligence gets framed in surprisingly narrow terms most of the time, as if it were some more-is-better number that could be assigned to a person in the manner of a batting average. It has always been measured by a varied series of glimpses of spatial abilities, verbal comprehension, word fluency, number facility, inductive reasoning, perceptual speed, deductive reasoning, rote memory, and the like. In recent decades, there has been a tendency to talk about these various subtests as ‘multiple intelligences.’ Indeed, why conflate these abilities by trying to boil intelligence down to a single number?

The short answer is that the single number seems to tell us something additional – while hazardous when overgeneralized, it’s an interesting bit of information. Here’s why: Doing well on one kind of intelligence subtest never predicts that you’ll do poorly on another; one ability never seems to be at the expense of another. On the other hand, an individual who does well on one such test will often perform better than average on the other subtests.

It’s as if there were some common factor at work, such as test-taking ability. The so-called ‘general factor g’ expresses this interesting correlation between subtests. The psychologist Arthur Jensen likes to point out that the two strongest influences on g are speed (such as how many questions you can answer in a fixed amount of time) and the number of items you can mentally juggle at the same time. Analogy questions A is to B as C is to [D, E, F]) typically require at least six concepts to be kept in mind simultaneously and compared.

Together, they make high IQ sound like a job description for a high-volume short-order cook, juggling the preparation of six different meals at the same time, hour after hour. Thus, high IQ might be without significance for the kind of lives that most people lead, or important only on those occasions demanding a quick versatility. A high IQ is usually necessary to perform well in very complex or fluid jobs (for example, being a doctor), and it’s an advantage in moderately complex ones (secretarial or police work), but it provides little advantage in work that requires only routine, unhurried decision making or simple problem solving (for example, for clerks and cashiers, whose reliability and social skills are likely to be far more important than their IQ).

IQ is certainly one fascinating aspect of intelligence, but it doesn’t subsume the others; we shouldn’t make the mistake of trying to reduce the subject of intelligence to a simple number on a rating scale. That would be like characterizing a football game in terms of one statistic, say, the percent of passes completed. Yes, over the football league as a whole, winning does significantly correlate with that statistic, but there’s a lot more to football than just percent-passes-completed; some teams win without completing a single pass, by emphasizing other strengths. IQ does correlate with ‘winning’ in many environments, but it’s not what the intelligence game is all about, any more than successful passing is what football is all about.

I think of intelligence as the high-end scenery of neurophysiology – the outcome of many aspects of an individual’s brain organization which bear on doing something one has never done before. We may not be able to explain intelligence in all its glory, but we now know some of the elements of an explanation. Some are behavioral, some are neurophysiological, and some are evolutionlike processes that operate in mere seconds. We even know something about the self-organizational principles that lead to emergent stuff – those levels-in-the-making, as when (to anticipate a later chapter) categories and metaphors compete for cerebral territory.

The big issue for understanding intelligence isn’t who has more but what intelligence is, when it’s needed, and how it operates. Some of what intelligence encompasses are cleverness, foresight, speed, creativity, and how many things you can juggle at once. More later.

Did our intelligence arise from having more of what other animals have? Just looking at the brain and judging it by its size, as if it were a contaloupe, is apt to be misleading. Only the outer shell, the cerebral cortex, is markedly involved in making novel associations. Most of the brain’s bulk comes from the insulation around the ‘wires’ that connect one part of the brain to another; the more insulation, the faster the messages flow. As animals become larger and distances greater, more insulation is needed to speed up transmission and keep the reaction times short; this insulation increases the bulk of the white matter even when the number of cortical neurons stays the same.

An orange peel is only a small part of an orange, and our cerebral cortex is even thinner: about 2 mm, the thickness of two dimes. Our cortex is extensively wrinkled; were it to be peeled off and flattened out, it would cover four sheets of typing paper. A chimpanzee’s cortex would fit on one sheet, a monkey’s on a postcard, a rat’s on a stamp. Were we to mark off a fine grid on the flattened surface, we’d find about the same number of neurons in each little grid square in all cortical regions (except primary visual cortex which, in all binocular animals, has lots of additional small neurons). So if you need more neurons for a particular function, you need more cortical surface area.

We tend to talk of demanding visual tasks for food-finding as ‘enlarging’ monkey visual cortex in later generations but not its auditory cortex, with evolution tending to produce a bulge here – and then, when some other selection pressure comes into play, a bump there. But there is now a strong suspicion that any non-olfactory natural selection for more brain space (say vision) results in more brain space for all the other functions as well – that it is often developmentally difficult to make regional enlargements of the brain. So enlarge one, enlarge them all may be the general rule, rather than an exception.

And if one evolutionary route to a free lunch isn’t enough, here’s another: new functions often first appear by making spare-time use of some preexisting part of the brain. Brain regions are, to some extent, multifunctional, resisting our attempts to label them. So, what preexisting functions might be most relevant to the quantum leap in cleverness and foresight during hominid evolution from the apes? Most would say language. I will argue that a ‘core facility’ common to language and to planning hand movements (and used in our spare time for music and dance) has even greater explanatory power than a special facility only for language functions.

Intelligence is sometimes described as a patchwork of know-how and know-what areas in the brain, all those perceptual mechanisms so sensitive to expectations. That is surely true, but if your definition of intelligence is so broad as to include most things that the brain does, such a formulation doesn’t advance your understanding any more than extending consciousness to cover plant life does. Catalogs are not explanations, no matter how interesting the list or how much the topics may need inclusion in an introductory course. It’s not my purpose to eliminate perceptual mechanisms from intelligence but to illuminate the underpinnings of guessing well and those levels of self-organization that produce stratified stability.

The Spanish physician Juan Huarte defined intelligence in 1575 as the ability to learn, exercise judgment, and be imaginative. In the modern literature, intelligence often connotes the capacity for thinking abstractly, for reasoning, and for organizing large quantities of information into meaningful systems. Not only does this sound like academics trying to define themselves, but it aims too high to be a definition that is readily extended to other animals. A better place to start for the what aspects is the animal behavior literature, where good operational definitions of intelligence center on versatility in problem solving.

Bertrand Russell once wryly noted, ‘Animals studied by Americans rush about frantically, with an incredible display of hustle and pep, and at last achieve the desired result by chance. Animals observed by Germans sit still and think, and at last evolve the solution out of their inner consciousness.’ Besides being a British commentary on the scientific fashions of 1927, Russell’s quip about problem-solving cleverness illustrates the usual false dichotomy between insight and random trial and error. Insight is, beyond argument, intelligent behavior. ‘Mere randomness’ is not, in the usual scheme of things; but we are thereby misled – of which more later.

I like Jean Piaget’s emphasis, that intelligence is what you use when you don’t know what to do. This captures the element of novelty, the coping and groping ability needed when there is no ‘right answer,’ when business as usual isn’t likely to suffice. Intelligent improvising. Think of jazz improvisations rather than a highly polished finished product, such as a Mozart or Bach concerto. Intelligence is about the process of improvising and polishing on the timescale of thought and action.

The neurobiologist Horace Barlow frames the issue a little more tightly, and points us toward experimentally testable aspects, by saying that intelligence is all about making a guess – not any old guess, of course, but one that discovers some new underlying order. ‘Guessing well’ neatly covers a lot of ground: finding the solution to a problem or the logic in an argument, happening upon an appropriate analogy, creating a pleasing harmony or a witty reply, correctly predicting what’s likely to happen next.

Indeed, you routinely guess what comes next, even subconsciously – say, in listening to a narrative or a melody. Getting a crying child to fill in the last word of each song line is an amazingly effective distraction, seen in many cultures. Subconscious prediction is often why a joke’s punch line or a P.D.Q. Bach musical parody brings you up short – you are surprised by the mismatch. Being a little wrong can be amusing, but substantial environmental incoherence is unpleasant, as when a day filled with job insecurity, noise, erratic drivers, and too many strangers leaves you frustrated, because of the frequent mismatch between what you expected and what actually happened.

Calvin’s Cure for Environmental Incoherence? Scale back the predictive challenges to a more comfortable level – not all the way into the boredom of surefire predictability but to where you’ll be right half the time. That way, you reassure yourself that you’re still competent at predicting. Perhaps that’s why, after a hard day awash in unpredictability, you tend to seek relief in ritual, music, or sitcoms – anything where you can again take pleasure in frequently guessing what comes next!

One of the beginner’s errors is to equate intelligence with purpose and complexity. Elaborate, complex behaviors initially seem like a reasonable place to look for signs of intelligence. After all, our language and foresight behaviors are surely aspects of intelligent behavior and they’re quite complex.

But many complex behaviors in animals are innate: no learning is needed as they’re wired in from birth. Such behaviors tend to be inflexible and often difficult to perform at will, just as sneezing and blushing are. These stereotyped movement patterns exhibit no more insight or understanding of purpose than does a computer program. They’re a set piece.

Both innate and learned behaviors can be long and complex. Consider, for example, the performance of an idiot savant, a person with enormous detailed recall but poor ability to make good use of the recollected information in a new context, by breaking the pattern into meaningful parts and recombining them. Whale song and insect nest building may be equally unintelligent.

That whales and birds link song sequences together is also not evidence of versatility. The most mindless of behaviors are often linked, the completion of one calling forth the next. Courtship behavior may be followed by intricate nest building, then segue into egg laying, then incubation, then the various stereotyped parental behaviors. Indeed, the more complex and ‘purposeful’ the behavior is, the further it may be from intelligent behavior, simply because natural selection has evolved a surefire way of accomplishing it, with little left to chance. Learning, after all, is usually focused on far simpler things than the complex chains of all-important behaviors.

The animal might understand its own behavior no better than we understand our yawn, or our tendencies to hug and kiss (clearly seen in bonobos and chimpanzees). Most animals in most contexts don’t appear to have much need for ‘understanding’ – in our sense of appreciating the underpinnings – and they don’t attempt innovations except by modest variations and a slow learning process. It’s as if thinking were a little-used backup, too slow and error-prone to be depended on in the normal course of things.

The best indicators of intelligence may be found in the simpler but less predictable problems that confront animals – those rare or novel situations for which evolution has not provided a standard response, so that the animal has to improvise, using its intellectual wherewithal. While we often take ‘intelligence’ to mean both a broad range of abilities and the efficiency with which they’re done, it also implies flexibility and creativity – in the words of the ethologists James and Carol Gould, an ‘ability to slip the bonds of instinct and generate novel solutions to problems.’ That narrows the what field quite a lot.

In tests of convergent thinking there is almost always one conclusion or answer that is regarded as unique, and thinking is to be channeled or controlled in the direction of that answer. . . . In divergent thinking, on the other hand, there is much searching about or going off in various directions. This is most obviously seen when there are no unique conclusions. Divergent thinking . . . is characterized . . . as being less goal-bound. There is freedom to go off in different directions. . . . Rejecting the old solution and striking out in some direction is necessary, and the resourceful organism will more probably succeed.

J. P. Guilford, 1959

Aren’t-they-clever stories are what many people recall when the topic of conversation turns to intelligence. Surely a dog qualifies as intelligent, they will insist. Most such stories turn out to hinge on how well a dog understands English or reads his owner’s mind.

Ethologists and animal psychologists will patiently reply that dogs are very social animals, expert in reading body language. A dog is always looking up to his owner, in the same way that a wild dog looks to the pack leader, asking, ‘What’s next, boss?’ or emotionally seeking reassurance in a juvenile manner, hoping to elicit benevolence. Talking to domesticated dogs plays into these innate tendencies, though your words per se may not carry the message. People don’t realize how much information is conveyed by the tone of voice and body language of the substitute leader (that’s you). If you read today’s newspaper headline to your dog in the same tone of voice, and with the same glances and postures, as you use to ask him to fetch your slippers, it might work just as well in evoking the desired behavior.

In many cases, there isn’t much to confuse the dog. The setting itself (people, places, situations, objects present) provides most of the information the dog needs to respond appropriately to a command. Most dogs have limited repertoires, and it’s therefore easy for them to guess correctly. Training a dog to fetch a dozen different items on command is a more difficult proposition, simply because it becomes harder for the dog to guess your intentions.

If you are confident that your dog understands words per se, you might try getting someone else to speak the words from another room over an intercom; this will eliminate most of the situational cues. Many smart animals cannot pass this severe a test of understanding spoken words, not even some extensively tutored chimpanzees who readily respond to graphical symbols. But dogs do pass the lesser test of performing the desired action most of the time, when the situation is familiar and the choices are obvious from the context.

The size of the response repertoire is one important factor in intelligence. Dogs have many instinctive behaviors, such as herding and alarm barks; they can learn many more. Even their communicative repertoire can reach impressive numbers with extensive training, as the psychologist Stanley Coren observes.

[My pet] dogs have a receptive language of about sixty-five words or phrases and about twenty-five signals or gestures for a total receptive vocabulary of about ninety items. They have a productive language of about twenty-five vocalizations and about thirty-five bodily gestures for a total productive vocabulary of about sixty items. They show no evidence of syntax or grammar. If they were human children, they would be demonstrating the level of language customary at around eighteen to twenty-two months of age. [Bonobos] that have learned [a sign or other symbolic] language can obtain [comprehension] scores equivalent to a child of around thirty months of age.

Speed of learning is also related to intelligence; one reason that dogs and dolphins achieve a wider repertoire of behavior with training is that they learn faster than cats usually do. So, ‘intelligence’ is quite a composite of other things, and many mental abilities are relevant. Perhaps it is making effective combinations of them that better constitutes intelligent behavior.

An animal’s selection of appropriate behavior may be the key to sorting out claims of animal intelligence. In many of the aren’t-they-clever animal stories, the animal isn’t thinking for itself, but merely responding to a command. Piaget’s element of creativity, in the face of an ambiguous task, is usually missing – except during the animal’s playful antics.

The scientific literature on nonhuman intelligence tries to cope with innovation, but since most putatively intelligent animal actions are not repeated actions, it’s hard to avoid a series of anecdotes (indeed, there’s a wonderful book of them about apes, Machiavellian Intelligence). The usual scientific hazards of anecdotal evidence can be somewhat reduced by emphasizing comparisons between species. For example, most dogs can’t untangle their leashes from around trees, but a chimpanzee seems to have what it takes. A leash-style snap fastener on the door will suffice to keep most small monkeys inside their cage, even if they can reach the fastener to fiddle with it. But the great apes can figure the fastener out, so you must use padlocks – and not leave the key lying around! Chimpanzees can practice deception: a chimp can guess what another animal is likely to be thinking, and can exploit this knowledge. But most monkeys don’t seem to have the mental machinery to deceive one another.

To many people, the essence of intelligence is such creative cleverness. When an animal is especially versatile at solving problems or inventing new moves, we consider that behavior to be particularly intelligent. But human intelligence is judged by additional standards.

When I tried cut this ‘creative cleverness’ definition of intelligence on one of my colleagues, he was dubious and started citing examples of the terminally clever.

You know, someone asks you how intelligent a certain person is, and you say, ‘Well, he’s certainly clever’ By this, you mean that he talks a good line – he’s versatile at improvising tactics in the short run but doesn’t follow through on his projects and lacks longer-term virtues, such as strategy, perseverance, and good judgment.

OK, I agreed, it also takes foresight to be truly intelligent. And chimps don’t think much about tomorrow, as far as anyone can tell from their behaviors, even if they occasionally do some planning on the half-hour timescale.

So maybe the flexible future is a human addition to ape intelligence. Intelligence also involves some imagination, I continued, remembering a high IQ group for whom I once gave an after-dinner speech. I had been surprised – in view of the fact that everyone in the audience had scored high on intelligence tests – at how unimaginative one of them was, and then I abruptly realized that I had always thought that IQ and imagination went hand in hand. But imagination contributes to intelligence only when shaped up into something of quality.

Patients with hallucinations are pretty imaginative, too, but that doesn’t necessarily make them highly intelligent.

It just goes to show that IQ measures only some aspects of what we more commonly understand as intelligent behavior. The very nature of IQ exams tends to preclude tests of creativity or the ability to make plans.

If I ever conceive any original idea, it will be because I have been abnormally prone to confuse ideas . . . and have thus found remote analogies and relations which others have not considered! Others rarely make these confusions, and proceed by precise analysis.

Kenneth J. W. Craik, The Nature of Explanation, 1943

Innovative behaviors are usually not new units: instead, they are composed of a novel combination of old elements: a different stimulus evokes a standard behavior, or some new combination of movements is used in response. How is sensory/movement innovation related to intelligence?

The sheer quantity of building-block types could be important. Cataloging the sensory and movement repertoires, as Stanley Coren did for dogs, is a useful exercise as long as one doesn’t take the stimulus-response dichotomy too literally. Sometimes responses appear without apparent triggers; there’s a lot of fiddling around, as when chimps strip the leaves off a branch for no apparent reason. Often the stimulus-response aspect is muted; the animal will seek out sensations as part of shaping the response. With those cautions, consider some classic examples of stimulus-response.

Many animals have sensory templates, which they try out for size (and shape) on what they see, rather like a child trying out a number of cookie cutters on the baked assortment of Christmas cookies, to see which (if any) fits a particular cookie. Baby birds, for example, crouch when a hawk flies overhead, a behavior suggesting that they were born with the image of a hawk wired into their bird brains. The reality is quite different: initially, they crouch when any sort of bird flies above them. They then come to recognize the sorts of birds they see every day; as a shape becomes familiar, they cease the response to it. Because of such habituation, they eventually crouch only in response to infrequently seen shapes, such as exotic birds that are just passing through – and to predators, such as hawks, which are infrequent because there aren’t very many of any species at the top of the food chain.

So the crouch is a response to novelty, not to a pre-wired ‘alarm’ search image. It’s as if the child found a misshapen cookie that none of the cookie cutters fitted, and was thereby distressed.

Composers note that while pure overtones (as from the flute) are relatively soothing, random overtones (as in heavy metal or the raspy voices of some singers, such as Mick Jagger) seem to signal threat or alarm, and I’ve long thought that the disordered sensations produced by nerve injuries are often perceived as painful (rather than merely nonsensical) for the same reason.

Besides sensory templates for familiar sights and sounds, animals also have familiar movement schemas, among which they pick and choose. A cormorant can decide whether to cruise around underwater in search of another meal, or fly away to another pond, or spread its wings to dry (cormorant feathers lack the oil that duck feathers have), or just stand around – presumably by consulting the weightiness of its wings, the fullness of its stomach, its sexual drives, and so forth. Decision making is something that all animals do; it is usually an economistlike weighing of sensations and drives, followed by a standard behavior from its repertoire, as modified by the circumstances.

Of course, we humans often do something similar in deciding on a restaurant, taking into account its menu, parking, cost, travel and waiting time, and ambiance – and somehow comparing all these factors with those of other restaurants. While such weighing of choices seems especially conscious, purposeful, and intentional, choice per se does not imply an extensive mental life – not of the kind we associate with creating novel additions to the list of choices for what to do next (‘Suppose there are any northern Vietnamese restaurants in town?’).

Curious, I took a pencil from my pocket and touched a strand of the [spider] web. Immediately there was a response. The web, plucked by its menacing occupant, began to vibrate until it was a blur. Anything that had brushed claw or wing against that amazing snare would be thoroughly entrapped. As the vibrations slowed, I could see the owner fingering her guidelines for signs of struggle. A pencil point was an intrusion into this universe for which no precedent existed. Spider was circumscribed by spider ideas; its universe was spider universe. All outside was irrational, extraneous, at best raw material for spider. As I proceeded on my way along the gully, like a vast impossible shadow, I realized that in the world of spider I did not exist.

Loren Elseley, The Star Thrower, 1978

Sometimes an animal tries out a new combination of sensory template and movement during play, and finds a use for that combination later on. So perhaps we should add play to our list of intelligence attributes.

Many animals, however, are playful only as juveniles. Being an adult is a serious business, with all those mouths to feed, so adults don’t have the time or inclination to fool around. A long juvenile period, characteristic of apes and humans, surely aids versatility because of the accumulation of useful combinations. In addition, some evolutionary trends, including domestication of animals, tend to cany over juvenile traits into adulthood – so that, too, might increase versatility.

You don’t learn just from your own experiences. You can copy the actions of others, as Japanese monkeys were observed to copy one inventive female’s technique for washing the sand off food. You may avoid what seems to spook others, even if you haven’t been personally threatened by it, and such ‘superstitious’ behavior can be passed on. The original reason for ‘Don’t step on the crack in the sidewalk’ may be lost, but the cultural transmission between generations continues for centuries, sufficient unto itself.

A wide repertoire of ‘good moves,’ of course, makes foresight a lot easier. Foresight initially seems simple, almost too simple to be a requirement for high intelligence. But that’s because we confuse foresight with species-specific seasonal behaviors.

Squirrels hoarding nuts for winter seems to be the standard example of planning ahead in the animal kingdom. And we now know how such things work. The hormone melatonin, released from the pineal gland during the hours of darkness, serves to warn of the approach of winter. Longer and longer nights result in the release of increasing amounts of melatonin, which in turn triggers food hoarding and new fur coats. It doesn’t take much of a brain to do that kind of ‘planning.’

There are, of course, other behaviors created by the brain’s initial wiring which serve to set things up for months ahead. Mating behaviors have the effect of producing offspring after a considerable delay. Seasonal migrations come with innate brain wiring or are learned by juveniles and become mindless adult rituals. Of course, such behavior isn’t the result of planning at all. Seasons are eminently predictable; and over the millennia, plants and animals have been shaped by evolution to sense the signs of approaching winter by means of the innate surefire mechanisms: hoarding nuts probably ‘feels good’ as the days shorten, much as does following the gradient of a sexual pheromone in the air.

Planning on the timescale of a few minutes is seen in some instances, but, as you’ll see, none should probably be called planning. Keeping a movement plan on hold – as when caged monkeys who have watched food being hidden are able to locate it twenty minutes later, when they are let out of their cages – is sometimes called ‘planning.’ But is it simply the memory of an intention? Another disputed type of evidence arises from spatial maneuvering. When bees are kidnapped and carried in a windowless container to a random location several kilometers distant and then released, they quickly set off on the optimal path to an unseen favorite food source. Is this planning, or are they just referencing memories of horizon profiles? Before setting off in the correct direction, they fly a few circles first to get oriented; they may well be scanning the horizon for clues.

Perhaps we should say that planning involves something novel, closer to the way in which we procrastinate, figuring out what can safely be put off until tomorrow (or avoided altogether). Indeed, I’d reserve the term for the assembling of multiple stages of the move in advance of action – not when you organize the later stages after getting the initial moves in motion, which goal-plus-feedback can accomplish.

Alas, there is surprisingly little evidence for this kind of multistage planning in the great apes, even in their frequent behaviors. None of the termite-fishing chimps, as the polymath Jacob Bronowski once pointed out, ‘spends the evening going round and tearing off a nice tidy supply of a dozen probes for tomorrow.’ Although wild chimps often seem to arrive at a distant fruit tree just as the fruit is ripening, how much of that is migration ritual and how much is all-in-advance planning of a unique route?

For most of your movements, such as raising a coffee cup to your lips, there is time for improvisation en route. If the cup is lighter than you remembered, you can correct its trajectory before it hits your nose. Thus, a complete advance plan really isn’t needed; a goal and periodic piecewise elaboration will suffice. You get started in the general direction and then correct your path, just as a moon rocket does. Most ‘planning’ stories involving animals fit into that mold.

Multistage planning is perhaps best seen in an advanced type of social intelligence: making a mental model of someone else’s mental model, then exploiting it. Imagine a chimp that cries ‘food’ in a place where there is no food, and then quietly circles back through the dense forest to where it actually saw the food earlier. While the other chimps beat the bushes at the site of the food cry, the chimp that uttered it gets to eat all the food rather than having to share it.

What’s really difficult is to make a detailed advance plan in response to a unique situation – like those leftovers in the refrigerator and what might go with them. It requires imagining multiple scenarios, whether you are a hunter plotting various approaches to a deer or a futurist spinning three scenarios bracketing what an industry might look like in another decade. Compared to apes, we do a lot of that: we are even capable of occasionally heeding the eighteenth-century admonition of Edmund Burke, ‘The public interest requires doing today those things that men of intelligence and goodwill would wish, five or ten years hence, had been done.’

So multistage planning for novel situations is surely an aspect of intelligence – indeed, one that appears greatly augmented in the transition from the ape brain to the human brain. But knowledge is, I think, a commonplace.

A base of existing knowledge is, of course, required for versatility, foresight, and creativity. You can’t be a poet or scientist without a good vocabulary, but definitions of intelligence that stress knowledge or memory’s synaptic mechanisms really do miss the mark; they’re mistaken reductionism – the practice of reducing something to its fundamental constituents, which for present purposes is carried a few steps too far. This is the mistake, as I explain in the next chapter, that the consciousness physicists often make.

For example, Shakespeare didn’t invent the vocabulary he used. He invented combinations of those words, most notably the metaphors that allow relationships to be imported from one level of discourse to another. In a similar manner, much intelligent behavior consists of new combinations of old things.

Deductive logic is another what aspect of intelligence – at least, of the human variety. Philosophers and physicists have, I suspect, been unduly impressed with the human faculty for logical reasoning. Logic might consist of guessing the underlying order of things, à la Horace Barlow, but only in situations where an unambiguous underlying order exists to be guessed (mathematics being the prime exemplar). Piecewise approximation, as with the guessing needed for long division, could operate subconsciously so rapidly as to seem like a leap to the finished ‘logical’ product. Could it be that logic is more a property of the subject matter than of the mental process – that guessing is the name of the game during mental calculations as well as during creative thinking?

The what list can be extended further, both for what is and what isn’t. But I am going to focus hereafter on Barlow’s guessing-at-order aspect and more generally on Piaget’s improvisation problem of how to proceed when the choice isn’t obvious. I realize that this excludes certain uses of the word ‘intelligence,’ as when we talk of intelligent design or military intelligence, but the guessing aspect buys us such a broad range of intelligence connotations that we will do well to organize analysis around it – provided we can avoid consciousness confusions and inappropriate levels of explanation.

The mixture of hormone-driven aggression, sexual and social lust for power, deceit and gamesmanship, friendship and spite, and good-and ill-natured fun ring familiar chords . . . there is no reasonable way to account for much of primate (and especially chimpanzee) behavior without assuming that these animals understand a great deal about what they are doing and seeking to do, and are inferring almost as much as humans do about the intentions and attitudes of their peers.

James L. Gould and Carol Grant Gould, The Animal Mind, 1994

CHAPTER 3

THE JANITOR’S DREAM

Human consciousness is just about the last surviving mystery. A mystery is a phenomenon that people don’t know how to think about – yet. There have been other great mysteries: the mystery of the origin of the universe, the mystery of life and reproduction, the mystery of the design to be found in nature, the mysteries of time, space, and gravity. These were not just areas of scientific ignorance, but of utter bafflement and wonder. We do not yet have all the answers to any of the questions of cosmology and particle physics, molecular genetics and evolutionary theory, but we do know how to think about them. . . . With consciousness, however, we are still in a terrible muddle. Consciousness stands alone today as a topic that often leaves even the most sophisticated thinkers tongue-tied and confused. And, as with all of the earlier mysteries, there are many who insist – and hope – that there will never be a demystification of consciousness.

Daniel C. Dennett, Consciousness Explained, 1991

As Charles Mingus said about jazz, you can’t improvise from nothing, you have to improvise from something. The Romans’ phrasing was Ex nihilo nihil fit. Creating a novel plan of action has to start somewhere and then refine things. The two greatest examples of creativity in action, species evolution and the immune response, both utilize a darwinian process to shape up crude beginnings into something of quality. But confusions about consciousness (not to mention confusions about levels of mechanisms) usually lead us astray when we attempt to apply darwinism to our mental lives. That’s probably why more than a century passed with so little progress on mental darwinism.

In the last chapter, I discussed something of what intelligence is and isn’t. Here I am going to attempt the same thing for consciousness, hoping to head off repetitions of those arguments that have sidetracked William James’s idea. There is wide overlap between the connotations of consciousness and intelligence, though the C word tends to refer to the waking-aware aspect of our mental lives, while intelligence tends to refer to the imagination or efficiency of our mental lives. Bear in mind that the higher types of intellect may actually require conscious (and therefore subconscious) processing.

How should we approach explaining the unknown? It is well to keep overall strategy in mind, especially whenever attractive shortcuts are offered as explanations by those whom the philosopher Owen Flanagan terms ‘the new mysterians.’ Using Dennett’s epigrammatic definition of a mystery, consider for a moment those physicists who are speculating about how quantum mechanics might have a role in consciousness, might provide ‘free will’ an escape route from ‘determinism’ via quantum mechanical processes down at the subcellular level, in the thin microtubules that often cluster near synapses.

I’m not going to take the space needed to do justice to their best-selling arguments (or rather the arguments of their best-selling books), but when you consider how little they actually encompass (let alone explain) of the wide range of themes involved in consciousness and intelligence, you might feel (as I do) that they’re just another case of ‘much ado about very little.’

Moreover, as studies of chaos and complexity have been teaching us, determinism is really a nonissue, suitable only for cocktail party conversational gambits and hardly in need of a quantum mechanical escape clause. With some notable exceptions (I call them ecclesiastical neuroscientists, after the great Australian neurophysiologist John C. Eccles), neuroscientists seldom talk in this way; indeed, we rarely engage in any sort of word games about consciousness.

It’s not for lack of interest; how the brain works is, after all, our primary preoccupation. Over our beers after a hard day at the neuroscience meetings, we tell each other that while we may not have wide-ranging explanations of consciousness yet, we do know what kinds of explanations don’t work. Word games produce more heat than light, and the same is true of explanations that simply replace one mystery with another.

Neuroscientists know that a useful scientific explanation for our inner life has to explain more than just a catalog of mental capabilities. It also has to explain the characteristic errors that the consciousness physicists ignore – the distortions of illusions, the inventiveness of hallucinations, the snares of delusions, the unreliability of memory, and our propensities to mental illnesses and seizures rarely seen in other animals. An explanation has to be consistent with many facts from the last century of brain research – with what we know about consciousness from studies of sleep, strokes, and mental illness. We have numerous ways of ruling out otherwise attractive ideas; I’ve heard a lot of them in thirty years of doing brain research.

There are various angles along which to cut the cake of our mental lives. I tried focusing on consciousness in The Cerebral Symphony. One reason that I’m going to hereafter avoid a discussion of consciousness in favor of intelligence underpinnings is that considerations of consciousness quickly lead to a passive observer as the end point, rather than someone who explores, who adventures within the world. You can see that in the many ‘consciousness’ connotations you’ll find in a dictionary:

Capable of or marked by thought, will, design, or perception.

Personally felt, as in ‘conscious guilt.’

Perceiving, apprehending, or noticing, with a degree of controlled thought or observation. (In other words, fully aware.)

Having mental faculties undulled by sleep, faintness, or stupor: ‘She became conscious after the anesthesia wore off.’ (In other words, awake.)

Done or acting with critical awareness: ‘He made a conscious effort to avoid the same mistakes.’ (Here, ‘deliberate’ may substitute for ‘conscious.’)

Likely to notice, consider, or appraise: ‘He was a bargain-conscious shopper.’

Marked by concern or interest: ‘She was a budgetconscious manager.’

Marked by strong feelings or notions: ‘They are a raceconscious society.’ (For these last three uses, ‘sensitive’ may be substituted.)

The philosopher Paul M. Churchland has recently made a more useful list, noting that consciousness:

utilizes short-term memory (or, as it is sometimes called, working memory).

is independent of sensory inputs, in that we can think about things not present and imagine unreal things.

displays steerable attention.

has the capacity for alternative interpretations of complex or ambiguous data.

disappears in deep sleep.

reappears in dreaming.

harbors the contents of several sensory modalities within a single unified experience.

Again, this list has the passive-observer focus rather than the explorer focus, but we see the Piagetian notion of intelligence incorporated into a consciousness definition, in the ‘alternative interpretations’ item.

Among scientists, there is a tendency to use consciousness to mean awareness and recognition; for example, Francis Crick and Christof Koch use consciousness when addressing the ‘binding problem’ in object recognition and recall. But just because one word (in English) is used to denote these widely different mental faculties doesn’t mean that they share the same neural mechanism. Other languages, after all, may assign one or another of the aforementioned ‘consciousness’ connotations its own word. Crick’s thalamocortical theory is most useful for thinking about object recognition, but it doesn’t say anything about anticipation or decision making – yet those are often among the connotations of consciousness, the word he uses. It’s easy to overgeneralize, just by the words you choose. This isn’t a criticism: there aren’t any good choices until we understand mechanisms better.

By now, the reader might reasonably conclude that consciousness connotations are some sort of intelligence test that examines one’s ability to float in ambiguity. Debates about consciousness regularly confuse these connotations with one another, the debaters acting as if they believed in the existence of a common underlying entity – ‘a little person inside the head’ – that sees all. To avoid this presumption of a common mechanism for all connotations, we can use different English words for different connotations, such as when we use ‘aware’ and avoid ‘conscious.’ I usually try to do this, but there are also pitfalls when you use alternative words. That’s because of what might be termed back-translation.

Physicians, for example, try to avoid the C word by talking instead about the level of arousal that can be achieved with some shouting and prodding of the patient (coma, stupor, alertness, or full orientation to time and place). That’s fine, until someone tries to translate back into C-word terminology; yes, a person in a coma is unconscious, but to say that consciousness is at the opposite end of the arousability scale may be seriously misleading.

Worse, equating ‘conscious’ with ‘arousable’ tends to be interpreted as ascribing consciousness to any organism that can experience irritation. Since irritability is a basic property of all living tissue, plant as well as animal, this extends consciousness to almost everything except rocks; some nonscientists are already talking about plant consciousness. While this is appealing to some people and appalling to others, scientifically it is simply bad strategy (even if true). If you throw everything into the consciousness pot and mix it up, you reduce your chances of understanding consciousness.

With so many major synonyms (aware, sensitive, awake, arousable, deliberate, and more), you can see why everyone gets a little confused talking about consciousness. One often hears the word’s connotation shift in the course of a single discussion; were this to happen to the word ‘lift,’ with one speaker meaning what hitchhikers get and the other meaning an elevator, we’d burst out laughing. But when we talk about consciousness, we often fail to notice the shift (and debaters even exploit the ambiguity to score points or sidetrack the argument).

And there’s more: at least within the cognitive neuroscience community, consciousness connotations include such aspects of mental life as the focusing of attention, vigilance, mental rehearsal, voluntary actions, subliminal priming, things you didn’t know you knew, imagery, understanding, thinking, decision making, altered states of consciousness, and the development of the concept of self in children – all of which grade over into the subconscious as well, all of which have automatic aspects that our ‘narrator of consciousness’ may fail to notice.

Many people think that the narratives we tell ourselves when awake or dreaming tend to structure our consciousness. Narratives are an important part of our sense of self, and not merely in an autobiographical sense. When we play a role – as when the four-year-old engages in make-believe, playing ‘doctor’ or ‘tea party’ – we must temporarily step outside of ourselves, imagine ourselves in someone else’s place, and act accordingly. (The ability to do this is one of the more useful definitions of a sense of self.)

But narratives are an automatic part of everyday life in our own skins. Starting around the age of three or four, we make stories out of most things. Syntax is often a junior version of narrative: just the word ‘lunch’ in a sentence sends us looking for variants of the verb ‘eat,’ for the food, the place, and persons present. A verb such as ‘give’ sends us searching for the three required nouns we need to fit into roles: an actor, an object given, and a recipient. There are lots of standard relationships, with familiar roles for the players, and we guess from the context what goes into any unfilled gaps. Often we guess well, but dreams illustrate the same kinds of confabulation seen in people with memory disorders, in which bad guesses are unknowingly tolerated.

‘Perception,’ it has been recently said, ‘may be regarded as primarily the modification of an anticipation.’ It is always an active process, conditioned by our expectations and adapted to situations. Instead of talking of seeing and knowing, we might do a little better to talk of seeing and noticing. We notice only when we look for something, and we look when our attention is aroused by some disequilibrium, a difference between our expectation and the incoming message. We cannot take in all we see in a room, but we notice if something has changed.

E. M. Gombrich, Art and Illusion, 1960

A sense of self is thought to go along with a fancy mental life, so let me briefly address the common notion that self-awareness (often called self-consciousness) involves sophisticated, ‘intelligent’ mental structures.

How do you know which muscles to move in order to mimic the action of someone else – say, in order to stick out your tongue in response to seeing such an action? Do you have to see yourself in a mirror first, to make the association between that sight and the muscle commands that will mimic it?

No. Newborn humans can imitate some of the facial expressions they see, without any such experience. This suggests that innate wiring connects at least some sensory templates with their corresponding movement commands – that we’re ‘wired to imitate’ to some extent. Such wiring might explain why some animals can recognize themselves in a mirror, while others treat their mirror image as another animal, to be coaxed or threatened. Chimps, bonobos, and orangutans can recognize themselves either immediately or within a few days’ experience; gorillas, baboons, and most other primates cannot. A capuchin monkey (Cebus are the most intelligent of the New World monkeys and the best tool users) with a full-length mirror in its cage may spend weeks threatening the ‘other animal.’ Ordinarily, one animal would back down after a brief period, acknowledging the other as dominant. But in the case of the mirror monkey, nothing is ever resolved; even if the capuchin tries acting submissive, so does the other animal. Eventually the monkey begins acting so depressed at the unresolved social conflict that the experimenters must remove the mirror.

What might self-recognition involve? Actions produce expectations about what sensory inflow will result from them (so-called efference copy), and so the perfect fit of these sensory predictions with the inputs from your skin and muscles during small movements would provide a way of recognizing yourself in an image. In the case of wild animals, a perfect fit of the image’s movements with internal predictions for facial movements would certainly be unusual, since they rarely see their own face.

The issue of self-consciousness in the animal literature could revolve about something as simple as the attention paid to predictions about facial sensations. That’s part of consciousness considerations, certainly, but hardly the pivot that some would make it. Self-recognition surely involves both Horace Barlow’s guessing right and Jean Piaget’s sophisticated groping, but I’d put it on the list of things that intelligence isn’t. Self-recognition is surely more to the point than quantum fields, however.

Do the enigmas of quantum mechanics really have something to do with such conscious aspects of our mental lives? Or is the invocation of QM in the consciousness context just another mistaken instance of suggesting that one area in which mysterious effects are thought to lurk – chaos, selforganizing automata, fractals, economics, the weather – might be related to another, equally mysterious one? Most such associations certainly conflate the unrelated, and when the two areas are at opposite ends of the spectrum of enigmatic phenomena, the argument is particularly suspicious.

Reducing things to basics – the physicists’ rallying cry – is an excellent scientific strategy, as long as the basics are at an appropriate level of organization. In their reductionist enthusiasm, the consciousness physicists act as if they haven’t heard of one of the broad characteristics of science: levels of explanation (frequently related to levels of mechanism). The cognitive scientist Douglas Hofstadter gives a nice example of levels when he points out that the cause of a traffic jam is not to be found within a single car or its elements. Traffic jams are an example of selforganization, more easily recognized when stop-and-go achieves an extreme form of quasi-stability – the crystallization known as gridlock. An occasional traffic jam may be due to component failure, but faulty spark plugs aren’t a very illuminating level of analysis – not when compared to merging traffic, comfortable car spacing, driver reaction times, traffic signal settings, and the failure of drivers to accelerate for hills.

The more elementary levels of explanation are largely irrelevant to traffic jams – unless they provide useful analogies. Indeed, packing principles, surface-to-volume ratios, crystallization, chaos, and fractals are seen at multiple levels of organization. That the same principle is seen at several levels does not, however, mean that it constitutes a level-spanning mechanism: an analogy does not a mechanism make.

Quasi-stable levels make selforganization easier to spot, especially when building blocks – such as crystals – emerge. Since we are searching for some useful analogies to help explain our mental lives, it is worth examining how levels of explanation have functioned elsewhere. The tumult of random combinations occasionally produces a new form of organization. Some forms, such as the hexagonal cells that appear in the cooking porridge if you forget to stir it, are ephemeral. Other forms may have a ‘ratchet’ that prevents backsliding once some new order is achieved. While crystals are the best known of these quasi-stable forms, molecular conformations are another, and it is even possible that there are quasi-stable forms at intermediate levels – such as microtubule quantum states where the consciousness physicists would like the action to be.

Stratified stability refers to stacking up such quasi-stable levels. Life-forms involve piling up quite a few of them; occasionally they collapse like a house of cards and the higher forms of organization dissolve (which is one way of thinking about death).

Between quantum mechanics and consciousness are perhaps a dozen of these persistent levels of organization: examples include chemical bonds, molecules and their selforganization, molecular biology, genetics, biochemistry, membranes and their ion channels, synapses and their neurotransmitters, the neuron itself, the neural circuit, columns and modules, larger-scale cortical dynamics, and so on. In neuroscience, one is always aware of these levels, because of the intense rivalry between neuroscientists working at adjacent levels.

An occasional alteration in consciousness is due to widespread failures in certain types of synapses. But a more appropriate level of inquiry into consciousness is probably at a level of organization immediately subjacent to that of perception and planning: likely (in my view), cerebral-cortex circuitry and dynamic selforganization involving firing patterns within a constantly shifting quiltwork of postage-stamp-sized cortical regions. Consciousness, in any of its varied connotations, certainly isn’t located down in the basement of chemistry or the subbasement of physics. This attempt to leap, in a single bound, from the subbasement of quantum mechanics to the penthouse of consciousness is what I call the Janitor’s Dream.

Quantum mechanics is probably essential to consciousness in about the same way as crystals were once essential to radios, or spark plugs are still essential to traffic jams. Necessary, but not sufficient. Interesting in its own right, but a subject related only distantly to our mental lives.

Yet, because mind seems ‘different’ from mere matter, many people still assume – despite all the foregoing – that this means some spooky stuff is needed to explain it. But the mind should be seen as something like a crystal – comprised of the same old matter and energy as everything else, just temporarily organized in some complicated way. This is hardly a new idea; witness Percy Bysshe Shelley in the early nineteenth century:

It has been the persuasion of an immense majority of human beings that sensibility and thought [as opposed to matter] are, in their own nature, less susceptible of division and decay, and when the body is resolved into its elements, the principle which animated it will remain perpetual and unchanged. However, it is probable that what we call thought is not an actual being, but no more than the relation between certain parts of that infinitely varied mass, of which the rest of the universe is composed, and which ceases to exist as soon as those parts change their position with respect to each other.

The traffic flow patterns in brains are far more complicated than those in vehicular movement; fortunately, there are in music some similarities that we can exploit for analogies. Understanding consciousness and intelligence will require better metaphors and actual mechanisms, not steps backward into word games or spooky stuff.

Ghosts are another version of spooky stuff, and for our analysis of creative mental life it’s worth looking at what has happened to the ghost concept. Ghosts illustrate the other essential creative aspect of mind, the role of memory.

The very presence of the word ‘ghost’ in most languages suggests that quite a few people have needed to talk about inexplicable things they’ve heard or seen. Why have so many people considered ghosts to be real? Is this where the notion of an incorporeal spirit world got started?

We now know that ghosts appear real because of mistakes made in the brain. Some are trivial, everyday mistakes and others arise from abnormalities in dreaming sleep; a few are stirred up by small epileptic seizures or the pathological processes seen in psychosis. We call them hallucinations; they involve false sounds more often than false sights. The people and pets that they feature are often scrambled a bit, just as they are in the jumble of our nighttime dreams.

Remember that what you see under normal circumstances owes its stability to a mental model that you construct. Your eyes are actually darting all over, producing a retinal image of the scene as jerky as an amateur video, and some of what you thought you saw was instead filled in from memory. In a hallucination, this mental model is carried to an extreme: memories stored inside your brain are interpreted as current sensory input. Sometimes this happens when you are struggling to wake up, when the paralysis of the muscles during dreaming sleep hasn’t worn off as fast as usual. Dream elements appear superimposed on the image of real people walking around the bedroom. Or you might hear a dead relative speak to you with a familiar phrase. Half the brain is awake, and the rest is still dreaming away. With any luck, you realize this and don’t try to place a more exotic construction on it. Each of us, after all, experiences nightly the symptoms of dementia, delusions and hallucinations in the course of our dreaming sleep; we’re accustomed to discounting such things.

Yet hallucinations can also happen when you are lying awake at night, or when you are working during the day. I suspect that many of these ‘ghosts’ are just simple cognitive mistakes, like one that recently happened to me: I heard a distinct crunching sound in the kitchen, which was repeated a moment later. Ah, I thought as I continued typing, the cat is finally eating her dry food. It took another two seconds before ‘Oops, let’s play that again.’ The cat, alas, had been dead for several months, and had had a long period of being fussy about her food. What I had faintly heard turned out to be the automatic defroster on our refrigerator – it’s somewhat more subtle than the racket made by icemakers – and I had routinely made a guess about what the sound meant without fully considering the matter.

We are always guessing, filling in the details when something is heard faintly. A squeaking screen door, blown by the wind, may sound enough like the I-want-food whine of your dear departed dog for you to ‘hear’ the dog again. Once this memory is recalled, it may be very hard to replay the actual sound you heard – and so the fill-in of details from memory becomes the perceived reality. This isn’t unusual; as William James noted a century ago, we do it all the time:

When we listen to a person speaking or [we] read a page of print, much of what we think we see or hear is supplied from our memory. We overlook misprints, imagining the right letters, though we see the wrong ones; and how little we actually hear, when we listen to speech, we realize when we go to a foreign theatre; for there what troubles us is not so much that we cannot understand what the actors say as that we cannot hear their words. The fact is that we hear quite as little under similar conditions at home, only our mind, being fuller of English verbal associations, supplies the requisite material for comprehension upon a much slighter auditory hint.

This fill-in from memory is part of what’s known as categorical perception; we just call it a hallucination when we are unaware of what triggered it. Unless a sound repeats, we may not be able to compare our filled-in perception of it to the original; fortunately, where visual phenomena are concerned, we can often manage a second look and catch the mistake before getting committed to ‘the apparition.’

We now know that suggestibility (it doesn’t even take hypnosis) and stress (it doesn’t even require grieving) can augment our natural tendencies to jump to conclusions, allowing memories to be interpreted as current reality. If I’d been stressed out over something, I might not have searched for an alternative explanation until it was too late to walk into the kitchen and find the sound’s true source. Later, upon recalling that I’d ‘heard’ the dead cat, I might have fallen into the common nonscientific explanations: ‘It was a ghost!’ or ‘I must be losing my mind! Maybe it’s Alzheimer’s!’ Both possibilities are frightening, and both are highly unlikely. But if they’re the only explanations that occur to you, you may make yourself quite unhappy.

Have the scientific explanations eliminated ghosts from our culture? At least for those at the educational level of juveniles, the whole notion of ghosts remains a cheap thrill (for exactly the same reason that dinosaurs are so popular with children: they’re the potent triple combination of big, scary, and safely dead). Temporal-lobe epileptics, before a physician explains their hallucinations to them, don’t think ghosts are funny at all. Grieving relatives may wish, in retrospect, that someone had warned them about meaningless hallucinations.

In this case, science (for those whose education includes it) can eliminate what was once a frightening mystery. Science doesn’t merely empower us, as in seeding better technologies; it also helps prevent trouble in the first place. Knowledge can be like a vaccine, immunizing you against false fears and bad moves.

There’s a second neuroscience ghost story: the philosopher Gilbert Ryle’s lovely phrase ‘the Ghost in the Machine’ refers to the little-person-inside manner in which we commonly refer to the ‘us’ inside our brains. It has led some researchers to talk about the ‘interface’ between ‘mind’ and brain, between the unknowable and the knowable. Descartes’s pineal gland proposal dressed up in modern clothes by the new mysterians?

We’re now making good progress in replacing such pseudo-spirits with better physiological analogies – and even, in some cases, with actual brain mechanisms. Just as an earlier generation of scientists usefully eliminated the external ghosts, I like to think that our currently evolving knowledge about the spirit substitutes will help people think more clearly about themselves and interpret their experiences more reliably, and will help psychiatrists to interpret the symptoms of mental illness.

The consciousness physicists, with their solution in search of a problem, surely aren’t intending to tell yet another ghost story. They’re just having a good time speculating, in the manner of science fiction writers. (Still, consider how odd it would be for neuroscientists to speculate about the enigmas of physics, even those neurophysiologists – and there are many – who once took several courses in quantum mechanics). But why do these physicists take themselves so seriously, when they’re ignoring a dozen levels of organization outside their own specialties? Specialization itself is perhaps part of the answer, and it demonstrates one of the hazards of intelligence.

Specialization in science is all about asking answerable questions, which requires focusing on the details – and that takes a lot of time and energy. None of us really wanted to give up those wonderful debates we carried on as undergraduates about the Big Questions. We cared about those questions. They’re what attracted us to science in the first place. They’re not obsolete, like the ghosts. But the subsequent intellectual development of working scientists sometimes reminds me of what it’s like to be in a canal lock as the water level drops.

At least in Seattle, that’s like being in a giant bathtub with a view of waterfront, fish ladders, mountains, and spectators. Once the plug is pulled, your boat sinks, and your attention is captured by the formation of the whirlpools in the lock, which are bouncing the boats about. They’re fascinating. If you stick an oar in one, you can spawn off secondary whirlpools. Self-similarity theories suggest themselves, and so begins a digression into fractals.

Should you look up from your experiments and your theorizing in this oversized bathtub, the view of your surroundings will have become a rectangular patch of sky. Now you’re looking out from inside a big wet box, whose walls are one or two stories high. In the patch of sunlight on the north wall of the box are some shadows of the people standing topside. As in Plato’s Cave, you start to interpret the shadows on the walls, making imperfect guesses about what’s really happening up there. What appears to be two people slugging each other turns out to be nothing more than one person standing in front of the other and gesturing wildly while carrying on a conversation.

Specialization can be like that – no more big picture, unless you come up for air occasionally and admire the scenery, see the fuller context.

The price of progress is often an unfamiliarity with other levels of organization, except for those just above or below that of your specialty. (A chemist might know biochemistry and quantum mechanics, but not much neuroanatomy.) When you’ve got no data but those supplied by your own mental life, it’s easy to give fanciful interpretations of the shadows on the wall. Still, sometimes that’s the best you can do, and Plato and Descartes did it very well in their day.

But when you can do better, why be satisfied with shadow boxing? Or continue to play word games? A word itself, one eventually realizes, is a very poor approximation of the process it represents. By the end of this book, the reader will, I hope, be able to imagine some neural processes that could result in consciousness – processes that can operate rapidly enough to constitute a quick intelligence.

Describing our mental lives has a well-known hang-up, the old subjectivity snare associated with point of view, but there are two other whirlpools we will also need to navigate around.

The passive observer, poised in the mental middle between sensation and action, is a point of view that leads to all sorts of needless philosophical trouble. Partly, that’s because sensation is only half of the loop, and we thereby ignore sensation’s role in preparing for action. Some of the more elaborate couplings of sensation to action are called ‘cortical reflexes,’ but we also need to understand how thought is coupled to action in an intelligent manner, when we grope for a novel course of action. Ignoring the mental middle, as the behavioral psychologists did a half century ago, is not a long-term solution. What neuroscientists often do is investigate the preparation for movement; that gets us closer to the thought process.

We often talk of our mental activities as being subdivided among sensing, thinking, and acting phases. But trouble arises because few things happen at one point in time and space. All of the interesting actions in the brain involve spatiotemporal patterns of cellular activity – not unlike what constitutes a musical melody, where the space is the keyboard or musical scale. All our sensations are patterns spread out in time and space, such as the sensation from your fingers as you get ready to turn to the next page. So too, all our movements are spatiotemporal patterns involving the different muscles and the times at which they are activated. When you turn the page, you are activating about as many muscles as you use in playing the piano (and unless you get the timing just right, you won’t be able to separate the next page from the rest). Still, we often try to understand mental events by treating them as if they actually occurred at one place and happened at one instant.

But what’s in the mental middle is also a spatiotemporal pattern – the electrical discharges of various neurons – and we shouldn’t count on these discharges being funneled through one point in space (such as a particular neuron) and a decision being made at one point in time (such as the moment when that particular neuron discharges an impulse), as if a perception or thought consisted of playing a single note, once. I know of only one such case in vertebrates (occasionally nature makes things convenient for neurophysiologists): it’s an escape reflex in fish, conveniently channeled through a single large brain-stem neuron, whose discharge initiates a massive tail flip. But higher functions inevitably involve large overlapping committees of cells, whose actions are spread out in time, and that’s a more difficult concept. Understanding higher intellectual function requires us to look at the brain’s spatiotemporal patterns, those melodies of the cerebral cortex.

In addition to the navigational hazards, we need to select our building blocks with care, so that we don’t simply replace one mystery with another. Premature closure is the most obvious hazard in selecting building blocks – sometimes we stop surveying candidate mechanisms too early, as when we explain via spirits or quantum fields.

We must also beware of hazards having to do with the end points of an ‘explanation’: the New Age everything-is-related-to-everything and the reductionistic explanations at an inappropriate level of organization (what the consciousness physicists and ecclesiastical neuroscientists do, in my not-so-humble opinion).

Explaining mental life is a big task, and you may have noticed that this is a reasonably thin book. As noted, instead of further exploring consciousness connotations, I’m going to cut the cake differently, focusing on the structures of our mental lives that are associated with intelligence. Intelligence is all about improvising, creating a wide repertoire of behaviors, ‘good moves’ for various situations. A focus on intelligence covers a lot of the same ground as does a focus on consciousness – but it avoids many of the navigational hazards. Most important, the good-moves repertoire is an end point very different from the snapshots of passive contemplation. Certainly it’s easier to find a continuity between ourselves and the rest of the animal kingdom by addressing the subject of intelligence, compared to the muddle we generate when we try to talk about animal ‘consciousness.’ And so the next task is to take a brief look at where good guessing might have come from, in evolutionary terms.

The paradox of consciousness – that the more consciousness one has, the more layers of processing divide one from the world – is, like so much else in nature, a trade-off. Progressive distancing from the external world is simply the price that is paid for knowing anything about the world at all. The deeper and broader [our] consciousness of the world becomes, the more complex the layers of processing necessary to obtain that consciousness.

Derek Bickerton, Language and Species, 1990

CHAPTER 4

EVOLVING INTELLIGENT ANIMALS

The apes I know behave every living, breathing moment as though they have minds that are very much like my own. They may not think about as many things, or in the depth that I do, and they may not plan as far ahead as I do. Apes make tools and coordinate their actions during the hunting of prey, such as monkeys. But no ape has been observed to plan far enough ahead to combine the skills of tool construction and hunting for a common purpose. Such activities were a prime factor in the lives of early hominids. These greater skills that I have as a human being are the reason that I am able to construct my own shelter, earn my own salary, and follow written laws. They allow me to behave as a civilized person but they do not mean that I think while apes merely react.

Sue Savage-Rumbaugh, 1994

Answering the how questions is often our closest approach to answering a why question. Just remember that the answers to how mechanisms come in two extreme forms, which are sometimes known as proximate and ultimate causation. Even the pros sometimes get them mixed up, only to discover that they’ve been arguing about two sides of the same coin, so I suspect that a few words of background are needed here.

When you ask, ‘How does that work?’ you sometimes mean how in a short-term, mechanical sense – how does something work in one person, right now. But sometimes you mean how in a long-term transformational sense – involving a series of animal populations that change during species evolution. The physiological mechanisms underlying intelligent behavior are the proximate how; the prehistoric mechanisms that evolved our present brains are the other kind of how. You can sometimes ‘explain’ in one sense without even touching upon the other sense of how. Such a false sense of completeness is, of course, a good way to get blindsided.

Furthermore, there are different levels of explanation in both cases. Physiological how questions can be asked at a number of different levels of organization. Both consciousness and intelligence are at the high end of our mental life, but they are frequently confused with more elementary mental processes – with what we use to recognize a friend or tie a shoelace. Such simpler neural mechanisms are, of course, likely to be the foundations from which our abilities to handle logic and metaphor evolved.

Evolutionary how questions also have a number of levels of explanation: just saying that ‘a mutation did it’ isn’t likely to be a useful answer to an evolutionary question involving whole populations. Both physiological and evolutionary answers at multiple levels are needed if we are to understand our own intelligence in any detail. They might even help us appreciate how an artificial or an exotic intelligence could evolve – as opposed to creation from top-down design.

Everyone was admiring the bald eagles as our cruise ship slipped through the narrow passage at the top end of the Strait of Georgia, between Vancouver Island and the mainland of British Columbia. In one eagle nest after another, busy parents were feeding open mouths.

I was watching the raven, myself. It had found a clam and was trying to break open the shell to get at the innards, which were thus far successfully holding the two halves of the shell tightly together. It picked up the clam in its beak, flew several stories high, and dropped the clam on a rocky area of shoreline. This had to be repeated three times before the raven could settle down to pick his meal out of the shattered shell.

Was that instinctive behavior, or learned by observing others, or learned by trial and accidental success, or intelligently innovative? Did some ancestral raven contemplate the problem and then guess the solution? We have a difficult time seeing the intermediate steps between ‘reacting’ and ‘thinking,’ yet we also have an unwarranted faith that ‘more is better’ – that having more behavioral options is better than having fewer.

Nature is full of specialists that do one thing very well, with no frills – like a character actor who only plays one kind of role, never a repertoire. Most animals are specialists. The mountain gorilla, for example, processes fifty monotonous pounds of assorted greenery every single day. The panda’s diet is just as specialized.

In terms of finding what they like to eat, neither gorilla nor panda needs to be any smarter than a horse. Their ancestors may have needed to be intelligent in a different niche, but now the gorilla and the panda have each retreated into a niche that doesn’t require much intelligence. The same is true of the big-brained marine mammals we saw on the Alaskan cruise – animals that now make their living in more or less the same way as the small-brained fish that specialize in eating other fish.

In comparison, a chimpanzee has a varied diet: fruit, termites, leaves – even meat, when it’s lucky enough to catch a small monkey or piglet. So the chimp has to switch around a lot, and that means a lot of mental versatility. But what aids in building up a wide repertoire? One can be born with many movement programs, or learn them, or recombine existing ones in ways that cause novel behaviors to emerge suddenly. Omnivores, such as the octopus, crow, bear, and chimpanzee, have many ‘moves,’ simply because their ancestors had to switch among various food sources. Omnivores need a lot more sensory templates too – images and sounds they are in search of.

The other way to accumulate novel behaviors is through social life and play, in both of which new combinations can be discovered. A long life span ought to help both learned and innovative behaviors accumulate, and a long life span is what even the smartest of the invertebrates, the octopus, lacks. (The octopus is about as smart as a rat in some ways.) Smart animals have arisen from various branches of the vertebrate tree of species – ravens among the birds, marine mammals, bears, the primate line.

If specialization is most commonly the name of the game, however, then what selects for versatility? A fickle environment is one answer – an answer that highlights the environmental factor in natural selection. But let me start with another major contributor to sophistication: social life itself, which involves the sexual-selection aspect of natural selection.

Social intelligence is another aspect of intelligence: I refer not to just mimicry but to the challenges that social life (living in groups) poses – challenges that require innovative problem solving. The British psychologist Nicholas Humphrey, for one, considers social interaction, not tool use, to be of primary importance in hominid evolution.

Certainly a social life is an enormous facilitator of an expanded repertoire of actions. Some animals aren’t around others of their species long enough to partake of observational learning. Except for brief mating opportunities, adult orangutans seldom encounter one another, because their food sources are so sparse that it takes a large area to support a single adult. A mother with one offspring is about the biggest social group (except for the transient alliances formed by adolescent orangs), so there’s not much opportunity for cultural transmission.

Social life, besides facilitating the spread of new techniques, is also full of interpersonal problems to be solved, like pecking orders. You may need to hide food from the view of the dominant animal, in order to keep it for yourself. You need a lot of sensory templates to avoid confusing one individual with another, and a lot of memory to keep track of your past interactions with each of your colleagues. The challenges of social life go well beyond the usual environmental challenges to survive and reproduce that the solitary orang confronts. It would therefore seem that a social life is central to the cultural accumulation of ‘good moves’ – though I suspect nevertheless that a sociable dog lacks the mental potential of the solitary orang.

Natural selection for social intelligence may not involve the usual staying-alive factors commonly stressed in adaptationist arguments. The advantages of social intelligence would instead manifest themselves primarily via what Darwin called sexual selection. Not all adults pass on their genes. In harem-style mating systems, only a few males get the chance to mate, after having outsmarted or outpushed the others. In female-choice mating systems, acceptability as a social companion is likely to be important for males; for example, they need to be good at grooming, willing to share their food, and so forth. The male who can spot approaching estrus better than other males, and who can persuade the female to go off into the bushes with him for the duration of estrus, away from the other males, will stand a much better chance of passing on his genes, even in a promiscuous mating system. (And this female-choice bootstrap might improve more than just intelligence: I argue elsewhere that female choice would have been an excellent setup for improving language abilities, were a female to insist on male language ability at least as good as her own.)

[S]ocial primates are required by the very nature of the system they create and maintain to be calculating beings; they must be able to calculate the consequences of their own behaviour, to calculate the likely behaviour of others, to calculate the balance of advantage and loss – and all this in a context where the evidence on which their calculations are based is ephemeral, ambiguous and liable to change, not the least as a consequence of their own actions. In such a situation, ‘social skill’ goes hand in hand with intellect, and here at last the intellectual faculties required are of the highest order. The game of social plot and counter-plot cannot be played merely on the basis of accumulated knowledge . . . It asks for a level of intelligence which is, I submit, unparalleled in any other sphere of living.

Nicholas Humphrey, Consciousness Regained, 1984

The most frequent environmental stress likely to drive natural selection occurs in the temperate zones. Once a year, there is a period of a few months when plants are largely dormant. Eating grass (which stays nutritious even when dormant) is one strategy for getting through the winter. Another, which is much more demanding of versatile neural mechanisms, involves eating animals that eat grass. The extant wild apes all live very close to the equator; while they may have to cope with a dry season, it’s nothing like winter’s withdrawal of resources.

Climate change is the next most common recurring stress, seen even in the tropics: annual weather patterns shift into a new mode. Multiyear droughts are a familiar example, but sometimes they last for centuries or even millennia. In some cases, there are state-dependent modes of climate. We saw an example in Glacier Bay, just west of Juneau. When explorers passed the mouth of Glacier Bay 200 years ago, they reported that it was full of ice. Now the glaciers have retreated nearly 100 kilometers, and Glacier Bay is open to the sea once more. A series of large glaciers remain in the side valleys, and our ship maneuvered to within a respectful distance of one of these walls of ice: large blocks of it were breaking off and falling into the ocean, even as we watched.

In discussing the local glaciers with a geologist on board, I learned that some were advancing (those are the ones we were taken to see) but that others were in retreat. Advance and retreat at the same time, even in the same valley, and sharing the same climate? What’s going on here? I asked.

It’s as if a glacier can get stuck in ‘advance mode’ for centuries or millennia, even if the climate cools in the meantime. For example, meltwater from a few hot summers can get underneath and erode the craggy connections to the bedrock, and so the glacier, even if the melting were to stop, can slide downhill faster. That in turn causes the ice to fracture rather than flow when going over bumps, and so more vertical cracks open up. Any meltwater ponds on the surface can then drain down to the bedrock, further greasing the skids and accelerating the movement. The tall mountain of ice starts to collapse by spreading sideways. Eventually you may see glacial surges of the mile-a-month variety – but in Glacier Bay, the ice pushes into the ocean, which erodes it away in giant chunks, that in turn may float away to warmer climates to melt.

Later in the trip we saw Hubbard Glacier, a cliff of ice 5 kilometers long and taller than our ship. Great blocks of ice, loosened by the waves, would periodically crash into the sea. Off to the right side of Yakutat Bay, we could see back up Russell Fjord. Only a decade earlier, the entrance to that fjord was blocked by a surge in Hubbard Glacier. The glacier’s advance was faster than the waves could chip it away, so it crept past the mouth of the fjord and dammed it up. Water started rising behind the ice dam, threatening the trapped sea mammals as the salt water became increasingly diluted with the fresh meltwater. When the lake level got up to about two stories above sea level, the ice dam broke.

We know all about glacial surges in Washington State, because they blocked the Columbia River at least 59 times about 13,000 years ago; each time the ice dam broke, a wall of water went racing across the middle of Washington, carving the terrain into scabland as it surged to the sea. (Perhaps the ground-shaking roar warned anyone who was trying to catch salmon in the river valleys to run for the hills.)

Damming up a fjord may have had even more serious consequences. Fjords are often cut off by glacial surges, just as mountain valleys are temporarily dammed by the rubble that avalanches deposit. But dammed-up fjords serve as natural reservoirs for fresh water, and when the ice dam finally breaks, enormous quantities of fresh water flood into the adjacent oceans, a half-year’s worth in only a half-day’s time. It layers over the ocean surface and only later mixes with the salt water. Unfortunately, that freshening of the surface layer could have major consequences in the case of Greenland’s fjords: it is potentially a mechanism for shutting down for a few centuries the North Atlantic Current, which warms Europe – a subject to which I will shortly return.

I tell you all this to point out that there is an enormous asymmetry between the buildup of ice and its subsequent meltdown; this is not at all like the exchange of energy involved in freezing and melting a tray of ice cubes. Buildup mode keeps any cracks filled with new snow and minimizes the greasing of the skids. Melting mode is like a house of cards collapsing in slow motion.

‘Modes of operation’ are familiar to us from cool-fan-heat modes of air-conditioning systems. Not only do glaciers have modes, but so do ocean currents and continental climates – modes that may be triggered in some cases by glacial surges far away. Sometimes annual temperature and rainfall switch back and forth so rapidly that they have major implications for the evolutionary process, giving versatile animals, like the raven, a real advantage over their lean-mean-machine competitors. That’s what this chapter is really about: how the evolutionary crank is turned to yield our kind of versatility – wide repertoires and good guessing get a special kind of boost from a series of climatic instabilities.

Paleoclimatologists have discovered that many parts of the earth suffer fairly abrupt climate changes. Decade-long droughts are one example, and we now know something of the thirty-year cycle by which the Sahara expands and contracts. The El Niño cycle, averaging about six years, now appears to have major effects on North American rainfall.

There have also been dozens of episodes in which forests have disappeared over several decades because of drastic drops in temperature and rainfall. In another abrupt change, the warm rains suddenly return a few centuries later – although the last time that Europe reverted to a Siberian-style climate, more than a thousand years passed before it switched back.

In the 1980s, when confirming evidence of these abrupt climate changes was discovered, we thought they were a peculiarity of the ice ages. (Ice sheets have come and gone during the last 2:5 million years, the major meltoffs occurring about every 100,000 years.) None of the abrupt cooling episodes have occurred in the last 10,000 years.

But it turns out that it’s only our present interglaciation that has been free of them (so far). The warm times after the last major meltoff, 130,000 years ago, were turbulent in comparison to the present interglaciation; that earlier 10,000-year warm period was punctuated with two abrupt cold episodes. One lasted 70 years, the other 750 years. During them, the German pine forests were replaced with scrubs and herbs now characteristic of central Siberia.

We have thus far been spared such civilization-threatening episodes. Climatically, we have been living in unusually stable times.

A climate flip-flop that eliminated fruit trees would be a disaster for regional populations of many monkey species. While it would hurt the more omnivorous as well, they could ‘make do’ with other foods, and their offspring might enjoy a population boom following the crunch, when few competitors would remain.

Such boom times temporarily have enough resources so that most offspring can survive to reproductive age, and this is true even of the odd variants thrown up by the gene shuffles that produce sperm and ova. In ordinary times, such oddities die in childhood, but in a boom time they face little competition; it’s as if the usual competitive rules had been suspended temporarily. When the next crunch comes, some odd variants may have better abilities to ‘make do’ with whatever resources are left. The traditional theme extracted from the darwinian process is survival of the fittest, but here we see that it is the rebound from hard times that promotes the creative aspects of evolution.

Though Africa was cooling and drying as upright posture was becoming established in hominids about four million years ago, brain size didn’t change much. So far, there’s not much evidence that brains enlarged during the climate changes in Africa between 3.0 million and 2.6 million years ago – a period in which many new species of African mammals appeared. This isn’t the place for an extended discussion of all the factors involved in human evolution, but it is important to note that hominid brain size begins to increase between 2.5 million to 2.0 million years ago and continues for an amazing fourfold expansion in cerebral cortex over the apes. This is the period of the ice ages, and although Africa wasn’t a major site of glaciers, the continent probably experienced major fluctuations in climate as the ocean currents rearranged themselves. An ice age is not confined to the Northern Hemisphere; the glaciers in the Andes change at the same time.

The first major episodes of floating ice in the Atlantic occurred at 2.51 million and 2.37 million years ago, with the winter ice pack reaching south to British latitudes. Ice sheets in Antarctica, Greenland, northern Europe, and North America have been with us ever since, melting off occasionally. As noted, we are currently in an interglaciation period, which started about 10,000 years ago. There is a stately rhythm of ice advance and retreat, associated with changes in the earth’s axial tilt and its orbit around the sun.

The season of the earth’s closest approach to the sun varies; perihelion is currently in the first week of January. Perihelion drifts around the calendar, returning to January in 19,000 to 26,000 years, depending on where the other planets are. The configurations of the other planets approximately repeat about every 400,000 years, though they come close to repeating about every 100,000 year. Their gravitational pull causes the shape of the earth’s orbit to vary from near-circular to ellipsoidal. (We’re currently about 3 percent farther away from the sun in July, and so receive 7 percent less heat.) Moreover, the tilt of the earth’s axis varies between 22.0° and 24.6°, a cycle taking 41,000 years. The last maximum tilt was 9,500 years ago; it’s currently 23.4° and declining. The three rhythms combine to contribute to a really major meltoff about every 100,000 years, typically when tilt is maximal and perihelion is also in June; that creates particularly hot summers in the high northern latitudes, where most ice sheets are situated.

Superimposed on the glacial slowness are the aforementioned episodes of abrupt cooling and rewarming. The first one to be discovered happened at a time – 13,000 years ago – when all those orbital factors were combining to produce hot summers in the Northern Hemisphere – indeed, half of the accumulated ice had already melted. The Younger Dryas (named for an arctic plant whose pollen was found deep beneath old lakes in Denmark) began quite suddenly. Ice cores from Greenland’s ice sheets show that it was as sudden as a drought. Annual rainfall decreased, winter storms grew in severity, and the average European temperature dropped by about 7°C (13°F) – all within several decades. This cold snap lasted more than a thousand years until, just as abruptly, the warm rains returned. (With regard to global warming from greenhouse gases, note that the last time an abrupt cooling happened, it was during a major episode of gradual global warming).

The Greenland ice cores go back only one-tenth of the 2.5 million years of the Pleistocene ice ages; only ice from the last 250,000 years remains in Greenland, because the antepenultimate meltoff exposed all the bedrock. But the cores do record the last two major meltoffs – the one that began 130,000 years ago and the most recent one, which began 15,000 years ago and was complete about 8,000 years ago. Most important, one can see annual ‘tree rings’ in the more recent millennia and count the years, sample their oxygen isotopes, and thereby deduce the sea surface temperature at the time the water evaporated in the mid Atlantic before falling as snow in Greenland.

The paleoclimatologists now can see dozens of abrupt events in the last 130,000 years, superimposed upon the glacial slowness – and even occurring during warm periods. Big glacial surges could be one factor – as I discuss in The Ascent of Mind – simply because a lot of fresh water floating on the ocean surface before mixing may well cause major changes in the ocean current that imports a lot of heat into the North Atlantic and helps keep Europe warm in the winter. That’s why I worry about a glacial surge producing an enormous freshwater reservoir in Greenland’s fjords: it could all be released in a day when an ice dam is finally breached. The last time I flew over the extensive fjord system on the east coast of Greenland at 70° north latitude, I was appalled to see fjords that, though open to the ocean, had the bathtub-ring appearance of drawn-down reservoirs. There was an ice-free area extending far above the high-tide line, and everywhere it appeared to be the same height; this suggests an enormous freshwater lake formed sometime since the last ice age, uniformly trimming the ice sheet.

Another cold flip would be devastating to agriculture in Europe, and to the half billion people it supports – and the effects of the Younger Dryas were seen worldwide, even in Australia and Southern California. While another one would threaten civilizations, the cold flips of the past probably played an important role in evolving humans from our apelike ancestors, simply because the episodes happened so rapidly.

A round man cannot be expected to fit into a square hole right away. He must have time to modify his shape.

Mark Twain

Whether or not versatility is important during an animal’s lifespan depends on the timescales: for both the modern traveler and the evolving ape, it’s how fast the weather changes and how long the trip lasts. When the chimpanzees of Uganda arrive at a grove of fruit trees, they often discover that the efficient local monkeys are already speedily stripping the trees of edible fruit. The chimps can turn to termite fishing, or perhaps catch a monkey and eat it, but in practice their population is severely limited by that competition, despite the fact that the chimpanzee’s brain is twice the size of that of its specialist rivals.

Versatility is not always a virtue, and more of it is not always better. As frequent airline travelers know, passengers who have only carry-on bags can get all the available taxicabs, while those burdened with three suitcases await their checked luggage. On the other hand, if the weather is so unpredictable and extreme that everyone has to travel with clothing ranging from swimsuits to Arctic parkas, the jack-of-all-trades has an advantage over the master of one. And so it is with behavioral versatility that allows a species to switch instantly from round to square holes.

Versatility might well require a bigger brain. But you need some pretty good reasons to balance out the disadvantages of a big brain. As the linguist Steven Pinker has noted:

Why would evolution ever have selected for sheer bigness of brain, that bulbous, metabolically greedy organ? A large-brained creature is sentenced to a life that combines all the disadvantages of balancing a watermelon on a broomstick . . . and, for women, passing a large kidney stone every few years. Any selection on brain size itself would have surely favored the pinhead. Selection for more powerful computational abilities (language, perception, reasoning, and so on) must have given us a big brain as a by-product, not the other way around!

How fast things change is important for any incremental-accumulations model of intelligence, whether it involves a bigger brain or merely a rearranged one. In any one climate, a specialist can eventually evolve that outperforms the overburdened generalist; however, anatomical adaptations occur much more slowly than the frequent climatic changes of the ice ages, making it hard for adaptations to ‘track’ the climate. Indeed, the abrupt transitions can occur within the lifetime of a single individual, who either has the reserve abilities needed to survive the crunch, or doesn’t.

This sudden-death-overtime argument applies to many omnivores, not just to our ancestors. But there aren’t any other examples around of fourfold brain enlargements in the last several million years, so an erratic climate by itself isn’t a surefire way of getting a swelled head. Something else was also going on, and the episodes of abrupt climate change probably exaggerated its importance, and kept those lean-mean-machine competitors from outcompeting the jack-of-all-trades types that evolved.

Everyone has a favorite theory for what this ‘something else’ was. (Nick Humphrey would pick social intelligence as the driver, for example.) My candidate is accurate throwing for hunting – handy for getting through the winter by eating animals that eat grass. But most people would pick language. Especially syntax.

[Language comprehension] involves many components of intelligence: recognition of words, decoding them into meanings, segmenting word sequences into grammatical constituents, combining meanings into statements, inferring connections among statements, holding in short-term memory earlier concepts while processing later discourse, inferring the writer’s or speaker’s intentions, schematization of the gist of a passage, and memory retrieval in answering questions about the passage . . . [The reader] constructs a mental representation of the situation and actions being described . . . Readers tend to remember the mental model they constructed from a text, rather than the text itself.

Gordon H. Bower and Daniel G. Morrow, 1990

I often find that a novel, even a well-written and compelling novel, can become a blur to me soon after I’ve finished it. I recollect perfectly the feeling of reading it, the mood I occupied, but I am less sure about the narrative details. It is almost as if the book were, as Wittgenstein said of his propositions, a ladder to be climbed and then discarded after it has served its purpose.

Sven Birkerts, 1994

CHAPTER 5

SYNTAX AS A FOUNDATION OF INTELLIGENCE

It is hard to imagine how a creature without language would think, but one may suspect that a world without any kind of language would in some ways resemble a world without money – a world in which actual commodities, rather than metal or paper symbols for the value of these, would have to be exchanged. How slow and cumbersome the simplest sale would be, and how impossible the more complex ones!

Derek Bickerton, Language and Species, 1990

Humans have some spectacular abilities, compared to our closest cousins among the surviving apes – even the apes that share much of our social intelligence, reassuring touches, and abilities to deceive. We have a syntactic language capable of supporting metaphor and analogical reasoning. We’re always planning ahead, imagining scenarios for the future, and then choosing in ways that take remote contingencies into account. We even have music and dance. What were the steps in transforming a chimpanzeelike creature into a nearly human one? That’s a question which is really central to our humanity.

There’s no doubt that syntax is what human levels of intelligence are mostly about – that without syntax we would be little cleverer than chimpanzees. The neurologist Oliver Sacks’s description of an eleven-year-old deaf boy, reared without sign language for his first ten years, shows what life is like without syntax:

Joseph saw, distinguished, categorized, used; he had no problems with perceptual categorization or generalization, but he could not, it seemed, go much beyond this, hold abstract ideas in mind, reflect, play, plan. He seemed completely literal – unable to juggle images or hypotheses or possibilities, unable to enter an imaginative or figurative realm . . . He seemed, like an animal, or an infant, to be stuck in the present, to be confined to literal and immediate perception, though made aware of this by a consciousness that no infant could have.

Similar cases also illustrate that any intrinsic aptitude for language must be developed by practice during early childhood. Joseph didn’t have the opportunity to observe syntax in operation during his critical years of early childhood: he couldn’t hear spoken language, nor he was ever exposed to the syntax of sign language.

There is thought to be a bioprogram, sometimes called Universal Grammar. It is not the mental grammar itself (after all, each dialect has a different one) but rather the predisposition to discover grammars in one’s surroundings – indeed, particular grammars, out of a much larger set of possible ones. To understand why humans are so intelligent, we need to understand how our ancestors remodeled the ape’s symbolic repertoire and enhanced it by inventing syntax.

Stones and bones are, unfortunately, about all that remain of our ancestors in the last four million years, not their higher intellectual abilities. Other species branched off along the way, but they are no longer around to test. We have to go back six million years before there are living species with whom we shared a common ancestor: the nonhominid branch itself split about three million years ago into the chimpanzee and the much rarer bonobo (the ‘chimpanzee of the Pygmies’). If we want a glimpse at ancestral behaviors, the bonobos are our best chance. They share more behavioral similarities with humans and they’re also much better subjects for studying language than the chimps that starred in the sixties and seventies.

Linguists have a bad habit of claiming that anything lacking syntax isn’t language. That, ahem, is like saying that a Gregorian chant isn’t music, merely because it lacks Bach’s use of the contrapuntal techniques of stretto, parallel voice leading, and mirror inversions of themes. Since linguistics confines itself to ‘Bach and beyond,’ it has primarily fallen to the anthropologists, the ethologists, and the comparative psychologists to be the ‘musicologists,’ to grapple with the problem of what came before syntax. The linguists’ traditional put-down of all such research (‘It isn’t really language, you know’) is a curious category error, since the object of the research is to understand the antecedents of the powerful structuring that syntax provides.

One occasionally gets some help from the well-known ontogeny-recapitulates-phylogeny crib, but human language is acquired so rapidly in early childhood that I suspect a streamlining, one that thoroughly obscures any original staging, rather as freeways tend to obliterate post roads. The fast track starts in infants with the development of phoneme boundaries: prototypes become ‘magnets’ that capture variants. Then there’s a pronounced acquisitiveness for new words in the second year, for inferring patterns of words in the third (kids suddenly start to use past tense -ed and plural -s with consistency, a generalization that occurs without a lot of trial and error), and for narratives and fantasy by the fifth. It is fortunate for us that chimps and bonobos lack such fast-tracking, because it gives us a chance to see, in their development, the intermediate stages that were antecedent to our powerful syntax.

Vervet monkeys in the wild use four different alarm calls, one for each of their typical predators. They also have other vocalizations to call the group together or to warn of the approach of another group of monkeys. Wild chimpanzees use about three dozen different vocalizations, each of them, like those of the vervets, meaningful in itself. A chimp’s loud waa-bark is defiant, angry. A soft cough-bark is, surprisingly, a threat. Wraaa mixes fear with curiosity (‘Weird stuff, this!’) and the soft huu signifies weirdness without hostility (‘What is this stuff?’).

If a waa-wraaa-huu is to mean something different than huu-wraaa-waa, the chimp would have to suspend judgment, ignoring the standard meanings of each call until the whole string had been received and analyzed. This doesn’t happen. Combinations are not used for special meanings.

Humans also have about three dozen units of vocalization, called phonemes – but they’re all meaningless! Even most syllables like ‘ba’ and ‘ga’ are meaningless unless combined with other phonemes to make meaningful words, like ‘bat’ or ‘galaxy.’ Somewhere along the line, our ancestors stripped most speech sounds of their meaning. Only the combinations of sounds now have meaning: we string together meaningless sounds to make meaningful words. That’s not seen anywhere else in the animal kingdom.

Furthermore, there are strings of strings – such as the word phrases that make up this sentence – as if the principle were being repeated on yet another level of organization. Monkeys and apes may repeat an utterance to intensify its meaning (as do many human languages, such as Polynesian), but nonhumans in the wild don’t (so far) string together different sounds to create entirely new meanings.

No one has yet explained how our ancestors got over the hump of replacing one-sound/one-meaning with a sequential combinatorial system of meaningless phonemes, but it’s probably one of the most important transitions that happened during ape-to-human evolution.

The honeybee appears, at least in the context of a simple coordinate system, to have broken out of the mold of one-sign/one-meaning. When she returns to her hive, she performs a ‘waggle dance’ in a figure-8 that communicates information about the location of a food source she has just visited. The angle of the figure-8 axis points toward the food. The duration of the dance is proportional to the distance from the hive: for example, at least in the traditional version of this story, three loops around the figure-8 would suggest 60 meters away to the average Italian honeybee, though 150 meters to a German one – a matter of genes rather than the company in which the bee was reared. Still, the linguists are not very impressed – in his Language and Species, Derek Bickerton notes:

All other creatures can communicate only about things that have evolutionary significance for them, but human beings can communicate about anything . . . Animal calls and signs are structurally holistic [and] cannot be broken down into component parts, as language can . . . Though in themselves the sounds of [human] language are meaningless, they can be recombined in different ways to yield thousands of words, each distinct in meaning . . . In just the same way, a finite stock of words . . . can be combined to produce an infinite number of sentences. Nothing remotely like this is found in animal communication.

With enough experience, various animals can learn a wide range of words, symbols, or human gestures – but one must be careful to distinguish between comprehension and the ability to originate fancy communications. They don’t necessarily go together.

One psychologist’s dog, as I noted earlier, understands about 90 items; the 60 it produces don’t overlap very much in meaning with the receptive ones. A sea lion has learned to comprehend 190 human gestures – but it doesn’t gesture back with anything near the same productivity. Bonobos have learned an even greater number of symbols for words and can combine them with gestures to make requests. A gray parrot has learned, over the course of a decade, a 70-word vocabulary that includes thirty object names, seven colors, five shape adjectives, and a variety of other ‘words’ – and can make requests with some of them.

None of these talented animals is telling stories about who did what to whom; they’re not even discussing the weather. But it is clear that our closest cousins, the chimpanzee and the bonobo, can achieve considerable levels of language comprehension with the aid of skilled teachers who can motivate them. The most accomplished bonobo, under the tutelage of Sue Savage-Rumbaugh and her co-workers, can now interpret sentences it has never heard before – such as ‘Kanzi, go to the office and bring back the red ball’ – about as well as a two-and-a-half-year-old child. Neither bonobo nor child is constructing such sentences, but they can demonstrate by their actions that they understand them. And comprehension comes first, production later, as language develops in children.

I often wonder how many of the limited successes in ape language studies were merely a matter of insufficient motivation; perhaps teachers have to be good enough to substitute for the normal self-motivating acquisitiveness of the young child. Or if the limited successes were from not starting with very young animals. If a bonobo could somehow become motivated in its first two years to comprehend new words at a rate approaching that of the year-old child, might the bonobo then go on to discover patterning of words in the manner of the pre-syntax child? But have it happen slowly enough for us to see distinct stages preceding serious syntax, the ones obscured by the streamlined freeways provided by the present human genome?

All of this animal communicative ability is very impressive, but is it language? The term language is used rather loosely by most people. First of all, it refers to a particular dialect such as English, Frisian, and Dutch (and the German of a thousand years ago, from which each was derived – and, further back, proto-Indo-European). But language also designates the overarching Category of communication systems that are especially elaborate. Bee researchers use language to describe what they see their subjects doing, and chimpanzee researchers do the same. At what point do animal symbolic repertoires become humanlike language?

The answer isn’t obvious. Webster’s Collegiate Dictionary offers ‘a systematic means of communicating ideas or feelings by use of conventionalized signs, sounds, gestures, or marks having understood meanings’ as one definition of language. That would encompass the foregoing examples. Sue Savage-Rumbaugh suggests that the essence of language is ‘the ability to tell another individual something he or she did not already know,’ which, of course, means that the receiving individual is going to have to use some Piagetian guessing-right intelligence in constructing a meaning.

But humanlike language? Linguists will immediately say ‘No, there are rules!’ They will start talking about the rules implied by mental grammar and questioning whether or not these rules are found in any of the nonhuman examples. That some animals such as Kanzi can make use of word order to disambiguate requests does not impress them. The linguist Ray Jackendoff is more diplomatic than most, but has the same bottom line:

A lot of people have taken the issue to be whether the apes have language or not, citing definitions and counter-definitions to support their position. I think this is a silly dispute, often driven by an interest either in reducing the distance between people and animals or in maintaining this distance at all costs. In an attempt to be less doctrinaire, let’s ask: do the apes succeed in communicating? Undoubtedly yes. It even looks as if they succeed in communicating symbolically, which is pretty impressive. But, going beyond that, it does not look as though they are capable of constructing a mental grammar that regiments the symbols coherently. (Again, a matter of degree – maybe there is a little, but nothing near human capacity.) In short, Universal Grammar, or even something remotely like it, appears to be exclusively human.

What, if anything, does this dispute about True Language have to do with intelligence? Judging by what the linguists have discovered about mental structures and the ape-language researchers have discovered about bonobos inventing rules – quite a lot. Let us start simple.

Some utterances are so simple that fancy rules aren’t needed to sort out the elements of the message – most requests such as ‘banana’ and ‘give’ in either sequence get across the message. Simple association suffices. But suppose there are two nouns in a sentence with one verb: how do we associate ‘dog boy bite’ in any order? Not much mental grammar is needed, as boys usually don’t bite dogs. But ‘boy girl touch’ is ambiguous without some rule to help you decide which noun is the actor and which is the acted upon.

A simple convention can decide this, such as the subject-verb-object order (SVO) of most declarative sentences in English (‘The dog bit the boy’) or the SOV of Japanese. In short word phrases, this boils down to the first noun being the actor – a rule that Kanzi probably has absorbed from the way that Savage-Rumbaugh usually phrases requests, such as ‘Touch the ball to the banana.’

You can also tag the words in a phrase in order to designate their role as subject or object, either with conventional inflections or by utilizing special forms called case markings – as when we say ‘he’ to communicate that the person is the subject of the sentence, but ‘him’ when he is the object of the verb or preposition. English once had lots of case markings, such as ‘ye’ for subject and ‘you’ for object, but they now survive mostly in the personal pronouns and in ‘who’/‘whom.’ Special endings can also tip you off about a word’s role in the phrase, as when -ly suggests to you that ‘softly’ modifies the verb and not a noun. In highly inflected languages, such markings are extensively used, making word order a minor consideration in identifying the role a word is intended to play in constructing the mental model of relationships.

[For] us to be able to speak and understand novel sentences, we have to store in our heads not just the words of our language but also the patterns of sentences possible in our language. These patterns, in turn, describe not just patterns of words but also patterns of patterns. Linguists refer to these patterns as the rules of language stored in memory; they refer to the complete collection of rules as the mental grammar of the language, or grammar for short.

Ray Jackendoff, Patterns in the Mind, 1994

The simpler ways of generating word collections, such as pidgins (or my tourist German), are what the linguist Derek Bickerton calls protolanguage. They don’t utilize much in the way of mental rules. The word association (‘boy dog bite’) carries the message, perhaps with some aid from customary word order such as SVO. Linguists would probably classify the ape language achievements, both comprehension and production, as protolanguage.

Children learn a mental grammar by listening to a language (deaf children by observing sign language). They are acquisitive of associations as well as new words, and one fancy set of associations constitutes the mental grammar of a particular language. Starting at about eighteen months of age, children start to figure out the local rules and eventually begin using them in their own sentences. They may not be able to describe the parts of speech, or diagram a sentence, but their ‘language machine’ seems to know all about such matters after a year’s experience.

This biological tendency to discover and imitate order is so strong that deaf playmates may invent their own sign language (‘home sign’) with inflections, if they aren’t properly exposed to one they can model. Bickerton showed that the children of immigrants invent a new language – a creole – out of the pidgin protolanguage they hear their parents speaking. A pidgin is what traders, tourists, and ‘guest workers’ (and, in the old days, slaves) use to communicate when they don’t share a real language. There’s usually a lot of gesturing, and it takes a long time to say a little, because of all those circumlocutions.

In a proper language with lots of rules (that mental grammar), you can pack a lot of meaning into a short sentence. Creoles are indeed proper languages: the children of pidgin speakers take the vocabulary they hear and create some rules for it – a mental grammar. The rules aren’t necessarily any of those they know from simultaneously learning their parents’ native languages. And so a new language emerges, from the mouths of children, as they quickly describe who did what to whom.

Which aspects of language are easy to acquire and which are difficult? Broad categories may be the easiest, as when the child goes through a phase of designating any four-legged animal as ‘doggie’ or any adult male as ‘Daddy.’ Going from the general to the specific is more difficult. But some animals, as we have seen, can eventually learn hundreds of symbolic representations.

A more important issue may be whether new categories can be created that escape old ones. The comparative psychologist Duane Rumbaugh notes that prosimians (lorises, galagos, and so forth) and small monkeys often get trapped by the first set of discrimination rules they are taught, unlike rhesus monkeys and apes, both of which can learn a new set of rules that violates the old one. We too can overlay a new category atop an old one, but it is sometimes difficult: categorical perception (the pigeonholing mentioned earlier, in association with auditory hallucinations) is why some Japanese have such a hard time distinguishing between the English sounds for L and R.

The Japanese language has an intermediate phoneme, a neighbor to both L and R. Those English phonemes are, mistakenly, treated as mere variants on the Japanese phoneme. Because of this ‘capture’ by the traditional category, those Japanese speakers who can’t hear the difference will also have trouble pronouncing them distinctly.

Combining a word with a gesture is somewhat more sophisticated than one-word, one-meaning – and putting a few words together into a string of unique meaning is considerably more difficult. Basic word order is helpful in resolving ambiguities, as when you can’t otherwise tell which noun is the actor and which the acted upon. The SVO declarative sentence of English is only one of the six permutations of those units, and each permutation is found in some human language. Some word orders are more frequently found than others, but the variety suggests that word order is a cultural convention rather than a biological imperative in the manner proposed for Universal Grammar.

Words to indicate points in time (‘tomorrow’ or ‘before’) require more advanced abilities, as do words that indicate a desire for information (‘What’ or ‘Are there’) and the words for possibility (‘might’ or ‘could’). It is worthwhile noting what a pidgin protolanguage lacks: it doesn’t use articles like ‘a’ or ‘the’ which help you know whether a noun refers to a particular object or simply the general class of objects. It doesn’t use inflections (-s, -ly, and the like) or subordinate clauses, and it often omits the verb, which is guessed from the context.

Though they take time to learn, vocabulary and basic word order are nonetheless easier than the other rule-bound parts of language. Indeed, in the studies of Jacqueline S. Johnson and Elissa L. Newport, Asian immigrants who learn English as adults succeed with vocabulary and basic word-order sentences, but have great difficulty with other tasks – tasks that those who arrived as children easily master. At least in English, the who-what-where-when-why-how questions deviate from basic word order: ‘What did John give to Betty?’ is the usual convention (except on quiz shows in which questions mimic the basic word order and use emphasis instead: ‘John gave what to Betty?’). Nonbasic word orders in English are difficult for those who immigrated as adults, and so are other long-range dependencies, such as when plural object names must match plural verbs, despite many intervening adjectives. Not only do adult immigrants commit such grammatical errors, but they can’t detect errors when they hear them. For example, the inflectional system of English alters a noun when it refers to a multiplicity (‘The boy ate three cookie.’ Is that normal English?) and alters a verb when it refers to past time (‘Yesterday the girl pet a dog.’ OK?). Those who arrived in the United States before the age of seven make few such recognition errors as adults, and there is a steady rise in error rate for adults who began learning English between the ages of seven and fifteen – at which age the adult error level is reached (I should emphasize that the linguists were, in all cases, testing immigrants with ten years’ exposure to English, who score normally on vocabulary and the interpretation of basic word-order sentences).

By the age of two or three, children learn the plural rule: add -s. Before that, they treat all nouns as irregular. But even if they had been saying ‘mice,’ once they learn the plural rule they may begin saying ‘mouses’ instead. Eventually they learn to treat the irregular nouns and verbs as special cases, exceptions to the rules. Not only are children becoming acquisitive of the regular rules at about the time of their second birthday but it also appears that the window of opportunity is closing during the school years. It may not be impossible to learn such things as an adult, but simple immersion in an English-language society does not work for adults in the way that it does for children aged two to seven.

Whether you want to call it a bioprogram or a Universal Grammar, learning the hardest aspects of language seems to be made easier by a childhood acquisitiveness that has a biological basis, just as does learning to walk upright. Perhaps this acquisitiveness is specific to language, perhaps it merely looks for intricate patterns in sound and sight and learns to mimic them. A deaf child like Joseph who regularly watched chess games might, for all we know, discover chess patterns instead. In many ways, this pattern-seeking bioprogram looks like an important underpinning for human levels of intelligence.

A dictionary will define the word grammar for you as (1) morphology (word forms and endings); (2) syntax (from the Greek ‘to arrange together’ – the ordering of words into clauses and sentences); and (3) phonology (speech sounds and their arrangements). But just as we often use grammar loosely to refer to socially correct usage, the linguists sometimes go to the opposite extreme, using overly narrow rather than overly broad definitions. They often use grammar to specify just a piece of the mental grammar – all the little helper words, like ‘near,’ ‘above,’ and ‘into,’ that aid in communicating such information as relative position. Whatever words like these are called, they too are quite important for our analysis of intelligence.

First of all, such grammatical items can express relative location (above, below, in, on, at, by, next to) and relative direction (to, from, through, left, right, up, down). Then there are the words for relative time (before, after, while, and the various indicators of tense) and relative number (many, few, some, the -s of plurality). The articles express a presumed familiarity or unfamiliarity (the for things the speaker thinks the hearer will recognize, a or an for things the speaker thinks the hearer won’t recognize) in a manner somewhat like pronouns. Other grammatical items in Bickerton’s list express relative possibility (can, may, might), relative contingency (unless, although, until, because), possession (of, the possessive version of -s, have), agency (by), purpose (for), necessity (must, have to), obligation (should, ought to), existence (be), nonexistence (no, none, not, un-), and so on. Some languages have verbal inflections that indicate whether you know something on the basis of personal experience or just at second hand.

So grammatical words help to position objects and events relative to each other on a mental map of relationships. Because relationships (‘bigger,’ ‘faster,’ and so forth) are what analogies usually compare (as in ‘bigger-is-faster’), this positioning-words aspect of grammar could also augment intelligence.

Syntax is a treelike structuring of relative relationships in your mental model of things which goes far beyond conventional word order or the aforementioned ‘positioning’ aspects of grammar. By means of syntax, a speaker can quickly convey a mental model to a listener of who did what to whom. These relationships are best represented by an upside-down tree structure – not the sentence diagraming of my high school days, but a modern version of diagraming known as an X-bar phrase structure. Since there are now some excellent popular books on this subject, I will omit explaining the diagrams here (whew!).

Treelike structure is most obvious when you consider subordinate clauses, as in the rhyme about the house that Jack built. (‘This is the farmer sowing the corn/ That kept the cock that crowed in the morn/ . . . That lay in the house that Jack built.’) Bickerton explains that such nesting or embedding is possible because

phrases are not, as they might appear to be, strung together serially, like beads on a string. Phrases are like Chinese boxes, stacked inside one another. The importance of this point can hardly be overestimated. Many people concerned with the origins of human language, or with the alleged language capacities of nonhuman species, have been led to propose grossly simplistic hypotheses about how language could have emerged, simply on the basis of a mistaken assumption. They assume that words are serially chained into phrases and phrases into sentences in pretty much the same way that steps are chained into walking. . . . Nothing could be further from the truth. . . . This can be seen by considering a phrase like the cow with the crumpled horn that Farmer Giles likes. Although no single word in this phrase is ambiguous, the phrase as a whole is, because we do not know whether it is the horn or the cow that Farmer Giles likes.

In addition to such ‘phrase structure’ (as this is called), there is ‘argument structure,’ which is particularly helpful in guessing the role of the various nouns in the sentence. If you see an intransitive verb, such as ‘sleep,’ you can be sure that one noun (or pronoun) will suffice to complete the thought – namely, the actor. This will be true in any language with a word for sleeping. Similarly, if a language has a verb meaning ‘beat,’ you can be sure that two nouns are involved, an actor and a recipient (and perhaps a third, for the instrument with which the beating is administered). A verb meaning ‘give’ calls for three nouns, as it also requires an item that is given to the recipient. So, any mental organization chart featuring ‘give’ will have three empty slots, which must be appropriately filled before you feel that you correctly ‘understand’ the sentence and can proceed to the next task. Sometimes the nouns are implicit, as in the exhortation ‘Give!’ where we fill in ‘you,’ ‘money,’ and ‘to me’ automatically.

As Bickerton notes, a sentence is like

a little play or story, one in which each of the characters has a specific role to perform. There is a finite and indeed very short list of these roles. Not all linguists are agreed as to exactly what they are, but most, if not all, would include the roles of Agent (JOHN cooked dinner), Patient or Theme (John cooked DINNER), Goal (I gave it TO MARY), Source (I bought it FROM FRED), Instrument (Bill cut it WITH A KNIFE), and Beneficiary (I bought it FOR YOU), as well as Time and Place.

No animal language in the wild has such structural features. At best, wild animal languages amount to a few dozen utterances and associated intensifiers (usually involving repetition, as in the circuits of the waggle dance or the repeats of a primate alarm cry), with combinations of utterances rarely utilized for new message types. With education, some animals have come to understand a consistent word order, so that they correctly respond to ‘Kanzi, touch the banana to the ball,’ in which word order is used to distinguish the actor from the acted upon.

Linguists, however, would like to place the language boundary well beyond such sentence comprehension: in looking at animal experiments, they want to see sentence production using a mental grammar; mere comprehension, they insist, is too easy. Though guessing at meaning often suffices for comprehension, the attempt to generate and speak a unique sentence quickly demonstrates whether or not you know the rules well enough to avoid ambiguities.

Yet that production test is more relevant to the scientist’s distinctions than those of the language-learner’s: after all. comprehension comes first in children. The original attempts to teach chimps the manual sign language of the deaf involved teaching the chimp how to produce the desired movements; comprehension of what the sign signified only came later, if at all. Now that the ape-language research has finally addressed the comprehension issue, it looks like more of a hurdle than anyone thought – but once an animal is past it, spontaneous production increases.

Linguists aren’t much interested in anything simpler than real rules, but ethologists and the comparative and developmental psychologists are. Sometimes, to give everyone a piece of the action, we talk about languages plural, ‘language’ in the sense of systematic communication, and Language with a capital L for the utterances of the advanced-syntax-using élite. All aid in the development of versatility and speed (and hence intelligence). While morphology and phonology also tell us something about cognitive processes, phrase structure, argument structure, and the relative-position words are of particular interest because of their architectural aspect – and that provides some insights about the mental structures available for the guessing-right type of intelligence.

Comprehension demands an active intellectual process of listening to another party while trying to figure out, from a short burst of sounds, the other’s meaning and intent – both of which are always imperfectly conveyed. Production, by contrast, is simple. We know what we think and what we wish to mean. We don’t have to figure out ‘what it is we mean,’ only how to say it. By contrast, when we listen to someone else, we not only have to determine what the other person is saying, but also what he or she means by what is said, without the insider’s knowledge that the speaker has.

Sue Savage-Rumbaugh, 1994

How much of language is innate in humans? Certainly the drive to learn new words via imitation is probably innate in a way that a drive to learn arithmetic is not. Other animals learn gestures by imitation, but preschool children seem to average ten new words every day – a feat that puts them in a whole different class of imitators. And they’re acquiring important social tools, not mere vocabulary: the right tool for the job, the British neuropsychologist Richard Gregory emphasizes, confers intelligence on its user – and words are social tools. So this drive alone may account for a major increment in intelligence over the apes.

There is also the drive of the preschooler to acquire the rules of combination we call mental grammar. This is not an intellectual task in the usual sense: even children of low-average intelligence seem to effortlessly acquire syntax by listening. Nor is acquisition of syntax a result of trial and error, because children seem to make fairly fast transitions into syntactic constructions. Learning clearly plays a role but some of the rigidities of grammar suggest innate wiring. As Derek Bickerton points out, our ways of expressing relationships (such as all those above/below words) are resistant to augmentation, whereas you can always add more nouns. Because of regularities across languages in the errors made by children just learning to speak, because of the way various aspects of grammar change together across languages (SVO uses prepositions such as ‘by bus,’ SOV tends to post-positions such as ‘bus by’), because of those adult Asian immigrants, and because of certain constructions that seem forbidden in any known language, linguists such as Noam Chomsky have surmised that something biological is involved – that the human brain comes wired for the treelike constructions needed for syntax, just as it is wired for walking upright:

Normal speech consists, in large part, of fragments, false starts, blends and other distortions of the underlying idealized forms. Nevertheless . . . what the child learns is the underlying [idealized form]. This is a remarkable fact. We must also bear in mind that the child constructs this [idealized form] without explicit instruction, that he acquires this knowledge at a time when he is not capable of complex intellectual achievements in many other domains, and that this achievement is relatively independent of intelligence.

There is, of course, a ‘language module’ in the brain – located just above the left ear in most of us – and Universal Grammar might be wired into it at birth. Monkeys lack this left lateral language area: their vocalizations (and the emotional utterances of humans) utilize a more primitive cortical speech area above the corpus callosum. Nobody knows yet whether apes have a lateral language area or similar arrangement.

If a young bonobo or chimpanzee had the two drives that young human children have – to seek out words and discover rules – in sufficient intensity and at the right time in brain development, would it self-organize a language cortex like ours and use it to crystallize a set of rules out of word mixtures? Or is that neural wiring innate in humans, there without the relevant experience and simply unused if the drives or opportunities are missing? Either, it seems to me, is consistent with the Chomskian claim. Universal Grammar might result from the ‘crystallization’ rules of the self-organization, arising just as ‘flashers’ and ‘gliders’ do from cellular automata.

And the way you experimentally distinguish between uniquely human innate wiring and input-driven crystallization is to push vocabulary and sentences on promising ape students, with clever motivation schemes attempting to substitute for the child’s untutored acquisitiveness. It is, I think, fortunate that the apes are borderline when it comes to having the linguists’ True Language, because by studying their struggles we might eventually glimpse the functional foundations of mental grammar. In the course of human evolution, the stepping-stones may have been paved over, overlaid by super-structures and streamlined beyond recognition.

Sometimes ontogeny recapitulates phylogeny (the baby’s attempts to stand up recapitulating the quadruped-to-biped phylogeny; the descent of the larynx in the baby’s first year partially recapitulating the ape-to-human changes). Yet, development can happen so rapidly that you fail to see the reenactment of evolutionary progress. If we could see the transition to fancier constructions in bonobos, however, we might be able to discover what sorts of learning augment syntax, what other tasks compete and so hinder language, and what brain areas ‘light up’ in comparison to those in humans. Besides the major implications for our view of what’s uniquely human, an understanding of ape linguistic foundations might help us teach the language-impaired, and might even reveal synergies that would aid language learning and better guessing. It is only through the efforts of skilled teachers of bonobos that we’re likely to answer questions about the stepping-stones.

Syntax is what you use, it would appear, to make those fancier mental models, the ones involving who did what to whom, why, when, and with what means. Or at least if you want to communicate such an elaborate understanding, you’ll have to translate your mental model of those relationships into the mental grammar of the language, then you order or inflect the words to help the listener reconstruct your mental model. It might, of course, be easier just to ‘think in syntax’ in the first place. In that sense, we’d expect the augmentation of syntax to result in a great augmentation of guessing-right intelligence.

The name of the game is to re-create your mental model in the listener’s mind. The recipient of your message will need to know the same mental grammar, in order to decode the string of words into approximately the same mental understanding. So syntax is about structuring relationships between items (words, usually) in your underlying mental model, not about the surface of things – such as SVO or inflections, which are mere clues. Your job as a listener is to figure out what sort of tree will provide an adequate fit to the string of words you hear. (Imagine being sent the numerical values for a spreadsheet and having to guess the spreadsheet formulas needed to interrelate them!)

The way this could work is that you try out a simple arrangement (actor, action, acted-upons, modifiers) and wind up with words left over. You try another tree, and discover that there are unfilled positions that can’t be left empty. You use those clues about tree structure provided by the speaker’s plurals and verbs – for example, you know that ‘give’ requires both a recipient and an item given. If there is no word (spoken or implied) to fill a required slot, then you scratch that tree and go on to yet another. Presumably you try a lot of different trees simultaneously rather than seriatim, because comprehension (finding a good enough interpretation of that word string) can operate at blinding speed.

In the end, several trees may fill properly with no words left over, so you have to judge which of the interpretations is most reasonable given the situation you’re in. Then you’re finished. That’s comprehension – at least in my (surely oversimplified) version of the linguists’ model.

Think in terms of a game of solitaire: you’re not finished until you have successfully uncovered all the face-down cards – while following the rules about descending order and alternate colors – and in some shuffles of the deck, it is impossible to succeed. You lose that round, shuffle the deck, and try again. For some word strings, no amount of rearranging will find a meaningful set of relationships – a story you can construct involving who did what to whom. If someone utters such an ambiguous word string to you, they’ve failed an important test of language ability.

For some sentences generated by a linguistically competent human, you have the opposite problem: you can construct multiple scenarios – alternative ways of understanding the word string. Generally, one of the candidates will satisfy the conventions of the language or the situation better than others, thus becoming the ‘meaning’ of the communication. Context creates default meanings for some items in the sentence, saving the speaker from producing a longer utterance. (Pronouns are such a shortcut.)

The kind of formal rules of compositional correctness you learned in high school are, in fact, violated all the time in the incomplete utterances of everyday speech. But everyday speech suffices, because the real test is in whether you convey your mental model of who did what to whom to your audience, and the context will usually allow the listener to fill in the missing pieces. Because a written message has to function without much of the context, and without such feedback as an enlightened or puzzled look on the listener’s face, we have to be more complete – indeed, more redundant – when writing than when speaking, making fuller use of syntax and grammatical rules.

Linguists would like to understand how sentences are generated and comprehended in a machinelike manner – what enables the blinding speed of sentence comprehension. I like to call this ‘language machine’ a lingua ex machina. That does, of course, invite comparison with the deus ex machina of classical drama – a platform wheeled on stage (the god machine), from which a god lectured the other actors, and more recently the term bestowed on any contrived resolution of a plot difficulty. Until our ‘playwrighting’ technique improves, our algorithms for understanding sentences will also seem contrived.

I’m going to propose how one such lingua ex machina could work, combining phrase structure and argument structure in an algorithmic way. Linguists will probably find it at least as contrived as other diagraming systems. But here’s a few paragraphs’ worth of Calvin’s Vacuum-Lifter Package-Carrying System, involving processes as simple as those of a shipping department or production line.

Let us say we have just heard or read a complete sentence, ‘The tall blond man with one black shoe gave the other one to her.’ How do we make a mental model of the action? We need to box up some of the pieces, and prepositional phrases are a good place to start. Our machine knows all the prepositions and takes the nouns adjacent to them (the following noun if the sentence is English, the preceding noun if it’s in Japanese) into the same box. I’ll use boxes with rounded corners to indicate the packaging of phrases – ‘with one black shoe’ and ‘to her.’ On occasion, nonlinguistic memories have to be brought to bear in order to box things up correctly, as in that ambiguous phrase ‘the cow with the crumpled horn that Farmer Giles likes.’ Knowing that Giles has a collection of horns over the fireplace could help you guess whether ‘that Farmer Giles likes’ should be boxed with ‘cow’ or with ‘crumpled horn.’

Verbs get special boxes, because of the special role they play. Had there been an -ly word (an adverb), or an auxiliary, such as ‘must,’ I would have boxed them up with the verb, even if they weren’t adjacent to it. Then we box up the noun phrases, incorporating any prepositional phrase boxes that modify them, so that we may have rounded boxes within rectangular boxes. If we have a nested phrase, it can function as a noun for purposes of the next boxing. Now we’ve got everything boxed up (there have to be at least two boxes but often there are more).

Next we’ve got to ‘lift’ them as a group and metaphorically carry this amalgamation away from the work space, understood at last. Will it get off the ground? There are a few different types of handles in my vacuum-lifter machine, and the one we must use depends on the verb we identified (in this case, the past tense of ‘give’). There is another vacuum sucker, for the noun phrase box containing the subject (I’ve drawn it as a little pyramid). You can’t have a sentence without both a subject and a verb, and if the subject is missing, air will be sucked in the opening, no vacuum will form, and the package lifter won’t lift. (That’s why I’ve used suckers here rather than hooks – to make a target obligatory.)

But, as I noted earlier, ‘give’ is peculiar, in that it requires two objects. (You can’t say, ‘I gave to her.’ Or ‘I gave it.’). Therefore this lift handle has two additional suction lines. I’ve also allowed it some nonvacuum lines – simple strings with hooks, which can carry as many optional noun phrases and prepositional phrases, however many that the verb allows.

Sometimes the suction tips and optional hooks need some guidance to find an appropriate target: for example, SVO might help the subject tip find the appropriate noun phrase – as might a case marker, such as ‘he.’ Other inflections help out, like gender or number agreement between verb and subject. The suction tips and the hooks could come with little labels on them for Beneficiary, Instrument, Negation, Obligation, Purpose, Possession, and so forth, mating only with words appropriate to those categories. Being able to lift the verb handle and carry all the packages, leaving none behind and with no unfilled suction tips, is what constitutes sentence recognition in this particular grammar machine. If a suction tip can’t find a home, no vacuum develops when you lift the handle, and your construction isn’t carried away. There’s no sense of completion.

As noted, each verb, once identified by the lingua ex machina, has a characteristic handle type: for instance, handles for intransitive verbs such as ‘sleep’ have only the one suction tip for the subject, but they have optional hooks, in case there are any extra phrases to be hauled along. ‘Sleep’ will support optional roles such as Time (‘after dinner’) and Place (‘on the sofa’) – but not Recipient.

There’s usually a vacuum tip for an Agent (though sometimes there isn’t an Agent – say, in sentences like ‘The ice melted’), perhaps other role-related suction tips, and some hooks for other possible roles in the verb’s storytelling repertoire.

And, of course, the same boxes-inside-boxes principle that allowed a prepositional phrase to serve as a noun can allow us to have sentences inside sentences, as in dependent clauses or ‘I think I saw him leave to go home.’

That’s the short version of my package-carrying system. If it seems worthy of Rube Goldberg, remember that he’s the patron saint of evolution.

I assume that, just as in a roomful of bingo players, many attempts at a solution are made in parallel, with multiple copies of the candidate sentence superimposed on different prototypical sentence scaffolds, and that most of these arrangements fail because of leftover words and unfilled suction tips. The version whose verb handle lifts everything shouts, ‘Bingo!’ and the deciphering game is over (unless, of course, there’s a tie).

Being able to lift everything is simply a test of a properly patterned sentence; note that, once lifted successfully, sequence and inflections no longer matter, because roles have been assigned. This lingua ex machina would lift certain kinds of nonsense – such as Chomsky’s famous example, ‘Colorless green ideas sleep furiously’ – but would, appropriately, fail to lift a nonsentence, such as ‘Colorless green ideas sleep them.’ (The ‘sleep’ verb handle has no hooks or suckers for leftover Objects.)

Though a sensible mental model of relationships may be the goal of communication, and ungrammatical sentences cannot be deciphered except through simple word association, grammatical patterns of words can nonetheless be generated that fit sentence expectations but have no reasonable mental model associated with them. The test of semantics is different than the test of grammar. Semantics is also the tie-breaker, deciding among multiple winners, in somewhat the same way as boxing matches without a knockout are decided on judges’ points. That’s also how we guess what Farmer Giles is likely to like, the cow or the horn.

While each sentence is a little story, we also build string-based conceptual structures far larger than sentences. They too have lots of obligatory and optional roles to fill. They come along in the wake of grammar, as the writer Kathryn Morton observes:

The first sign that a baby is going to be a human being and not a noisy pet comes when he begins naming the world and demanding the stories that connect its parts. Once he knows the first of these he will instruct his teddy bear, enforce his world view on victims in the sandlot, tell himself stories of what he is doing as he plays and forecast stories of what he will do when he grows up. He will keep track of the actions of others and relate deviations to the person in charge. He will want a story at bedtime.

Our plan-ahead abilities gradually develop from childhood narratives and are a major foundation for ethical choices, as we imagine a course of action, imagine its effects on others, and decide not to do it.

By borrowing the mental structures for syntax to judge other combinations of possible actions, we can extend our plan-ahead abilities and our intelligence. To some extent, this is done by talking silently to ourselves, making narratives out of what might happen next, and then applying syntax-like rules of combination to rate (a decision on points, again) a candidate scenario as dangerous nonsense, mere nonsense, possible, likely, or logical. But our intelligent guessing is not limited to language-like constructs; indeed, we may shout, ‘Eureka!’ when a set of mental relationships clicks into place, yet have trouble expressing this understanding verbally for weeks thereafter. What is it about human brains that allows us to be so good at guessing complicated relationships?

We do not realize how deeply our starting assumptions affect the way we go about looking for and interpreting the data we collect. We should recognize that nonhuman organisms need not meet every new definition of human language, tool use, mind, or consciousness in order to have versions of their own that are worthy of serious study. We have set ourselves too much apart, grasping for definitions that will distinguish man from all other life on the planet. We must rejoin the great stream of life from whence we arose and strive to see within it the seeds of all we are and all we may become.

Sue Savage-Rumbaugh, 1994

[We] can understand neither ourselves nor our world until we have fully understood what language is and what it has done for our species. For although language made our species and made the world we inhabit, the powers it unleashed drove us to understand and control our environment, rather than explore the mainspring of our own being. We have followed that path of control and domination until even the most daring among us have begun to fear where it may lead. Now the engine of our quest for power and knowledge should itself become the object that we seek to know.

Derek Bickerton, 1990

CHAPTER 6

EVOLUTION ON-THE-FLY

Foresight of phenomena and power over them depend on knowledge of their sequences, and not upon any notion we may have formed respecting their origin or inmost nature.

John Stuart Mill, Auguste Comte and Positivism, 1865

The problems are solved, not by giving new information, but by arranging what we have known since long.

Ludwig Wittgenstein, Philosophical Investigations, 1953

‘One thing follows another’ is a fairly simple concept, one that many animals can master. Indeed, it’s what most learning is all about; for Pavlov’s dogs, it was bell tends to be followed by food.

More than two things may be chained; many animals have elaborate song sequences, not to mention all those elaborate locomotion sequences, such as gaits. Acquiring vocabulary and understanding basic word order are, we just saw, relatively easy language tasks for both humans and bonobos.

If sequence is so elementary, why is planning ahead so rare in the animal kingdom, except for those trivial cases of foresight that mere melatonin can handle so well? What additional mental machinery is required in order to plan for a novel contingency? (Perhaps argument structure, as in those verb-lifting handles?) How do we do something we’ve never done before, with no exact memories to guide us? How do we even imagine such a thing?

We are always saying something we’ve never said before. The other novelty generator, operating just as frequently in our lives (though often subconsciously), is that ‘What happens next?’ predictor, mentioned in chapter 2 in the context of humor and the distressful effects of environmental incoherence.

Perhaps the mechanisms for foresight are similar to those used in the fancier aspects of mental grammar, the ones involving long-term dependencies, as when basic word order is replaced by the alternate forms for the who-what-when questions. Perhaps the trees used by phrase structure, or the obligatory roles of argument structure, are mental mechanisms that are useful for foresight in a more general way.

Mental grammar provides our most detailed set of insights into those mental structures that might be handy for intelligent guessing. This chapter will take a look at three more: chunking, sequencing, and darwinian processes.

Juggling a half-dozen things at the same time is one of those abilities measured by multiple-choice tests, particularly analogy questions (A is to B as C is to [D, E, F]). It also shows up in our ability to remember phone numbers for a long enough time to dial them. Many people can hang on to a seven-digit number between five and ten seconds, but will resort to writing it down if faced with an out-of-area number or an even longer international one.

The limitation, it turns out, is not the number of digits; it’s the number of chunks. I remember San Francisco’s area code, 415, as a single chunk, but the number 451 means nothing to me, so I would have to remember it as three chunks: 4, 5, and 1. Chunking refers to the process of collapsing 4, 1, and 5 into the entity 415. A ten-digit San Francisco phone number, such as 4153326106, is, to me, only eight chunks; our schemes for using nondialed separators when writing down numbers – as in (415)332–6106 or 415.332.6106 – are essentially aids to chunking. Since we are already familiar with many two-digit numbers as single words – for example, ‘nineteen’ – the Parisian 42–60–31–25 style of separators makes for more easily memorized eight-digit number strings.

How many chunks can you hang onto? That varies among people, but the typical range forms the title of a famous 1956 paper by the psychologist George Miller: ‘The Magical Number Seven, Plus or Minus Two.’ It’s as if the mind had room for only a limited number of items – at least, in the work space used for current problems. When you get close to your limit, you try to collapse several items into one chunk so as to make more room. Acronyms are a version of chunking, making one ‘word’ from many. Indeed, many new words are just substitutes for a longer phrase, as when someone invented ambivalence as a shortcut, to save a whole paragraph of explanation. A dictionary is a compendium of chunking over the centuries. The combination of chunking and rapid speech, so that much meaning can be accommodated within the brief span of short-term memory, has surely been important for holding as much information as possible in mind at the same time.

So one of the first lessons about working memory is that there’s seemingly a limited scratch pad, better suited to a half-dozen items than twice that number. This limitation probably has some implications for intelligence (certainly for IQ tests!), but the key feature of intelligent acts is creative divergent thinking, not memory per se. What we need is a process that will produce good guesses.

Language and intelligence are so powerful that we usually assume that more and more would be better and better. Evolutionary theorists, however, are fond of demonstrating that evolution is full of dead-end stabilities that can prevent such straightforward ‘progress’ and they like to point out evolution’s indirect routes involving multipurpose organs. Many organs are actually multipurpose and change their relative mix of functions over time. (When did that gas exchange organ in fish, known as the ‘swim bladder’ because of its role in neutralizing buoyancy, become a lung?) And, if the analogy to computer software is to be believed, it’s far easier for the brain to be multipurpose than it is for any other organ system. Some regions of the brain are surely multipurpose too.

So, in asking about how neural machinery for foresight or language got started, we must bear in mind that the underlying mechanisms might serve multiple functions, any one of which could be driven by natural selection and so incidentally benefit the others. They might be like what architects call core facilities, such as the rooms for the photocopy machines and the mailboxes. The mouth, for example, is a multipurpose core facility involved with drinking, tasting, ingesting, vocalization, and emotional expression; in some animals, also with breathing, cooling off, and fighting.

Bundling (paying for one thing, but getting something else ‘free’) is a familiar marketing strategy. What human abilities might come bundled together like the proverbial ‘free lunch’ that comes with the cost of the drinks? In particular, might syntax or planning come bundled with some other ability, simply because they can make spare-time use of a core facility?

I realize that a ‘free lunch’ explanation is going to offend the sensibilities of the more Calvinist of the strict adaptationists in evolutionary theory – the ones that think that every little feature has to pay its own way. But strict accounting isn’t always the name of the game. As noted earlier (enlarge one, enlarge them all), mammalian brain enlargements tend not to come piecemeal. And a free lunch is just another way of looking at what the original adaptationist himself emphasized. Charles Darwin reminded his readers, in a caution to his general emphasis on adaptations, that conversions of function were ‘so important.’

In the midst of converting function – swim bladder into lung, for example – there is likely a multifunctional period (indeed, the multifunctional period could last forever). During it, an anatomical feature formerly under natural selection for one function gives an enormous boost to some new function, far beyond whatever natural selection the new function has experienced so far. Lungs were ‘bootstrapped’ by earlier buoyancy considerations. What brain functions have bootstrapped others, and does it tell us anything about intelligence?

In considering transitions of organs, it is so important to bear in mind the probability of conversion from one function to another.

Charles Darwin, The Origin of Species, 1859

We certainly have a passion for stringing things together in structured ways, ones that go far beyond the sequences produced by other animals. Besides words into sentences, we combine notes into melodies, steps into dances, and elaborate narratives into games with procedural rules. Might structured strings be a core facility of the brain, useful for language, story-telling, planning ahead, games, and ethics? Might natural selection for any of these abilities augment the common neural machinery, so that improved grammar incidentally serves to expand plan-ahead abilities?

Some beyond-the-apes abilities – music, for example – are puzzling, because it is hard to imagine environments that would give the musically gifted an evolutionary advantage over the tone deaf. To some extent, music and dance are surely secondary uses of that very neural machinery that was shaped up by structured strings more exposed to natural selection, such as language.

What other beyond-the apes abilities were likely to have been under strong natural selection? As improbable as it initially seems, planning ballistic movements may have once promoted language, music, and intelligence. Apes have elementary forms of the rapid arm movements that we’re experts at – hammering, clubbing, and throwing – and one can imagine hunting and toolmaking scenarios that in some settings were important additions to the basic hominid gathering and scavenging strategies. If the same ‘structured string’ core facility is used for the mouth as is used for ballistic hand movements, then improvements in language might promote manual dexterity. It could work the other way, too: accurate throwing opens up the possibility of eating meat regularly, of being able to survive winter in the temperate zone – and of talking all the better as an incidental benefit, a ‘free lunch.’

Choosing between hand movements involves finding a candidate movement program – likely a characteristic firing pattern of cortical neurons – and then some more candidates. Little is yet known about how this transpires in the human brain, but a simple model involves multiple copies of each movement program, each competing for space in the brain. The program for an open palm might make copies more readily than the program for making a V-sign or a precision pincer grip.

Ballistic movements (so named because beyond a certain point there is no opportunity to modify the command) require a surprising amount of planning, compared to most movements. They also likely require lots of clones of the movement program.

For sudden limb movements lasting less than about an eighth of a second, feedback corrections are largely ineffective, because reaction times are so long. Nerves conduct too slowly, and decisions aren’t made quickly enough; feedback might help plan for next time, if the target hasn’t run away by then, but it’s no help in real time. For the last one-eighth second of clubbing, hammering, throwing, and kicking, the brain has to plan every detail of the movement and then spit it out, rather like punching a roll for a player piano and then letting it roll.

We need nearly complete advance planning for ballistic movements during ‘get set,’ with no reliance on feedback. Hammering requires planning the exact sequence of activation for dozens of muscles. In the case of throwing, the problem is difficult for an additional reason: there is a launch window – a range of times when the projectile can be released and still hit the target. Release occurs shortly after the velocity peaks, as the projectile sails out of the decelerating hand. Getting this peak velocity to occur at exactly the right time, at the appropriate angle from the horizontal, is the trick.

Given the launch-window problems, you can see why planning is so difficult for human ballistic movements. Launch windows depend on how far away the target is, and on how big it is. Let’s say that, eight tries out of ten, you can hit a rabbit-sized target from the length of one parallel parking space – which implies a launch window of 11 milliseconds. Hitting the same target from twice the distance with equal reliability means releasing within a launch window about eight times narrower, 1.4 msec. Neurons are not exactly atomic clocks when it comes to timing accuracy; there is a lot of jitter when impulses are produced, enough so that any one neuron would have trouble hitting the broad side of a barn if it had to time the ball’s release all by itself.

Happily, many noisy neurons are better than a few – so long as they’re all ‘doing their own thing’ and thereby making their own mistakes. Combining them can average out some of the noise. You can see this principle at work in the heart, making the heartbeat more regular. A fourfold increase in the number of pacemaker cells serves to cut the heartbeat jitter in half. To reduce ballistic release jitter eightfold requires averaging the output of 64 times as many noisy neurons as you needed to program the original throw. If you want to hit that same rabbit-sized target at three times the distance with that same eight-out-of-ten-times reliability, count on needing to recruit a lot of helpers: you will require 729 times as many neurons as the number sufficient for generating your standard short throw. It’s redundancy, but in a different sense from, say, the three ways every large airplane has of lowering the landing gear.

So now we have a third insight into relevant brain mechanisms for fancy sequences: besides those trees and handles of syntax, besides those limited scratch-pad memories that encourage chunking, we see that fancy sequences of activation such as the ballistic movements probably share cerebral real estate with other fancy sequences – and that some need hundredfold levels of redundancy when precision timing is important.

Lots of planning space is also needed when you are throwing at a nonstandard target distance – one for which you don’t have a stored movement plan (as you might for throwing darts or basketball free-throws). For nonstandard shots, you need to create an array of variants between two standard programs and pick the one that will come closest to hitting your target. Improvisation takes space. If, once you select the ‘best’ variant, all the other variants change to conform to it, then you would have the redundancy needed for staying inside the launch window. Imagine a roomful of soloists, all singing somewhat different melodies and then converging on the one that they could sing as a chorus. And then, for real precision, recruiting a lot of helpers, just as the expert choir recruits the audience in the Hallelujah Chorus.

A core facility for structured sequences could solve a lot of problems. Does one actually exist? If so, we might occasionally see some synergy or conflict between similar movements.

Charles Darwin was one of the first to suggest hand-to-mouth synergies in his 1872 book on the expression of the emotions: ‘Thus persons cutting anything with a pair of scissors may be seen to move their jaws simultaneously with the blades of the scissors. Children learning to write often twist about their tongues as their fingers move, in a ridiculous fashion.’

What kind of sequences are we talking about, anyway? Rhythmic movements per se are ubiquitous: chewing, breathing, locomotion, and so forth. They can be implemented by simple circuits at the level of the spinal cord. Like the simple onething-follows-another of learning, there is nothing distinctively cerebral about rhythm or other sequences. But novel sequences, that’s the rub. If there is a common sequencer for the fancier novel movements, where is it located in the brain?

Sequencing in itself doesn’t require a cerebral cortex. Much movement coordination in the brain is done at a subcortical level, in places known as the basal ganglia and the cerebellum. But novel movements tend to depend on the premotor and prefrontal cortex, in the rear two-thirds of the frontal lobes.

There are other regions of the cerebral cortex that are likely to be involved with sequential activities. The dorsolateral portions of the frontal lobe (dorso = top, lateral = side; if you had a pair of horns growing out of your forehead, these regions would lie beneath them) are crucial for delayed-response tasks. You show a monkey some food and allow him to watch where you hide it – but force him to wait twenty minutes before being allowed to go after it. Monkeys with damage to the dorsolateral frontal cortex will fail to retain that information. It may not be a failure of memory but a problem of formulating a lasting intention, perhaps even an ‘agenda.’

The great Russian neurologist Alexander Luria described a patient in bed with his arms under the covers. Luria asked him to raise his arm. He couldn’t seem to do that. But if Luria asked him to remove his arm from under the covers, he could do that. If Luria then asked him to raise his arm up and down in the air, the patient could do that, too. His difficulty was in planning the sequence – he got stuck on the condition of working around the obstacle of the confining bedcovers. Left prefrontal damage gives patients difficulty in unfolding a proper sequence of actions – or perhaps in planning them in the first place. Patients with damage to the left premotor cortex have trouble chaining the actions together into a fluent motion – what Luria called a kinetic melody.

Tumors or strokes in the bottom of the frontal lobe, just above the eyes, also affect sequences of activities, such as going shopping. One famous patient, an accountant, had a high IQ and did quite well on a battery of neuropsychological tests. Yet he had big problems in organizing his life: he was fired from a series of jobs, went bankrupt, and underwent two divorces in a two-year period as a result of impulsive marriages. Nonetheless, this man was often unable to make simple, rapid decisions – say, about what toothpaste to buy or what to wear. He would get stuck making endless comparisons and contrasts, often making no decision at all or a purely random one. If he wanted to go out for dinner, he had to consider the seating plan, the menu, the atmosphere, and the management of each possible restaurant. He might drive by them to see how busy they were, and even then would be unable to choose among them.

There are two major lines of evidence that suggest the lateral language area above the left ear also has a lot to do with nonlanguage sequencing. The Canadian neuropsychologist Doreen Kimura and her coworkers showed that left-lateral stroke patients with language difficulties (aphasia) also have considerable difficulty executing hand and arm movement sequences of a novel sort, a condition known as apraxia. (A fancy, though not novel, sequence would be taking your keys out of your pocket, finding the right one, inserting it into the lock, turning the key, and then pushing on the door.)

The Seattle neurosurgeon George Ojemann and his coworkers further showed, using electrical stimulation of the brain during epilepsy operations, that much of the left-lateral language specialization is involved with listening to sound sequences. These regions include the part of the frontal lobe adjacent to Broca’s Area, the top of the temporal lobe on either side of the primary auditory cortex, and some of the parietal lobe in back of the map of the skin surface. (In other words, they’re ‘perisylvian,’ bordering the Sylvian fissure.) The big surprise was that these exact same areas seem heavily involved in producing oral-facial movement sequences – even nonlanguage ones, such as mimicking a series of facial expressions.

One of the hazards of naming things in the brain is that we expect something called the language cortex to be devoted to language. But data such as Ojemann’s show that, at its core, the cortical specialization is far more generalized, concerned with novel sequences of various kinds: hand as well as mouth, sensation as well as movement, mimicry as well as narrative.

Not only can many species learn abstract symbols and a simple language, but some clearly can learn categories. Indeed, animals often overgeneralize, in the same way that a baby goes through a phase of calling all adult males ‘Daddy.’ Relationships can be learned, such as is-a or is-larger-than. A banana is a fruit, a banana is larger than a chestnut.

Closer to intelligence is the power of analogies, metaphors, similes, parables, and mental models. They involve the comparing of relationships, as when we make an imperfect analogy between is-bigger-than and is-faster-than, by inferring that bigger-is-faster.

We humans can mentally operate in a familiar domain (for example, filing a document in a file folder or throwing it in a wastebasket) and carry this relationship over to a less familiar domain (saving or deleting computer files, perhaps by means of moving icons on a screen). We can make a gesture in one mental domain and have it interpreted in another. These mappings all break down somewhere – and, in Robert Frost’s words, we have to know how far we can ride a metaphor, judge when it’s safe.

Consider the mapping from one domain to another that Umberto Eco creates here:

The fact is that the world is divided between users of the Macintosh computer and users of MS-DOS compatible computers. I am firmly of the opinion that the Macintosh is Catholic and that DOS is Protestant. Indeed, the Macintosh is counterreformist and has been influenced by the ‘ratio studiorum’ of the Jesuits. It is cheerful, friendly, conciliatory, it tells the faithful how they must proceed step by step to reach – if not the Kingdom of Heaven – the moment in which their document is printed. It is catechistic: the essence of revelation is dealt with via simple formulae and sumptuous icons. Everyone has a right to salvation.

DOS is Protestant, or even Calvinistic. It allows free interpretation of scripture, demands difficult personal decisions, imposes a subtle hermeneutics upon the user, and takes for granted the idea that not all can reach salvation. To make the system work you need to interpret the program yourself: a long way from the baroque community of revelers, the user is closed within the loneliness of his own inner torment.

You may object that, with the passage to Windows, the DOS universe has come to resemble more closely the counterreformist tolerance of the Macintosh. It’s true: Windows represents an Anglican-style schism, big ceremonies in the cathedral, but there is always the possibility of a return to DOS to change things in accordance with bizarre decisions. . . .

And machine code, which lies beneath both systems (or environments, if you prefer)? Ah, that is to do with the Old Testament, and is Talmudic and cabalistic.

Most mappings are simpler, as when objects are associated with a sequence of phonemes (as in naming). Chimpanzees, with some effort, can learn simple analogies, such as A is to B as C is to D. If the chimp could apply such mental manipulations to events in its everyday life, instead of using them only while at the testing apparatus, it would be a more capable ape. Humans, obviously, keep mapping into more and more abstract domains, notching stratified stability up a few more levels.

Safety is the big problem with trial combinations, ones that produce behaviors that have never been done before. Bigger isn’t always faster. Even simple reversals in order can yield dangerous novelty, as in ‘Look after you leap.’ In 1943, in his book The Nature of Explanation, the British psychologist Kenneth Craik proposed that

the nervous system is . . . a calculating machine capable of modeling or paralleling external events. . . . If the organism carries a ‘small-scale model’ of external reality and of its own possible actions within its head, it is able to try out various alternatives, conclude which is the best of them, react to future situations before they arise, utilise the knowledge of past events in dealing with the future, and in every way to react in a much fuller, safer and more competent manner to the emergencies which face it.

Humans can simulate future courses of action and weed out the nonesence off-line; as the philosopher Karl Popper has said, this ‘permits our hypotheses to die in our stead.’ Creativity – indeed, the whole high end of intelligence and consciousness – involves playing mental games that shape up quality.

What sort of mental machinery might it take to do something of the sort that Craik suggests?

The American psychologist William James was talking about mental processes operating in a darwinian manner in the 1870s, little more than a decade after Charles Darwin published On the Origin of Species. The notion of trial and error was developed by the Scottish psychologist Alexander Bain in 1855, but James was using evolutionary thinking in addition.

Not only might darwinism shape up a better brain in two million years without the guiding hand of a master potter, but another darwinian process, operating in the brain, might shape up a more intelligent solution to a problem on the milliseconds-to-minutes timescale of thought and action. The body’s immune response also appears to be a darwinian process, whereby antibodies that are better and better fits to the invading molecule are shaped up in a series of generations spanning several weeks.

Darwinian processes tend to start from the biological basic: reproduction. Copies are always happening. One theory of making up your mind is that you form some plans for movement – making an open hand, or a V-sign, or a precision pincer movement – and that these alternative movement plans reproductively compete with one another until one ‘wins.’ According to that theory, it takes a critical mass of command clones before any action is finally initiated.

Darwinism requires a lot more than just reproduction and competition, however. When I try to abstract the essential features of a darwinian process from what we know about species evolution and the immune response, it appears that a Darwin Machine must possess six essential properties, all of which must be present for the process to keep going:

It involves a pattern. Classically, this is the string of DNA bases called a gene. As Richard Dawkins pointed out in The Selfish Gene, the pattern could also be a cultural one such as a melody, and he usefully coined the term meme for such patterns. The pattern could also be the brain activity patterns associated with thinking a thought.

Copies are somehow made of this pattern. Cells divide. People hum or whistle a tune they’ve overheard. Indeed, the unit pattern (that’s the meme) is defined by what’s semi-reliably copied – for example, the gene’s DNA sequence is semi-reliably copied during meiosis, whereas whole chromosomes or organisms are not reliably copied at all.

Patterns occasionally change. Point mutations from cosmic rays may be the best-known alterations, but far more common are copying errors and (as in meiosis) shuffling the deck.

Copying competitions occur for occupation of a limited environmental space. For example, several variant patterns called bluegrass and crabgrass compete for my backyard.

The relative success of the variants is influenced by a multifaceted environment. For grass, the operative factors are nutrients, water, sunshine, how often the grass is cut, and so on. We sometimes say that the environment ‘selects,’ or that there is selective reproduction or selective survival. Charles Darwin called this biasing by the term natural selection.

The next generation is based on which variants survive to reproductive age and successfully find mates. The high mortality among juveniles makes their environment much more important than that of adults. This means that the surviving variants place their own reproductive bets from a shifted base, not from where the center of the variations was at conception (this is what Darwin called the inheritance principle). In this next generation, a spread around the currently successful is again created. Many new variants will be worse than the parental average, but some may be even better ‘fitted’ to the environment’s collection of features.

From all this, one gets that surprising darwinian drift toward patterns that almost seem designed for their environment. (There! I actually managed to work ‘intelligent design’ into this intelligence book; maybe there’s hope yet for ‘military intelligence.’)

Sex (which is shuffling genes using two decks) isn’t essential to the darwinian process, and neither is climate change – but they add spice and speed to it, whether it operates in milliseconds or millennia. A third factor accelerating the darwinian process is fragmentation and the isolation that follows: the darwinian process operates more quickly on islands than on continents. For some fancy darwinian processes requiring speed (and the timescale of thought and action certainly does), that might make fragmentation processes essential. A decelerating factor is a pocket of stability that requires considerable back-and-forth rocking in order to escape from it; most stable species are trapped in such stabilizing pockets.

People are always confusing particular parts, such as ‘natural selection,’ with the darwinian whole. But no one part by itself will suffice. Without all six essentials, the process will shortly grind to a halt.

People also associate the darwinian essentials exclusively with biology. But selective survival, for example, can be seen when flowing water carries away the sand and leaves the pebbles behind. Mistaking a part for the process (‘Darwinism is selective survival’) is why it has taken a century for scientists to realize that thought patterns may also need to be repeatedly copied – and that copies of thoughts may need to compete with copies of alternative ones on ‘islands’ during a series of mental ‘climate changes’ in order to rapidly evolve an intelligent guess.

In our search for suitable brain mechanisms for guessing intelligently, we now have (1) those nested boxes of syntax that underlie strings; (2) argument structure with all its clues about probable roles; (3) those relative position words such as near-into-above; (4) the limited size of scratch-pad memory and the consequent chunking tendencies; and (5) common core facilities for fancy sequences, with quite a lot of need for extra copies of the neural patterns used to produce ballistic movements. Our sixth clue, from darwinian processes, now appears to be a whole suite of features: distinctive patterns, copying them, establishing variants via errors (with most of the variants coming from the most successful), competition, and the biasing of copying competitions by a multifaceted environment. What’s more, it looks as if the multifaceted environment is partly remembered and partly current.

Fortunately, there is some overlap of darwinian considerations with those from the ballistic movements: darwinian backyard work spaces might utilize the ‘get set’ scratch pads, and darwinian copying could help produce the jitter-reducing movement command clones. What else might correspond? In particular, what are those patterns that we might need to clone, on the timescale of thought and action?

Thoughts are combinations of sensations and memories – or, looked at another way, thoughts are movements that haven’t happened yet (and maybe never will). They’re fleeting and mostly ephemeral. What does this tell us?

The brain produces movements by means of a barrage of nerve impulses going to the muscles, whether of the limbs or the larynx. Each muscle is activated at a somewhat different time, often only briefly; the whole sequence is timed as carefully as the finale of a fireworks display. A plan for a movement is like a sheet of music or a player-piano roll. In the latter case, the plan covers eighty-eight output channels and the times at which each key is struck, and, indeed, the ballistic movements involve almost as many muscles as the piano has notes. So a movement is a spatiotemporal pattern not unlike a musical refrain. It might repeat over and over, like the rhythms of locomotion, but it could also be more like a one-shot arpeggio, triggered by another temporal pattern.

Some spatiotemporal patterns in the brain probably qualify for the name cerebral code. Though individual neurons are more sensitive to some features of an input than others, no single neuron represents your grandmother’s face. Just as your sense of a color depends on the relative activity in three different cone pathways from the retina, and a taste can be represented by the relative amounts of activity in about four different types of tongue receptors, so any one item of memory is likely to involve a committee of neurons. A single neuron, like any one key on the piano, is likely to play different roles in different melodies (most often, of course, its role is to keep quiet – again, like a piano key).

A cerebral code is probably the spatiotemporal activity pattern in the brain which represents an object, an action, or an abstraction such as an idea – just as bar codes on product packages serve to represent without resembling. When we see a banana, various neurons are stirred by the sight: some of the neurons happen to specialize in the color yellow, others in the short straight lines tangent to the banana’s curve. Evoking a memory is simply reconstituting such a pattern of activity, according to the cell-assembly hypothesis put forward in 1949 by the Canadian psychologist Donald O. Hebb.

So, the banana committee is like a melody, if we imagine the neurons involved as unpacked along a musical scale. Some neurophysiologists think that the involved neurons all have to fire synchronously, as in a chord, but I think that a cerebral code is more like a short musical melody, comprised of chords and individual notes; we neurophysiologists just find it easier to interpret chords than we do scattered single notes. What we really need are the families of strange attractors associated with words, but that’s another book! (The Cerebral Code.)

Music is the effort we make to explain to ourselves how our brains work. We listen to Bach transfixed because this is listening to a human mind.

Lewis Thomas, The Medusa and the Snail, 1979

We know that long-term memories cannot be spatiotemporal patterns. For one thing, they survive even massive shutdowns of the electrical activity in the brain, as in seizures or coma. But we now have lots of examples of how to convert a spatial pattern into a spatiotemporal one: musical notation, player pianos, phonograph records – even bumps in a washboarded road waiting for a car to come along and recreate a bouncing spatiotemporal pattern.

This is what Donald Hebb called dual-trace memory: a short-term active version (spatiotemporal) and a long-term spatial-only version similar to a sheet of music or the grooves on a phonograph record.

Some of these ‘cerebral ruts’ are as permanent as those in the grooves of a phonograph record. The bumps and ruts are, essentially, the strengths of the various synapses that predispose the cerebral cortex to produce a repertoire of spatiotemporal patterns, much like the connection strengths in the spinal cord predispose it to produce the spatiotemporal patterns we know as walking, trotting, galloping, running, and so forth. But short-term memories can be either active spatiotemporal patterns (probably what is called ‘working memory’ in the psychology literature) or transient spatial-only patterns – temporary ruts that somewhat overwrite the permanent ruts but don’t vibrate (they merely fade in a matter of minutes). They’re simply the altered synaptic strengths (what is called ‘facilitation’ and ‘long-term potentiation’ in the neurophysiological literature), the bumps left behind by a repetition or two of the characteristic spatiotemporal pattern.

The truly persistent bumps and ruts are unique to the individual, even to each identical twin, as the American psychologist Israel Rosenfield explains:

Historians constantly rewrite history, reinterpreting (reorganizing) the records of the past. So, too, when the brain’s coherent responses become part of a memory, they are organized anew as part of the structure of consciousness. What makes them memories is that they become part of that structure and thus form part of the sense of self; my sense of self derives from a certainty that my experiences refer back to me, the individual who is having them. Hence the sense of the past, of history, of memory, is in part the creation of the self.

Copying is going to be needed over long distances in the brain. Like a fax machine, the brain must take a pattern and make a distant copy of it, perhaps on the other side of the brain. The pattern cannot be physically transported in the manner of a letter, so telecopying is likely to be important when the visual cortex wants to tell the language area that an apple has been seen. The need for copying suggests that the pattern we seek is the working memory, that active spatiotemporal pattern, since it is difficult to see how ‘ruts’ would otherwise copy themselves at a distance.

A darwinian model of mind and my analysis of the activity of throwing suggest that many clones might be needed locally, not just a few in distant places. Furthermore, in a darwinian process, an activated memory must somehow compete with other spatiotemporal patterns for occupation of a work space. And the other question we must answer is, What decides if one such ‘melody’ is better than another?

Suppose a spatiotemporal pattern, produced in one little part with the aid of some appropriate ‘ruts,’ manages to induce the same melody in another cortical area that lacks those ruts. But the pattern can nonetheless be performed there, thanks to the active copying process nearby, even if it might not sustain itself without the driving patterns, the same way a square dance might fizzle out without a caller. If an adjacent area has bumps and ruts that are ‘close enough,’ the melody might catch on better, and die out less readily, than some other imposed melody. So resonating with a passive memory could be the aspect of the multifaceted environment that biases a competition.

In this way, the permanent bumps and ruts bias the competition. But so do the fading ones that were made by spatiotemporal activity patterns in that same patch of cortex a few minutes earlier. So, too, do the current active inputs to the region from elsewhere – the ones that are (like most synaptic inputs) in themselves too weak to induce a melody or create ruts. Probably most important is the background of secretions from the four major diffuse projection systems, the ones associated with the serotonin, norepinephrine, dopamine, and acetylcholine neuromodulators. Other emotional biases surely come from the neocortical projections of the such subcortical brain sites as the amygdala. Thalamic and cingulate gyrus inputs may bias competitions elsewhere, in the name of shifting your attention from external to memorized environments. Thus the current real-time environment, memories of near-past and long-past environments, emotional state, and attention all change the resonance possibilities, all likely bias the competition that shapes up a thought. Yet they could do it without themselves forming up clones to compete for cortical territory.

The picture that emerges from such theoretical considerations is one of a quilt, some patches of which enlarge at the expense of their neighbors as one code copies more successfully than another. As you try to decide whether to pick an apple or a banana from the fruit bowl (so my theory goes), the cerebral code for apple may be having a cloning competition with the one for banana. When one code has enough active copies to trip the action circuits, you might reach for the apple.

But the banana codes need not vanish; they could linger in the background as subconscious thoughts, undergoing variations. When you unsuccessfully try to remember someone’s name, the candidate codes might continue copying for the next half hour, until suddenly Jane Smith’s name seems to ‘pop into your mind,’ because your variations on the spatiotemporal theme finally hit a resonance good enough to generate a critical mass of identical copies. Our conscious thought may be only the currently dominant pattern in the copying competition, with many other variants competing for dominance, one of which will win a moment later, when your thoughts seem to shift focus.

It may be that darwinian processes are only the frosting on the cognitive cake; it may be that much is routine or rulebound. But we often deal with novel situations in creative ways, as when you decide what to fix for dinner tonight. You survey what’s already in the refrigerator and on the kitchen shelves. You think about a few alternatives, keeping track of what else you might have to fetch from the grocery store. All this can flash through your mind within seconds – and that’s probably a darwinian process at work, as is speculating about what tomorrow might bring.

We build mental models that represent significant aspects of our physical and social world, and we manipulate elements of those models when we think, plan, and try to explain events of that world. The ability to construct and manipulate valid models of reality provides humans with our distinctive adaptive advantage; it must be considered one of the crowning achievements of the human intellect.

Gordon H. Bower and Daniel G. Morrow, 1990

Conflicts of representation are painful for a variety of reasons. On a very practical level, it is painful to have a model of reality that conflicts with those of the people around you. The people around you soon make you aware of that. But why should this conflict worry people, if a model is only a model, a best guess at reality that each of us makes? Because nobody thinks of it in that way. If the model is the only reality you can know, then that model is reality, and if there is only one reality, then the possessor of a different model must be wrong.

Derek Bickerton, 1990

CHAPTER 7

SHAPING UP AN INTELLIGENT ACT FROM HUMBLE ORIGINS

The schematicism by which our understanding deals with the phenomenal world . . . is a skill so deeply hidden in the human soul that we shall hardly guess the secret trick that Nature here employs.

Immanuel Kant, Kritik der reinen Vernunft, 1787

‘Why,’ said the Dodo, ‘the best way to explain it is to do it.’

Lewis Carroll, Alice’s Adventures in Wonderland, 1865

Is this chapter really necessary? Well, no – in the sense that many people could skip to the last chapter without realizing that something was missing.

It all depends on how satisfied you are with organization charts. Some people don’t want to know any more. ‘Skip the details,’ they say, ‘and just stick with the executive summary.’ But this chapter really isn’t about the details omitted from the last chapter – it’s written from a different perspective, bottom-up rather than inferred from principles.

Principles are, unfortunately, rather like organization charts – a sketchy, convenient fiction. Real organizations have a flow of information and decision making that isn’t captured by the boxes and labels. Charts fail to take account of people and how they talk to one another, fail to take account of the ‘institutional memory.’ They fail to take account of how experts can also be generalists, of how decisions taken at one level interact with those taken at another. Any schematic account of the brain will share the shortcomings of organization charts.

This account of intelligence has, so far, failed to take much account of neurons – the nerve cells of the brain – and how they talk to one another, how they remember past events, how they collectively make decisions on a local and regional scale. Some of that simply isn’t known yet, but it is certainly possible to sketch out a plausible account of copying competitions among the cerebral codes.

Whenever you are talking science, a good general rule is always to give a specific example – even if it is only a possible mechanism rather than a well-established one.

That’s what this chapter provides: an example of how our cerebral cortex might function as a Darwin Machine and, in the process, create that constantly shifting focus of consciousness, even those subconscious thoughts that every so often pop into the foreground, unbeckoned. It shows how we might achieve the off-line ability to simulate our future actions in the real world – an ability that is the essence of guessing-right intelligence.

The inability to imagine a mechanism that could produce mind is at the heart of many of the Janitor’s Dream and the mind-in-a-computer objections. This chapter describes the building blocks with which I can imagine how a thinking machine could be constructed. Your mileage may vary – but here’s your chance, just one chapter long, to see a bottom-up mechanistic example of how our mental lives might operate, both consciously and subconsciously, both for the novel and the routine.

Gray matter isn’t really gray, except in a dead brain; in a living brain, it has a rich blood supply. Think of those rivers that run reddish-grayish-brown after a thunderstorm, and you’ll have the right hue for the dynamic ‘gray matter.’

The white matter in the brain, however, is really white, a porcelain hue, because of the fat that insulates the long, stringy part of a neuron. This part, which is called the ‘axon,’ is analogous to a wire and carries the neuron’s output signal to near and distant targets. ‘Myelin’ is the proper name for its fatty insulation. White matter is simply wire bundles, going every which way, much as you would see in the basement of a telephone-central-office building. The bulk of the brain is insulated wires connecting the parts that do the hard work, which are far smaller.

At one end of the axon is the neuron’s cell body, the globular part of the cell containing the nucleus, with the DNA blueprints for the cell’s day-to-day operation and maintenance. There are lots of treelike branches, called dendrites, arising from the cell body. Because cell bodies and dendrites lack the white insulation, large collections of them look ‘gray.’ The far end of a neuron’s axon appears to be touching the dendrite of a downstream neuron – though, if you look carefully with an electron microscope, you’ll see a little gap between the two cells called a synapse. Into this no-man’s-land the upstream neuron releases a little neurotransmitter, which drifts across the gap and opens up some channels through the membrane of the downstream neuron. (Though there are some retrograde neurotransmitters in addition, a synapse is usually a one-way street, so it’s useful to refer to ‘upstream’ and ‘downstream’ neurons.)

Overall, a single neuron looks like a bush, or the root of some herb such as ginger. It is the typical unit of computation, summing up the influences of a few thousand inputs – most of them excitatory, and some of them inhibitory, like deposits and checks – and speaking, in a single voice, to several thousand hardwired listeners.

The message sent from this ‘checking account’ mostly concerns its ‘account balance’ and how fast that balance is increasing. No message is sent unless the balance exceeds some threshold. Big deposits generate big messages, like interest payments with a bonus. But, just as piano keys don’t produce any sound unless struck hard enough, cortical neurons are usually silent unless input conditions are surging – and then their output is proportional to how much they’re stimulated by that account balance. (Oversimplified binary models usually treat a neuron as more like a harpsichord key, with a threshold but no gradation in volume for harder hits.)

Though the messages from short neurons can be simpler, neurons with axons longer than about 0.5 mm always utilize a signal booster: the impulse, a brief up-and-down voltage change of a standard size (like the loudness of that harpsichord key). Amplified and fed into a loudspeaker, the impulse sounds like a click (and we talk of the neuron ‘firing’). To get around the standard-size limitation, impulses usually repeat at a rate proportional to the account balance, the same way that a few quick repetitions of a harpsichord note may imitate a hard-struck piano note. Sometimes – especially in the cerebral cortex – just a few inputs, out of thousands, can conspire to trigger an impulse.

The really interesting gray matter is that of the cerebral cortex, because that’s where most of the novel associations are thought to be made – where the sight of a comb, say, is matched up to the feel of a comb in your hand. The cerebral codes for sight and feel are different, but they become associated somehow in the cortex, along with those for hearing the sound /kōm/ or hearing the characteristic sounds that the teeth of a comb make when they’re plucked. You can, after all, identify a comb in any of these ways. It’s hypothesized that there are specialized places in the cortex, called ‘convergence zones for associative memories,’ where those different modalities come together.

On the production side, you have linked cerebral codes for pronouncing /kōm/ and for generating the movements that manipulate a comb through the hair on your head. So between the sensory version of the word ‘comb’ and the various movement manifestations, we expect to find a dozen different cortical codes associated with combs.

The cortical areas that do all this associating for us are a thin layer of icing on the cake of the white matter. The cerebral cortex is only about 2 mm thick, though it is deeply wrinkled. The neocortex (which is all of the cerebral cortex except for the hippocampus and some of the olfactory areas) has a surprisingly uniform packing density (with the exception of one layer of the primary visual cortex). If you made a grid atop the cortical surface, each square millimeter would have about 148,000 neurons beneath it – whether it was language cortex or motor cortex. But a sideways look, at the layers within that 2 mm depth, reveals some regional differences.

It’s the icing of this cake that contains the layers, not the cake itself. A better bakery analogy might be a flaky pie crust made of croissantlike layers. The deepest layers are like an out-box, their wires mostly heading out of the cortex, bound for distant subcortical structures, such as the thalamus or the spinal cord. The middle layer is an in-box, with wires arriving from the thalamus and other such places. The superficial layers are like an interoffice-box; they make ‘corticocortical’ connections with the superficial layers of other regions, both adjacent and distant. It’s their axons that go through the corpus callosum to the other side of the brain – but most of the interoffice mail is delivered locally, within several millimeters. Such axon branches run sideways, rather than detouring through the white matter like the longer ‘U-fiber’ branches.

Some regions have big in-boxes and small out-boxes, just like the ones to be found on the editorial-department desk that deals with letters to the editor. Superimposed on this stacked horizontal organization, moreover, is a fascinating set of vertical arrangements, similar to newspaper columns.

If we go around wiretapping the individual neurons in the cerebral cortex, we discover that neurons with similar interests tend to be vertically arrayed there, forming cylinders known as cortical columns, which cut through most of the layers. It’s almost like a club that self-organizes out of a crowd at a party, where people of similar interests tend to cluster together. We have naturally given names to these cortical clubs. Some of the names reflect their size, some their seeming specialties (so far as we know them).

The thin cylinders, or minicolumns, are only about 0.03 mm in diameter (that’s a very thin hair, closer to the threads of a spider web). The best-known examples of these are the visual cortex’s orientation columns, whose neurons seem to like visual objects with a line or border tilted at a particular angle. The neurons in one minicolumn will respond best to boundaries tilted at 35°, those in another will like horizontals or verticals, and so forth.

You can look in a microscope and see (well, it takes some doing, even after a century of progress in neuroanatomical technique) a group of cortical neurons bundled together like stalks of celery. There is a tall ‘apical dendrite’ that stretches up toward the cortical surface from the cell body (which is often triangular in appearance, hence the name ‘pyramidal neuron’). It is those apical dendrites of the pyramidal neurons that are bundled together, with 0.03 mm between adjacent bundles. There are about a hundred neurons in a minicolumn organized around one of those bundles, though the bundle at any one level might only have a dozen apical dendrites in it. Bundling is commonplace outside visual cortex, so minicolumns are likely a common element of cortical organization, just from the anatomy – but elsewhere we are ignorant of what the neurons of a minicolumn are ‘interested in.’

Other ‘interest groups’ tend to be much larger and comprised of more than a hundred minicolumns; these so-called macrocolumns are 0.4–1.0 mm across (that’s a thin pencil lead) and sometimes appear more like elongated curtain folds than like proper cylinders. Such macrocolumns seem to result from an organization of the inputs – for example, in visual cortex those axons carrying information from the left eye tend to alternate every 0.4 mm with those being relayed from the right eye. Inputs from other parts of the cortex itself tend to do the same thing; for example, looking at the cortical area just in front of the corpus callosum, you can see the inputs from the prefrontal cortex forming a macrocolumn, flanked on either side by macrocolumns formed by a clustering of parietal-lobe inputs.

The cortical neurons interested in color tend to cluster together (though not exclusively) in ‘blobs.’ Unlike macrocolumns, blobs don’t extend through all layers of the cortex; they’re found only in the superficial layers – up there with the interoffice mail. And they’re not exclusively comprised of color specialists: perhaps only 30 percent of the neurons in a blob are color sensitive. The distances between blobs are similar (if not identical) to the those of the macrocolumns.

Next level of organization? On the basis of layer thickness changing, there are fifty-two ‘Brodmann Areas’ in each human hemisphere. At a boundary between Areas, you’ll see the relative thickness of those interoffice-in-out stacked boxes change, as if the relative amounts of incoming, outgoing, and interoffice mail differed on adjacent ‘desks.’

Area 17 is better known as the primary visual cortex, but generally it is premature to put functional labels on these areas in the manner of departments on an organization chart (Area 19, for example, has a half-dozen functional subdivisions). A Brodmann Area averages 21 cm2 in unwrinkled area. If the visual cortex ratio holds elsewhere, that’s on the order of 10,000 macrocolumns and a million minicolumns in the average cortical area.

That factor of a hundred keeps recurring: a hundred neurons to a minicolumn, roughly a hundred minicolumns to a macrocolumn, a hundred times a hundred macrocolumns to a cortical area (which makes me wonder if we’re missing an intermediate ‘super-column’ or ‘mini-area’ organization on the scale of a hundred macrocolumns), and there are just over a hundred Brodmann Areas when you total those in both cerebral hemispheres.

Can we extend this hundredfold multiplier further? It does put us into the scale of social organizations: What’s a hundred brains? That suggests certain legislative bodies such as the US Senate. And the United Nations is representative of more than a hundred legislatures.

Permanent elements of brain organization, such as cortical areas or minicolumns, are nice to know about. But we also need to understand those temporary work spaces of the brain – something closer to scratch pads and buffers – that are likely superimposed on the more permanent forms of anatomical organization.

To deal with the novel, we are indeed going to need some empirical types of organization, like those hexagonal cells that form in the cooking oatmeal when you forget to stir it – forms that are used temporarily and then disappear. Occasionally these forms of organization are recalled to life if some aspect of them earlier formed enough ‘ruts’ in the landscape of interconnection strengths – in which case the empirical organization became a new memory or habit.

In particular, we need to know about the cerebral codes – those patterns that represent each of the words of our vocabulary, and so forth – and what creates them. At first, it appears that we are dealing with a four-dimensional pattern – the active neurons scattered through three-dimensional cortex, as they perform in time. But largely because the minicolumns seem to organize all the cortical layers around similar interests, most people working on cortex think of it as a two-dimensional sheet, rather like the retina (yes, the retina is 0.3 mm thick and is subdivided into a few layers, but the mapping is clearly for a two-dimensional image).

So we can try thinking of two dimensions, plus time, for cortex (which is, of course, the way we apprehend the images on a movie screen or computer terminal) – perhaps with transparent overlays when the different cortical layers do different things. Just imagine the human cortex flattened out on those four sheets of typing paper like pie crust, with little patches lighting up like message-board pixels. What patterns will we observe when that cortex is seeing a comb? When the word ‘comb’ is heard, or said? When the cortex is commanding a hand to comb the hair?

Memory recall may consist of the creation of a spatiotemporal sequence of neuron firings – probably a sequence similar to the firing sequence at the time of the input to memory, but shorn of some of the nonessential frills that promoted it. The recalled spatiotemporal pattern would be something like a message board in a stadium, with lots of little lights flashing on and off, creating an overall pattern. A somewhat more general version of such a Hebbian cell assembly would avoid anchoring the spatiotemporal pattern to particular cells, to make it more like the way the message board can scroll. The pattern continues to mean the same thing, even when it’s implemented by different lights.

Though we tend to focus on the lights that turn on, note that lights that stay off also contribute to the pattern; if they are turned on randomly – by seizures, for example – they fog the pattern. Something similar to this fogging seems to happen in concussions: while an injured football player is being helped off the field, he can often tell you what play he was running, but ten minutes later he can’t remember what happened to him. Injury slowly causes a lot of neurons to ‘light up’ and patterns therefore become obscured in the manner of bright fog – what mountain climbers call ‘white-outs.’ (Just remember: blackouts are sometimes from white-outs.)

What’s the most elementary pattern that means something? A major clue, it seems to me, is that pattern copying is needed, for various reasons.

Before DNA leapt to prominence, geneticists and molecular biologists were searching for a molecular structure that was capable of being reliably copied during cell division. One of the reasons that the double helix structure was so deeply satisfying when it was discovered in 1953 by Crick and Watson (and I write this while temporarily at the University of Cambridge, just across the courtyard from the building where they worked) was that it provided a way of making a copy, via the complementary pairs of DNA bases (C bonds with G, A pairs with T). Unzip the double helix into two separate halves and each DNA position on a half-zipper will soon be paired with another of its opposite type, just from all the loose ones floating around in the nucleotide soup. This gives you two identical double helices, where there was only one before. This copying principle paved the way for the understanding of the genetic code (how those DNA triplets ‘represented’ the amino acid string that folds up into a protein) a few years later.

Is there a similar copying mechanism for cerebral activity patterns, and might it help us identify the most relevant of the Hebbian cell assemblies? That’s the one we could properly call the cerebral code because it is the most elementary way of representing something (a particular connotation of a word, an imagined object, and so forth).

Copying hasn’t been observed in the brain yet – we don’t currently have tools of sufficient spatial and temporal resolution, though we’re close. But there are three reasons why I think it’s a safe bet.

The strongest argument for the existence of copying is the darwinian process itself, which is inherently a copying competition biased by a multifaceted environment. It’s so elementary a method for shaping up randomness into something fancy that it would be surprising if the brain didn’t use it.

Copying is also what’s needed for precision ballistic movements, such as throwing – those dozens-to-hundreds of clones of the movement-command patterns that are required to hit the launch window.

Then there’s that faux fax argument of the last chapter: communication within the brain requires the telecopying of patterns.

Since 1991, my favorite candidate for a local neural circuit that could make copies of spatiotemporal patterns has been the mutually reinforcing circuitry of the interoffice-mail layers. The wiring of those superficial layers of cerebral cortex is, in a word, peculiar. Indeed, to a neurophysiologist, almost alarming. I look at those circuits and wonder how runaway activity is reined in, why seizures and hallucinations aren’t frequent events. But those same circuits have some crystallization tendencies that ought to be particularly good at cloning spatiotemporal patterns.

Of the hundred neurons in a minicolumn, about thirty-nine are superficial pyramidal neurons (that is, their cell bodies reside in the superficial layers II and III). It’s their circuitry that is peculiar.

Like all other pyramidal neurons, they secrete an excitatory neurotransmitter, usually glutamate. There’s nothing peculiar about glutamate per se; it’s one of the amino acids, more typically used as a building block of peptides and proteins. Diffusing across the synapse, the glutamate opens up several types of ion channels through the membrane of the next cell’s dendrite. The first channel specializes in letting sodium ions through; that in turn raises the internal voltage of the downstream neuron.

A second downstream channel activated by glutamate is known as the NMDA channel, and it allows calcium ions into the downstream neuron along with some more sodium. NMDA channels are particularly interesting to neurophysiologists because they contribute to so-called long-term potentiation (LTP), a change in synaptic strength that endures for some minutes in neocortex. (Minutes, actually, are closer to the neurophysiological ‘short-term,’ but LTP sometimes lasts days in the hippocampus – which is an older and simpler version of cortex – and that’s where the ‘long-term’ name originated.)

LTP occurs when there is near synchrony (within dozens to hundreds of milliseconds) of several inputs to the downstream neuron; it simply turns up the ‘loudness control’ for those inputs for a few minutes. These are the ‘bumps and ruts’ that temporarily make it easier to recreate a particular spatiotemporal pattern. LTP is our best candidate for a short-term memory that can survive a distraction. It is also thought to contribute the scaffolding for the construction of truly long-lasting structural changes in synapses – the permanent bumps and ruts that aid in the recreation of long-unused spatiotemporal patterns.

The interoffice layers are where most of the NMDA channels are located, and where most of the neocortical LTP occurs. These superficial layers have two more peculiarities, both of them having to do with the connections that their pyramidal neurons make with one another. On average, a cortical neuron contacts fewer than 10 percent of all neurons within a radius of 0.3 mm. But roughly 70 percent of the excitatory synapses on any superficial-layer pyramidal neuron are derived from pyramidal neurons less than 0.3 mm away, so these neurons may be said to have an unusually strong propensity to excite one another. To a neurophysiologist, that raises all sorts of red flags: it’s a perfect setup for instability and wild oscillations, unless it’s carefully regulated.

There is also a peculiar patterning to these ‘recurrent excitatory’ connections – a patterning not seen in the lower cortical layers. The axon of a superficial pyramidal neuron travels sideways a characteristic distance without making any synapses with other neurons, and then it produces a tight terminal cluster. Like an express train, it skips intermediate stops. In the primary visual cortex, the distance from the cell body to the center of the terminal cluster is about 0.43 mm in primary visual cortex; next door in a secondary visual area, it’s 0.65 mm; in the sensory strip, it’s 0.73 mm; and in motor cortex of monkeys, it’s 0.85 mm. Let me, for convenience, just call this skip-spacing a generic 0.5 mm. The axon may then continue for an identical distance and sprout another terminal cluster, and this express train line may continue for some millimeters.

This skip-spacing is distinctly peculiar in the annals of cortical neuroanatomy. Its function is unknown, but it certainly does make you think that regions 0.5 mm apart might be doing the same thing on occasion – that there could be repeating patterns of activity, in the manner of recurring patterns within wallpaper.

The skip-spacing, you may have noticed, is the same half millimeter or so as the distance between macrocolumns. Color blobs, too, are about that far apart from one another. Yet there’s a difference.

A second superficial pyramidal neuron 0.2 mm from the first will itself have an axon with different express stops, still at 0.5 mm skips but each cluster landing 0.2 mm from those of the first. In my undergraduate days, the Chicago Transit Authority had exactly such a system of A trains and B trains, one taking the ‘even’ stops and the other the ‘odd’ numbered ones, with a few common stops for transferring between trains. Of course, any one subway stop is sometimes stretched out over more than a city block – and our superficial pyramidal neurons are also not located at a single point, as their dendritic tree spreads sideways from the cell body, often 0.1 mm or more.

Contrast this to macrocolumns. So far, they’ve been territories within which there is common source of input, as if you could draw a fence around a group of minicolumns on the basis of their all being on the same mailing list. And the blobs have an output target in common (secondary cortical areas specializing in color). So we’re not talking macrocolumns with our sideways-running excitatory axon branches, though perhaps the skip-spacing is a cause (or effect) of the macrocolumns at an adjacent level of organization. Imagine a forest where tree branches interdigitate, where each tree has a telephone line leaving it and contacting a distant tree, not only bypassing the intermediate ones, but leaping over the common-input fences subdividing the forest.

Sideways ‘recurrent’ connections are common in real neural networks; lateral inhibition was the topic of two Nobel Prizes (to Georg von Békésy in 1961 and H. Keffer Hartline in 1967). It tends to sharpen up fuzzy boundaries in a spatial pattern (while they may compensate for fuzzy optics, they can also produces a few side effects, such as some of the visual illusions). But our superficial pyramidal neurons are excitatory to one another, suggesting that their activity could feed on itself like a spreading brushfire, unless held in check by inhibitory neurons. What’s going on here? Is recurrent excitation why the cerebral cortex is so prone to epileptic seizures, when the inhibitory neurons are fatigued?

Furthermore, the standard skip-spacing means that a round-trip might be possible – a reverberating circuit, of the kind postulated by early neurophysiologists. Two neurons that are 0.5 mm apart may keep each other going. A neuron has a refractory period – a kind of ‘dead zone’ – after an impulse is produced: for a millisecond or so, it is almost impossible to initiate another impulse. The travel time over that 0.5 mm is also about a millisecond, and then the synaptic delay slows delivery by another half a millisecond – so if the connections between the two neurons were otherwise strong enough, you can imagine the second neuron’s impulse getting back to the first neuron about the time it has recovered its ability to generate another impulse. But usually connection strength between neurons isn’t strong enough, and usually such rapid firing cannot be kept up, even if it does get started. (In the heart, however, connection strengths between adjacent cells are indeed strong enough, and circus re-excitation is an important pathology when injury slows travel times.)

If the implication of cortex’s standard skip-spacing isn’t an impulse chasing its tail, then what is it? Probably synchronization.

If you sing in the chorus, you get in sync with the others by hearing them – usually hearing yourself coming in too late or starting too early. But you, of course, are also influencing them. Even if everyone is a little hard of hearing, everyone soon gets synchronized, thanks to all that feedback.

Your position in that chorus is very much like that of a superficial pyramidal neuron in the neocortex, getting excitatory inputs from neighbors on all sides. Networks like this have been extensively studied, even if the one in superficial neocortex has not; synchronization will occur even with only small amounts of feedback (which is why I postulated that you were hard of hearing, just then). Two identical pendulums will tend to synchronize if they are adjacent, just from the air and shelf vibrations they create. Menstrual cycles are said to synchronize in women’s dormitories. Though harmonic oscillators, such as the pendulums, take a while to get in sync, nonlinear systems, such as impulse production in neurons, can synchronize very quickly, even if the mutual connection strengths are relatively weak.

And what does this tendency to synchronize have to do with copying spatiotemporal patterns? Happily, it’s all a matter of simple geometry, the kind that the ancient Greeks discovered while staring at the tile mosaics of their bathhouse floors (and that many of us have rediscovered in wallpaper patterns).

Let us suppose that a ‘banana committee’ is forming among all the superficial pyramidal neurons scattered around the primary visual cortex that respond to one feature or another of the banana you’re looking at. The lines forming the outline of the banana are a particularly effective prod to those neurons that specialize in boundaries and their orientation. Then there are those blob neurons that like yellow.

Since they tend to excite one another, given that 0.5 mm skip-distance for their axon terminal clusters, there is going to be a tendency for them to synchronize – not that all impulses in the neuron I’ll call Yellow One will be synchronized with those in Yellow Two, but a certain percentage will occur within a few milliseconds of one another.

Suppose now that there is another superficial pyramidal neuron, 0.5 mm equidistant from both Yellow One and Yellow Two. Perhaps it only receives a weak yellow input, so that it isn’t actively firing away, signaling yellow. Now, however, Yellow Three is getting inputs from both One and Two. Furthermore, some of those inputs from One and Two – the synchronized ones – will arrive at Three’s dendrites together. (They both have the same 0.5 mm travel distance.) This is exactly what hi-fi buffs call ‘sitting in the hot spot,’ equidistant from both speakers at the apex of an equilateral triangle (move even slightly to either side and the stereo illusion collapses into the nearest speaker, leaving you with mono sound). At the cortical hot spot near Three, the two synaptic inputs summate, 2 + 2 = 4 (approximately). But the distance remaining to the impulse threshold may be 10, so Three still remains silent.

Not very interesting. But these are glutamate synapses in the superficial cortical layers, so they’ve got NMDA channels across the synapse to let both sodium and calcium into the downstream neuron. Again, not so important – by itself.

But I temporarily omitted telling you why neurophysiologists find NMDA channels so fascinating compared with other synaptic channels: they are sensitive not only to arriving glutamate but also to the preexisting voltage across the post-synaptic membrane. Raise that voltage and the next glutamate to arrive will cause a bigger effect, sometimes twice the standard amount. This is because many of the NMDA channels are normally sitting there plugged up: there’s a magnesium ion stuck in the middle of the tunnel through the membrane; increased voltage will pop it out of there – and that in turn allows formerly blocked sodium and calcium to flow into the dendrite on the next occasion when arriving glutamate opens up the gates.

The consequence of this is important: it means that synchronously arriving impulses are more effective than 2 + 2 would predict: the sum could be 6 or 8 instead (welcome to nonlinearity). Repeated near-synchronization of two inputs is even more effective, as they clean the magnesium plugs out of each other’s channels. Pretty soon, those repeatedly synchronous inputs from Yellow One and Yellow Two might be able to trigger an impulse from Yellow Three.

Standard-distance mutual re-excitation and NMDA synaptic strength augmentation have this interesting hand-and-glove fit, all because of the tendency to synchronize. Emergent properties often come from just such combinations of the seemingly unrelated.

We now have three active neurons, forming the corners of an equilateral triangle. But there might be a fourth, over on the other side of One and Two, also equidistant at 0.5 mm away. There isn’t very much data yet on how many axon branches there are from a single superficial pyramidal neuron – but looking down from the top, in one dye-filled and exhaustively reconstructed superficial pyramidal neuron, showed branches in many directions. So there ought to be a doughnutlike ring of excitation, about 0.5 mm away from the neuron. Two such rings, with centers 0.5 mm apart – as from Yellow One and Two – have two intersections, just as in that plane geometry exercise about bisecting a line.

So it wouldn’t be surprising if Yellow One and Yellow Two, once they got their act in sync, managed to recruit a Yellow Four as well as a Yellow Three. And there are other neurons at the hot spot of the pair formed by One and Three: perhaps a Yellow Five will join the chorus, if it already has enough other inputs to put the paired inputs within range of its threshold. As you can see, there is a tendency to form a triangular array of often-synchronized neurons that could extend for a few millimeters across the cortical surface.

Because one neuron can become surrounded by six others, all telling it to fire at a certain time, we have error correction: even if a neuron tries to do something different, it is forced back to the choral pattern that has become established by its insistent neighbors. That is essentially an error-correction procedure, just what the faux fax needs – if only the long corticocortical axon terminals did what the local ones do: fan out into patches about 0.5 mm apart rather than ending in a point.

And they do fan out in a patchy manner – in about the right ballpark.

The notion of ‘convergence zones’ for associative memories raises the issue of maintaining the identity of a spatiotemporal code during long-distance corticocortical messaging, such as through the corpus callosum from the left side to the right of the brain. Distortions of the spatiotemporal pattern by a lack of precise topographic mappings (axon terminations are always fanning out, not ending in a single point), or a dispersion in time (conduction velocities are not uniform), might be unimportant where the information flows in only the one direction – in that case, one arbitrary code is simply replaced by another arbitrary code in that pathway.

But because the connections between distant cortical regions are typically (six in every seven paths) reciprocal, any distortions of the original spatiotemporal firing pattern during forward transmission would need to be compensated in the reverse path, in order to maintain the characteristic spatiotemporal pattern as the local code for a sensory or motor schema. You could straighten out the distortion with an inverse transform, just as in decompressing a compressed file. Or you could fix it with the aforementioned error-correction mechanism. Or you could just live with different codes locally meaning the same thing, like names and nicknames – what’s called a degenerate code, as when six different DNA triplets all code for leucine. I used to think that either alternative was more likely than an error-correction scheme, but then I didn’t realize how simply error correction could emerge from the crystallization that ought to accompany recurrent excitation and synchrony-sensitive NMDA channels.

Imagine an optical fiber array connecting one cortical area with its homologous one on the other side. Real optical fiber bundles subdivide an image into dots, then faithfully pipe each dot a long distance so that, looking at the end of the fiber bundle, you see a pattern of lighted dots identical to that at the front end.

An axon is not like a light pipe because of all the ‘sprouts’ at each end. It doesn’t end in a point: a single axon fans out into many terminals, spreading over macrocolumn dimensions. Bundles of real axons also aren’t like a coherent fiberoptic bundle, where neighbors remain faithful neighbors; real axons can get intertwined with one another, so that a dot goes astray and ends up displaced at the other end. Real axons also vary somewhat in conduction velocity: impulses that started out together may arrive at different times, distorting the spatiotemporal pattern.

But the local error-correction property suggests that none of this might matter very much, at the far end of a corticocortical bundle. What’s being sent is a redundant spatiotemporal pattern, thanks to those triangular arrays on the originating end. Each point on the distant end might get an input from a dead-on-target axon, plus up to six inputs from neighbors 0.5 mm away back home; yes, some get lost, and some impulses arrive too late, but a receiving neuron preferentially pays attention to the repeatedly synchronous inputs, and perhaps only a few of them are needed to reproduce the firing pattern of the originating point, effectively ignoring the stragglers and the wanderers.

Once a small region of spatiotemporal pattern is re-formed again on the distant end, it can expand to clone a larger territory, just as explained earlier. So synchronized triangular arrays make it possible for sloppy wiring to send spatiotemporal patterns over long distances in the cortex – provided you start with a dozen or so spatial repeats of the spatiotemporal pattern and end with a sufficient territory of the same pattern on the far end.

How big might an array become? It might be confined to its original Brodmann area, if the skip-spacing changed at the boundary. For example, in primary visual cortex, the skip-spacing in monkeys is 0.43 mm, and next door in the secondary visual area it’s 0.65 mm; recruiting across the boundary might not work, but that’s an empirical question – we’ll just have to see. And recruiting more neurons into the triangular array requires candidates that are already mildly interested in the banana.

So the triangular array of Yellows might not be too much larger than the part of the visual cortex receiving the image of the yellow banana. The neurons sensitive to line orientation might have been doing the same thing, too: several getting in sync, recruiting a chorus of the predisposed, and so forming another 0.5 mm triangular array centered elsewhere. For each separately detected feature of the banana, there would be a different triangular array – and not necessarily extending the same distances across the cortex. Looking down on the flattened cortex (and assuming that a minicolumn lights up when an impulse fires), we would see a lot of flickering lights.

If we restricted our field of view to a 0.5 mm circle, we would be unlikely to see much synchrony, just one of the Yellows firing a few times a second, one of the Lines firing a dozen times a second, and so on. But if we broadened our field of view to several millimeters, we would see a half-dozen spots lighting up at once, then another group lighting up. Each specialty has its own triangular array; taken together, the various arrays constitute a Banana Committee.

Note that the original committee of Yellows and Lines might have been larger than 0.5 mm across, back before recruitment began to fill in things. Even if the original committee was scattered over a few millimeters, the triangular arrays serve to create a unit pattern that is much smaller (and potentially easier to recreate, when recalling the pattern). We have, in effect, compacted the code into a smaller space than it originally occupied, as well as making redundant copies. That has some interesting implications.

This is a spatiotemporal pattern having something to do with a banana’s representation, but is it the cerebral code for banana? I’d call that the smallest such pattern that didn’t omit anything important – the elementary pattern from which the triangular arrays of Lines and Yellow could be recreated.

If we zoom in, shrinking our field of view of the flickering minicolumns, what area will it cover at the point where we can no longer find synchronized minicolumns? Yes, it’s about 0.5 mm, but it isn’t a 0.5 mm circle – it is a hexagon that is 0.5 mm across between parallel faces. This is a simple matter of geometry: corresponding points (say, the upper right corners) of hexagonal tiles form triangular arrays. Anything larger than that hexagon will start including some redundant points that are represented by another of their triangular array (and we’d sometimes see two synchronized points in our restricted view of view).

The elementary pattern wouldn’t usually fill the hexagon (I imagine it as a dozen minicolumns active, out of a hundred or more in the hexagon – but the rest have to stay silent in order not to fog the pattern). We wouldn’t be able to see the boundaries outlined – so that we wouldn’t see a honeycomb when we looked down on the cortical surface while a territory was being cloned. Indeed, when wallpaper designers create a repeating pattern, they often make sure that the pattern unit’s boundary cannot be easily detected, so that the overall pattern will appear seamless. Though the triangular arrays do the recruitment and create the compact pattern, it is as if hexagons were being cloned.

The triangular synchronicity doesn’t necessarily last for very long – it’s an ephemeral form of organization, and it might be wiped out during certain phases of an EEG rhythm associated with decreases in cortical excitability. If we want to recreate a spatiotemporal pattern that has died out, we could get it started from within two adjacent hexagons – indeed, from any two adjacent hexagons that the extended banana mosaic covered originally. It wouldn’t have to be the original pairs. The memory trace – the essential bumps and ruts for resurrecting the spatiotemporal pattern – could be as small as the circuitry in two adjacent hexagons.

So repeated copying of the minimal pattern could colonize a region, in much the same way that a crystal grows or wallpaper repeats an elementary pattern. If the melody recurred enough times before it stopped, LTP might linger in such a way that the spatiotemporal pattern was easily restarted, at one place or another.

If the spatial pattern was relatively sparse, several cerebral codes (say, the ones for Apple and Tangerine) could be superimposed to give you a category, such as Fruit. If you tried superimposing several letters from a dot-matrix printer, you’d get a black mess. But if the matrix is sparsely filled, you can probably recover the individual members, because they each produce such distinctive spatiotemporal patterns. So this type of code could also be handy for forming categories that could be decomposed into examples, just as superimposed melodies can often be heard individually. Thanks to the telecopying aspect, you could form multimodal categories – such as all of the connotations of comb.

My friend Don Michael suggests that meditation might correspond to creating, via a mantra, a large mosaic of a nonsense code, one without significant resonances or associations. If you maintained it long enough to wipe the slate clean of cares and preoccupations, allowing those short-term ruts to fade, it might give you a fresh start in accessing long-term memory ruts without getting hung up on short-term concerns.

[Meditation’s] exquisite state of unconcerned immersion in oneself is not, unfortunately, of long duration. It is liable to be disturbed from inside. As though sprung from nowhere, moods, feelings, desires, worries and even thoughts incontinently rise up, in a meaningless jumble, and the more far-fetched and preposterous they are, and the less they have to do with that on which one has fixed one’s consciousness, the more tenaciously they hang on. . . . The only successful way of rendering this disturbance inoperative is to keep on breathing, quietly and unconcernedly, to enter into friendly relations with whatever appears on the scene, to accustom oneself to it, to look at it equably and at last grow weary of looking.

Eugen Herrigel, Zen in the Art of Archery, 1953

There are some attractive features to what emerges from this analysis of the superficial pyramidal neurons: Donald Hebb would have loved it, because it shows how some of the most puzzling features of short-and long-term memory might be explained with cell assemblies (the memory trace is stored in a distributed way, with no one site crucial for its recall, and so forth). The gestalt psychologists would have liked the way that it makes possible the comparison of figure and ground by the triangular arrays potentially extending beyond the object boundaries, a spatiotemporal pattern forming that represents the figure-ground combination, rather than just one or the other.

And I like to think that Charles Darwin and William James would have liked the idea that mental life involves copying competitions biased by a multifaceted environment. Sigmund Freud might have been intrigued with the mechanism it suggests for how subconscious associations could occasionally pop into the foreground of consciousness.

While I think that divergent thinking is the most important application of the neocortical Darwin Machine, let me first illustrate how it might work with a convergent thinking problem. Suppose that something whizzes past you and disappears under a chair. You thought it was round, and maybe orange or yellow, but it was moving very quickly, and now it’s out of sight, so you can’t get a second look. What was it? How do you guess, when the answer isn’t obvious? Your process first needs to find some candidates, then it needs to compare them for reasonableness.

Happily, cloning competitions can do that. There’s a tentative cerebral code for the object, formed by all the feature detectors that it activated: color, shape, motion, and maybe the sound of it bouncing on the floor. This spatiotemporal pattern starts making clones of itself, in a manner of speaking.

Whether it can set up a clone next door depends on the resonances next door, those bumps in the road provided by the pattern of synaptic strengths and by whatever else is going on in the adjacent cortex. If you’d seen such an object many times before, there might be a perfect resonance – but you haven’t. Still, the tentative cerebral code has specialty components of Round, Yellow, Fast. Tennis balls have such attributes, and you have a good tennis-ball resonance, so the adjacent area pops into the melody for Tennis Ball (a nice feature of attractors is that a near fit can be captured and transformed to the characteristic pattern). Cloning with poor resonances leads to dropouts of some components, so perhaps your Tangerine resonance captures a variant in another patch of cortex despite the color not being quite right.

What about cloning competitions? Here we have Unknown, Tennis Ball, and Tangerine cerebral codes cloning away. Perhaps Apple pops out as well: if you saw someone eating an apple a few minutes ago, there would be temporary ruts for Apple, because of the NMDA synapses that were strengthened in that pattern. But then Apple is overrun by the Tangerine pattern, which is cloning away. Over on the other side of Unknown’s current territory, Tennis Ball is doing quite well and eventually it overrides and replaces Unknown, even encroaching on Tangerine’s territory. At about this time, you say, ‘I think that was a tennis ball,’ because there were finally enough clones in the Tennis Ball chorus to get a coherent message through to your left-lateral language cortex, over the corticocortical pathways from the occipital lobe to the temporal lobe.

Something else happens now: a new spatiotemporal pattern starts cloning through the work space; this time, you see something very familiar (the chair) and a critical chorus of Chair is quickly established without any real competition, because the sensory spatiotemporal pattern hits instantly on a resonance before any variants have time to get going. The NMDA synapses used in the Tennis Ball and Tangerine patterns are still jazzed up, however, and for another five minutes it will be easier than usual to recreate either of these spatiotemporal patterns in the parts of the work space that they last occupied. Perhaps Tangerine continues to clone and make mistakes, hitting upon the Orange Fruit resonance – so that a minute later, you wonder if you were wrong about that tennis ball.

That’s how it could happen – how I imagine that our subconscious processes sometimes come up with someone’s name a half hour too late. The pattern resonances are not unlike how we imagine locomotion to work in the spinal cord: there’s a connectivity – all those synaptic strengths between the various neurons – and, given certain initial conditions, you can pop into the resonance for the spatiotemporal pattern that implements Walk. With other initial conditions, you pop instead into Jog, Lope, Run, or Hopscotch.

In the sensory cortex, you may pop into Orange or Tangerine even when you see fruit that is neither. As I mentioned in chapter 5, categories are why the Japanese have so much trouble with English L and R sounds: both are captured by their mental category for a particular Japanese phoneme. Reality is quickly replaced by mental models. As Henry David Thoreau said, ‘We hear and apprehend only what we already half know.’

The cortex is in the business of quickly learning new patterns, whether sensory or movement, and creating variations on them. The variations allow for competitions to determine what pattern best resonates with the connectivities, and these in turn are often biased by a number of sensory inputs and emotional drives.

Relationships, too, can be coded by spatiotemporal patterns – just as sensory or movement schemas are. Just combine codes to make a new arbitrary pattern, in the same way that a left-hand rhythm can be superimposed on a right-hand melody.

The lingua ex machina of chapter 5 offered some specific examples of what fancy relationships (as in a sentence) might involve – all those obligatory and optional roles. Those obligatory arguments of a verb such as give are about relationships, and cognitive dissonance results when an obligatory role goes unfilled (as, alas, advertising agencies have discovered; Give Him forces you to read the billboard again to see what you missed, and thereby remember the ad better).

So, is a sentence simply one big spatiotemporal pattern, cloning away in competition with other sentence codes? Yes, but not always. We don’t require copying competitions in order to make a decision; simple rating schemes ought to suffice, if nothing particularly new is involved. Recall the cormorant of chapter 2: rating schemes will do for its decision making, because the choices (swim, dive, dry wings, fly away, look around a little longer) are already well shaped by evolution over the generations. Copyable schemas aren’t everything, once you get close enough to standard meanings.

The superficial cortical layers in many primates have the standard skip-wiring that predicts the ephemeral triangular arrays. It is not known how often any animal uses this wiring for cloning wallpaperlike hexagonal patterns; perhaps it only happens briefly, during prenatal development – as a sort of test pattern that guides use-dependent connections – and never occurs again. Or perhaps some areas of cortex are committed to full-time specialization and never clone such ephemeral patterns, while other areas often support sideways copying and become erasable workspaces for darwinian shaping-up processes. Since clones of movement commands would be particularly useful for throwing – they can reduce timing jitter – perhaps there was some natural selection for big work spaces in the hominid evolution of throwing accuracy. They’re all empirical questions. Once we have improved the resolution of our recording techniques, we’ll have to see where hexagonal cloning lies on the spectrum of possibilities.

But something very close to such cloning competitions is needed to satisfy the essentials for the Darwin Machine – that’s the real reason why I’ve led the reader through this cortical maze. Here, at least, we have (1) a distinctive pattern; (2) copying; (3) variation; (4) possible competitions for work spaces; (5) multifaceted environments (both current and memorized) to bias the competition; and (6) a next generation more likely to have variants established from the clones with the biggest territories (big territories have more perimeter, which is where variants can escape error-correction tendencies and get started cloning their new pattern).

In a longer book about the neocortical Darwin Machine itself (The Cerebral Code), I’ll explain all about the spice and speed that you’d get from cerebral analogues of sex, islands, and climate change. And speed we need, if a darwinian process in the brain is to work fast enough to provide our guessing-right intelligence.

We keep trying to carve up the cerebral cortex into specialized ‘expert’ modules. It’s a good research strategy to look for specialization, but I don’t take it seriously as an overview of how the association cortex works. We need some erasable work spaces, and we need to be able to recruit helpers for difficult tasks. That suggests that any ‘expert’ modules are also generalists – as when a neurosurgeon acts as a paramedic in an emergency. One of the things I like about the ephemeral hexagonal mosaic is that it suggests a resolution of the expert-generalist dilemmas: even a cortical area with ‘expert’ long-term ruts could serve as a work space, using overlaid short-term ruts to bias competitions.

Such a mosaic also suggests a way that subconscious thoughts could meander and occasionally pop some relevant fact from the past into your stream of consciousness. Best of all, because variants themselves can clone their way to temporary success, the patchwork quilt is creative – it can be shaped up from humble beginnings into something of quality. Even higher forms of relationships, such as metaphor, seem likely to arise, because the cerebral codes are arbitrary and capable of forming new combinations. Who knows – perhaps by now you’ve even acquired a cerebral code for Umberto Eco’s Mac-PC analogy.

The synchronized triangular arrays with such interesting implications for darwinian copying competitions turn out to have implications for fancy language as well, potentially giving intelligence a boost from another direction.

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probablespluyt · 3 years ago

Text

ENGINEERING IN THE ANCIENT

WORLD

J. G. Landels

University of Reading

University of California Press Berkeley and Los Angeles

University of California Press

Berkeley and Los Angeles, California

This revised edition first published 2000

First published 1978. First paperback printing 1981

transmitted in any form or by an means, electronic or mechanical, including photocopy, recording or any other information storage and retrieval system, without prior permission in writing from the publisher.

Library of Congress Catalog Card Number: 76-52030

ISBN 0-520-22782-4

0908 07 06 05 0403 02 01 00

l0987654321

Printed and bound in the EU

Contents

POWER AND ENERGY SOURCES

Man-power

Animal power

Water power

Wind power

Steam power

WATER SUPPLIES AND ENGINEERING

Appendix -

The sizes of measurement nozzles,

and

Frontinus'

arithmetic.

WATER PUMPS

CRANES AND HOISTS

CATAPULTS

SHIPS AND SEA TRANSPORT

133

Appendix-Methodsof estimating the

maximum

speeds of oared vessels

166

LAND TRANSPORT

170

THE PROGRESS OF THEORETICAL KNOWLEDGE186

THE PRINCIPAL GREEK AND ROMAN WRITERS

ON TECHNOLOGICAL SUBJECTS

199

Hero of Alexandria

199

Vitruvius

208

Frontinus

211

Pliny

215

APPENDIX: THE RECONSTRUCTION OF A TRIREME

219

SOME FURTHER THOUGHTS

225

BIBLIOGRAPHY

229

INDEX 233

Preface to the second edition

THE purpose of this book is to discuss and illustrate a number of technological achievements in the Greek and Roman world. Twenty years ago most of the information on these topics was con-tained (if anywhere at all) in a number of highly specialized stud-ies, not all of them easily accessible, and few of them written by classical scholars. What I attempted to do was 'to give the reader (whether a student of classical civilization or a layman interested in the history of engineering) some insight into the mechanical skills of the two most fascinating civilizations of ancient Europe'. In the twenty years since the publication of the first edition there

has been a considerable upsurge of interest in ancient technol-

ogy, and a number of major works have been published, includ-

ing an important source-book. It has been fully recognized that

arguments based on technical constraints which remain today

exactly as they were two thousand years ago can be useful in solv-

ing some historical problems-an approach which was pioneered by the late Professor J.E.Gordon. There have, accordingly, been a number of projects carried out, some of them involving a fruitful collaboration between classicists, technologists and archaeologists ( in whichever order of priority the reader considers appropriate). It is no longer justifiable therefore to complain, as I did in the preface to the first edition, that 'in most standard histories, the archaeological evidence is treated in a descriptive way, and very little attempt is made to envisage mechanical contrivances in action', or that 'the written sources are not always examined in detail, and the Greek and Latin terminology is not usually ana-lysed.'

The main text of the first edition has been reprinted without change. The translations of passages quoted from Latin and Greek authors were all my own; other versions may be superior in liter-ary merit, but even the most eminent translators can sometimes make extraordinary mistakes on technical matters, such as the

8 ENGINEERING IN THE ANCIENT WORLD

techniques of boat-building used by Odysseus in OdysseyV. Two sections have been added at the end-an appendix (pp. 219-24) on the reconstruction of the trireme which was completed in 1987, and a section containing some further thoughts, mostly on mat-ters to which my attention was drawn by reviewers and correspond-ents. Also the bibliography has been expanded and updated, so far as time and space have allowed.

In writing the first edition I was helped by a number of scholars in various disciplines, and here I must acknowledge once more my indebtedness to Professor J.E. Gordon, who died in 1998. He allowed me to see his notes on a course of lectures on the history of naval architecture (the graph on p. 167 was reproduced with his kind permission), and gave much helpful advice on the engi-neering problems of catapults. I also received much useful infor-mation on archaeological finds from Dr (now Professor) Michael Fulford.

More recently, Dr Michael Lewis has given valuable help with bibliographical references, and Mr Digby Stevenson has kept me informed of his researches on catapult spring materials. But my most important debt is to Dr Boris Rankov, who has been most helpful in giving prompt and expert answers to my questions on rowing matters, and has kindly allowed me to see a draft of his chapter on the sea trials of Olympiaswhich is due to appear early in 2000 in a new edition of Morrison and Coates' The Athenian Trireme (CUP).

Twenty years later, I have once again to thank my wife Jocelyn for her help and encouragement.

Reading, September 1999 J.G. Landels

Power and energysources

THE sources of power available in classical antiquity were severely limited by comparison with those of the present day. Virtually all work was done by man-power or animal power, and the kind of constraint which this imposed may be seen from a simple illustra-tion. One gallon of petrol may seem very expensive nowadays, but if used in an ordinary engine of average efficiency it will do the equivalent work of about 90 men, or of nine horses of the smallish size used in the ancient world, for one hour. Water power was used for pumping and industrial purposes, but probably not much before the first century B.c. The theoretical possibilities of steam power, hot air expansion and windmills were known, but appar-ently never exploited except on a very small scale, and not in use-ful or practical applications.

MAN-POWER

The most common mode of employing man-power was in the handling an<l porterage of small burdens of the order of 20-80lb (9-36kg). This is discussed in detail in Chapter 7, and all that needs to be done here is to note a very important limitation, which should be quite obvious, but is all too often forgotten. If a burden requires more than one man to handle it, its size and shape must be such as to allow the necessary number of men to stand close enough and get a grip on it. For example, in the fifth century B.c. the columns of Greek temples were built up from a number of sections, called 'column drums'; these might be anything up to 6ft 6in (2m) in diameter. The only possible place to grip such a lump of stone is around the lower edge, and it would be very difficult for more than 18 men to get into position to grip it at once. It follows, therefore, that if its total weight was more than about a ton (as it often was), they would be unable to lift it up off the ground, let alone move it, turn it round or position it on a column. They might just be able to roll it along level ground on its edge, but that

10 ENGINEERING IN THE ANCIENT WORLD

would be all. When, therefore, people say 'of course they had thou-sands of slaves to do the building for them', two facts should be remembered. Though the Pharaohs in Egypt may have had vast resources of manpower, Greek and Roman building contractors rarely had more than a small labour force, and in any case, no matter how many they may have assembled for the more ambitious projects, they could never have man-handled the larger stones used in classical buildings. Either one of the lifting devices described in Chapter 4 must have been employed or else the very slow and extravagant method of building a ramp, and dragging the stones up the slope on rollers.

There were two important mechanical devices for harnessing man-power. One was the capstan or windlass, particularly useful on cranes or aboard ship. The power could be transmitted over a distance by ropes, its direction could be changed by pulleys, and the force could be multiplied by block-and-tackle arrangements.

The windlass itself has a built-in mechanical advantage. It was also found to be ideal where traction was required, of low power but finely and accurately controlled. Two medical uses illustrate this.

One was the so-called 'bench of Hippocrates'-a plinth with a windlass at each end to provide the extension needed for reduc-ing fractures and dislocations of the arms and legs. The other was

a device apparently used by some gynaecologists-a small capstan mounted below a 'midwifery stool', used for extracting a foetus from the uterus.*

It is generally agreed that the Greeks and Romans did not, apparently, discover or use the crank in place of the handspikes on a windlass. Hero of Alexandria speaks of something called a 'handholder' (cheirolabe) for turning axles. This might have been a crank, but there is no proof that it was. There was at least one situation in which the main advantage of the crank could have been exploited, and where its disadvantage would not have been

noticed-the repeater catapult. Since it was not used on that weapon, it seems almost certain that it was not known to the designers.

How serious a drawback was the lack of this device? The answer

seems to be-rather less than is sometimes suggested. The only real advantage of using a crank is speed. A single grip (firm, but loose enough to allow the handle to turn in the palms of the hands)

*Hippocrates, On joints chapter 72: Soranus, Gynaeceia XXI, 68.

POWER AND ENERGY SOURCES

can be maintained all the time, whereas with handspikes the grip has to be changed, usually four times per revolution. But in situa-tions where speed is less important, the crank has a positive disad-vantage. The force which can be applied to it varies according to its position in relation to the operator, reaching a minimum twice during each revolution when the handle crosses a line drawn through the operator's shoulders and the axis of the crank, and a maximum when it is roughly at right-angles to that line. This is why a car starting-handle used to be be so arranged that the points at which most force is needed to turn it occurred when the han-dle was at 'two o'clock' and 'eighto'clock'. Thisimposesaserious limitation on the crank. When it is under continuous loading (e.g. on a crane when the load is raised, or a well-head when the bucket is full), the reverse thrust applied to the crank handle by the load must never exceed the minimum applied by the operator at the two weakest points of the cycle. If it does, the handle will fly back-wards, and once it has started swinging round the load may acquire momentum and make the handle impossible to stop. To avoid this danger, most modern cranked winches are fitted with a ratchet. Such a device, dating from the late fifth century B.c., was found near some naval installations at Sunium, and may have been used on a winch for hauling ships up slipways.

The implications for ancient devices worked by handspikes are clear enough. For cranes or hoists of any kind the use of a crank would have lowered the handling capacity by some 20-30%, and it seems rather improbable that a slight increase of speed would justify that sacrifice. On the repeater catapult the slider was fitted with pawls and a ratchet, and would only fly forward a short dis-tance if the tension on the draw-back cord were relaxed. It would therefore have been reasonably safe to use a crank on the capstan at the rear of the machine and thereby speed up the loading

operation-a particularly important benefit, for that particular weapon.

The other mechanical device was the treadmill-a pair of verti-cal wheels with treads (like those of a step-ladder) between them. It has become very difficult nowadays to talk, or even to think about this apparatus unemotionally, and in purely engineering terms, but in fact, if well designed, it can be one of the most effi-cient devices for this purpose, and the most comfortable for the

operator-in so far as any continuous, monotonous physical work

12 ENGINEERING IN THE ANCIENT WORLD

can be comfortable. The basic action is not unlike that of pedalling a bicycle, and it is significant that recent attempts to reach the absolute limits of the human body's capabilities, in the develop-ment of man-powered flight, have mostly used that arrangement.

The difference is that a cyclist pulls on the handlebars, and uses the abdominal muscles as well as the leg muscles; the treadmill operator uses the reaction from lifting his body weight, mainly with the leg muscles.

A very useful feature of the treadmill, especially when used on a crane, is that the torque, which determines the pull on the hoist-ing-cable, can be easily and accurately adjusted by the operator shifting his position on the wheel. The maximum torque is obtained when the operator treads the wheel at a point on a level with the axle ( this can only be done from the outside). If he treads above that point (outside) or below it (inside) the torque is less, and if he stands directly above or below the axle it is zero. Thus the amount of torque required between the maximum and zero, can be obtained by moving forwards or backwards.

This may possibly afford an explanation of a rather mysterious length of wood with notches along one side, found near the Roman water pumps in the Rio Tinto mines. When these pumps (which themselves acted as treadmills) were being used in a series, it would be very important to keep the output of each of them constant, and consistently the same as that of the pumps above and below --otherwise the sumps would either empty or overflow. If this piece of wood was one of two beams supporting a movable handrail, the necessary adjustments for men of different weights working the same pumps at different times could be made by shifting the rail along one or two notches, forwards to reduce output or backwards to increase it.

A second valuable feature of the man-powered treadmill is its mobility. The crane shown on the monument of the Haterii (p. 84) could presumably have been dismantled, and its jib laid horizon-tally on one or more carts, while the treadmill itself could have been rolled along any reasonably level road (that was also one method used for transporting column-drums). There was, in fact, no other suitable power source available. Wind power is hope-lessly unreliable, and a builder would be extremely lucky to have water power available on the site at all, let alone near enough to any particular building. A glance at the later history of cranes shows

POWER AND ENERGY SOURCES

that the treadmill continued to serve this need right through the Middle Ages and Renaissance, and that the first alternative to be made effectively mobile was steam, as used on railway breakdown cranes. Indeed, the problem is still with us. Owing to difficulties of gearing and transmission the internal combustion engine is not very suitable for large cranes, and the cost of laying supply cables makes it uneconomical to use electricity for anything less than a large and lengthy building project.

The Greeks and Romans also used manpower for the propul-sion of virtually all fighting ships. Merchant ships, except for quite small ones, were normally under sail. Warships used sails on long voyages, or while cruising on patrol, but in battle conditions, or during a battle alert, they usually left mast, yard and mainsail ashore, to cut down weight to the absolute minimum, and relied entirely on rowers.

ANIMAL POWER

From remote antiquity there has been a contrast between the work-ing animals used in the Mediterranean area and those used in northern Europe. The predominance of the horse in northern Europe, closely related to climatic and ecological factors, could never have occurred in classical Greece, and did not affect Roman practice to any great extent except in so far as Roman armies came into contact with the peoples of France, Germany and central Europe. The situation in classical Greece is summed up both accurately and poetically by Aeschylus in a passage of his Prometheus Bound. The hero, describing his services to mankind, says (lines 462-6)

'And I was the first to link oxen beneath the yoke

With yoke-straps, to be man's slaves, and with their bodies' strength

Give him relieffrom the heaviest of his toil;

And to the chariot-pole I brought

Horses that love the guiding reins,

Delight and pride of massive wealth and luxury'.

The slowness and ugliness of oxen (a generic word, meaning 'great knobbly beasties' is used in the Greek original) is contrasted with the speed and elegance of horses. The assertion in the last line, that horses were expensive to buy and maintain, is borne out by

14 ENGINEERING IN THE ANCIENT WORLD

the fact that several words denoting social and economic status in classical Greece were connected with horses. The word hippeus, referring to a particular income-group, originally meant a man wealthy enough to own his own horse and (in wartime) to fight in the cavalry of the citizen army. In Athens the next lower property-classification was zeugi,tes, meaning a man who owned a pair of oxen. The historian Herodotus, wishing to stress the great wealth of a particular family, calls them tethrippotrophon-able to maintain a four-horse racing chariot (for entry at the races during the great games at Olympia, Delphi and elsewhere). The 'conspicuous con-sumption' of such a family must have made a deep impression.

By contrast, a pair of oxen could be fed much more cheaply, on inferi-Jr fodder of a kind available in areas of Greece and Italy where the paJture was not adequate to support horses. They yielded a rt turn on the owner's investment; they could pull a heavier load than two horses of comparable size. Their progress was slower, but then speed was not the most important considera-tion in ancient farming or transport. Farm animals had to be fed all the time, whether in use or not; a transport contractor would naturally want to complete each job as soon as possible to be ready for the next. But to use horses to speed up his operations would have been quite impractical. And finally-an important point for people living close to subsistence level-when their working life was over, oxen could serve as food. The meat would be tough as old boot, no doubt, and would need a long spell in the stewpot, but it would be better than nothing. The Greeks and Romans, for reasons not clearly defined but presumably religious, did not as a rule eat horsemeat.

The one advantage that the horse had over the ox was speed, and it was precisely in those situations where speed outweighed

everything else that the horse was used-in warfare and in chariot-racing. The high mobility of the cavalry gave that arm its particular role in battle tactics, and on the race-course a chariot, made as light as possible, and drawn by a matched team of two or four horses, represented the ultimate in speed to the Greeks from the eighth century B.c. onwards, and to the Romans after them.

Oxen, then, propelled the heavy lorries of the ancient world, and highly-bred horses its Aston Martins and its Lamborghinis. Between these extremes of utility and luxury came the small travelling vehicle for passengers or light merchandise, drawn by

POWER AND ENERGY SOURCES

donkeys or mules. These animals could move rather faster than oxen, but not as fast as horses. They cost a little more to feed (in proportion to their weight and pulling capacity) than oxen, but only about 60-70% of the cost of horses.

The use of animals in transport, and the problems connected with harness, are discussed in Chapter 7. Apart from transport, the use of animal power was rare. In mining operations it seems to have been almost negligible, for obvious practical reasons. Unless there was access via horizontal tunnels ('adits'), it would be very difficult indeed to get animals into or out of a mine, and ancient workings did not normally include entrance edits or any galleries or spaces in which animals could be kept, fed and housed underground. The haulage of ores and spoil seems to have been done exclusively by man-power, using buckets on ropes, and it was extracted via the nearest shaft, not taken along any great distance underground.

Until about the first century s.c. animals were not used in mill-ing. The only type of mill which can be operated by a horse or donkey is a rotary mill, and that invention did hot come into the classical Greek world at all. The so-called Pompeian mill, with a fixed lower stone of conical shape, and a rotating upper stone shaped like an hour-glass was quite certainly designed to be turned by animal power, despite the fact that the space available in some of the buildings for the animals to walk round seems very limited indeed. The earlier 'pushing' type of mill, in which a grinding stone is pushed back and forth over a trough, must have depended on human effort. Such work was sometimes imposed on slaves as a punishment, but at all times it had to be done by someone, and as a punishment it was probably not much more severe than the 'spud-bashing' to which army offenders used to be subjected-a tedious, irksome job which nobody would do from choice. Some illustrations of rotary mills being turned by horses give a highly idealized picture of noble steeds striding around; in real life, the oldest and most broken-down horses and donkeys were put to this kind of work-the last stage on the road to the knacker's yard.

Finally, there is a bizarre invention described in a Latin work written in the latter half of the fourth century A.D., but almost certainly never constructed. The author's name is not known, and the work is usually referred to as Anonymus De Relms Bellicis. Oxen are used to propel a ship (Fig. 1). They walk around in pairs, at opposite ends of a capstan-pole on a vertical axle. Through a

16 ENGINEERING IN THE ANCIENT WORLD

gearing system (not described, but clearly a crown wheel and pinion, as used in water-mills) this axle drives a horizontal one

athwart the ship, with a paddle wheel on each end-the descrip-tion of the paddles has some verbal resemblances to Vitruvius' description of an undershot water wheel (X, 5, 1.) We are not told whether the paddle-wheel shaft was higher or lower than the platform on which the oxen walked, but since they were 'in the

Fig. l. Oxen used to propel a ship.

hold of the ship', it seems more likely to have been the former. The total number of oxen is not specified, except that there was more than one pair. Though there is no theoretical reason why this should not work, the whole idea does not sound very practi-cal. The space needed for the oxen to move around would be

considerable-a circle of 10ft (3m) diameter at the very least. If we assume three capstans, the ship would require a beam of about 13ft (4m) and a length overall of at least 43ft (13m), and at 'six oxpower' such a vessel would be rather under-engined. Commu-nication between the 'bridge' and the 'engine-room' might also be a trifle difficult.

WATER POWER

Early Greek poetry contains striking passages in which the destruc-tive force of rushing water is used as a piece of telling imagery, but the problems of harnessing such power and using it to drive machin-

POWER AND ENERGYSOURCES

ery were apparently not explored until the early part of the first century B.C. According to the geographer Strabo (XII, 3, 40) a water-mill was built in the kingdom of Mithridates, at Kabeira in the Pontus (near the modern Niksar, N. central Turkey) in the first century B.C., some time before the earliest in Greece or Italy. There may be a simple explanation for this. The basic require-ment for a water-wheel is a water supply which is steady all the year round, and, if it is to be anything more than a toy, the quantity of water needed is quite large. Mithridates' city was close to a sub-stantial river, the Lycus (modern Kelkit) which, though the local rainfall is no greater than that of Greece or Italy, has a large catch-ment area. Relatively few of the rivers and streams of Greece and Italy (except in the north) maintain a substantial rate of flow dur-ing the dry season. However, the effect of this geographical fact on the history of the water-wheel should not be exaggerated. Once the basic idea has been put into practice, the conservation and management of limited or fluctuating water supplies follows soon afterwards.

Our knowledge of Greek and Roman attempts to harness water power rests on rather meagre evidence. Among the literary sources, Vitruvius (late first century B.c.) is much the most im-portant, and he gives a clear description of an undershot wheel, which is discussed below. Two other allusions are important for the question of dating. A Greek epigram in the Palatine Anthol-ogy (IX, 418) speaks of the joyful release from drudgery which a water-mill has brought to the women servants who previously had to grind by hand. Its author was almost certainly Antipater of Thessalonika, who was closely associated with a Roman noble family, the Pisones. He lived and worked in Italy at the end of the first century B.c., and is probably referring to the installation of such a mill on a country estate. His poem would be contem-porary with Vitruvius' work, but there is one interesting differ-ence between the two. Antipater speaks of the Nymphs (which personify the water) as 'leaping down onto the topmost part of the wheel'. Though this has been disputed, there is really little doubt that he is talking about an overshot wheel-a more effi-cient type than Vitruvius' -and this raises a question of priority, which will be discussed later.

Closely related to this is an allusion in Lucretius' poem On the Nature of the Universe,where the poet is speaking about the move-

18 ENGINEERING IN THE ANCIENT WORLD

ment of the heavenly bodies (V, 509-33, particularly 515-6). It is a difficult and obscure passage, but the gist is that one explanation of the apparent diurnal rotation of the heavens is that a current of air circulates around the universe, causing the 'sphere' to rotate 'as we see rivers turning wheels and buckets (rotasatque haustra) '. Since Lucretius uses this as an illustration, he clearly assumes that water-wheels are familiar to his readers, and as he was writing some 40 years earlier than Vitruvius and Antipater, this suggests that

the use of water power to work pumps (bucket-wheels or bucket-chains, see Chapter 3) came earlier than its use for mill-ing.

Other literary allusions add little or nothing to this. The arch-aeological evidence is equally scarce, but very informative. Two

important wheel sites have been excavated-one in the Agora at Athens, to the south of where the restored Stoa of Attalus now stands, dating from mid or late fifth century A.O. The other is at Barbegal, near Arles in southern France ijust north of the Ca-margue). A very big installation was built there by the Romans in the late third or early fourth century, and was probably in use for the greater part of 100 years. It contained eight pairs of wheels, each driving millstones in a mill-chamber beside the wheel-pit, and its output would have been adequate not only for the 10,000 inhabitants of Arles, but for some area around. The presence of a Roman garrison might account for this. The remains are not very extensive, but the main essentials can be reconstructed from them. Evidence of an undershot wheel ( in the form of chalk incrusta-tion, the wood having all disappeared) has been found at Venafrum in central Italy, and a speculative reconstruction can be seen in the technology section of the Naples Museum.

There are three basic types of water-wheel-the vertical-shaft, the undershot and the overshot. The vertical-shaft wheel has a number of blades inclined at an angle of about 30° to the vertical, fixed to a hub near the bottom of the shaft. The water is directed onto the blades through a wooden trough which slopes down at a steep angle, so that the water strikes them at high speed. This requires a situation where there is a drop of some 10-12 ft (3m) immediately beside the water source. Sometimes a pit can be dug for this purpose, but adequate arrangements have to be made for the spent water to drain away from it. Since the shaft is vertical, it can be made to tum millstones directly, without any need for gears.

POWER AND ENERGY SOURCES

In the absence of any conclusive evidence, some historians of the subject have used the following argument: This is the 'most primitive' form of water-wheel, so, since the Romans developed the more sophisticated undershot and overshot wheels (for which we have good evidence), we must assume that they started with the vertical-shaft type. The parallel between this supposed sequence and that attested for Renaissance Europe is also invoked in sup-port. This a prioriargument is attractive, but it does rest on two doubtful assumptions (a) that milling was the first operation for

which water power was used-and the passage from Lucretius

quoted above makes this very doubtful-and (b) that gearing of some sort had not been previously invented for other purposes, such as coupling animals to a water-pump. Archaeological evidence (or rather, the lack of it) does not help to decide the question. No certainly identifiable Greek or Roman remains of this type of wheel have been found, but the entire structure, including all the water-guidance system, would have been made of perishable material. By contrast, the overshot wheel required a stone-built wheel-pit, which has good chances of survival, and can be identi-fied as such.

The second basic type of wheel is the undershot, sometimes called 'Vitruvian' from that author's description (X, 5). It is highly significant, and consistent with the evidence from Lucretius, that he first introduces the water-wheel as a power source for working a bucket-chain, and then says, 'It is also used for corn milling, the design being the same except that there is a gear-wheel on one end of the axle ... ' He makes no mention of the vertical-shaft wheel. The structure he describes is very simple (Fig. 2). It consists of a spoked wheel of unspecified diameter, with vanes or paddles around its circumference (Vitruvius calls them pinnae, a word used elsewhere to mean the wing-feathers of a bird), which are driven round by the current in the river. There is nothing in his words to suggest that a mill-leat was channelled off for the purpose.

The third and most efficient type of wheel is the overshot (Fig.

3). Using the same kind of argument as with the vertical-shaft wheel, it is usually held that this was developed from the under-shot wheel, the intermediate stage in this process being the so-called 'breast-shot' wheel, which is a simple modification of the under-shot, the water being supplied through a trough level with the

20 ENGINEERING IN THE ANCIENT WORLD

- :.-

--:.-

--➔

-=-

~~=

-----~

----

Fig. 2. Undershot water-wheel.

Fig. 3. Overshot water-wheel.

axle, so that the main force on the paddles is from the water falling, not merely flowing past. But there is another equally attractive hypothesis--that the overshot wheel was conceived independently of any other type, by simply reversing the action of the bucket-wheel. If one can put power into that machine and get water out

POWER AND ENERGY SOURCES

of the top, why not put water into the top and get power out of it? In fact, this possibility would be clearly demonstrated each time somebody finished a spell of work treading a bucket-wheel. It would have to be slowly reversed until all its buckets were emptied, and the pull it exerted during that operation would be clearly felt. The bucket-wheel was certainly in use by Vitruvius' time, perhaps for some while before, and though he does not describe an over-shot wheel, that might be due to the fact that the undershot type was the only one he had seen.

The question of priority, then, is not easy to answer; but in power output and efficiency the overshot wheel is well ahead. The struc-ture required for an undershot wheel is simply a vertical wall be-side a river or stream,* and, if the water supply is limited, some sort of partial dam to narrow the channel and make it flow more rapidly in the region of the wheel. The potential power output depends on two factors-the velocity of the water flow and the areaofthevaneson which the water impinges (the 'scanned area').

To take a simple example. If the area of each vane is l,000cm 2 (just over 1 sq ft) we may assume that roughly this area is being scanned at any one time. (The exact figure depends on the number of vanes, the diameter of the wheel, and other factors, but this will do as a crude approximation.) If the water flows past at about 150 cm/see (5ft/sec) the theoretical power available is about¼ h.p. (186 watts), but as the undershot wheel can only be made about 22% efficient at the best, this would provide a real power of only about -loh. p., or half the power output of a man working a tread-mill. If the water flows twice as fast, the power is increased eight times and things look better. The theoretical power available is nearly 2 h.p., and the actual output might be about 0.4 h.p.-the equivalent of four men. On the other hand, the water supply for such a performance could not be obtained from anything less than a small river, with a flow of (say) 125 gall/sec, which might be around 12ft wide (3.5m) and 4in (10cm) average depth in cross-section.

The overshot wheel can be made much more efficient-up to 65% or even 70%. Provided that the wheel revolves fast enough, and the boxes are large enough to catch all the water as it comes from the launder, most of the potential energy in the water can be

*For an example, see the Byzantine mosaic in the Palace of the Emperors, illustrated in Antiquity XIII (1939) pp. 354-6 and Plate VII.

22 ENGINEERING IN THE ANCIENT WORLD

utilized. This potential energy can be worked out quite simply from the rate of the water flow, and the depth of fall which, as a rough approximation, may be taken as equal to the diameter of the wheel. The lesser rate of flow given in the last paragraph (31 gall or 140l/sec), if delivered to an overshot wheel of 7ft (2.13 m) in diameter, would give a theoretical power output of just under 4 h.p. (nearly 3000 watts), and an actual output of perhaps 2-2½ h. p. The power of each of the sixteen wheels at Barbegal might have been of this order. For a modern (and slightly depressing) comparison, a very small motor-cycle engine devel-ops about the same power.

Overshot and undershot wheels may usefully be compared in

two other respects-behaviour under extra load and cost of con-struction. They behave in opposite ways under extra load. Since an undershot wheel is absorbing kinetic energy from the moving water, its torque depends on the difference between the velocity of the water on arrival and the speed of the paddles. To put it very simply, it generates power by slowing the water down. There-fore, if extra loading is put on the wheel (e.g. by using bigger millstones or putting bigger buckets on a chain) it will turn more slowly, but will develop more torque. Conversely, the overshot wheel has a minimum working speed, below which the water begins to overflow the boxes and spill into the pit, reducing the power output and efficiency. These factors must be taken into account when designing the wheel and the gearing, which will be dis-cussed later.

In point of cost, the undershot wheel has the great advantage that no pit is needed, that any riverside situation can be used ( this may reduce transport costs, which were high) and no engineering is required to raise the water to the necessary height. This has to be done for an overshot wheel, and may be very expensive. If the gradient of the river bed is slight, it may be necessary to build an artificial channel 200--300yards long, support it above ground level and make it waterproof. The cost of constructing the aqueduct to feed the Barbegal system must have been very considerable. The efficiency of the undershot wheel is much less, but this need not have worried the ancient engineers all that much. Where fuel is expensive (as in the modern petrol engine) efficiency is the first essential, and must be achieved at almost any cost, but where the energy source is running water, and 'costs nothing', the only

POWER AND ENERGYSOURCES

requirement of a wheel is that it should deliver enough power to do the work. If the choice lay between an undershot wheel which would just about turn the millstones and an overshot one which would turn them faster, but would cost four or five times as much, and might have to be built some miles away, the undershot would be preferred. Where the water supply was too small for anything less efficient than the overshot, there was no choice. This was prob-ably the case in the Athenian Agora

Revolvingstont

Fig. 4. Water-mill gears with toothed wheels.

It is not difficult to see, from Vitruvius' clear description and from the evidence of the Agora mill, how the water-wheel, turning on a horizontal axle, was coupled to the upper millstone on a vertical axle (Fig. 4.) 'A toothed disc (dentatum) is keyed on to the end of the axle, and turns in a vertical plane, at the same speed as the wheel.' (The odd phrase in cultrum, which has not been satisfactorily explained, is omitted from this translation.)

'Close to this disc is another larger one, toothed in the same way ( item dentatum) and horizontally placed, with which it engages

24 ENGINEERING IN THE ANCIENT WORLD

(continetur). 'Vitruvius is clearly talking about two crown wheels. We use the word 'toothed' more loosely, of a flat cog-wheel with radial teeth, but if one thinks of an animal skull, with curving jawbone and teeth at right angles to the 'rim', it will be seen that Vitruvius' usage is really more exact. Marks made by the rim of the vertical gear-wheel on the edge of the gear-pit in the Athenian Agora mill confirm that the teeth were not radial. Vitruvius' ex-pression 'toothed in the same way' (item dentatum) suggests that the so-called lantern pinion (Fig. 5) with two discs was not

Fig. 5. Water mill gears with toothed wheel and lantern pinion.

known to him; a Roman wood-and-metal pinion of this type has been found in Germany* but what part it played in mill machinery (if any) has not been satisfactorily explained. Doubt has been cast on Vitruvius' statement that the horizontal gear-wheel ( coupled to the millstones) was larger than the vertical one on the wheel-shaft, since this would mean that the millstone was geared down, and turned more slowly than the water-wheel. Some schol-ars have arbitrarily changed the text (from maius to minus) to avoid this problem. It is true that later European mills had the opposite arrangement, the millstones being geared up by as much as 2½:l, but these were big, powerful overshot wheels, and the type which

*Illustrated in L. A. Moritz, Grain-mills and Flaur in Classical Antiquity

(OUP 1958) Plate 14(c).

POWER AND ENERGY SOURCES

Vitruvius describes might not have developed enough power even for a 1 :1 gear ratio. The consequences are not nearly so disastrous as some historians suggest. The miller simply worked more slowly,

and estimates of flour production should take this into account.

Water-wheels were clearly used for water-raising and for mill-ing. We might expect some other applications, but the only evi-dence we have is a brief and tantalizing allusion in Ausonius' poem on the River Moselle, written about the middle of the fourth cen-tury A.D. Speaking of the River Erubius (the Ruwar) he says:

'He, turning the millstones with rapid, whirling motion,

And drawing the screeching saws through smooth white stone, Listens to an endless uproar from each of his banks' (362-4)

Ausonius' style is not exactly straightforward, and it is difficult to be sure exactly what he means, but he certainly seems to be saying that water-wheels were used to drive saws for cutting stone. The noise was incessant because the power-driven saws, unlike those in an ordinary mason's yard, did not stop for a breather every few minutes. Pliny (Nat. Hist. 36, 159) mentions stone from this area and from others which 'can be cut with a saw of the kind they use for cutting wood-even more easily than wood, so they say'. It was used for roof and gutter tiles, and was almost certainly some form of soapstone.

But how did the river 'draw' the saws through stone? Trahere would be a strange word to use (even for Ausonius) of a circular saw, though that was perhaps known in antiquity. Did the wheel have a cam and lever, or a crank and connecting-rod to push the saw back and forth? In the absence of any evidence for either we can only guess, and regret all the more that no technical writings have survived from that area or from that period.

Mention was made at the beginning of this section of the de-structive power of a river in spate. Though this power itself was not put to useful purpose, some Roman mining installations in Spain, by 'imitating nature', achieved a great saving of manpower and time. Large reservoirs, known as 'hushing tanks', were con-structed on the hillsides above the workings, with sluices at one end which could be rapidly opened. When the tanks were filled ( in some cases via a fairly long aqueduct) the sluices were released, and a great wave of water rushed over the workings, carrying away

26 ENGINEERING IN THE ANCIENT WORLD

with it large quantities of spoil. The same water supply, regulated down to a steady trickle, could also be used for washing ores.

WIND POWER

Although the Greeks and Romans harnessed and used wind power for sailing ships, they do not appear to have developed the rotary windmill as a power source. This is strange, and no satisfactory reason has yet been offered. They were perfectly well aware that by adjusting the set of the sail a boat could be made to travel at an angle to the direction of the wind, and a very slight development of this idea could have led to the type of sail-mill to be seen nowadays on Mykonos and in Crete. But we have no evidence for any such machine in classical antiquity. The one and only mention of harnessing windpower is in the Pneumatica of Hero of Alexandria (I, 43), and, being unparal-leled, it has come under suspicion as a later interpolation. But there is nothing in the vocabulary or style of the Greek which is inconsistent with the rest of Hero's works, nor is it easy to see what motive could have prompted anyone to insert such a pas-sage into a fairly well-known text some time in the Middle Ages, when the windmill had come into general use.

Hero's machine, in which wind power is used to blow an organ, is crude but workable. Only a very sketchy outline of the instru-ment itself is given, with no mention of a keyboard or air reser-voir. This may mean that it was something like an 'Aeolian harp' (the introductory sentence says 'it makes a noise like a pipe when the wind blows') or perhaps we are meant to fill in the details from the very full description of an organ given in the previous chapter. The air pump consists of a piston and cylinder, the piston compressingon the down-stroke (Fig. 6). Novalvesarementioned, but we must assume the same kind of arrangement as that given in Chapter 3, except that the cylinder is inverted. It is worked by a rocker-arm, which has on its opposite end a small horizontal plate. The windmill itself is mounted on a separate base, so that it can be

turned round as required to face the wind-perhaps through an arc of 90°. It has a single axle, with two discs (tympania- 'little drums') on it. One has projecting radial rods which, as it turns round (anti-clockwise in the diagram) push down the small plate and lift the piston. As each rod slips off the plate, the piston is allowed to fall, and its weight then forces the air out into the

POWER AND ENERGY SOURCES

organ pipes. The other disc on the same axle is fitted with 'vanes, like the so-called anemouria '. The word translated as 'vanes' (platai) is used elsewhere to mean oar-blades, which suggests that they were wooden, and rigid. The word anemourion does not occur any-where else except as a proper name for a promontory in Asia Minor, but must mean something like 'wind-fan'.

Fig. 6. Hero's windmill for blowing an organ.

Here we have a crude and rather inefficient substitute for the cam, converting the rotary motion of the windmill to the up-to-down motion of the pump. We are not told how many radial rods

were used-probably two at the most, since the interval between each thrust would otherwise be too short to allow the piston to empty the cylinder. Hero says 'they (the rods) strike the plate at longish intervals' (ek dia/,eimmatos), which also suggests that the windmill was designed to turn slowly, with a pitch of perhaps only 5-10° on the vanes.

The device was clearly a toy, but why did nobody (apparently) see its potential as a power source? Perhaps its scale was the real reason. A power source, by definition, had to be something which

could replace a man or a small animal-that is, something which developed about¼ h.p. at least. It may well be that a small wind-mill, with rigid wooden vanes, was simply not thought of in this category, and nobody tried experimenting with a bigger and bet-ter one. But it is still very puzzling.

28 ENGINEERING IN THE ANCIENT WORLD

STEAM POWER

The failure of the Greeks and Romans to harness steam as a power source was without doubt one of the many factors which prevented industrialization in their society. How near they came to develop-ing a workable steam engine is a much-debated question.

Fig. 7. Hero's steam machine.

Once again it is Hero of Alexandria who provides the only mention in the literary sources of devices worked by steam (Pneumatica II, 6 and 11). The second of these is 'a ball which spins round on a pivot when a cauldron is boiled'. He does not give this device a name, though aeolipyle( or aeolipile)is sometimes used-mistakenly, because that was a different device altogether. The design is simple (Fig. 7). Pressure builds up in the cauldron, and steam passes through the pipe FGH into the sphere, from which it escapes at various points, but mainly through the bent tubes IJK and LMN. As the steam is forced out in one direction (from the outlets), it causes a reaction thrust in the opposite direction, and makes the sphere revolve. The principle is that

POWER AND ENERGY SOURCES

of jet propulsion, and the device described in Chapter 3 of the same book, in which figurines are made to revolve inside a trans-parent altar, works in the same way, except that the expansion of heated air is used instead of steam.

Could this form of steam engine ever have been used as a practi-cal power source? The answer is, almost certainly not. It operates best at a high speed, and would have to be geared down in a high ratio. Hero could have managed that, since the worm gear was familiar to him, but not without friction loss. Inadequate heat trans-fer from the burning fuel to the cauldron would keep the effi-ciency low, but the worst problem of all is the 'sleeve joint', where the pipe FGH enters the sphere. When making a working recon-struction of this device, I had the greatest difficulty in reaching a compromise between a loose joint which leaks steam and lowers the pressure, and a tight one which wastes energy in friction. It is in the realm of possibility that, given the technology of Hero's age, overall efficiency might have been as low as 1 %. If so, then even if a large-scale model could have been built, to deliver toh.p. and do the work of one man, its fuel consumption would have been enormous, about25,000 B.T.U. (26.8 X 106 joules) per hour. The labour required to procure and transport the fuel, stoke the fire and maintain the apparatus would have been much more expensive than that of the one man it might replace, and the machine would be much less versatile.

In his introductory chapter, Hero speaks of his various devices as providing 'some of them useful everyday applications, others quite remarkable effects'. We must conclude that the steam en-gine came into the second category. Its most remarkable feature is in fact the speed of rotation. My own working model has achieved speeds of the order of 1,500 rpm, and, with the possible exception of a spinning top, the ball on Hero's machine may well have been the most rapidly rotating object in the world of his time.

It is true that this toy (as it may justly be called) does not incor-porate the essential elements of a useful steam engine, but it is equally true that all those elements are to be found in various other devices which Hero describes. To make a conventional steam engine it is necessary to develop techniques of making metal cylinders, and pistons to fit them; but this problem was tackled in the design of the force pump, and there is even a possibility that 'lapping' was used (seep. 76). It is not in fact necessary to have an

30 ENGINEERING IN THE ANCIENT WORLD

efficient method of converting rectilinear to rotative motion for the construction of a basic steam engine. The earliest working ones were of the beam type, which worked piston pumps without cranks or rotative motion. The one other essential is the valve mechanism, and Hero had devised one for what is usually known

as 'Hero's Fountain'-a device exactly like a modem insecticide sprayer, in which liquid is forced out of a container by compressed air (Pneumatica I, 10.) Water had to be controlled under pressures of the order of 5-6 lb/ sq in (0.35 kg/ cm 2). The type of valve he used is not ideal for steam, but it would have done to start with, and might have been improved in the light of experience. An even more significant feature of the 'fountain' is that Hero uses a spheri-cal pressure-vessel on a special stand, showing clearly that he was aware that sheet metal of a given thickness will stand up to greater internal pressure in that form than in any other. In the progress of boiler design, this might have been the first advance on the bunged-up cauldron.

But there was no progress--not even a beginning. What Hero failed to do, and nobody else apparently tried to do, was to com-bine these essential elements--boiler, valves, pistons and cylinder-to form a steam engine. Why did he not? Perhaps he never thought of reversing the action of a piston pump, forcing liquid or air into the cylinder and taking thrust from the piston. One toy which came very near to this was a 'jumping ball' (Pneumatica II, 6), in which a light ball (made of thin sheet metal?) was blown up into the air by a jet of steam from a boiling cauldron. But where ex-panding hot air, or compressed air, was used to move something mechanically, it was done either by inflating a bladder, which lifted up a weight, or else by shifting water or mercury from one side to the other of a counterbalanced system, which then swung up or down and operated the mechanism by chains and pulleys. These two methods are exemplified in Pneumatica I, 38 and 39.

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PREFACE

The essays contained in this volume were written on different occasions mostly in response to requests for a popular presentation of the results of the author's investigations. The title of the volume characterizes their general tendency as an attempt to analyze life from a purely physico-chemical viewpoint. Since they deal to a large extent with the personal work of the author, repetition was unavoidable, but in view of the technical difficulties presented by some of the topics this may serve to facilitate the understanding of the subject.

The author wishes to thank the editors and publishers who gave their consent to the reprinting of these essays: Professor J. McKeen Cattell, of Columbia University, Professor Albert Charles Seward, of the University of Cambridge, England, Ginn & Co., of Boston, G. P. Putnam's Sons, of New York and London, and the J. B. Lippincott Company, Philadelphia.

THE ROCKEFELLER INSTITUTE

FOR MEDICAL RESEARCH

April 4, 1912

I. INTRODUCTORY

It is the object of this paper to discuss the question whether our present knowledge gives us any hope that ultimately life, i.e., the sum of all life phenomena, can be unequivocally explained in physico-chemical terms. If on the basis of a serious survey this question can be answered in the affirmative our social and ethical life will have to be put on a scientific basis and our rules of conduct must be brought into harmony with the results of scientific biology.

It is seemingly often taken for granted by laymen that "truth" in biology, or science in general, is of the same order as "truth" in certain of the mental sciences; that is to say, that everything rests on argument or rhetoric and that what is regarded as true today may be expected with some probability to be considered untrue tomorrow. It happens in science, especially in the descriptive sciences like paleontology or zoology, that hypotheses are forwarded, discussed, and then abandoned. It should, however, be remembered that modern biology is fundamentally an experimental and not a descriptive science; and that its results are not rhetorical, but always assume one of two forms: it is either possible to control a life phenomenon to such an extent that we can produce it at desire (as, e.g., the contraction of an excised muscle); or we succeed in finding the numerical relation between the conditions of the experiment and the biological result (e.g.,

1 Address delivered at the First International Congress of Monists at Hamburg, September 10, 1911; reprinted from Popular Science Monthly, January, 1912, by courtesy of Professor J. McKeen Cattell.

Mendel's law of heredity). Biology as far as it is based on these two principles cannot retrogress, but must advance.

II. THE BEGINNING OF SCIENTIFIC BIOLOGY

Scientific biology, defined in this sense, begins with the attempt made by Lavoisier and Laplace (1780) to show that the quantity of heat which is formed in the body of a warm-blooded animal is equal to that formed in a candle, provided that the quantities of carbon dioxide formed in both cases are identical. This was the first attempt to reduce a life phenomenon, namely, the formation of animal heat, completely to physico-chemical terms. What these two investigators began with primitive means has been completed by more recent investigators—Pettenkofer and Voit, Rubner, Zuntz and Atwater. The oxidation of a food-stuff always furnishes the same amount of heat, no matter whether it takes place in the living body or outside.

These investigations left a gap. The substances which undergo oxidations in the animal body—starch, fat, and proteins— are substances which at ordinary temperature are not easily oxidized. They require the temperature of the flame in order to undergo rapid oxidation through the oxygen of the air. This discrepancy between the oxidations in the living body and those in the laboratory manifests itself also in other chemical processes, e.g., digestion or hydrolytic reactions, which were at first found to occur outside the living body rapidly only under conditions incompatible with life. This discrepancy was done away with by the physical chemists, who demonstrated that the same acceleration of chemical reactions which is brought about by a high temperature can also be accomplished at a low temperature with the aid of certain specific substances, the so-called catalyzers. This progress is connected pre-eminently with the names of Berzelius and Wilhelm Ostwald. The specific substances

which accelerate the oxidations at body temperature sufficiently to allow the maintenance of life are the so-called ferments of oxidation.

The work of Lavoisier and Laplace not only marks the beginning of scientific biology, it also touches the core of the problem of life; for it seems that oxidations form a part, if not the basis, of all life phenomena in higher organisms.

III. THE " RIDDLE OF LIFE"

By the "riddle of life" not everybody will understand the same thing. We all, however, desire to know how life originates and what death is, since our ethics must be influenced to a large extent through the answer to this question. We are not yet able to give an answer to the question as to how life originated on the earth. We know that every living being is able to transform food-stuffs into living matter; and we also know that not only the compounds which are formed in the animal body can be produced artificially, but that chemical reactions which take place in living organisms can also be repeated at the same rate and temperature in the laboratory. The gap in our knowledge which we feel most keenly is the fact that the chemical character of the catalyzers (the enzymes or ferments) is still unknown. Nothing indicates, however, at present that the artificial production of living matter is beyond the possibilities of science.

This view does not stand in opposition to the idea of Arrhenius that germs of sufficiently small dimensions are driven by radiation-pressure through space; and that these germs, if they fall upon new cosmic bodies possessing water, salts, and oxygen, and the proper temperature, give rise to a new evolution of organisms. Biology will certainly retain this idea, but I believe that we must also follow out the other problem: namely, we must either succeed in producing

living matter artificially, or we must find the reasons why this is impossible.

IV. THE ACTIVATION OF THE EGG

Although we are not yet able to state how life originated in general, another, more modest problem, has been solved, that is, how the egg is caused by the sperm to develop into a new individual. Every animal originates from an egg and in the majority of animals a new individual can only then develop if a male sex-cell, a spermatozoon, enters into the egg. The question as to how a spermatozoon can cause an egg to develop into a new individual was twelve years ago still shrouded in that mystery which today surrounds the origin of life in general. But today we are able to state that the problem of the activation of the egg is for the most part reduced to physico-chemical terms. The egg is in the unfertilized condition a single cell with only one nucleus. If no spermatozoon enters into it, it perishes after a comparatively short time, in some animals in a few hours, in others in a few days or weeks. If, however, a spermatozoon enters into the egg, the latter begins to develop, i.e., the nucleus begins to divide into two nuclei and the egg which heretofore consisted of one cell is divided into two cells. Subsequently each nucleus and each cell divides again into two, and so on. These cells have, in many eggs, the tendency to remain at the surface of the egg or to creep to the surface, and later such an egg forms a hollow sphere whose shell consists of a large number of cells. On the outer surface of this hollow sphere cilia are formed and the egg is now transformed into a free-swimming larva. Then an intestine develops through the growing in of cells in one region of the blastula and gradually the other organs, skeleton, vascular system, etc., originate. Embryologists had noticed that occasionally the unfertilized eggs of certain animals, e.g., sea-urchins,

THE MECHANISTIC CONCEPTION OF LIFE

worms, or even birds, show a tendency to a nuclear or even a cell division; and R. Hertwig, Mead, and Morgan had succeeded in inducing one or more cell divisions artificially in such eggs. But the cell divisions in these cases never led to the development of a larva, but at the best to the formation of an abnormal mass of cells which soon perished.

I succeeded twelve years ago in causing the unfertilized eggs of the sea-urchin to develop into swimming larvae by treating them with sea-water, the concentration of which was

FIG. 1

FIG. 2

FIG. 1.—Unfertilized egg of the sea-urchin surrounded by spermatozoa. Only the heads of the spermatozoa are drawn, since at the magnification used the tails were not visible.

FIG. 2.—The same egg immediately after the entrance of the spermatozoon. The egg is surrounded by a larger circle, the fertilization membrane, which is formed through the action of the spermatozoon. This formation of a fertilization membrane can be induced by a purely chemical treatment of the egg.

raised through the addition of a small but definite quantity of a salt or sugar. The eggs were put for two hours into a solution the osmotic pressure of which had been raised to a certain height. When the eggs were put back into normal sea-water they developed into larvae and a part of these larvae formed an intestine and a skeleton. The same result was obtained in the eggs of other animals, star-fish, worms, and mollusks. These experiments proved the possibility of substituting physico-chemical agencies for the action of the living spermatozoon, but did not yet explain how the spermatozoon causes the development of the egg, since in

these experiments the action of the spermatozoon upon the egg was very incompletely imitated. When a spermatozoon enters into the egg it causes primarily a change in the surface of the egg which results in the formation of the so-called membrane of fertilization. This phenomenon of membrane formation which had always been considered as a phenomenon of minor importance did not occur in my original method of treating the egg with hypertonic sea-water. Six years ago while experimenting on the Californian sea-urchin, Strongylo-centrotus purpuratus, I succeeded in finding a method of causing the unfertilized egg to form a membrane without injuring the egg. This method consists in treating the eggs for from one to two minutes with sea-water to which a definite amount of butyric acid (or some other monobasic fatty acid) has been added. If after that time the eggs are brought back into normal sea-water, all form a fertilization membrane in exactly the same way as if a spermatozoon had entered. This membrane formation or rather the modification of the surface of the egg which underlies the membrane formation starts the development. It does not allow it, however, to proceed very far at room temperature. In order to allow the development to go farther it is necessary to submit the eggs after the butyric acid treatment to a second operation. Here we have a choice between two methods. We can either put the eggs for about one half-hour into a hypertonic solution (which contains free oxygen); or we can put them for about three hours into sea-water deprived of oxygen. If the eggs are then returned to normal sea-water containing oxygen they all develop; and in a large number the development is as normal as if a spermatozoon had entered.

The essential feature is therefore the fact that the development is caused by two different treatments of the egg; and that of these the treatment resulting in the formation of the membrane is the more important one. This is proved

THE MECHANISTIC CONCEPTION OF LIFE

FIG. 5

FIGS. 3, 4, and 5.—Segmentation of the sea-urchin egg, resulting in the formation of two cells (Fio. 5). The changes from Fig. 3 to Fig. 5 occur in about one minute or less time. This segmentation occurs after fertilization or after the chemical treatment of the egg described in the text.

FIG. 6

FIG. 7

FIGS. 6 and 7.—The sea-urchin egg divided into four and eight cells respectively.

10 THE MECHANISTIC CONCEPTION OF LIFE

by the fact that in certain forms, as for instance the star-fish, the causation of the artificial membrane formation may suffice for the development of normal larvae; although here, too, the second treatment increases not only the number of larvae, but also improves the appearance of the larvae, as R. Lillie found.

The question now arises, how the membrane formation can start the development of the egg. An analysis of the

FIG. 8 FIG. 9

FIG. 8.—Blastula. First larval stage of the sea-urchin egg. At the surface of the cells cilia are formed and the larva begins to swim and reaches the surface of the water.

FIG. 9.—Gastrula stage. The intestine begins to form and the first indication of the skeleton appears in the form of fine crystals.

process and of the nature of the agencies which cause it yielded the result that the unfertilized egg possesses a superficial cortical layer, which must be destroyed before the egg can develop. It is immaterial by what means this superficial cortical layer is destroyed. All agencies which cause a definite type of cell destruction—the so-called cytolysis— cause also the egg to develop, as long as their action is limited to the surface layer of the cell. The butyric acid treatment of the egg mentioned above only serves to induce the destruction of this cortical layer. In the eggs of some animals this cortical layer can be destroyed mechanically by shaking the

THE MECHANISTIC CONCEPTION OF LIFE

egg, as A. P. Mathews found in the case of star-fish eggs and I in the case of the eggs of certain worms. In the case of the eggs of the frog it suffices to pierce the cortical layer with a needle, as Bataillon found in his beautiful experiments a year ago. 1 The mechanism by which development is caused is apparently the same in all these cases, namely, the destruction of the cortical layer of the eggs. This can be caused generally by certain chemical means which play a role also in bacteriology; but it can also be caused in special cases by mechanical means, such as agitation or piercing of the cortical layer. It may be mentioned parenthetically that foreign blood sera have also a cytolytic effect, and I succeeded in causing membrane formation and in consequence the development of the sea-urchin egg by treating it with the blood of various animals, e.g., of cattle, or the rabbit.

Recently Shearer has succeeded in Plymouth in causing a number of parthenogenetic plutei produced by my method to develop beyond the stage of metamorphosis, and Delage has reported that he raised two larvae of the sea-urchin produced by artificial parthenogenesis to the stage of sexual maturity. We may, therefore, state that the complete imitation of the developmental effect of the spermatozoon by certain physico-chemical agencies has been accomplished.

I succeeded in showing that the spermatozoon causes the development of the sea-urchin egg in a way similar to that

1 This method does not work with the eggs of fish and is apparently as limited in its applicability as the causation of development by mechanical agitation.

FIG. 10.—Pluteus stage of Strongy-locentrotus purpuratus. S skeleton; D intestine.

in my method of artificial parthenogenesis; namely, by carrying two substances into the egg, one of which acts like the butyric acid and induces the membrane formation, while the other acts like the treatment with a hypertonic solution and enables the full development of the larvae. In order to prove this for the sea-urchin egg foreign sperm, e.g., that of the star-fish, must be used. The sperm of the sea-urchin penetrates so rapidly into the sea-urchin egg that almost always both substances get into the egg. If, however, starfish sperm is used for the fertilization of the sea-urchin egg, in a large number of cases, membrane formation occurs before the spermatozoon has found time to penetrate entirely into the egg. In consequence of the membrane formation the spermatozoon is thrown out. Such eggs behave as if only the membrane formation had been caused by some artificial agency, e.g., butyric acid. They begin to develop, but soon show signs of disintegration. If treated with a hypertonic solution they develop into larvae. In touching the egg contents the spermatozoon had a chance to give off a substance which liquefied the cortical layer and thereby caused the membrane formation by which the further entrance of the spermatozoon into the egg was prevented. If, however, the star-fish sperm enters completely into the egg before the membrane formation begins, the spermatozoon carries also the second substance into the egg, the action of which corresponds to the treatment of the egg with the hypertonic solution. In this case the egg can undergo complete development into a larva.

F. Lillie has recently confirmed the same fact in the egg of a worm, Nereis. He mixed the sperm and eggs of Nereis and centrifuged the mass. In many cases the spermatozoa which had begun to penetrate into the egg were thrown off again. The consequence was that only a membrane formation resulted without the spermatozoon penetrating into the

egg. This membrane formation led only to a beginning but not to a complete development. We may, therefore, conclude that the spermatozoon causes the development of the egg in a way similar to that which takes place in the case of artificial parthenogenesis. It carries first a substance into the egg which destroys the cortical layer of the egg in the same way as does butyric acid; and secondly a substance which corresponds in its effect to the influence of the hyper-tonic solution in the sea-urchin egg after the membrane formation.

The question arises as to how the destruction of the cortical layer can cause the beginning of the development of the egg. This question leads us to the process of oxidation. Years ago I had found that the fertilized sea-urchin egg can only develop in the presence of free oxygen; if the oxygen is completely withdrawn the development stops, but begins again promptly as soon as oxygen is again admitted. From this and similar experiments I concluded that the spermatozoon causes the development by accelerating the oxidations in the egg. This conclusion was confirmed by experiments by O. Warburg and by Wasteneys and myself in which it was found that through the process of fertilization the velocity of oxidations in the egg is increased to four or six times its original value. Warburg was able to show that the mere causation of the membrane formation by the butyric acid treatment has the same accelerating effect upon the oxidations as fertilization.

What remains unknown at present is the way in which the destruction of the cortical layer of the egg accelerates the oxidations. It is possible that the cortical layer acts like a solid crust and thus prevents the oxygen from reaching the surface of the egg or from penetrating into the latter sufficiently rapidly. The solution of these problems must be reserved for further investigation.

14 THE MECHANISTIC CONCEPTION OF LIFE

We therefore see that the process of the activation of the egg by the spermatozoon, which twelve years ago was shrouded in complete darkness, is today practically completely reduced to a physico-chemical explanation. Considering the youth of experimental biology we have a right to hope that what has been accomplished in this problem will occur in rapid succession in those problems which today still appear as riddles.

V. NATURE OF LIFE AND DEATH

The nature of life and of death are questions which occupy the interest of the layman to a greater extent than possibly any other purely theoretical problem; and we can well understand that humanity did not wait for experimental biology to furnish an answer. The answer assumed the anthropomorphic form characteristic of all explanations of nature in the prescientific period. Life was assumed to begin with the entrance of a "life principle" into the body; that individual life begins with the egg was of course unknown to primitive or prescientific man. Death was assumed to be due to the departure of this "life principle" from the body.

Scientifically, however, individual life begins (in the case of the sea-urchin and possibly in general) with the acceleration of the rate of oxidation in the egg, and this acceleration begins after the destruction of its cortical layer. Life of warm-blooded animals—man included—ends with the cessation of oxidation in the body. As soon as oxidations have ceased for some time, the surface films of the cells, if they contain enough water and if the temperature is sufficiently high, become permeable for bacteria, and the body is destroyed by micro-organisms. The problem of the beginning and end of individual life is physico-chemically clear. It is, therefore, unwarranted to continue the statement that in addition to the acceleration of oxidations the beginning of

individual life is determined by the entrance of a metaphysical "life principle" into the egg; and that death is determined, aside from the cessation of oxidations, by the departure of this "principle" from the body. In the case of the evaporation of water we are satisfied with the explanation given by the kinetic theory of gases and do not demand that —to repeat a well-known jest of Huxley—the disappearance of the "aquosity" be also taken into consideration.

VI. HEREDITY

It may be stated that the egg is the essential bearer of heredity. We can cause an egg to develop into a larva without sperm, but we cannot cause a spermatozoon to develop into a larva without an egg. The spermatozoon can influence the form of the offspring only when the two forms are rather closely related. If the egg of a sea-urchin is fertilized with the sperm from a different species of sea-urchin, the larval form has distinct paternal characters. If, however, the eggs of a sea-urchin are fertilized with the sperm of a more remote species, e.g., a star-fish, the result is a sea-urchin larva which possesses no paternal characters, as I found and as Godlewski, Kupelwieser, Hagedoorn, and Baltzer were able to confirm. This fact has some bearing upon the further investigation of heredity, inasmuch as it shows that the egg is the main instrument of heredity, while apparently the spermatozoon is restricted in the transmission of characters to the offspring. If the difference between spermatozoon and egg exceeds a certain limit the hereditary effects of the spermatozoon cease and it acts merely as an activator to the egg.

As far as the transmission of paternal characters is concerned, we can say today that the view of those authors was correct who, with Boveri, localized this transmission not only in the cell nucleus, but in a special constituent of the nucleus,

16 THE MECHANISTIC CONCEPTION OF LIFE

the chromosomes. The proof for this was given by facts found along the lines of Mendelian investigations. The essential law of Mendel, the law of segregation, can in its simplest form be expressed in the following way. If we cross two forms which differ in only one character every hybrid resulting from this union forms two kinds of sex-cells in equal numbers; two kinds of eggs if it is a female, two kinds of spermatozoa if it is a male. The one kind corresponds to the pure paternal, the other to the pure maternal type. The investigation of the structure and behavior of the nucleus showed that the possibility for such a segregation of the sex-cells in a hybrid can easily be recognized during a given stage in the formation of the sex-cells, if the assumption is made that the chromosomes are the bearers of the paternal characters. The proof for the correctness of this view was furnished through the investigation of the heredity of those qualities which occur mainly in one sex; e.g., color blindness which occurs preeminently in the male members of a family.

Nine years ago McClung published a paper which solved the problem of sex determination, at least in its essential feature. Each animal has a definite number of chromosomes in its cell nucleus. Henking had found that in a certain form of insects (Pyrrhocoris) two kinds of spermatozoa exist which differ in the fact that the one possesses a nucleolus while the other does not. Montgomery afterward showed that Henking's nucleolus was an accessory chromosome. McClung first expressed the idea that this accessory chromosome was connected with the determination of sex. Considering the importance of this idea we may render it in his own words:

A most significant fact, and one upon which almost all investigators are united in opinion, is that the element is apportioned to but one-half of the spermatozoa. Assuming it to be true that the chromatin is the important part of the cell in the matter of heredity,

then it follows that we have two kinds of spermatozoa that differ from each other in a vital matter. We expect, therefore, to find in the offspring two sorts of individuals in approximately equal numbers, under normal conditions, that exhibit marked differences in structure. A careful consideration will suggest that nothing but sexual characters thus divides the members of a species into two well-defined groups, and We are logically forced to the conclusion that the peculiar chromosome has some bearing upon the arrangement.

I must here also point out a fact that does not seem to have the recognition it deserves; viz., that if there is a cross-division of the chromosomes in the maturation mitoses, there must be two kinds of spermatozoa regardless of the presence of the accessory chromosome. It is thus possible that even in the absence of any specialized element a preponderant maleness would attach to one-half of the spermatozoa, due to the "qualitative division of the tetrads."

The researches of the following years, especially the brilliant work of E. B. Wilson, Miss Stevens, T. H. Morgan, and others, have amply confirmed the correctness of this ingenious idea and cleared up the problem of sex determination in its main features.

According to McClung each animal forms two kinds of spermatozoa in equal numbers, which differ by one chromosome. One kind of spermatozoa produces male animals, the other female animals. The eggs are all equal in these animals. More recent investigations, especially those of E. B. Wilson, have shown that this view is correct for many animals.

While in many animals there are two kinds of spermatozoa and only one kind of eggs, in other animals two kinds of eggs and only one kind of spermatozoa are formed, e.g., sea-urchins and certain species of birds and of butterflies (Abraxas'). In these animals the sex is predetermined in the egg and not in the spermatozoon. It is of interest that, according to Guyer, in the human being two kinds of spermatozoa exist and only one kind of eggs; in man, therefore, sex is determined by the spermatozoon.

THE MECHANISTIC CONCEPTION OF LIFE

How is sex determination accomplished? Let us take the case which according to Wilson is true for many insects and according to Guyer for human beings, namely, that there are two kinds of spermatozoa and one kind of eggs. According to Wilson all unfertilized eggs contain in this case one so-called

FIGS. 11-16 (after E. B. Wilson).—Diagrammatic presentation of sex determination in an insect (Protenor). a a are the nuclei of unfertilized eggs. Each contains one sex chromosome marked X; the other six dark spots are the chromosomes which are supposed to transmit hereditary characters not connected with sex. b and c represent the two different types of sperm; b containing a sex chromosome X, c being without such a chromosome.

d represents the constitution of the egg nucleus after it is fertilized by a spermatozoon of the type b containing a sex chromosome. This egg now has two sex chromosomes and therefore will give rise to a female, e represents a fertilized egg after a spermatozoon of the type c (without a sex chromosome) has entered it. This egg contains after fertilization only one sex chromosome X and hence will give rise to a male.

sex chromosome, the X-chromosome. There are two kinds of spermatozoa, one with and one without an X-chromosome. Given a sufficiently large number of eggs and of spermatozoa, one-half of the eggs will be fertilized by spermatozoa with and one-half by spermatozoa without an X-chromosome. Hence one-half of the eggs will contain after fertilization two X-chromosomes each and one-half only one .X-chromosome

each. The eggs containing only one X-chromosome give rise to males, those containing two X-chromosomes give rise to females—as Wilson and others have proved. This seems to be a general law for those cases in which there are two kinds of spermatozoa and one kind of eggs.

These observations show why it is impossible to influence the sex of a developing embryo by external influences. If, for example, in the human being a spermatozoon without an ^-chromosome enters into an egg, the egg will give rise to a boy, but if a spermatozoon with an X-chromosome gets into the egg the latter will give rise to a girl. Since always both kinds of spermatozoa are given off by the male it is a mere matter of chance whether a boy or a girl originates; and it agrees with the law of probability that in a large population the number of boys and girls born within a year is approximately the same. 1

These discoveries solved also a series of other difficulties. Certain types of twins originate from one egg after fertilization. Such twins have always the same sex, as we should expect, since the cells of both twins have the same number of X-chromosomes.

In plant lice, bees, and ants, the eggs may develop with and without fertilization. It was known that from fertilized eggs in these animals only females develop, males never. It was found that in these animals the eggs contain only one sex chromosome; while in the male are found two kinds of spermatozoa, one with and one without a sex chromosome. For Phylloxera and Aphides it has been proved with certainty by Morgan and others that the spermatozoa which contain no sex chromosome cannot live, and the same is probably true for bees and ants. If, therefore, in these animals an egg is

1 It is stated that the number of males born exceeds that of the females by a slight percentage. If this statement is correct it must be due to a secondary cause, e.g., a greater motility or greater duration of life of the male spermatozoon. Further researches will be needed to clear up this point.

fertilized it is always done by a spermatozoon which contains an JT-chromosome. The egg has, therefore, after fertilization in these animals always two X-chromosomes and from such eggs only females can arise.

It had been known for a long time that in bees and ants the unfertilized eggs can also develop, but such eggs give rise to males only. This is due to the fact that the eggs of these animals contain only one X-chromosome and from eggs with only one chromosome only males can arise (at least in the case of animals in which the male is heterozygous for sex).

The problem of sex determination has, therefore, found a simple solution, and simultaneously Mendel's law of segregation also finds its solution.

In many insects and in man the cells of the female have two sex chromosomes. In a certain stage of the history of the egg one-half of the chromosomes leave the egg (in the form of the "polar-body") and it keeps only half the number of chromosomes. Each egg, therefore, retains only one X or sex chromosome. In the male the cells have from the beginning only one X-chromosome and each primordial spermatozoon divides into two new (in reality into two pairs of) spermatozoa, one of which contains an JsT-chromosome while the other is without such a chromosome. What can be observed here directly in the male animal takes place in every hybrid; during the critical, so-called maturation division of the sexual cell in the hybrid, a division of the chromosomes occurs, whereby only one-half of the sex-cells receive the hereditary substance in regard to which the two original pure forms differ.

That this is not a mere assumption can be shown in those cases in which the hereditary character appears only, or preeminently, in one sex as, e.g., color blindness which appears mostly in the male. If a color-blind individual is mated with an individual with normal color vision the heredity of color

blindness in the next two generations corresponds quantitatively with what we must expect on the assumption that the chemical substances determining color vision are contained in the sex chromosomes. In the color-blind individual something is lacking which can be found hi the individual with normal color perception. The factor for color vision is obviously transmitted through the sex chromosome. In the next generation color blindness cannot appear, since each fertilized egg contains the factor for color perception. In the second generation, however, the theory demands that one-half of the males should be color blind. In man these conditions cannot be verified. T. H. Morgan has found in a fly (Drosophila) a number of similar sex-limited characters which behave like color blindness, e.g., lack of pigment in the eyes. These flies have normally red eyes. Morgan has observed a mutation with white eyes, which occurs hi the male. When he crossed a white-eyed with a red-eyed female all flies of the first generation were red-eyed, since all flies had the factor for pigment in their sex-cells; in the second generation all females and exactly one-half of the males had red eyes, the other half of the males, however, white eyes, as the theory demands.

From these and numerous similar breeding experiments of Correns, Doncaster, and especially of Morgan, we may conclude with certainty that the sex chromosomes are the bearers of those hereditary characters which appear pre-eminently in one sex. We say pre-eminently, since theoretically we can predict cases in which color blindness or white eyes must appear also in the female. Breeding experiments have shown that this theoretical prediction is justified. The riddle of Mendel's law of segregation finds its solution through these experiments and incidentally also the problem of the determination of sex which is only a special case of the law of segregation, as Mendel already intimated.

-s

The main task which is left here for science to accomplish is the determination of the chemical substances in the chromosomes which are responsible for the hereditary transmission of a quality, and the determination of the mechanism by which these substances give rise to the hereditary character. Here the ground has already been broken. It is known that for the formation of a certain black pigment the cooperation of a substance—tyrosin—and of a ferment of oxidation—tyrosinase —is required. The hereditary transmission of the black color through the male animal must occur by substances carried in the chromosome which determine the formation of tyrosin or tyrosinase or of both. We may, therefore, say that the solution of the riddle of heredity has succeeded to the extent that all further development will take place purely in cytological and physico-chemical terms.

While until twelve years ago the field of heredity was the stamping ground for the rhetorician and metaphysician it is today perhaps the most exact and rationalistic part of biology, where facts cannot only be predicted qualitatively, but also quantitatively.

VII. THE HARMONIOUS CHARACTER OF THE ORGANISMS

It is not possible to prove in a short address that all life phenomena will yield to a physico-chemical analysis. We have selected only the phenomena of fertilization and heredity, since these phenomena are specific for living organisms and without analogues in inanimate nature; and if we can convince ourselves that these processes can be explained physico-chemically we may safely expect the same of such processes for which there exist a-priori analogies in inanimate nature, as, e.g., for absorption and secretion.

We must, however, settle a question which offers itself not only to the layman but also to every biologist, namely, how we shall conceive that wonderful "adaptation of each part to the

whole " by which an organism becomes possible. In the answer to this question the metaphysician finds an opportunity to put above the purely chemical and physical processes something specific which is characteristic of life only: the "Zielstrebigkeit," the "harmony" of the phenomena, or the "dominants" of Reinke and similar things.

With all due personal respect for the authors of such terms I am of the opinion that we are dealing here, as in all cases of metaphysics, with a play on words. That a part is so constructed that it serves the "whole" is only an unclear expression for the fact that a species is only able to live—or to use Roux's expression—is only durable, if it is provided with the automatic mechanism for self-preservation and reproduction. If, for instance, warm-blooded animals should originate without a circulation they could not remain alive, and this is the reason why we never find such forms. The phenomena of "adaptation" cause only apparent difficulties since we rarely or never become aware of the numerous faultily constructed organisms which appear in nature. I will illustrate by a concrete example that the number of species which we observe is only an infinitely small fraction of those which can originate and possibly not rarely do originate, but which we never see since their organization does not allow them to continue to exist long. Moenk-haus found ten years ago that it is possible to fertilize the egg of each marine bony fish with the sperm of practically any other marine bony fish. His embryos apparently lived only a very short time. This year I succeeded in keeping such hybrid embryos between distantly related bony fish alive for over a month. It is, therefore, clear that it is possible to cross practically any marine teleost with any other.

The number of teleosts at present in existence is about 10,000. If we accomplish all possible hybridizations 100,000,000 different crosses will result. Of these teleosts only a very small proportion, namely about one one-hundredth of 1 per cent,

can live. It turned out in my experiments that the heterogeneous hybrids between bony fishes formed eyes, brains, ears, fins, and pulsating hearts, blood and blood-vessels, but could live only a limited time because no blood circulation was established —in spite of the fact that the heart beat for weeks—or that the circulation, if it was established at all, did not last long.

What prevented these heterogeneous fish embryos from reaching the adult stage? The lack of the proper "dominants"? Scarcely. I succeeded in producing the same type of faulty embryos in the pure breeds of a bony fish (Fundulus heteroclitus) by raising the eggs in 50 c.c. of sea-water to which was added 2 c.c. 1/100 per cent NaCN. The latter substance retards the velocity of oxidations and I obtained embryos which were in all details identical with the embryos produced by crossing the eggs of the same fish with the sperm of remote teleosts, e.g., Ctenolabrus or Menidia. These embryos, which lived about a month, showed the peculiarity of possessing a beating heart and blood, but no circulation. This suggests the idea that heterogeneous embryos show a lack of "adaptation" and durability for the reason that in consequence of the chemical difference between heterogeneous sperm and egg the chemical processes in the fertilized egg are abnormal.

The possibility of hybridization goes much farther than we have thus far assumed. We can cause the eggs of echinoderms to develop with the sperm of very distant forms, even mollusks and worms (Kupelwieser); but such hybridizations never lead to the formation of durable organisms.

It is, therefore, no exaggeration to state that the number of species existing today is only an infinitely small fraction of those which can and possibly occasionally do originate, but which escape our notice because they cannot live and reproduce. Only that limited fraction of species can exist which possesses no coarse disharmonies in its automatic mechanism of preservation and reproduction. Disharmonies and faulty attempts in

nature are the rule, the harmonically developed systems the rare exception. But since we only perceive the latter we gain the erroneous impression that the " adaptation of the parts to the plan of the whole" is a general and specific characteristic of animate nature, whereby the latter differs from inanimate nature. If the structure and the mechanism of the atoms were known to us we should probably also get an insight into a world of wonderful harmonies and apparent adaptations of the parts to the whole. But in this case we should quickly understand that the chemical elements are only the few durable systems among a large number of possible but not durable combinations. Nobody doubts that the durable chemical elements are only the product of blind forces. There is no reason for conceiving otherwise the durable systems in living nature.

VIII. THE CONTENTS OF LIFE

The contents of life from the cradle to the bier are wishes and hopes, efforts and struggles, and unfortunately also disappointments and suffering. And this inner life should be amenable to a physico-chemical analysis? In spite of the gulf which separates us today from such an aim I believe that it is attainable. As long as a life phenomenon has not yet found a physico-chemical explanation it usually appears inexplicable. If the veil is once lifted we are always surprised that we did not guess from the first what was behind it.

That in the case of our inner life a physico-chemical explanation is not beyond the realm of possibility is proved by the fact that it is already possible for us to explain cases of simple manifestations of animal instinct and will on a physico-chemical basis; namely, the phenomena which I have discussed in former papers under the name of animal tropisms. As the most simple example we may mention the tendency of certain animals to fly or creep to the light. We are dealing in this case with the manifestation of an instinct or impulse which the

animals cannot resist. It appears as if this blind instinct which these animals must follow, although it may cost them their life, might be explained by the same law of Bunsen and Roscoe, which explains the photochemical effects in inanimate nature. This law states that within wide limits the photochemical effect equals the product of the intensity of light into the duration of illumination. It is not possible to enter here into all the details of the reactions of these animals to light; we only wish to point out in which way the light instinct of the animals may possibly be connected with the Bunsen-Roscoe law.

The positively heliotropic animals—i.e., the animals which go instinctively to a source of light—have in their eyes (and occasionally also in their skin) photosensitive substances which undergo chemical alterations by light. The products formed in this process influence the contraction of the muscles—mostly indirectly, through the central nervous system. If the animal is illuminated on one side only, the mass of photochemical reaction products formed on that side in the unit of time is greater than on the opposite side. Consequently the development of energy in the symmetrical muscles on both sides of the body becomes unequal. As soon as the difference in the masses of the photochemical reaction products on both sides of the animal reaches a certain value, the animal, as soon as it moves, is automatically forced to turn toward one side. As soon as it has turned so far that its plane of symmetry is in the direction of the rays, the symmetrical spots of its surface are struck by the light at the same angle and in this case the intensity of light and consequently the velocity of reaction of the photochemical processes on both sides of the animal become equal. There is no more reason for the animal to deviate from the motion in a straight line and the positively heliotropic animal will move in this line to the source of light. (It was assumed that in these experiments the animal is under the influence of only one source of light and positively heliotropic.)

THE MECHANISTIC CONCEPTION OF LIFE

In a series of experiments I have shown that the heliotropic reactions of animals are identical with the heliotropic reactions of plants. It was known that sessile heliotropic plants bend

FIG. 18

FIG. 19

FIGS. 18 and 19.—Positive heliotropism of the polyps of Eudendrium. The new polyp-bearing stems all grow in the direction of the rays of light which is indicated by an arrow in each figure. (From nature.). These animals bend in the same way to the light as the stems of positively heliotropic plants kept under similar conditions.

their stems to the source of light until the axis of symmetry of their tip is in the direction of the rays of light. I found the same phenomenon in sessile animals, e.g., certain hydroids and worms. Motile plant organs, e.g., the swarm spores of plants, move to the source of light (or if they are negatively

THE MECHANISTIC CONCEPTION OF LIFE

heliotropic away from it), and the same is observed in motile animals. In plants only the more refrangible rays from green to blue have these heliotropic effects, while the red and yellow rays are little or less effective; and the same is true for the heliotropic reactions of animals.

It has been shown by Blaauw for the heliotropic curvatures of plants that the product of the intensity of a source of light into the time required to induce a heliotropic curvature is a

FIG. 2Q.—Positive heliotropism of a marine worm (Spirographia). (From nature.) The light fell into the aquarium from one side only and the worms all bent their heads toward the source of light, as the stems of positively heliotropic plants would do under the same conditions.

constant; and the same result was obtained simultaneously by another botanist, Froschl. It is thus proved that the Bunsen-Roscoe law controls the heliotropic reactions of plants. The same fact had already been proved for the action of light on our retina.

The direct measurements in regard to the applicability of Bunsen's law to the phenomena of animal heliotropism have not yet been made. But a number of data point to the probability that the law holds good here also. The first of these facts is the identity of the light reactions of plants and animals. The second is at least a rough observation which harmonizes with the Bunsen-Roscoe law. As long as the intensity of light or the mass of photochemical substances at the surfaces of the

30 THE MECHANISTIC CONCEPTION OF LIFE

animal is small, according to the law of Bunsen, it must take a comparatively long time until the animal is automatically oriented by the light, since according to this law the photochemical effect is equal to the product of the intensity of the light into the duration of illumination. If, however, the intensity of the light is strong or the active mass of the photochemical substance great, it will require only a very short time until the difference in the mass of photochemical reaction products on both sides of the animal reaches the value which is necessary for the automatic turning to (or from) the light. The behavior of the animals agrees with this assumption. If the light is sufficiently strong the animals go in an almost straight line to the source of light; if the intensity of light (or the mass of photosensitive substances on the surface of the animal) is small the animals go in irregular lines, but at last they also land at the source of light, since the directing force is not entirely abolished. It will, however, be necessary to ascertain by direct measurements to what extent these phenomena in animals are the expression of Bunsen-Roscoe's law. But we may already safely state that the apparent will or instinct of these animals resolves itself into a modification of the action of the muscles through the influence of light; and for the metaphysical term "will" we may in these instances safely substitute the chemical term "photochemical action of light."

Our wishes and hopes, disappointments and sufferings have their source in instincts which are comparable to the light instinct of the heliotropic animals. The need of and the struggle for food, the sexual instinct with its poetry and its chain of consequences, the maternal instincts with the felicity and the suffering caused by them, the instinct of workmanship, and some other instincts are the roots from which our inner life develops. For some of these instincts the chemical basis is at least sufficiently indicated to arouse the hope that their analysis, from the mechanistic point of view, is only a question of time.

IX. ETHICS

If our existence is based on the play of blind forces and only a matter of chance; if we ourselves are only chemical mechanisms—how can there be an ethics for us? The answer is, that our instincts are the root of our ethics and that the instincts are just as hereditary as is the form of our body. We eat, drink, and reproduce not because mankind has reached an agreement that this is desirable, but because, machine-like, we are compelled to do so. We are active, because we are compelled to be so by processes in our central nervous system; and as long as human beings are not economic slaves the instinct of successful work or of workmanship determines the direction of their action. The mother loves and cares for her children, not because metaphysicians had the idea that this was desirable, but because the instinct of taking care of the young is inherited just as distinctly as the morphological characters of the female body. We seek and enjoy the fellowship of human beings because hereditary conditions compel us to do so. We struggle for justice and truth since we are instinctively compelled to see our fellow beings happy. Economic, social, and political conditions or ignorance and superstition may warp and inhibit the inherited instincts and thus create a civilization with a faulty or low development of ethics. Individual mutants may arise in which one or the other desirable instinct is lost, just as individual mutants without pigment may arise in animals; and the offspring of such mutants may, if numerous enough, lower the ethical status of a community. Not only is the mechanistic conception of life compatible with ethics: it seems the only conception of life which can lead to an understanding of the source of ethics.

II. THE SIGNIFICANCE OF TROPISMS FOR PSYCHOLOGY

THE SIGNIFICANCE OF TROPISMS FOR PSYCHOLOGY 1

A mechanistic conception of life is not complete unless it includes a physico-chemical explanation of psychic phenomena. Some authors hold that even if a complete physico-chemical analysis of these phenomena were possible today it would leave the ''truly psychical" unexplained. We do not need to enter into a discussion of such an objection since we are still too far from the goal. We are at least able to show for a limited group of animal reactions that they can be explained unequivocally on a purely physico-chemical basis, namely, phenomena which the metaphysician would classify under the term of animal "will."

Through the writings of Schopenhauer and E. von Hart-mann I became interested in the problem of will. When as a student I read Munk's investigations on the cerebral cortex I believed that they might serve as a starting-point for an experimental analysis of will. Munk stated that he had succeeded in proving that every memory image in a dog's brain is localized hi a particular cell or group of cells and that any one of these memory images can be extirpated at desire. Five years of experiments with extirpations in the cerebral cortex proved to me without doubt that Munk had become the victim of an error and that the method of cerebral operations may give data concerning the path of nerves in the central nervous system but that it teaches little about the dynamics of brain processes.

A better opportunity seemed to offer itself in the study of the comparative psychology of the lower animals in which

1 Lecture delivered at the Sixth International Psychological Congress at Geneva, 1909. (After a translation hi Popular Science Monthly by Miss Grace B. Watkinson.) Reprinted by courtesy of Professor James McKeen Cattell.

36 THE MECHANISTIC CONCEPTION OF LIFE

the mechanism for memory is developed but slightly or not at all. It seemed to me that some day it must become possible to discover the physico-chemical laws underlying the apparently random movements of such animals; and that the word " animal will" was only the expression of our ignorance of the forces which prescribe to animals the direction of their apparently spontaneous movements just as unequivocally as gravity prescribes the movements of the planets. For if a savage could directly observe the movements of the planets and should begin to think about them, he would probably come to the conclusion that a "will action " guides the movements of the planets just as a chance observer is today inclined to assume that "will" causes animals to move in a given direction.

The scientific solution of the problem of will seemed then to consist hi rinding the forces which determine the movements of animals, and in discovering the laws according to which these forces act. Experimentally, the solution of the problem of will must take the form of forcing, by external agencies, any number of individuals of a given kind of animals to move in a definite direction by means of their locomotor apparatus. Only if we succeed in this have we the right to assume that we know the force which under certain conditions seems to a layman to be the will of the animal. But if one part only of the animals moves in this definite direction and the other does not, we have not succeeded in finding the force which unequivocally determines the direction of their movement.

One other point should be observed. If a sparrow flies down to a seed lying on the ground, we speak of an act of will, but if a dead sparrow falls upon the seed this does not appear to us as such. In the latter case purely physical forces are concerned, while in the former chemical reactions are also taking place in the sense-organs, nerves, and muscles of the animal. We speak of an act of will, only when this latter complex, that is, the natural movement of locomotion, plays its part also, and

it is only with this sort of reactions that we have to deal in the psychology of the will.

Some experiments on winged plant lice may serve as an introduction to the methods of prescribing to animals the direction of their progressive movements.

In order to obtain the material, potted rose bushes or Cinerarias infected with plant lice are brought into a room and placed in front of a closed window. If the plants are allowed to dry out, the aphids (plant lice), previously wingless, change into winged insects. After this metamorphosis the animals leave the plants, fly to the window, and there creep upward on the glass. They can then easily be collected by holding a test-tube underneath and touching one animal at a time from above with a pen or scalpel, which causes the animals to drop into the test-tube. In this manner a sufficiently large number, perhaps twenty-five or fifty suitable subjects for the experiment, may be obtained. With these animals it may be demonstrated that the direction of their movement toward the light is definitely determined—provided that the animals are healthy and that the light is not too weak. The experiment is so arranged that only a single source of light, e.g., artificial light, is used.

The animals place themselves with their heads toward the source of light and move toward it in as straight a line as the imperfection of their locomotor apparatus allows, approaching as near to the source of light as their prison (the test-tube) permits. When they reach that end of the test-tube which is directed toward the source of light, they remain there, stationary, in a closely crowded mass. If the test-tube is turned 180° the animals again go straight toward the source of light until the interference of the glass stops their further progressive movements. 1 It can be demonstrated in these animals that the

1 Loeb, Der Heliotropismus der Tiere und seine Uebereinstimmung mit dem Heliotropismus der Pflanzen, Wiirzburg, 1889. Translated in Studies in General Physiology, 1906.

38 THE MECHANISTIC CONCEPTION OF LIFE

direction of their progressive movement is just as unequivocally governed by the source of light as the direction of the movement of the planets is determined by the force of gravity.

The theory of the compulsory movements of aphids under the influence of light is as follows: Two factors govern the progressive movements of the animals under these conditions; one is the symmetrical structure of the animal, and the second is the photochemical action of light. We will consider the two separately. In regard to the photochemical action of light, we know today that a great many chemical reactions of Organic bodies are accelerated by light. Especially is this true of oxidations. 1 The mass of facts is already so great that we are justified in assuming that the determining action of light upon animals and plants is in its last analysis due to the fact that the rate of certain chemical reactions in the cells of the retina or of other photosensitive regions of the organisms is modified by light; with increasing intensity of light the rate of certain chemical reactions, e.g., oxidation, increases.

The second factor is the symmetrical structure of the animal. As expressed in the gross anatomy of the animal, the right and left halves of the body are symmetrical. But it is my belief that such a symmetry exists in a chemical sense, as well as in an anatomical, by which I mean that symmetrical regions of the body are chemically identical and have the same metabolism, while non-symmetrical regions of the body are chemically different, and in general have a quantitatively or qualitatively different metabolism. In order to illustrate this difference it is only necessary to point out that the two retinae, which are certainly symmetrical, have an identical metabolism, while a region of the skin which is not symmetrical with the retina has a different metabolism. The individual points on

1 Luther, Die Aufgaben der Photochemie, Leipzig, 1905; C. Neuberg, Biochem. Zeitschr., XIII, 305, 1908; Loeb, The Dynamics of Living Matter, New York, 1906. In addition, see the work of Ciamician, as also of Wolfgang Ostwald (Biochem. Zeitschr., 1907).

the retina are also chemically unlike. The observations upon visual purple, the differences in the color sensitiveness of the fovea centralis, and the peripheral parts of the retina indicate that the points of symmetry of the two retinae are chemically alike, the non-symmetrical points chemically unlike.

Now if an unequal amount of light falls upon the two retinae the photochemical reactions in the one which receives more light will also be more accelerated than those in the other. The same naturally holds true for every other pair of symmetrical photosensitive surface elements. For it should be mentioned that photochemical substances are not found in the eyes only, but also in other places on the surface of many animals. In planarians, as my experiments and those of Parker have shown, not only the eyes, but also parts of the skin, are photosensitive. But if more light falls upon one retina than upon the other, the chemical reactions will also be more accelerated in the one retina than in the other, and accordingly more intense chemical changes will take place in one optic nerve than in the other. S. S. Maxwell and C. D. Snyder have demonstrated, independently of each other, that the rate of the nerve impulse has a temperature coefficient of the order of magnitude which is characteristic for chemical reactions. From this we must conclude that when two retinae (or other points of symmetry) are illuminated with unequal intensity, chemical processes, also of unequal intensity, take place in the two optic nerves (or in the sensory nerves of the two illuminated points). This inequality of chemical processes passes from the sensory to the motor nerves and eventually to the muscles connected with them. We conclude from this that with equal illumination of both retinae the symmetrical groups of muscles of both halves of the body will receive equal chemical stimuli and thus reach equal states of contraction, while, when the rate of reaction is unequal, the symmetrical muscles on one side of the body come into stronger action than

40 THE MECHANISTIC CONCEPTION OF LIFE

those on the other side. The result of such an inequality of the action of symmetrical muscles of the two sides of the body is a change in the direction of movement on the part of the animal.

The change in the direction of movement can result either in a turning of the head and, in consequence, of the whole animal toward the source of light, or in a turning of the head and the animal in the opposite direction. The structure of the central nervous system is segmental and the head segments generally determine 1 the behavior of the other segments with their accessory parts.

In the winged aphids the relations are as follows: Suppose that a single source of light is present and that the light strikes the animal from one side. As a consequence the activity of those muscles which turn the head or body of the animal toward the source of light will be increased. 2 As a result the head, and with it the whole body of the animal, is turned toward the source of light. As soon as this happens, the two retinae become illuminated equally. There is therefore no longer any cause for the animal to turn in one direction or the other. It is thus automatically guided toward the source of light. In this instance the light is the "will" of the animal which determines the direction of its movement, just as it is gravity in the case of a falling stone or the movement of a planet. The action of gravity upon the movement of the falling stone is direct, while the action of light upon the direction of movement of the aphids is indirect, inasmuch as the animal is caused only by means of an acceleration of photochemical reactions to move in a definite direction.

1 Loeb, Comparative Physiology of the Brain and Comparative Psychology, New York and London, 1900.

* If two sources of light of equal intensity are at an equal distance from the animal, it will move hi a direction at right angles to a line connecting the two sources of light, because hi this base both eyes are similarly influenced by the light. Herein, as Bonn has rightly said, the machine-like heliotropic reaction of animals differs from the movement of a human being toward one of two sources of light, the movement in the latter case not being determined by heliotropism.

We will now designate as positively heliotropic those animals which are forced to turn their head or move toward the source of light, and as negatively heliotropic those animals which are oriented or compelled to move in the opposite direction. 1

The aphids serve here only as an example. The same phenomena of positive heliotropism may be demonstrated with equal precision in a great many animals, vertebrates as well as invertebrates. We cannot, of course, give here an account of all these cases. The reader who is interested in them must look into the voluminous literature upon this subject. Heliotropism is unusually common among the larvae of marine animals and insects, but also not lacking in sexually mature individuals.

Heliotropic animals are therefore in reality photometric machines. According to photometric laws the intensity of light varies with the sine of the angle at which the light strikes a surface element of the animal (or with the cosine of the angle of incidence). The animal is oriented by the light in such a way that symmetrical elements of its photosensitive surface are struck at about the same angle. In the presence of only one source of light this condition is fulfilled if the axis of symmetry of the animal moves in the direction of the rays of light. In this case the velocity of photochemical reactions on both sides of the animal is the same and there is no reason why it should deviate from this direction in its progressive motions.

Experiments on the heliotropism of plants as well as on the perception of light by our retina have shown that the effect of light equals the product of the intensity into the duration of illumination. This law is identical with the general law of Bunsen and Roscoe which states that the chemical effect of light is within wide limits equal to this product. We do not yet know whether or not Bunsen's law holds good for the heliotropic animals. If it does, we shall have to substitute

1 Whether an animal is positively or negatively heliotropic depends upon the fact whether the light causes an increase or a decrease in the tension of the muscles. Why light should have these opposite effects is as yet unknown.

42 THE MECHANISTIC CONCEPTION OF LIFE

this law for what the metaphysician calls the will of these animals.

Ill

The winged aphids serve as an example, because they fulfil the above-mentioned requirement, namely, that all individuals, without exception, move toward the light. For mechanistic science it is a methodological postulate that the same law acts without exception, or that the exception must be satisfactorily explained. It was soon found, as was to be expected, that not all organisms in their natural condition are equally suitable for these experiments. Many animals show no heliotropism at all; many show only a slight reaction, while others show it in a degree as pronounced as do the winged aphids. The problem therefore presented itself of producing heliotropism artificially in animals which, under natural conditions, show no positive heliotropism. If small crustaceans of a fresh-water pond or lake are taken with a plankton net at noontime or in the afternoon and placed hi an aquarium which is illuminated from one side only, it is often found that these animals move about in the vessel pretty much at random and distribute themselves irregularly. Some seem to go more toward the source of light, others in the opposite direction, and the majority perhaps pay no attention to the light.

This condition changes instantly if we add to the water some acid, preferably carbonic acid, which easily penetrates the cells of the animal. To every 50 c.c. of the fresh water a few cubic centimeters of water charged with carbon dioxide are slowly added. If the correct amount is added all the individuals become actively positively heliotropic and move in as straight a line as the imperfection of their swimming movements permits, toward the source of light, and remain there closely crowded together on the illuminated side of the vessel. If the vessel is turned 180°, they go directly back again to the lighted side of the vessel. Every other acid acts like carbonic acid and

alcohol acts in the same manner, only more weakly and much more slowly. Animals which were previously indifferent to light become, under carbonic acid treatment, complete slaves of the light. 1

How does the acid produce this result? We will assume that it acts as a sensitizer. The light produces chemical changes, for instance, oxidation, on the surface of the animal, especially in the eye, as was suggested in the case of the aphids. The mass of photochemical substance which is acted upon by the light is often relatively small, so that even when the light strikes the crustacean (copepod) on one side only, the difference in the chemical changes on the two sides of the body remains still too small to call forth a difference in tension or action in the muscles of the two sides of the body, sufficient to turn the animal toward the source of light. But if we add an acid this could act as a catalyzer, as, for instance, in the catalysis of esters. In the catalysis of esters, the acid acts, according to Stieglitz, only to the extent of increasing the active mass of the substance which undergoes a chemical change. In order to fix our ideas provisionally we will assume that the acid makes the animal more strongly positively heliotropic by increasing the active mass of the photosensitive substance. In this way the same intensity of light which before produced no heliotropic reaction now may cause a very pronounced positively heliotropic reaction; because if now the animal is struck on one side only by the light, the difference in the reaction products in both retinae becomes rapidly large enough to cause automatically a difference in the action of the muscles of both sides of the body and a turning of the head toward the source of light.

In certain forms, for instance, hi Daphnia and in certain marine copepods, a decrease in temperature also increases the tendency to positive heliotropism. If the mere addition of acid is not sufficient to make Daphniae positively heliotropic,

i Loeb, Pfliigers Archiv, CXV, 564, 1906.

44 THE MECHANISTIC CONCEPTION OF LIFE

this may often be accomplished by simultaneously reducing the temperature.

The animals which are strongly positively heliotropic and those animals which do not react at all to light offer no difficulties to the observer. Nevertheless, some zoologists seem to have found difficulty in explaining the behavior of those animals which come between the two extremes. For instance, one writer has asserted that with greater intensity of light the laws of heliotropic orientation hold good, while with a lessened light intensity the animals react to light by the method of " trial and error." From a chemical standpoint the behavior of animals at low intensity is easily to be understood. If a positively heliotropic animal is illuminated from one side, a compulsory turning of the head toward the source of light occurs only when the difference in the rate of certain photochemical reactions in the two eyes reaches a certain value. If the intensity of the light is sufficient and the active mass of photochemical substance in the animal great enough, it requires only a short time, for instance, the fraction of a second, before the difference in the mass of the reaction products formed on the two sides of the animal reaches the value necessary for the compulsory turning of the head toward the source of light. In this case the animal is a slave of the light; in other words, it has hardly time to deviate from the direction of the light rays; for if it turns the head even for the fraction of a second from the direction of the light rays, the difference in the photochemical reaction products in the two retinae becomes so great that the head is at once turned back automatically toward the source of light. But if the intensity of the light or the photosensitiveness of the animal is lessened the animal may deviate for a longer period from the direction of the light rays. Such animals do eventually reach the lighted side of the vessel, but they no longer go straight toward it, moving instead in zig-zag lines

or very irregularly. It is therefore not a case of a qualitative, but of a quantitative, difference in the behavior of heliotropic animals under greater or lesser illumination, and it is therefore erroneous to assert that heliotropism determines the movement of animals toward the source of light only under strong illumination, but that under weaker illumination an essentially different condition exists.

Still another point is to be considered. We have seen that acid increases the sensitiveness of certain animals to light, possibly by increasing the active mass of the photochemical substance. Every animal is continually producing acids in its cells, especially carbonic acid and lactic acid; and such acids increase the tendency hi certain animals to react heliotropically. It probably produces also substances which could have the opposite effect and which decrease the heliotropic sensitiveness of the animals. Fluctuations in the rate of the production of these substances will also produce fluctuations in the heliotropic sensitiveness of the animal. If, for instance, the active mass of the photosensitive substance in a copepod is relatively small, a temporary increase in the production of carbonic acid can increase the photosensitiveness of the animal sufficiently to cause it to move for the period of a few seconds directly toward the source of light. Later the production of carbonic acid decreases and the animal again becomes indifferent to light and can move in any direction. Then the production of carbonic acid increases again and the animal goes again, for a short time, toward the light. Such animals finally gather at the lighted side of the vessel because the algebraic sum of the movements in the other directions becomes zero according to the law of chance. But it is plain that such animals do not reach the source of light by a straight path. A writer who is not trained to interpret the variations in the behavior of such an animal chemically and physiologically, can naturally give no explanation of their significance. If he is forced to find an

46 THE MECHANISTIC CONCEPTION OF LIFE

explanation he will wind up with the suggestion of "trial and error" which is no more chemical or scientific than the explanations of metaphysicians in general.

Some authors have, it seems, worked only with animals which were not pronouncedly heliotropic and whose photo-sensitiveness wavered about the threshold of stimulation in the manner described above. Such animals are not suitable for experiments in heliotropism and it is necessary to first increase their photosensitiveness if the laws of the action of light upon them are to be investigated.

I also believe that observations upon animals which are not sufficiently photosensitive have caused many writers to assert that heliotropic animals do not place themselves directly in the line of the rays of light, 1 but that they first have to learn the right orientation. A very striking experiment contradicts this assertion. The larvae of Balanus perforatus develop entirely in the dark. If the ovary filled with mature larvae is placed in a watch crystal filled with sea-water in the dark, the larvae emerge at once and, if they are brought into the light, they move at once to the side of the watch crystal nearest to the window. They were, therefore, pronouncedly positively heliotropic before they came under the influence of the light.

In experiments with winged aphids I often found that after having gone through the heliotropic reactions a few times they react much more quickly to light than at the beginning. This might be interpreted as a case of "learning." In so far as it is not a case of a lessening of the stickiness of the feet or the removal of some other purely mechanical factor which retards the rate of movement, it may be brought about by the carbonic or lactic acids produced through the muscular activity. 2

1 Provided that only a single source of light is present.

2 The so-called " staircase " phenomenon of stimulation of a muscle is ascribed, probably rightly, also to the formation of acid. This phenomenon, that is, the increase of the amount of contraction with every new stimulus, is, however, comparable to or identical with the increase in the rate of reactions in the experiments described here.

As far back as 1889 I pointed out that the photosensitive-ness of an animal is different in different physiological conditions and that, therefore, under natural conditions, heliotropism is found often only in certain developmental stages, or in certain physiological states of an animal. I have already mentioned that in the aphids distinct heliotropic reactions may only be expected when the animals have developed wings and have left the plant. The influence of the chemical changes which take place in animals upon heliotropism is much more distinct hi the larvae of Porthesia chrysorrhoea. The larvae hatch from the eggs in the fall and, as young larvae, hibernate in a nest. The rising temperature in the spring drives them out of the nest, and they can also be driven out of the nest in winter by an increase in temperature. When driven out of the nest in this condition they are strongly positively heliotropic and I have never found in natural surroundings any animals whose heliotropic sensitiveness was more pronounced than it is in the young larvae of Chrysorrhoea. But as soon as the animals have once eaten, the positive heliotropism disappears and does not return even if they are again allowed to become hungry. 1 In this case it is clear that the chemical changes directly or indirectly connected with nutrition lead to a permanent diminution or disappearance of the photochemical reaction. In ants and bees the influence of substances from the sexual organs seems to be the determining factor in the production of positive heliotropism. The ant workers show no heliotropic reactions, while in the males and females, at the time of sexual maturity, a distinct positive heliotropism develops, the intensity of which continues to increase.

It is a well-known fact that during sexual maturity special substances are formed which influence various organs. For

1 Loeb, op. cit., p. 24. (This latter fact has been overlooked by several writers.)

instance, Leo Loeb has found that the substances which are set free by the bursting of an egg follicle cause a special sensitiveness in the non-pregnant uterus, so that every mechanical stimulus causes the latter to form a decidua. In this way he could cause the formation of any number of deciduae in non-pregnant uteri, while without the circulation of follicle substance in the blood the uterus did not react in this manner.

It is a common phenomenon that animals in certain larval stages are positively heliotropic, while in others they are not sensitive to light or are even negatively heliotropic. I will not discuss these facts further in this place, but refer my readers to my earlier papers.

This change in the heliotropic sensitiveness, produced by certain metabolic products in the animal body, is of great biological significance. I pointed out in former papers that it serves to save the lives of the above-mentioned young larvae of Chrysor-rhoea. When the young larvae are awakened from their winter sleep by the sunshine of the spring they are positively heliotropic. Their positive heliotropism leaves them no freedom of movement, but forces them to creep straight upward to the top of a tree or branch. Here they find the first buds. In this way their heliotropism guides them to their food. Should they now remain positively heliotropic they would be held fast on the ends of the twigs and would starve to death. But we have already mentioned that after having eaten they once more lose their positive heliotropism. They can now creep downward, and the restlessness which is characteristic of so many animals 1 forces them to creep downward until they reach a new leaf, the odor or tactile stimulus of which stops the progressive movement of the machine and sets their eating activity again in motion.

The fact that ants and bees become positively heliotropic at the time of sexual maturity plays an important role in the

1 The physico-chemical cause of this "restlessness" which is noticeable in many insects and crustaceans is at present unknown.

vital economy of these creatures. As is well known, the mating of these insects takes place during, the so-called nuptial flight. I found that among the male and female ants of a nest the heliotropic sensitiveness increases steadily up to the time of the nuptial flight and that the direction of their flight follows the direction of the rays of the sun. I gained the impression that this nuptial flight is merely the consequence of a very highly developed heliotropic sensitiveness. The case seems to be similar among the bees according to the following experiment described by Kellogg. The bees were ready to swarm out of the opening of the box used for the experiment when he suddenly removed the dark covering of the box so that the light now entered it from above. The heliotropic sensitiveness of the animals was so great that they crept upward within the box, following the direction of the light rays, and were not able to make the nuptial flight. Thus, according to these observations the bees at the time of the nuptial flight are positively heliotropic machines.

These observations may serve as examples of the way in which the analysis of the vital phenomena of certain animals shows tropisms to be elements of these phenomena. Many observations of a similar nature are found in the papers of Georges Bohn, Parker, Rddl, 1 and myself.

Under the influence of the theory of natural selection the view has been accepted by many zoologists and psychologists that everything which an animal does is for its best interest. The exact doctrine of heredity, founded by Mendel and advanced to the position of a systematic science in 1900, reduces this idea to its proper value. It is only true that species possessing tropisms which would make reproduction and preservation of the species impossible must die out.

1 Radl, Der Phototropismus der Tiere, Leipzig, 1903.

50 THE MECHANISTIC CONCEPTION OF LIFE

Galvanotropism illustrates this fact in a striking manner. If a galvanic current is passed through a trough filled with water, and animals are placed hi this trough, it can be observed that an orientation in relation to the direction of the current takes place in many of the animals, and that they move in the direction either of the positive or of the negative current. This phenomenon we call galvanotropism. In galvanotropism the current lines or the current curves play the same role as the light rays in heliotropism. At those points where the current curves enter the cells 1 a collection of ions takes place which influences the chemical reactions. The number of species which show typical galvanotropic reactions is not so great as the number of those showing typical heliotropism. In my opinion this difference is the result of the physical difference in the action of light and of the electric current. Light acts essentially upon the free surface of the animal, while the electric current affects all the cells and nerves. Thus the action of the current upon the skin becomes complicated and modified by its simultaneous effect upon the nerve branches and upon the central nervous system. The result is thus much more complicated than that of the action of light where essentially only the effect upon the skin and retina is involved. For this reason, a distinct galvanotropism is found more often in organisms with a simple structure, as, for instance, in unicellular organisms, than in vertebrates, although it is also demonstrable in the latter.

Galvanotropism is, however, purely a laboratory product. With the exception of a few individuals, which have in recent years fallen into the hands of physiologists who happened to be working on galvanotropism, no animal has ever had the chance to come under the influence of an electric current. And yet galvanotropism is a remarkably common reaction among animals. A more direct contradiction of the view that the

reactions of animals are determined by their needs or by natural selection could hardly be found.

One might be led to suppose that galvanotropism and heli-otropism are not comparable. They are, however, as a matter of fact, phenomena of the same category with the exception of the aforementioned fact, that light acts generally only upon the surface of the skin, while the electric current influences all the cells of the body. As already mentioned, the disturbing complications arising from this latter circumstance disappear for the most part when we work with unicellular organisms, and we should expect that galvanic and heliotropic reactions would more nearly resemble one another in this case, provided that we work with organisms possessing both forms of sensitiveness. And this expectation is fulfilled. The algae of the species Volvox show heliotropism and galvanotropism. The investigations made by Holmes and myself upon heliotropism, as well as those of Bancroft upon the galvanotropism of these organisms indicate that the mechanism of these reactions in Volvox is the same and the degree of determinism of the heliotropic and galvanotropic reactions in Volvox is equally great.

Claparede raises the objection that the galvanotropic reactions are purely compulsory, while the heliotropic reactions are governed by the "interest of the animal." 1 Such a view, however, is not supported by the facts. The reason why heliotropism may occasionally, as we have seen, be of use, while galvanotropism has no biological significance, is because the electric current does not exist in nature. It can, however, be shown also that heliotropism is just as useless to many animals as galvanotropism. For instance, I pointed out twenty years ago that some varieties of animals which do not live in the light at all, for instance, the larvae of the goat moth, which live under the bark of trees, may show positive heliotropism. I found, moreover, that the crab, Cuma Rathkii, which lives in the mud of

1 Clapar&de, "Les tropismes devant la psychologie," Journ. f. Psychologic und Neurologic, XIII, 150, 1908.

THE MECHANISTIC CONCEPTION OF LIFE

the harbor at Kiel, when brought into the light and removed from the mud shows positive heliotropism. It is, therefore, just as incorrect to assert that the heliotropic reactions are

governed by the biological interests of the animal as that this is true for galvanotrop-ism. We must, therefore, free ourselves at once from the overvaluation of natural selection and accept the consequences of Mendel's theory of heredity, according to which the animal is to be looked upon as an aggregate of independent hereditary qualities.

FIG. 21.—Arrangement to prove that positively heliotropic animals move toward the source of light even if by so doing they go from the. sunlight into the shade. W W is a window through which sunlight S falls into the room. By a piece of board d e the sunlight S is prevented from striking the region b c of a table near the window and this part of'the table is in the shade. Only the daylight D can reach this part of the table.

A test-tube a c is put on this table at right angles to the plane of the window. At the beginning of the experiment the animals (e.g., the winged aphides) are all at a. The animals move at once toward the window, but instead of remaining at b they keep on moving from the direct sunlight into the shade toward the source of light until they all reach the end of the tube c near the window (in the shade) where they remain permanently.

VII

The attempt has been made to prove that organisms are attuned to a certain intensity of light and so regulate their

heliotropism that they

invariably reach that intensity of light which is best suited to their well-being. I believe that this is also a suggestion forced upon the investigators by the extreme application of the theory of natural selection. I have made experiments upon a large number of animals, but, with a clear

arrangement of the physical conditions of the experiment, I have never found a single indication of such an adaptation. In every case it has been shown that positively heliotropic animals are positive to any intensity of light above the threshold. Thus winged plant lice or wingless larvae of Chrysorrhoea or copepods, which have been made heliotropic by acids, go toward the light whether the source of light is the direct sunlight or reflected light from the sky or weak lamp light, provided that the (threshold) value of the intensity of light required for the reaction is exceeded. Indeed, I have been able to show that positively heliotropic animals also move toward the source of light even if the arrangement is such that by so doing they go from the light into the shadow. 1 I have never observed a ''selection" of a suitable intensity of light.

What probably lies behind these interpretations of the " selection of a suitable intensity of light" is the fact that under certain conditions reaction products formed by the photochemical action of light may inhibit the positive heliotropism. I found a very clear instance of this sort in the newly hatched larvae of Balanus perforatus, which are positively, heliotropic. If they are placed in the light of a quartz mercury lamp (of Heraus), which is very rich in ultra-violet rays, the positively heliotropic larvae soon become negatively heliotropic. For these experiments the larvae should be placed only in a very shallow depth of sea-water.

Even in a strong light which is not so rich in ultra-violet rays as the light of the mercury lamp, it is sometimes possible to cause positively heliotropic animals to become negatively heliotropic. This is the case, for instance, with the larvae of Polygordius. But it would be wrong in this case to speak of an adaptation of the animal to a certain intensity of light.

1 Quite often without even stopping for a moment. In animals sensitive to differences (see next chapter) a stopping occurs in this experiment in the passing from the light into the shadow, but they go, nevertheless, immediately on in the direction of the source of light. The reader will find a further account of this experiment in my book on The Dynamics of Living Matter.

54 THE MECHANISTIC CONCEPTION OF LIFE

In my opinion it is merely a case where a metabolic product either alters the photochemical action or so influences the central nervous system that the excitation of the retina by the light weakens the tonus of the muscles, instead of strengthening it.

Some of the other mistakes have perhaps also arisen because the writers worked with complicated experimental conditions instead of with simple ones, for instance, because they used a hollow prism filled with ink in order to produce a gradual decrease in the light intensity. In the semidarkness thus produced, the intensity of light often remains beneath or near the threshold of stimulation, and the writers fall victims to that class of errors which we have already pointed out in speaking of the influence of lesser intensities of light.

VIII

Heliotropic phenomena are determined by the relative rates of chemical reactions occurring simultaneously in symmetrical surface elements of an animal. There is a second class of phenomena which is determined by a sudden change in the rate of chemical reactions in the same surface elements. Reactions to a sudden change in the intensity of light are shown most clearly in marine tube-worms, whose gills are exposed to light. If the intensity of the light in the aquarium is suddenly diminished the worms withdraw quickly into their tubes. A sudden increase in the intensity of light has no such effect. With other forms, for instance, with planarians, a sudden decrease in the intensity of the light causes a decrease in movement. Such animals gather chiefly in parts of the space where the intensity of light is relatively small. I have designated such reactions as the expression of sensitiveness to changes in the intensity of a stimulus ("Unterschiedsempfindlichkeit") differential sensibility, in order to distinguish them from tropisms. 1

1 Loeb," Ueber die Umwandlung positiv heliotropischer Tiere, u.s.w.," Pfliigert Archiv, 1893. See also the recent investigations of Georges Bonn, La naissance de I'intelligence, Paris, 1909; "Les essais et les erreurs chez les etioles de mer," Bull.

It is hardly necessary to point out here that the effects of rapid changes in intensity, when they are very marked, can easily complicate and entirely obscure the heliotropic phenomena. In Hypotricha and other infusoria this differential sensibility is very pronounced in response to sudden touch or sudden alteration of the chemical medium, and like the tube-worms they thereupon draw back very quickly. Since their locomotor organs are not symmetrical, but are arranged in a peculiar unsymmetrical manner, they do not, after the next progressive movement, return to the former direction of movement, but deviate sideways from it, and it is therefore easy to understand that such animals do not furnish the best material for demonstrating the laws of heliotropism, especially since they possess only a slight photochemical sensitiveness. But Jennings 1 has with special preference used observations on such organisms to argue against the theory of tropisms. Just as the action of a constant current in muscles and nerves is different from that of an intermittent current, so we find an analogous case in the action of light. If we wish to trace all animal reactions back to physico-chemical laws we must take into consideration besides the tropisms not only the facts of the differential sensibility but also all other facts which exert an influence upon the reactions. The influence of that mechanism which we call " associative memory" also belongs in this category, but we cannot discuss this further at this place. The reader is referred to my book 2 as well as to the more recent works of Bohn, La naissance de Vintelligence* and La nouvelle psychologic animate.* Let us bear in mind that "ideas" also

Inst. gen. psychol., 1907; "Intervention des reactions oscillatoires dans les tro-pismes," Ass. franc, d. Sciences, 1907.

1 Jennings, The Behavior of Lower Organisms, 1906.

2 Comparative Physiology of the Brain and Comparative Psychology, New York and London, 1900.

=» Paris, "Biblioth6quede philosophic scientiflque," 1909.

4 Paris, " Biblioth&que de philosophic contemporaine," 1911.

can act, much as acids do for the heliotropism of certain animals, namely, to increase the sensitiveness to certain stimuli, and thus can lead to tropism-like movements or actions directed toward a goal.

Besides light and the electric current, the force of gravity also has an orienting influence upon a number of animals. The majority of such animals are forced to turn their heads away from the center of the earth and to creep upward. It was uncertain for a long time how the orientation of cells in relation to the center of gravity of the earth could influence the rate of the chemical reactions within, but it has been suggested that an enlargement or shifting of the reacting surfaces formed the essential connecting link. If it is assumed that in such geo-tropically sensitive cells two phases (for instance, two fluid substances which are not at all, or not easily, miscible, or one solid and one fluid substance) of different specific gravities are present, which react upon one another, a reaction takes place at the surfaces of contact. Every enlargement of the latter increases the mass of reacting molecules. A shifting of the surfaces would act in the same manner. Finally, a third possibility remains which could perhaps be realized in plant roots and stems. If in the geotropically sensitive elements two masses of different specific gravity are present, only one of which reacts to the flowing sap in the center or the periphery of the stem, the cells of the upper side of a stem which is laid horizontally will acquire a different rate of reaction from those of the lower side, because in the former the specifically heavier substances are directed toward the center of the stem, while in the latter the specifically lighter ones are directed toward the center. Consequently, one side will grow faster than the other, hence the geotropic bending. 1 In the frog's egg, we can actually demonstrate directly the existence of two substances of different

1 Chapter on "Tropisms" in Dynamics of Living Matter.

specific gravity and can study their behavior, since in this case they are of different color.

In animals it has been observed that orientation toward the center of gravity of the earth often becomes less compulsory when the inner ear has been removed. Mach first pointed out the possibility that the otoliths are responsible for this. He believed that they might press upon the end-organs of the sensory nerves and every change of pressure might cause a correction of the position of the animal. It is generally assumed that this view has been verified by experiment but I cannot entirely agree with it although I once described experiments which seemed to support Mach's otolith theory. I had found that when the otoliths of the inner ear of the shark are scraped out with a sharp spoon the normal orientation of the animal suffers; but if the otoliths are simply washed out from the inner ear by a weak current of sea-water the orientation does not so easily suffer.

In the latter case, it is doubtful whether all the otolith powder has been removed from the ear. The problem was solved by experiments on flounders, which have only a single large otolith that can easily be removed from the ear. E. P. Lyon carried out these experiments, which showed that no disturbance of the orientation resulted from this operation. We may conclude, therefore, that in my experiments of scraping out the otoliths a disturbance of the orientation occurred, because in so doing the nerve endings in the ears were injured. We have, therefore, no right to maintain that the orientation of animals in relation to the center of gravity of the earth is regulated by the pressure of the otoliths upon the nerve endings, but that this regulation takes place in the nerve endings themselves, and probably, indeed, as a result of the existence there of two different phases of different specific gravity which react upon one another. Through the change of orientation of the cells in relation to the center of gravity of the earth, the two

phases undergo a shifting by means of which a change in the rate of reaction is brought about according to one of the ways described above. Since then I have looked through the literature on the function of the otoliths or statoliths, and have reached the conclusion that all writers who assert that the removal of the otoliths disturbs the geotropic orientation of animals have been victims of the same fallacy as myself. They have injured or removed the nerve endings. In the only case in which a removal of the otoliths without tearing or other injury of the nerve endings can be justifiably assumed, no disturbance of the orientation occurred.

While in my own work I have aimed to trace the complex reactions of animals back to simpler reactions like those of plants and finally to physico-chemical laws, the opposite tendency has lately been gaining influence. Some botanists, namely, Haberlandt, Nemec, and F. Darwin, endeavor to show that the relatively simpler reactions of plants may be traced back to the more complex relations found in animals. Instead of deriving the tropic reactions of plants as directly as possible from the law of mass action or the law of Bunsen and Roscoe, they try to show that "sense-organs" exist in the cells of plants and France even attributes to the latter a "soul" and "intelligence." I believe that in order to be consistent, these writers ought to base the law of mass action upon the assumption of the existence of sense-organs, souls, and intelligence in the molecules and ions. It is probably unnecessary to emphasize the fact that it is better for the progress of science to derive the more complex phenomena from simpler components than to do the contrary. For all "explanation" consists solely in the presentation of a phenomenon as an unequivocal function of the variables by which it is determined, and if in nature we find a function of two variables, it does not, hi my opinion, tend toward progress to assert that this is a case of functions of more than two variables, without furnishing sufficient proof for this assertion.

These writers explain the geotropic reactions of plants by saying that in certain cells starch grains are present which serve the purpose of the otoliths in animals. These starch grains are believed to press upon the sense-organs or nerve endings in the plant cells concerned and the "pressure-sense" of the plant is then supposed to give rise to the geotropic curvature. I have no opposition to offer to the assumption that the starch grains change their position with a change in the position of the cells, and I am also willing to pass over for the present the view that the starch grains form one of the two phases in the cell. But I see no necessity for assuming besides this the existence of intracellular sense-organs which perceive the pressure of the starch grams. This is, in my opinion, an unnecessary complication of simple relations.

The progress of natural science depends upon the discovery of rationalistic elements or simple natural laws. We find that there are two classes of investigators in biology, grouped according to their attitude toward such simple laws or rationalistic elements. One seems to aim at the denial of the existence of such simple laws and every new case which does not fall at once under such a law offers an opportunity for them to point out the inadequacy of the latter. The other group of investigators aims to discover and not to disprove laws. When such investigators have discovered a simple law which is generally applicable, they know that an apparent exception does not necessarily overthrow the law, but that possibly an opportunity is offered for a new discovery and an extension of the old law. Mendel's laws have been brilliantly confirmed in a number of cases. In some cases of apparent deviations (from these laws), however, it has not always been possible at once to recognize the cause. One group of investigators has recognized that these deviations do not indicate the incorrectness of Mendel's laws, but that they are merely the

result of secondary and often minor complications; the latter investigators have from this standpoint made further fruitful discoveries. The role of the other group of investigators in this case has consisted, primarily, in an attempt to minimize the importance of Mendel's laws and thus to retard the progress of science.

The case is similar in the realm of tropisms. Tropisms and tropism-like reactions are elements which pave the way for a rationalistic conception of the psychological reactions of animals and I believe, therefore, that it is in the interest of the progress of science to develop further the theory of animal tropisms. The fact that in an electric current the same animal often moves differently from what it does under the influence of light finds its explanation for the observer conversant with physical chemistry in the fact that the electric current causes changes in the concentration of ions within, as well as upon the surface, while the chemical action of light is essentially limited to the surface. Certain writers, however, leave this difference in the action of the two agents out of consideration and make use of the difference in the behavior of certain organisms in response to light and to the electric current, to assert that it is not permissible to speak of tropisms as being governed by general laws; in other words, they say that tropisms are without significance. Animals in general are symmetrically built and the motor elements of the right and left sides of the body usually act symmetrically. Consequently the heliotropic orientation, for instance, comes about as we have already described. There are animals, however, which move sideways, for instance, certain crabs, such as the fiddler crab. Holmes has found that these crustaceans also go sideways toward the light. Jennings draws from this fact the following conclusions: "The symmetrical position is an incident of the reaction, not its essence."

In other words, he uses these observations of Holmes to

indicate that the role ascribed to symmetry has no importance for the theory of tropisms. I am, however, inclined to draw another conclusion, namely, that in the fiddler crabs in the first place there is an entirely different connection between the retina and the locomotor muscles from that in other crustaceans, and that, secondly, there is a special peculiarity in regard to the function of the two retinae whereby they do not act like symmetrical surface elements. I believe that a new discovery may be made here. 1

These data may suffice to explain my point of view. To me it is a question of making the facts of psychology accessible to analysis by means of physical chemistry. In this way it is already possible to reduce a set of reactions, namely, the tropisms to simple rationalistic relations. Many animals, because their body structure is not only morphologically, but also chemically, symmetrical, are obliged to orient their bodies in a certain way in relation to certain centers of force, as, for instance, the course of light, an electric current, the center of gravity of the earth, or chemical substances. This orientation is automatically regulated according to the law of mass action. The application of the law of mass action to this set of reactions is thus made possible. I consider it unnecessary to give up the term " comparative psychology," but I am of the opinion that the contents of comparative psychology will under the influence of the above-mentioned endeavors be different from the contents of speculative psychology. But I believe also that the further development of this subject will fall more to the lot of biologists trained in physical chemistry than to the specialists in psychology or zoology, for it is in general hardly

1 From which I expect, furthermore, that they will only confirm still more the laws of heliotropism. This expectation is based upon analogous relations in the pleuronectids, which I cannot, however, discuss further here. However, probably no one will maintain that the existence of the pleuronectids invalidates all laws in regard to the symmetrical body structure.

to be expected that zoologists and psychologists who lack a physico-chemical training will feel attracted to the subject of tropisms.

In closing let me add a few remarks concerning the possible application of the investigations of tropisms.

I believe that the investigation of the conditions which produce tropisms may be of importance for psychiatry. If we can call forth in an animal otherwise indifferent to light by means of an acid a heliotropism which drives it irresistibly into a flame; if the same thing can be brought about by means of a secretion of the reproductive glands, we have given, I believe, a group of facts, within which the analogies necessary for psychiatry can be called forth experimentally and can be investigated.

These experiments may also attain a similar value for ethics. The highest manifestation of ethics, namely, the condition that human beings are willing to sacrifice their lives for an idea is comprehensible neither from the utilitarian standpoint nor from that of the categorical imperative. It might be possible that under the influence of certain ideas chemical changes, for instance, internal secretions within the body, are produced which increase the sensitiveness to certain stimuli to such an unusual degree that such people become slaves to certain stimuli just as the copepods become slaves to the light when carbon dioxide is added to the water. Since Pawlow and his pupils have succeeded in causing the secretion of saliva in the dog by means of optic and acoustic signals, it no longer seems strange to us that what the philosopher terms an "idea" is a process which can cause chemical changes in the body.

III. SOME FUNDAMENTAL FACTS AND CONCEPTIONS CONCERNING THE COMPARATIVE PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM

SOME FUNDAMENTAL FACTS AND CONCEPTIONS CONCERNING THE COMPARATIVE PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM 1

1. The understanding of complicated phenomena depends upon an analysis by which they are resolved into their simple elementary components. If we ask what the elementary components are in the physiology of the central nervous system, our attention is directed to a class of processes which are called reflexes. A reflex is a reaction which is caused by an external stimulus, and which results hi a coordinated movement, the closing of the eyelid, for example, when the conjuctiva is touched by a foreign body, or the narrowing of the pupil under the influence of light. In each of these cases, changes in the sensory nerve endings are produced which bring about a change of condition in the nerves. This change travels to the central nervous system, passes from there to the motor nerves, and terminates in the muscle-fibers, producing there a contraction. This passage from the stimulated part to the central nervous system, and back again to the peripheral muscles, is called a reflex. There has been a growing tendency in physiology to make reflexes the basis of the analysis of the functions of the central nervous system, and consequently much importance has been attached to the processes underlying them and the mechanisms necessary for reflex.

The name reflex suggests a comparison between the spinal cord and a mirror. Sensory stimuli were supposed to be reflected from the spinal cord to the muscles; destruction of the spinal cord would, according to this, make the reflex impossible,

1 Reprinted from Loeb, J., Comparative Physiology of the Brain and Comparative Psychology (1899). By courtesy of G. P. Putnam's Sons of New York and London.

just as the destruction of the mirror might prevent the reflection of light. This comparison, however, of the reflex process in the central nervous system with the reflection of light has, long since, become meaningless, and at present few physiologists in using the term reflex think of its original significance. Instead of this, another feature in the conception of the term reflex has gained prominence, namely, the purposeful character of many reflex movements. The closing of the eyelid and the narrowing of the pupil are eminently purposeful, for the cornea is thereby protected from hurtful contact with foreign bodies, and the retina from the injurious effects of strong light. Another striking characteristic in such reflexes has also been emphasized. The movements which are produced are so well planned and coordinated that it seems as though some intelligence were at work either in devising or in carrying them out. The fact, however, that even a decapitated frog will brush with its foot a drop of acetic acid from its skin, suggests that some other explanation is necessary. A prominent psychologist has maintained that reflexes are to be considered as the mechanical effects of acts of volition of past generations. 1 The ganglion-cell seems the only place where such mechanical effects could be stored up. It has therefore been considered the most essential element of the reflex mechanism, the nerve-fibers being regarded, and probably correctly, merely as conductors.

Both the authors who emphasize the purposefulness of the reflex act and those who see in it only a physical process have invariably looked upon the ganglion-cell as the principal bearer of the structures for the complex coordinated movements in reflex action.

I should have been as little inclined as any other physiologist to doubt the correctness of this conception had not the establishment of the identity of the reactions of animals and plants to light proved the untenability of this view and at the

i A statement for which no trace of experimental proof exists.

same time offered a different conception of reflexes. The flight of the moth into the flame is a typical reflex process. The light stimulates the peripheral sense-organs, the stimulus passes to the central nervous system, and from there to the muscles of the wings, and the moth is caused to fly into the flame. This reflex process agrees in every point with the heliotropic effects of light on plant organs. Since plants possess no nerves and no ganglia, this identity of animal with plant heliotropism can force but one inference—these heliotropic effects must depend upon conditions which are common to both animals and plants. At the end of my book on heliotropism 1 I expressed this view in the following words: "We have seen that, in the case of animals which possess nerves, the movements of orientation toward light are governed by exactly the same external conditions, and depend in the same way upon the external form of the body, as in the case of plants which possess no nerves. These heliotropic phenomena, consequently, cannot depend upon specific qualities of the central nervous system." On the other hand, the objection has been raised that destruction of the ganglion-cells interrupts the reflex process. This argument, however, is not sound, for the nervous reflex arc in higher animals forms the only protoplasmic bridge between the sensory organs of the surface of the body and the muscles. If we destroy the ganglion-cells or the central nervous system, we interrupt the continuity of the protoplasmic conduction between the surface of the body and the muscles, and a reflex is no longer possible. Since the axis cylinders of the nerves and the ganglion-cells are nothing more than protoplasmic formations, we are justified in seeking in them only general protoplasmic qualities, unless we find that the phenomena cannot be explained by means of the latter alone.

2. A further objection has been raised, that although these

1 Loeb, J., Der Heliotropismus der Tiere und seine Uebereinstimmung mit dem Heliotropismus der Pfianzen, WiirzbuTg, 1890. A preliminary note on these experiments appeared January, 1888.

reflexes occur in plants possessing no nervous system, yet in animals where ganglion-cells are present the very existence of the ganglion-cells necessitates the presence in them of special reflex mechanisms. It was therefore necessary to find out if there were not animals in which coordinated reflexes still continued to exist after the destruction of the central nervous system. Such a phenomenon could be expected only in forms in which a direct transmission of stimuli from the skin to the muscle or direct stimulation of the muscle is possible, in addition to the transmission through the reflex arc. This is the case, for instance, in worms and in ascidians. I succeeded 1 in demonstrating in Ciona intestinalis that the complicated reflexes still continue after removal of the central nervous system. 2

A study, then, of comparative physiology brings out the fact that irritability and conductibility are the only qualities essential to reflexes, and these are both common qualities of all protoplasm. The irritable structures at the surface of the body, and the arrangement of the muscles determine the character of the reflex act. The assumption that the central nervous system or the ganglion-cells are the specific bearers of reflex mechanisms cannot hold. But have we now to conclude that the nerves are superfluous and a waste ? Certainly not. Their value lies hi the fact that they are quicker' and more sensitive conductors than undifferentiated protoplasm. Because of these qualities of the nerves, an animal is better able to adapt itself to changing conditions than it possibly could if it had no nerves. Such power of adaptation is absolutely necessary for free animals.

3. While some authors explain all reflexes on a psychical basis, the majority of investigators explain in this way only a

1 Loeb, J., Untersuchungen zur physiologischen Morphologic der Tiere, II, Wurzburg, 1892.

2 This animal closes the oral opening when we touch it. This is a reflex comparable to the closing of the eyelid if we touch the cornea. The central nervous sytem of the animal consists of one ganglion. When the latter is removed the oral opening still closes upon mechanical stimulation.

certain group of reflexes—the so-called instincts. Instincts are defined in various ways, but no matter how the definition is phrased the meaning seems to be that they are inherited reflexes so purposeful and so complicated in character that nothing short of intelligence and experience could have produced them. To this class of reflexes belongs the habit possessed by certain insects of laying their eggs on the material which the larvae will afterward require for food. When we consider that the female fly pays no attention to her eggs after laying them, we cannot cease to wonder at the seeming care which nature takes for the preservation of the species. How can the action of such an insect be determined if not by mysterious structures which can only be contained in the ganglion-cells ? How can we explain the inheritance of such instincts if we believe it to be a fact that the ganglion-cells are only the conductors of stimuli ? It was impossible either to develop a mechanics of instincts or to explain their inheritance in a simple way from the old standpoint, but our conception makes an explanation possible. Among the elements which compose these complicated instincts, the tropisms (heliotropism, chemotropism, geotropism, stere-otropism) play an important part. These tropisms are identical for animals and plants. The explanation of them depends first upon the specific irritability of certain elements of the body-surface, and, second, upon the relations of symmetry of the body. Symmetrical elements at the surface of the body have the same irritability; unsymmetrical elements have a different irritability. Those nearer the oral pole possess an irritability greater than that of those near the aboral pole. These circumstances force an animal to orient itself toward a source of stimulation in such a way that symmetrical points on the surface of the body are stimulated equally. In this way the animals are led without will of their own either toward the source of the stimulus or away from it. Thus there remains nothing for the ganglion-cell to do but to conduct the stimulus, and

70 THE MECHANISTIC CONCEPTION OF LIFE

this may be accomplished by protoplasm in any form. For the inheritance of instincts it is only necessary that the egg contain certain substances — which will determine the different tropisms—and the conditions for producing bilateral symmetry of the embryo. The mystery with which the ganglion-cell has been surrounded led not only to no definite insight into these processes, but has proved rather a hindrance in the attempt to find the explanation of them.

It is evident that there is no sharp line of demarkation between reflexes and instincts. We find that authors prefer to speak of reflexes in cases where the reaction of single parts or organs of an animal to external stimuli is concerned; while they speak of instincts where the reaction of the animal as a whole is involved (as is the case in tropisms).

4. If the mechanics of a number of instincts is explained by means of the tropisms common to animals and plants, and if the significance of the ganglion-cells is confined, as in all reflex processes, to their power of conducting stimuli, we are forced to ask what circumstances determine the coordinated movements in reflexes, especially in the more complicated ones. The assumption of complicated but unknown and perhaps unknowable structures in the ganglion-cells served formerly as a convenient terminus for all thought in this direction. In giving up this assumption, we are called upon to show what conditions are able to determine the coordinated character of reflex movements. Experiments on galvanotropism of animals suggest that a simple relation may exist between the orientation of certain motor elements in the central nervous system and the direction of the movements of the body which is called forth by the activity of these elements. This perhaps creates a rational basis for the further investigation of coordinated movements. 1 .

1 Since this was written von Uexkuell found a law which will go far in explaining the mechanism of coordination, namely, that a stretched muscle shows an increased irritability while the contracted muscle shows a decreased irritability. Since

5. We must also deprive the ganglion-cells of all specific significance in spontaneous movements, just as we have done in the case of simple reflexes and instincts. By spontaneous movements we mean movements which are apparently determined by internal conditions of the living system. Strictly speaking, no movements of animals are exclusively determined by internal conditions, for atmospheric oxygen and a certain range of temperature are always necessary in order to preserve the activity beyond a short period of time.

We must discriminate between simple and conscious spontaneity. In simple spontaneity we must consider two kinds of processes, namely, aperiodic spontaneous processes and rhythmically spontaneous or automatic processes. The rhythmical processes are of importance for our consideration. Respiration and the heart beat belong in this category. The respiratory movements seem to indicate that automatic activity can arise in the ganglion-cells, and from this the conclusion has been drawn that all automatic movements are due to specific structures of the ganglion-cells. Recent investigations, however, have transferred the problem of rhythmical spontaneous contractions from the field of morphology into that of physical chemistry. The peculiar qualities of each tissue are partly due to the fact that it contains certain ions (Na, K, Ca, and others) in definite proportions. By changing these proportions, we can impart to a tissue properties which it does not ordinarily possess. If in the muscles of the skeleton the Na ions be increased and the Ca ions be reduced, the muscles are able to contract rhythmically like the heart. It is only the presence of Ca ions in the blood which prevents the muscles of our skeleton from beating rhythmically in our body. As the muscles contain no ganglion-cells, it is certain that the power of rhythmical spontaneous contractions is not due to the specific

the contraction of one group of muscles necessitates the stretching of their antagonists the coordinated character of locomotive action seems to become intelligible (1912).

72 THE MECHANISTIC CONCEPTION OF LIFE

morphological character of the ganglion-cells, but to definite chemical conditions which are not necessarily confined to ganglion-cells. 1

The coordinated character of automatic movements has often been explained by the assumption of a " center of coordination," which is supposed to keep a kind of police watch on the different elements and see that they move in the right order. Observations in lower animals, however, show that the coordination of automatic movements is caused by the fact that that element which beats most quickly forces the others to beat in its own rhythm. Aperiodic spontaneity is still less a specific function of the ganglion-cell than rhythmical spontaneity. The swarm spores of algae, which possess no ganglion-cells, show spontaneity equal to that of animals having ganglion-cells.

6. Thus far we have not touched upon the most important problem in physiology, namely, which mechanisms give rise to that complex of phenomena which are called psychic or conscious. Our method of procedure must be the same as in the case of instincts and reflexes. We must find out the elementary physiological processes which underlie the complicated phenomena of consciousness. Some physiologists and psychologists consider the purposefulness of the psychic action as the essential element. If an animal or an organ reacts as a rational human being would do under the same circumstances, these authors declare that we are dealing with a phenomenon of consciousness. In this way many reflexes, the instincts especially, are looked upon as psychic functions. Consciousness has been ascribed even to the spinal cord, because many of its functions are purposeful. We shall see in the following chapters that many of these reactions are merely tropisms which may occur in exactly the same form in plants. Plants must therefore have a psychic life, and, following the argument, we must ascribe it to machines also, for the tropisms depend

only on simple mechanical arrangements. In the last analysis, then, we would arrive at molecules and atoms endowed with mental qualities. We can dispose of this view by the mere fact that the phenomena of embryological development and of organization in general show a degree of purposefulness which may even surpass that of any reflex or instinctive or conscious act. And yet we do not consider the phenomena of development to be dependent upon consciousness.

On the other hand, physiologists who have appreciated the untenable character of such metaphysical speculations have held that the only alternative is to drop the search for the mechanisms underlying consciousness and study exclusively the results of operations on the brain. This would be throwing out the \Aheat with the chaff. The mistake made by metaphysicians is not that they devote themselves to fundamental problems, but that they employ the wrong methods of investigation and substitute a play on words for an explanation by means of facts. If brain physiology gives up its fundamental problem, namely, the discovery of those elementary processes which make consciousness possible, it abandons its best possibilities. But to obtain results, the errors of the metaphysician must be avoided and explanations must rest upon facts, not words. The method should be the same for animal psychology that it is for brain physiology. It should consist in the right understanding of the fundamental process which recurs in all psychic phenomena as the elemental component. This process, according to my opinion, is the activity of the associative memory, or of association. Consciousness is only a metaphysical term for phenomena which are determined by associative memory. By associative memory I mean that mechanism by which a stimulus brings about not only the effects which its nature and the specific structure of the irritable organ call for, but by which it brings about also the effects of other stimuli which formerly acted upon the organism almost or quite

simultaneously with the stimulus in question. 1 If an animal can be trained, if it can learn, it possesses associative memory. By means of this criterion it can be shown that Infusoria, Coelenterates, and worms do not possess a trace of associative memory. Among certain classes of insects (for instance, ants, bees, and wasps), the existence of associative memory can be proved. It is a comparatively easy task to find out which representatives of the various classes of animals possess, and which do not possess, associative memory. Our criterion therefore might be of great assistance in the development of comparative psychology.

7. Our criterion puts an end to the metaphysical ideas that all matter, and hence the whole animal world, possesses consciousness. We are brought to the theory that only certain species of animals possess associative memory and have consciousness, and that it appears in them only after they have reached a certain stage in their ontogenetic development. This is apparent from the fact that associative memory depends upon mechanical arrangements which are present only in certain animals, and present in these only after a certain development has been reached. The fact that certain vertebrates lose all power of associative memory after the destruction of the cerebral hemispheres, and the fact that vertebrates in which the associative memory either is not developed at all or only slightly developed (e.g., the shark or frog) do not differ, or differ but slightly, in their reactions after losing the cerebral hemispheres, support this view. The fact that only certain animals possess the necessary mechanical arrangements for associative memory, and therefore for consciousness, is not stranger than the fact that only certain animals possess the mechanical arrangements for uniting the rays from a luminous point in one point on the retina. The liquefaction of gases is an example of a sudden

1 Loeb, J., "Beitrage zur Gehirnphysiologie der Wuriner," Pfliigers Archiv, LVI, 247, 1894.

change of condition which may be produced when one variable is changed; it is not surprising that there should be sudden changes in the ontogenetic and phylogenetic development of organisms when there are so many variables subject to change, and when we consider that colloids easily change their state of matter.

It becomes evident that the unraveling of the mechanism of associative memory is the great discovery to be made in the field of brain physiology and psychology. But at the same time it is evident that this mechanism cannot be unraveled by histological methods, or by operations on the brain, or by measuring reaction times. We have to remember that all life phenomena are ultimately due to motions or changes occurring in colloidal substances. The question is, Which peculiarities of the colloidal substances can make the phenomenon of associative memory possible? For the solution of this problem the experience of physical chemistry and of the physiology of the protoplasm must be combined. From the same sources we must expect the solution of the other fundamental problems of brain physiology, namely, the process of conduction of stimuli.

IV. PATTERN ADAPTATION OF FISHES AND THE MECHANISM OF VISION

PATTERN ADAPTATION OF FISHES AND THE MECHANISM OF VISION 1

The mechanism of the action of the brain is entirely unknown to us. We are unable to look into the active brain and the objective results of brain action are in general so different in their nature from the external stimulus which leads to the action that we are prevented in most cases from drawing any conclusions concerning the nature of the processes occurring in the brain.

From results obtained in experiments on dogs Munk stated years ago that there existed a projection of the retina on a part of the cortex which he had designated as the visual sphere and that the extirpation of definite parts of this sphere caused blindness in definite parts of the retina. I repeated these experiments but was not able to confirm his statements. Henschen has recently, however, furnished the proof, on the basis of excellent pathological observations on man, that such a projection after all exists, but that it is situated in another part of the cortex from where Munk had believed it to be, namely, in the area striata. Minkowski was able to confirm Henschen's conclusions through experi aents on dogs. These observations and experiments suggest the possibility that in vision an image is formed not only on the retina but also on the cortex.

The possibility that vision is based on the formation of an image in the brain is supported by a group of facts which to my knowledge have never received any consideration in this connection.

i Reprinted from Physiologisches Centralblatt, XXV, No. 22, 1912. This note is given merely as a suggestion concerning the mechanism underlying certain brain processes.

80 THE MECHANISTIC CONCEPTION OF LIFE

It has been known for some time that many animals, especially certain fishes, adapt their color and pattern to the ground upon which they happen to be. This fact has been extensively utilized for the theory of natural selection. It seems to me that the same facts furnish also the proof that an image of the objects is formed in the brain. Pouchet many years ago showed that the adaptation of fishes to the ground ceases as soon as their eyes are removed or as soon as the formation of retinal images is prevented through the turbidity of the refractive media of the eye. This fact (confirmed by many observers) proves that the harmony between color and pattern of the skin of fishes with their surroundings is transmitted through the retinal image; in other words, that the so-called adaptation of fishes to their surroundings is only the transmission of the retinal image to the skin.

It has, moreover, been shown that the destruction of the optic fibers and the optic ganglia in the brain acts like the extirpation of the eyes; and finally it has been proved that the cutting of the sympathetic fibers which go to the pigment cells of the skin also prevents the formation of a picture of the ground on the skin. Hence we know the path by which the retinal image is transferred to the skin of fishes. One station is the ending of the optic fibers in the brain. Since we are able to prove the existence of an image of the object on the retina of fishes; since it is proved that the image on the skin of the fish is a picture of the retinal image but not of the object (in this case the ground) itself; since, moreover, the transmission of the retinal image upon the skin takes place through the optic nerve, it follows that the image must pass the central stations of the optic nerve during the transmission to the skin.

An image consists of a number of points of different intensity of light, the mutual arrangement of which is definite and characteristic for the object. Sumner has shown that certain fishes are able to reproduce on their skin rather complicated

patterns (e.g., a chess board), which form the bottom of the aquarium. This reproduction of the pattern is somewhat imperfect, but if we deduct the secondary disturbing factors the fact remains that the pattern on the skin is a tolerably true picture of the pattern of the ground. There exists, therefore, a definite arrangement of the images of the different luminous points of the ground on the retina and a similar arrangement of the images of the luminous points on the skin of the fishes. We may consider each point of the retinal image as a luminous or a stimulating point which produces a corresponding image point in the primary optic ganglia through the action of the nerve-fiber through which it is connected with the ganglia. Every image point in the primary optic ganglia may be considered again as a luminous or stimulating point which through the mediation of a special nerve-fiber influences an individual chromatophore or a small group of chromatophores of the skin. Considering the fact that the retina is a mosaic, we cannot well imagine the transmission of the retinal image upon the skin in any other way than by assuming that the relative arrangement of the individual points of the retinal image is preserved in the optic fibers and the end ganglia of the optic nerve. Under this assumption a relative distribution of the stimulating intensities must occur in the primary optic ganglion which corresponds to the distribution of the image points on the retina and which again can be called an image.

These observations in fish and the conclusions drawn in this note suggest the idea that vision is a kind of telephotography.

V. ON SOME FACTS AND PRINCIPLES OF PHYSIOLOGICAL MORPHOLOGY

ON SOME FACTS AND PRINCIPLES OF PHYSIOLOGICAL MORPHOLOGY 1

I. HETEROMORPHOSIS 2

The various organs of the higher animals have a definite arrangement; from the shoulders arms originate, from the hips legs, but we never see legs growing out from the shoulders or arms from the hips. In the lower animals the same definite arrangement of organs exists.

Fig. 22 gives a diagram of a hydroid, Antennularia anten-nina, which is quite common in the Bay of Naples. From a bundle of roots or stolons a straight stem arises to a height of six inches or more. From this main stem originate, in regular succession, short and slender branches, which carry polyps on their upper sides.

In this animal we never find a root originating at the apex, or in place of a branch, or polyps originating on the under side of a branch.

In observing these phenomena the question arose: What are the circumstances which determine that only one kind of organ shall originate at certain places in the body? It occurred to me that the answer to this question might be obtained by finding out first of all whether or not it were possible to make any desired organ of an animal grow at any desired place. In case this could be done, the question to be decided was whether the same circumstances by which the arrangement of organs can be changed experimentally also determine the arrangement of

1 Reprinted from Biological Lectures delivered at the Marine Biological Laboratory of Woods Hole, 1893, by courtesy of Ginn & Co.

2 Untersuchungen zur physiologischen Morphologic der Tiere. I, Hetero-morphosis, Wiirzburg, 1891. II, Organbildung und Wachsthum, Wurzburg, 1892. Translated in Studies in General Physiology.

THE MECHANISTIC CONCEPTION OF LIFE

\ \ \ \

/ /

FIG. 23.—Diagram of normal regeneration if a piece a b of Antennularia is hung up vertically in the water. The piece forms roots W at the lower end b and a new stem S at the upper end a. The old normal arrangement of organs is thus restored through the process of regeneration.

-s

FIG. 24.—Diagram of heteromorphic regeneration in Antennularia. A piece a b cut out of the stem is hung up in an inverted position, i.e., the root end b upward and the stem end a downward. In this case the apical end a forms roots W, and the basal end b forms a new stem S which grows upward.

organs in the natural development. The hydroid, Antennularia antennina, above mentioned, seemed to afford a suitable subject for experimentation in an attempt to solve this problem and the following simple experiments were performed.

A piece ab (Fig. 23) of an Antennularia was cut out and hung up vertically in the water of the aquarium, the apical end a above and the root end b below. It was found that after a few days the root end 6 had formed little roots, W, which

FIG. 22.—A piece of the normal stem of Antennularia an-tennina,& hydroid of the Bay of Naples. Approximately natural size. S S, stem. W, stolons or roots.

PHYSIOLOGICAL MORPHOLOGY

grew downward, and the apical end, a, had formed a new stem, S.

A similar piece was cut out from another specimen and was hung upside down in the aquarium (Fig. 24). The root end 6, which was now above, formed a new stem, S, and the apical end a, which was below, formed roots, W. In the newly formed stem the arrangement of the organs was the same as in the normal animal, namely, the branches which were growing

FIG. 25.—From nature. Regeneration of a piece a b cut out from the stem of Antennularia and put horizontally into the water. The branches on the lower side which had ceased to grow, grow downward as stolons and attach themselves to solid bodies. On the upper side a new stem c d grows vertically upward.

obliquely upward bore polyps on their upper side. From this we see that it was possible to substitute a root for a stem and an apex for a root. This phenomenon of the substitution of one organ for another I termed heteromorphosis. If the excised piece of an Antennularia was placed horizontally instead of vertically in the aquarium, something still more remarkable occured, namely, the branches on the lower side suddenly began to grow vertically downward, and these downward growing elements were no longer branches but roots (Fig. 25). This could be proved by their physiological reactions, for the roots attach themselves to the surface of solid bodies, e.g., the glass

THE MECHANISTIC CONCEPTION OF LIFE

of the aquarium, while the stems never show such a reaction. These new parts growing out from the branches of the under side of the stem attached themselves to the solid bodies with which they came in contact. Moreover, they were positively geotropic (that is, they grew toward the center of the earth),

while the branches never showed any positive geo-tropism. The branches on the upper side were not transformed into roots. They either perished or gave rise to long, slender, perfectly straight stems, which grew vertically upward. These stems, as a rule, were too slender to bear branches, but at parts of the upper surface of the main stem there originated new stems (c d, Fig. 25), which grew

Fio. 26. — Diagrammatic regeneration in a piece a b of a stem of Antennularia put obliquely into the water. On the upper side of the stem a b new stems S, S., S,,, grow vertically upward, while at the lower end of the piece o b opposite the new stems roots W,

,, W,,, grow out. This influe

uence of gravitation is found only in Antennularia antennina, not in other forms of Antennularia.

vertically upward and produced the typical little branches bearing polyps.

If we brought the stem into an oblique position (Fig. 26), with the apex a upward, from every element of the main stem new stems and roots originated, but with this difference, that stems always originated from the upper side of an element and roots from its lower side. If the stem were placed in an oblique position, with the root end above, the branches on the under side grew out as roots, and at the upper end a stem arose as usual.

What circumstances had all these experiments in common ? The stems always originated from the upper end or side of an element, and roots always from the lower side or end of the same element. These facts can be explained only on the assumption that in this case gravitation determines the place of origin of organs.

Now we may ask whether the action of this force, gravitation, is also responsible for the natural arrangement of the organs in this form, namely, that roots appear only at the base of the stem and never at the apex or in the place of a branch. I believe that this is the case. By reason of its negative geotropism, the stem grows vertically upward. Gravitation does not permit roots to arise at any place except at the under side of the organs, and that is, under normal conditions, at the base of the stem. The same force determines that polyps can originate only on the upper side of branches, and thus the general arrangement of organs is brought about by gravitation. But how does gravitation determine that stems grow on the upper and roots at the under side? This is a question to which we shall return later.

Fig. 27 gives a drawing of an example of heteromorphosis in Margelis, a hydroid common at Woods Hole, upon which another set of experiments was carried on. If we cut off a stem, or a small piece of a stem of this hydroid, and place it in a dish containing sea-water, protecting it carefully from every motion, a curious change takes place in the organism. Almost all, and in some cases all, of the stems which touch the glass give rise to roots that spread out and very soon cover a large area of the glass. In this way the apical end of a stem may continue to grow as a totally different organ, namely, as a root. Every organ not in contact with some solid body gives rise to polyps. Even the main root, if not in contact with a solid body, no longer grows as a root, but gives rise to a great number of small polyps which appear at the end of long stems. Fig. 27, which Mr.

THE MECHANISTIC CONCEPTION OF LIFE

Tower was kind enough to draw for me, shows a branch which formed roots at its apex and polyps at its roots in this manner.

FIG. 27.—Heteromorphosis in Margelis, a hydroid. At a and b, where the points of stems touch the ground of the aquarium, new roots or stolons grow out.

The stem touched the bottom of the dish with the apical ends, a and b. All these ends gave rise to roots. From the upper side of the original root, which was not in contact with the

FIG. 28.—Heteromorphosis in Pennaria. A piece a b of this hydroid was cut 9ut and put into a jar with sea-water. The ends a and b touched the bottom of the jar. At both points new roots grew out.

glass, later on small polyps grew out. Every place which

was in contact with solid bodies gave rise to roots, and every

place which was in contact with sea-water gave rise to polyps.

This is not the only species of hydroid found at Woods Hole

in which such forms of heteromorphosis can be produced. Another form, Pennaria, is just as favorable. In Pennaria I succeeded repeatedly in producing roots at both ends of a small stem that bore no polyps (Fig. 28)1

In these experiments on Margelis and Pennaria organs brought into contact with solid bodies continue to grow as roots, if they grow at all. Organs surrounded on all sides by water continue to grow in the form of polyps, if they grow at all. In Margelis, contact with a solid body plays the same r61e as did gravitation in the case of Antennularia. In what way the contact may have an influence shall be mentioned later on, but here one more point may be mentioned. In Antennularia, gravitation not only determines the place of origin of the various organs, but also the direction of their growth; the stem, growing upward, is negatively geotropic, the root, growing downward, is positively geotropic. In Pennaria, the nature of the contact not only determines the place of origin of the various organs, but also the direction of their growth. If we bring an outgrowing polyp of Pennaria into contact with a solid body, the polyp begins to grow away from the body, and the new stem is very soon nearly perpendicular to the part of the surface with which it came into contact.

I have called this form of irritability stereotropism. We

1 In a Tubularian I was able to produce the opposite result, namely, to get an animal that ended at both ends in a polyp and had no root. Weismann seems to assume, in his Germ Plasm, that the latter result is to be explained by the principle of natural selection, inasmuch as an animal without polyps could not continue to live, and hence it would be impossible to produce roots at both ends. In Pennaria this supposed impossibility was realized; one may say that these roots in Pennaria may give rise later on to polyps. In the special case that I observed they did not, although as a rule they do; but the same is the case in Tubularia, in which polyps also arise from the roots. It might be said, perhaps, that the formation of roots in Pennaria is, for some reason, absolutely necessary; but it is just as easy to produce polyps at both ends. Even if it were possible to reconcile these facts with the principles of natural selection, causal or physiological morphology would not gain thereby, as the circumstances that determine the forms of animals and plants are only the different forms of energy in the sense in which this word is used by the physicist, and have nothing to do with natural selection.

may speak of positive stereotropism in the case of the root, and of negative stereotropism in the case of the polyp.

Here, too, we may ask whether the contact with foreign bodies, which in these experiments determines the arrangement of the various organs, may not have the same effect in the natural development of the organism. I believe that such is the case. Negative stereotropism forces the polyps to grow away from the ground into the water, and hence parts surrounded by water form polyps only. Positive stereotropism forces roots in contact with the ground to hold to it, hence parts in contact with the ground give rise to roots only. Thus it happens that, under ordinary circumstances, in this animal we find roots only at the base where it touches the ground. In other hydroids the place of origin of the different organs is determined by light, and in others we find more complicated relations.

It may appear from the foregoing that such cases of hetero-morphosis are confined to hydroids, but such is not the case. We find similar cases in Tunicates. Ciona intestinalis, a solitary ascidian, has eye-spots around the two openings into the pharyngeal cavity. If we make an incision eye-spots are formed on both sides of the incision. 1

II. POLARIZATION

While the foregoing experiments were in progress, I observed that in many animals I was unable to produce any kind of heteromorphism. These animals showed, in regard to the formation of organs, a phenomenon with which we are familiar in a magnet. If a magnet is broken into pieces, every piece has its north pole on that side which in the unbroken magnet was directed toward the north. Likewise, there are animals every piece of which produces, at either end, that organ toward

i Since this was written phenomena of heteromorphosis have been produced in many animals. Herbst found that in crustaceans an antenna could be caused to be formed in the place of an excised eye, Van Duyne, Bardeen, and Morgan observed phenomena of heteromorphosis in Planarians and so on (1912).

PHYSIOLOGICAL MORPHOLOGY

which it was directed in the normal condition. We may speak

in such cases of polarization. The clearest example of this I

found in an actinian, Cerianthus membranaceus. If we cut a rectangular piece, c d ef, out

of the body-wall of Cerianthus new tentacles

soon begin to grow out of this piece, but

only from the side ef (Fig. 29), which was

directed toward the oral end of the animal. Nothing of the sort occurs in the side c e, or d c , or / d. The production of tentacles takes place before any other regeneration begins. The same polarization is shown in the following variation of the preceding experiment. If we make an incision, acb (Fig. 30), into the body-wall of the actinian, only the lower lip, b c, produces tentacles, while the upper lip, ac, produces none. The two ends heal together in such a way that one-half of a mouth, with its surrounding tentacles, b (Fig. 31), is formed. It is curious to see how these tentacles behave if we offer them bits of meat. They endeavor to force them into the new oral disc, where the mouth should be, and only after a struggle

of some minutes do they give up the futile attempt. I tried

in every possible way to produce tentacles in the aboral end

of a piece which had been cut out, but without success.

Hydra behaves, as regards polarization, a little differently

from Cerianthus. If we make an incision in the stem, a

FIG. 29.—Diagrammatic. If a piece c d ef is cut out from the wall of Cerianthus, a sea anemone, new tentacles are formed only at the upper cut ef.

FIG. 30.—Diagrammatic. If an incision a c b is made into the body of Cerianthus new tentacles grow out only from the lower edge c b.

THE MECHANISTIC CONCEPTION OF LIFE

whole new oral pole grows out, but otherwise it too shows polarization.

A good many animals, so far as we know, reproduce only the lost organ, but never show any heteromorphism. We see,

FIG. 31.—From nature. Formation of a second head in Cerianthus after a lateral incision at b. Only a fraction of the normal number of tentacles are formed corresponding to the fraction of the periphery laid bare by the incision. No new mouth is formed, but if a piece of meat is offered to the group of tentacles at b they seize it and press it to the place where a mouth ought to be, showing the purely machine-lilte character of all these reactions.

therefore, that while in some animals we are able to produce heteromorphosis, in others the most definite polarization exists, and we are able to produce regeneration of lost parts only in the arrangement which exists in the normal animal. In this case we must assume that unknown internal conditions determine the arrangement of limbs.

In addition to examples of heteromorphosis or polarization occurring separately, we find cases hi which both phenomena

PHYSIOLOGICAL MORPHOLOGY

are exhibited by the same animal. If we cut out a sufficiently large piece of the stem of Tubularia mesembryanthemum, and place it in the bottom of a dish of water, carefully protected from jarring, the anterior end of the piece gives rise to a new polyp, the posterior end to a root; but if we hang up the stem in such a way that the posterior end does not touch the surface of the glass, and is sufficiently provided with oxygen, this end, too, produces a polyp, and we have a true case of heteromorphosis (Fig. 32). In all cases the polyp at the oral end is formed first, and a relatively long time (one or more weeks) elapses before the aboral polyp is formed. Under one condition, however, I could cause the stem to form a polyp at the aboral as quickly as at the oral end, namely, by inhibiting or retarding the formation of the oral polyp. This could be done readily by diminishing the supply of oxygen at the oral end. In such cases the aboral polyps were produced almost as quickly as the oral polyps. 1

III. THE MECHANICS OF GROWTH IN ANIMALS

In order to arrive at an explanation of the phenomena of organization we must ask what the physical forces are that determine the formation of a new organ. We know that the ultimate sources of energy for all the functions of living bodies

FIG. 32. — Heteromorphosis in Tubularia. From nature. The normal Tubularia ends at one end in a stolon, at the other in a head or polyp. If a piece a 6 is cut out and suspended in water a new head or polyp c and d is formed at both ends. We can thus produce an animal which terminates in a head at both ends of its body: while in Fig. 28 an animal was represented which ended at both ends in a stolon or foot.

i It was found later independently by both Godlewski and myself that if we ligature the stem of a Tubularian the polyps at both ends are formed simultaneously (1912).

are chemical processes. The question is, How can these chemical forces be brought into relation with the visible changes which take place in the formation of a new organ ? The answer to this question is to be obtained by a knowledge of the mechanics of growth. It is very remarkable that the mechanics of growth forms almost an empty page in the history of animal morphology and physiology. I can refer here only to the few experiments I have made on this subject; but fortunately the subject has been worked out very carefully in plants, and as my experiments show that the conditions for growth in animals are, to a certain extent at least, the same as the conditions for growth in plants, we have the beginning of a basis for work.

A brief outline of the manner of growth in plants is as follows: Before the cell grows it forms substances which attract water from the surroundings, or, as the physicist expresses it, it forms substances which determine a higher osmotic pressure within the cell than did the substances from which they originate. The walls of the cell, or rather the protoplasmic layer that lines the cell-wall, possesses peculiar osmotic properties, in consequence of which it allows molecules of water to pass through freely while remaining resistant to the passing through of the molecules of many salts dissolved in the water. The result is that when substances of higher osmotic pressure are formed inside the cell, water from the outside passes in until the pressure within again equals the pressure without. The cell-wall becomes stretched and, according to Traube, new material is precipitated in the enlarged interstices, thus rendering growth permanent. This method of growth is most conspicuous, perhaps, in the germinating seed. The rising temperature in spring produces in the seed substances of higher osmotic pressure (with greater attraction for water) than the substances from which they originate. The result is that water enters the seed; by the pressure of the water within the cells their walls are stretched out and the seed grows. The chemical and

osmotic changes are the sources for the energy which is needed to overcome the resistance to growth. 1

In order to ascertain whether I could determine what are the mechanical causes of growth in animals, I began at Naples some experiments on Tubularia mesembryanthemum. I chose long stems belonging to the same colony and distributed them in a series of dishes containing sea-water of different concentrations. In some of the dishes the concentration had been raised by adding sodium chloride, and in others it had been lowered by adding distilled water. According to the laws of osmosis the amount of water absorbed by the cells of these Tubularians differed with the concentration of the sea-water, the amount being greatest in the most diluted solution and least in the most concentrated solution. If now in reality the mechanics of growth is the same for animals as for plants, we should expect that the more diluted the sea-water the more rapid would be the growth in the Tubularian stem. Of course, finally, a limit is reached where the water begins to have a poisonous effect. It was found, indeed, that within certain limits of concentration the increase in the length of the stems during the same period was greatest in the most diluted and least in the most concentrated sea-water. It is remarkable that the maximum of growth took place not in sea-water of normal concentration, but in more diluted sea-water, though this of course may not be the case in all animals. The following curve (Fig. 33) will give an idea of the dependence of growth upon the concentration of the sea-water in Tubularia. The values for the amount of sodium chloride, in 100 cubic centimeters of sea-water, are represented on the axis of the abscissa, the values for the increase in growth on the axis of ordinates.

These and similar experiments, which for lack of space cannot be mentioned here, show that growth in animals is

1 The substance which is formed and which causes the swelling may be an acid. I found that acids cause a swelling of muscles and it has since been shown that this is a general phenomenon.

THE MECHANISTIC CONCEPTION OF LIFE

determined by the same mechanical forces which determine growth in plants. An obstacle to such a conclusion seems to lie in the fact that many plant-cells have solid walls, while this is not the case in most animal cells. The solid cell-wall, however, does not determine the peculiar character of growth. This character is determined first, by chemical processes within the cell, which result in a higher osmotic pressure, and, secondly, by the osmotic qualities of the outer layer of protoplasm, which

FIG. 33.—Curve representing the influence of diluted ' sea-water. The abscissae represent the concentrations, the ordinates the corresponding growth in the unit of time. The maximum growth is at a concentration between 2 and 3 per cent of salt, while the normal concentration is indicated by the vertical line between 3 and 4.

allows water to pass through freely, but does not allow all salts dissolved in it to do the same. Both these qualities are independent of the solid cell-wall, and I see no reason why the animal cell should not agree in these two salient features with the plant-cell.

In order that the foregoing explanation of the mec hanism of growth in the animal cell might be based only upon known processes, it was necessary to find out whether, in case of growth, chemical processes of such a character take place that substances of higher osmotic pressure are formed than those from which they originate. Everyone knows that by exercise our muscles increase in size. No satisfactory explanation of this fact has

been given. If my interpretation of the method of growth were correct, I must expect that during activity substances are formed in the muscle, which determine a higher osmotic pressure than those from which they originate. This is exactly the case. Ranke had already shown that the blood of a tetanized frog loses water and that this water is taken up by the muscles. In experiments which were carried on by Miss E. Cooke in my laboratory, we were able to show directly that during activity the osmotic pressure inside the cell-wall is raised. We determined the concentration of a solution of NaCl, or rather of a so-called Ringer's mixture, hi which the gastroconemius of a frog neither lost nor took up water. We found that while this concentration for the resting gastroconemius was about 0.75 per cent to 0.85 per cent, for the gastroconemius that had been tetanized from twenty to forty minutes it varied from 1.2 per cent to 1.5 per cent. 1

This increase of osmotic pressure inside the muscle-cell leads, during normal activity, to a taking up of water from the blood and lymph, and the consequence is an increase in volume. The same muscle, as soon as it ceases to be active, begins to decrease in size. Activity, therefore, plays the same r61e in the growth of a muscle that the temperature plays in the growth of the seed.

I tried to ascertain whether segmentation, like growth in general, is influenced by the amount of water contained in the cell. If we decrease the amount of water in the egg of the sea-urchin segmentation is retarded, and if we use a sufficiently high concentration of sea-water it may be stopped entirely. Therefore the amount of water contained in the cell plays still another role in the process of organization and influences the process of cell-division.

1 This increase in osmotic pressure is probably caused by the formation of acid. Two years after the publication of this lecture I showed that the muscle swells in an isomotic solution if this solution is acid. The recent work of Pauli and Handovski indicates that the swelling is caused through a formation of salt between the acid and a weak base, e.g., a protein. The protein salt is more strongly dissociated than the protein base (1912).

100 THE MECHANISTIC CONCEPTION OF LIFE

IV. THE ARTIFICIAL PRODUCTION OF DOUBLE AND MULTIPLE MONSTROSITIES IN SEA-URCHINS 1

The idea that the formation of the vertebrate embryo is a function of growth has been made the basis of the embryological investigations of His. In a masterly way, His has shown how inequality of growth determines the differentiation of organs. In the blastoderm of a chick, for example, the first step in the formation of the embryo is a process of folding. There originates a head fold, a tail fold, a medullary groove, and the system of amniotic folds. According to His, all these processes of folding are due simply to inequalities of growth, the center of the blastoderm growing more rapidly than the periphery. It can be shown, very simply, that such a process of unequal growth must, indeed, lead to the formation of exactly such a system of folds as we find in the blastoderm of a chick. If we take a thin, flat plate of elastic rubber, and lay it on a drawing-board, we can imitate the stronger growth in the center by sticking two tacks into the middle of the rubber, a short distance apart, and then pulling them in opposite directions. In this way we may imitate unequal growth, the center growing faster than the periphery. If we then fix the tacks in the drawing-board, so that the rubber in the middle remains stretched, we get the same system of folds as that shown by the embryo of a chick. I mention this way of demonstrating the effects of unequal growth as the ideas of His are still doubted by some morphologists.

His raised the question, Why is growth different in different parts of the blastoderm? But instead of trying to answer it from the physiological standpoint he answered it from the anatomical standpoint. According to him, the different regions of the unsegmented egg correspond already to the different regions of the differentiated embryo. But this so-called theory

1 Another method of producing twins from one egg is discussed in the last chapter of this book.

of preformed germ-regions gives no answer to the question, why some parts of the embryo grow faster than others. Nevertheless, it is not necessarily in opposition to the theory of growth offered in the preceding chapter. Starting with the idea of His, we may well imagine that the different regions of the ovum are somewhat different chemically, and that these chemical differences of the different germ-regions determine the differences of growth in the blastoderm. Thus the phenomena of heteromorphosis would show that, in some animals at least, the arrangement of preformed germ-regions may be changed by gravitation, light, adhesion, etc.

It must be asked, however, what, from the standpoint of causal morphology, determines the arrangement of the different germ-regions in the egg. If we answer " heredity," causal morphology can make no use of such an explanation. Our blood has the temperature of about 37°, but although our parents had the same temperature, the heat of our blood is not inherited, but is the result of certain chemical processes in our tissues. Still it may be possible that the molecular forces of the chemically different substances of the egg determine a separation of these substances and thereby give rise to the chief directions of the future embryo.

Driesch has shown 1 that by shaking a sea-urchin's egg in the four-cell stage the four cells may be separated, and each one be capable of giving rise to a complete embryo, which differs only in size from the normal embryo. If the theory of preformed germ-regions with its later modifications were true, we should expect that every one of the isolated cells would give rise to one-fourth of an embryo. But it has been said that the artificial isolation of one cleavage-cell causes a process of post-generation or regeneration. Driesch, moreover, changed the mode of the first cleavage by submitting the ovum to one-sided pressure. In this way the nuclei were brought into somewhat

1 Zeitschrift f. wissensch. Zoologie, LIII, LV.

102 THE MECHANISTIC CONCEPTION OF LIFE

different places from those they would have held in the case of normal segmentation. Still, normal embryos resulted. One might object again that the preformation of the germ-regions existed in the protoplasm, and not in the nucleus. I have made a series of experiments to the results of which these objections cannot be made. I shall describe these experiments somewhat fully, as they have not yet been published, though I cannot enter into details at this place.

I brought eggs of a sea-urchin, within ten to twenty minutes after impregnation, into sea-water that had been diluted by the

FIG. 34 FIG. 35

FIG. 34.—Fertilized egg of a sea-urchin (Arbacia) put into dilute sea-water. The protoplasm swells until the membrane m bursts and part of the protoplasm b flows out; each of the two droplets may develop into a blastula, so that from such an egg two larvae may arise, as indicated in Fig. 35.

addition of about 100 per cent distilled water. In this solution the eggs took up so much water that the membrane (m, Fig. 34) burst and part of the protoplasm escaped in the form of a drop (b, Fig. 34), which often, however, remained hi connection with the protoplasm inside the membrane after the eggs were brought back into normal sea-water. These eggs gave rise to adherent twins, the ejected part b of the protoplasm, as well as the part remaining inside the membrane, developing into a normal and perfectly complete embryo. The part of the protoplasm, which at first had connected the two drops, formed the part where the twins remained grown together. Of course, it often happened that, by accident or rapid movement, the twins were separated, and they then developed into perfectly normal single embryos. Since we cannot assume that in every case the

same part of the protoplasm escapes, we must conclude that every part of the protoplasm may give rise to fully developed embryos without regard to preformed germ-regions. 1 In many eggs a repeated outflow of the protoplasm takes place. In such cases each of the drops of the protoplasm may give rise to an embryo, and I obtained not only double embryos, but triplets and quadruplets all grown together.

It is remarkable that the development of these monstrosities goes on nearly at the same rate as that of the normal embryo, provided they are equally well supplied with oxygen and equally protected from microbes and infusoria. The development in most eggs takes place hi so regular and typical a manner that it seems as if there were a prearrangement of some kind. It is, however, perfectly well possible that this prearrangement consists in a separation of different liquid substances hi the ovum by the molecular qualities of these liquids. Such a separation, of course, might be called a preformation of germ-regions, but it would be something totally different from what is now understood by that term.

V. THEORETICAL REMARKS

1. All life phenomena are determined by chemical processes. This is equally the case whether we have to do with the contraction of a muscle, with the process of secretion, or with the formation of an embryo or a single organ. One of the steps that physiological morphology has to take is to show in every case the connecting link between the chemical processes and the formation of organs. I have tried to show that in a few cases at least this connecting link was to be sought in the changes of osmotic pressure determined by the chemical changes which take place in the growing organ.

But this fact alone does not explain why it is that we get

1 In the light of more recent experiments it is possible, that after all only such pieces can develop into a normal embryo which contain the different germ-regions (1912).

104 THE MECHANISTIC CONCEPTION OF LIFE

differences in the forms of organs. In order to understand this we must bear in mind that the processes of growth must necessarily be different for different organs, as for example in the formation of a root, and the formation of a stem. As growth is a process in which energy is used up in overcoming the resistance to growth, differences of growth can only be determined either by differences in the amount of energy set free in the growing organ or by differences in resistance. Differences in the energy must be the outcome of differences in the chemical processes which determine growth. Therefore we are led to the idea that differences in the forms of different organs must be determined by differences in their chemical constitution, or, if the chemical constitutions be similar, by differences in resistance to growth. That organs which differ in shape are very often chemically different is a well-known fact. The formation of urea in the liver and the synthesis of hippuric acid by the kidneys are the consequences of chemical differences.

In this way we are led through the mechanics of growth to a conclusion which forms the nucleus of Sachs's theory of organization, namely, "that differences in the form of organs are accompanied by differences in their chemical constitution, and that according to the principles of science we have to derive the former from the latter." According to Sachs there are at least as many "spezifische Bildungsstoffe" in a plant as there are different organs. 1

2. In adopting the theory of Sachs and applying it to animal morphology, we must avoid a mistake very often made even in the case of good theories, namely, the endeavor to explain special cases which are complicated by unknown conditions. Huyghens explained by his theory of light the phenomena of refraction, but he could not and did not attempt to explain the sensations of color. For these phenomena the wave theory of

1 J. Sachs, Stoff und Form der Pflanzenorgane, Gesammelte Abhandlungen, II, 1893.

light remains true, but color sensations depend not only on the wave motion of the ether, but also on the chemical and physical structure of the retina. I think it perfectly safe to say that every animal has specific germ substances, and that the germ substances of different animals differ chemically. Its chemical qualities determine that from a chick's egg only a chick can arise. But it would be a mistake to attempt at present an explanation of how the unknown chemical nature of the germ determines all the different organs and characters that belong to the species. For instance, the yolk sac of the Fundulus embryo has a tiger-like coloration. We might say that these markings may be due to a certain arrangement of molecules or complexes of molecules (determinants), which later on give rise to the colored places of the yolk sac, but I found that this coloration originates in a manner much more simple. The pigment cells are formed irregularly on the surface of the yolk. The pigment is chemically closely related to hemoglobin, and so its formation may from the first be connected with the formation of the blood corpuscles. But the arrangement of the pigment cells during the first days of development is not such as to produce any definite markings. They lie upon the walls of the blood-vessels as well as in the spaces between the capillaries (Fig. 36). Later on, however, all of the pigment cells have crept upon the surface of the neighboring bloodvessels (Fig. 38). I succeeded experimentally in showing it to be probable that some of the substances contained in the blood determine this reaction. These substances, if they diffuse from the blood-vessel and touch the chromatophore, make, according to the laws of surface tension, the protoplasm of the chromatophore flow toward and at last over the blood-vessel and form a sheath around it, while the gaps between the blood-vessels become empty of chromatophores. In this way the chroma-tophores are arranged in stripes, and possibly changes in the surface tension, and not a preformed arrangement of the germ,

106 THE MECHANISTIC CONCEPTION OF LIFE

FIG. 38

FIGS. 36, 37, and 38.—From nature. The origin of the pattern on the yolk sac of a fish embryo (Fundulus heteroclitus). Fig. 36 is a drawing of the bloodvessels at the surface of the yolk sac at an early stage of development. The black pigment cells show no definite orientation in regard to the blood-vessels. Fig. 37, the same egg a few days later. Here we notice that some pigment cells show a tendency to creep on the blood-vessels. Fig. 38, the same egg still a few days later. The black pigment cells have completely crept on the blood-vessels and formed a sheath around them. The red chromatophores are omitted in this drawing.

This was the first observation proving that tropisms play a role in the arrangement of the organs in the body.

determine the marking. We do not know what processes determine the coloration of animals which owe their markings to interference colors, but the task of deriving such a coloration in the adult from a similar arrangement of molecules in the germ plasm would prove too much even for a genius like Huyghens, and without the possibility of such a derivation the theory is of no use.

3. The reasons why roots grow on the under side of the stem of Antennularia and stems on the upper side can only be given when the special physical and chemical conditions inside the stem of Antennularia have been worked out. At present we can only think of possibilities. It is possible that the hypothetical root substances of Sachs may have a greater specific gravity than the substances which form stems, and therefore take the lowest position in the cell. Since outgrowth can take place only at the free surface of a stem or branch, roots can on this assumption grow only at the under side and stems only at the upper side of an element. But there are still other possibilities which we must omit here. In the case of Margelis and other hydroids, it might happen that contact with solid bodies produced an increase of surface hi the touched elements in case they contained specific root substances, while the opposite took place in the case of elements containing polyp substances. The consequence would be an increase hi the surface of the roots if they came into contact with solid bodies, while polyps only would grow out in the opposite direction. I found, indeed, in some forms at Naples that roots of hydroids which grew free in the water began to grow much faster and to branch off more abundantly when brought into contact with solid bodies. But in these cases we must wait with our attempts at explanation until the physical and chemical conditions for the form are worked out. For the same reasons I will not go into a discussion of the question of what determines the polarization of animals like Cerianthus. It may suffice to suggest the possibility

108 THE MECHANISTIC CONCEPTION OF LIFE

that in polarized animals the tissues or cells may have such a peculiar structure as to allow the specific formative substances to migrate or arrange themselves only in one direction, while in cases of heteromorphosis migration or arrangement in every direction or in several directions is possible.

4. The egg of a sea-urchin under normal conditions gives rise to but one embryo. This circumstance is due simply to the geometrical shape of the protoplasm, which, under normal conditions, is that of a sphere. When we make the eggs burst, the protoplasm outside the egg membrane and that which remains within it assume spherical forms, by reason of the surface tension of the protoplasm. When this happens, as a rule, we get twins, if two separate segmentation cavities are formed, and only one embryo, if both cavities communicate with one another. Whether the first or the second case will happen depends upon the molecular condition of the part of the protoplasm connecting the two drops. Therefore, the number of embryos which come from one egg is not determined by the preformation of germ-regions in the protoplasm, or nucleus, but by the geometrical shape of the egg and the molecular condition of the protoplasm, in so far as these circumstances determine the number of blastulae. In my experiments, I got double or triple embryos when the egg formed two or three droplets or spheres, as every sphere gives rise to a blastula. In Driesch's experiments, one single cell of the four-cell stage necessarily formed a whole embryo after it had been isolated, as it assumed the shape of a single sphere or ellipsoid. Of course, there must be a limit to the number of embryos that can arise from one egg; but the limit is not due to any preformation, but to other circumstances, the chief one being that with too small an amount of protoplasm the formation of a blastula— from merely geometrical reasons, as there must be a minimum size for the cleavage-cells—becomes impossible. 1 Without the

1 1 stated that the minimal size is about one-eighth of the mass of the sea-urchin's egg and I do not think that this is very far off the limit.

formation of the blastula, of course it is not possible to get the later stages which are determined by the blastula.

I have chosen the name Physiological Morphology for these investigations, inasmuch as their object has been to derive the laws of organization from the common source of all life phenomena, i.e., the chemical activity of the cell. In what way this is to be done is indicated in the chapter on the mechanics of growth.

But the aim of Physiological Morphology is not solely analytical. It has another and higher aim, which is synthetical or constructive, that is, to form new combinations from the elements of living nature, just as the physicist and chemist form new combinations from the elements of non-living nature.

VI. ON THE NATURE OF THE PROCESS OF FERTILIZATION

ON THE NATURE OF THE PROCESS OF FERTILIZATION 1

Experimental biology is a very recent science. Not until recently have biologists begun to become conscious of the uncertainty of conclusions which are not tested and verified by adequate experiments.

Leeuwenhook demonstrated in 1677 the existence of motile elements in the sperm, the so-called spermatozoa. He believed that the spermatozoa represented the future embryo. The majority of his contemporaries assumed that the spermatozoa were parasitic organisms which had nothing to do with fertilization. The idea that spermatozoa are not parasites did not subside until it was proved about 160 years later that the spermatozoa originate from the cells of the testes.

That sperm was needed to bring about fertilization of the egg was too obvious a fact to escape even those biologists who never made an experiment, but that the spermatozoa and not the liquid constituents were the essential element in the sperm was a fact which could not be established except experimentally. It was generally assumed that no direct contact between sperm and egg was necessary arid that something volatile contained in the sperm, the imaginary "aura seminalis" was sufficient for the act of fertilization. That contact between sperm and egg was really necessary for fertilization was at last proved experimentally by Jacobi (1764) who showed that fish eggs can only be fertilized if the sperm is brought into direct contact with the eggs; and by Spallanzani who put the males of frogs during the act of cohabitation into trousers and convinced

i Reprinted from Biological Lectures delivered at Woods Hole, 1899, by courtesy of Ginn & Co., Boston.

113

114 THE MECHANISTIC CONCEPTION OF LIFE

himself that under such conditions the eggs remained unfertilized although the "aura seminalis" was not prevented from acting upon the eggs. This ended the reign of the "aura seminalis."

It was reserved to two experimenters, Prevost and Dumas (the latter the famous chemist) to prove that the spermatozoa are the essential element in the sperm. They made the simple experiment of filtering the sperm and demonstrated that the sperm whose spermatozoa had been retained by the filter had lost its power of fertilizing the eggs. But even this did not convince many of the descriptive biologists and nine years later K. E. von Baer still expressed the opinion that spermatozoa had nothing to do with fertilization. In 1843 the entrance of the spermatozoon into the egg was directly observed by Barry and this fact has since been verified by an endless number of investigators for the egg of all kinds of animals. It is probably no exaggeration to say that with the general recognition of the experimental method in biology it would probably have taken about as many years as it took centuries to establish the simple fact that the spermatozoon is the essential element in sperm.

The mere observation of the fact that the spermatozoon must enter the egg in order to bring about fertilization did not lead to any understanding of the mechanism of the activation of the egg. Nevertheless four theories or rather suggestions were offered.

The first theory of fertilization is a morphological one. According to this theory, it is the morphological structure of the spermatozoon which is responsible for the process of fertilization.

The second theory is a chemical one. According to this theory it is not a definite morphological or structural element of the spermatozoon, but a chemical constituent, that causes the development of the egg. Against this second view Miescher raised the objection that his investigations showed the same

compounds in the egg and the spermatozoa. I do not believe that this objection is valid. We know that simple variations in the configuration of a molecule have an enormous effect upon life phenomena. This is shown among others by the work of Emil Fischer on the relation between the molecular configuration of sugars and their fermentability. When Miescher made his experiments he was not familiar with such possibilities. Moreover, Miescher was not able to state whether the spermatozoa contain enzymes or not.

A third theory was a physical theory (Bischof). This theory assumes that a peculiar condition of motion exists in the spermatozoon which is transmitted to the egg and causes its development. It should be said, however, that this idea is not so very different from the chemical conception, because it assumes exactly the same for the spermatozoon that Liebig assumes for the enzymes. Liebig thought that the enzymes owed their power of producing fermentation to the motions of certain atoms or groups of atoms.

The fourth conception is the stimulus conception, which was originated by His. According to this conception the egg is considered as a definite machine which if once wound up will do its work hi a certain direction. The spermatozoon is the stimulus which causes the egg to undergo its development. It is to be said in connection with this stimulus conception that the main point at issue is omitted as to whether the stimulus carried by the spermatozoon is of a physical or a chemical character, and in this way, of course, the stimulus conception is nothing but a disguised repetition of the chemical or physical theory of fertilization.

All these theories are so vague that we do not need to be surprised that none of them has led to any further discovery. If we want to make new discoveries in biology, we must start from definite facts and observations, and not from vague speculations. Among these observations the most important

116 THE MECHANISTIC CONCEPTION OF LIFE

are those on parthenogenesis. It had been observed for a long time that the unfertilized egg of the silkworm can develop parthenogenetically. It was, moreover, known that plant lice can give rise to new generations without fertilization. The most impressive fact concerning the parthenogenesis of animals was contributed by Dzierzon, who discovered that the unfertilized eggs of bees develop and give rise to males, while the fertilized eggs give rise to females. Similar conditions seem to exist in wasps. It is, moreover, certain that a few crustaceans show parthenogenesis.

A beginning of parthenogenetic development had been observed in the case of a great many marine animals which develop outside of the female in sea-water. It was found that such eggs when left long enough in sea-water may divide into two or three cells, but no farther. On the other hand, in ovaries of mammals now and then eggs were found that were segmented into a small number of cells. 1 These facts and the occurrence of a certain class of tumors in the ovary, the so-called teratomata, suggest the possibility of at least partial parthenogenesis in the eggs of mammals. But all these phenomena were considered to be of a pathological character. It must be, however, admitted that we cannot utilize these facts with any degree of certainty for the theory of fertilization, as in this case certainty can only be obtained by the experiment. It was not until very recently that such experiments were made.

Eight years ago I observed that if the fertilized eggs of the sea-urchin were put into sea-water whose concentration was raised by the addition of some neutral salt they were not able to segment, but that the same eggs, when put back after they had been in such sea-water for about two hours, broke up into a large number of cells at once instead of dividing successively

i Hertwig, O., Die Zelle und die Gewebe, p. 239, Jena, 1893.

into two, four, eight, sixteen cells, etc. Of course it is necessary for this experiment that the right increase in the concentration of the sea-water be selected. The explanation of this fact is as follows: The concentrated sea-water brings about a change in the condition of the nucleus which permits a division and a scattering of the chromosomes in the egg. 1 As soon as the egg is put back into normal sea-water it at once breaks up into as many cleavage-cells as nuclei or distinct chromatin masses had been preformed in the egg. Morgan tried the same experiment on the unfertilized eggs of the sea-urchin, and found that the unfertilized egg, if treated for several hours with concentrated sea-water, was able to show the beginning of a segmentation when put back into normal sea-water. A small number of eggs divided into two or four cells, and, in a few cases, went as far as about sixty cells, but no larvae ever developed from these eggs. Morgan 2 had used the same concentration of sea-water as Norman 3 and I had used in our previous experiments. I had added about 2 grams of sodium chloride to 100 c.c. of sea-water. Norman used instead of this 3J grams of MgCl 2 to 100 c.c. of sea-water, and Morgan used the same concentration. Mead 4 made an observation somewhat similar to Morgan's upon Chaetopterus. He found that by adding a very small amount of KC1 to sea-water he could force the unfertilized eggs of Chaetopterus to throw out their polar bodies. The substitution of a little NaCl for KC1 did not have the same effect. While continuing my studies on the effects of salts upon life phenomena, I was led to the fact that the peculiar actions of protoplasm are influenced to a great extent by the ions contained in the solutions which surround the cells. As is

1 Loeb, J., "Experiments on Cleavage," Journ. of Morph., VII, 1892.

2 Morgan, T. H., "The Action of Salt Solutions, etc.," Arch. f. Entwickelungs-mechanik, VIII, 1899.

3 Norman, W. W., " Segmentation of the Nucleus without Segmentation of the Protoplasm," Arch. f. Entwickelungsmechanik, III, 1896.

4 Mead, A., " The Rate of Cell-Division and the Function of the Centrosome," Woods Hole Biol. Led., 1898.

118 THE MECHANISTIC CONCEPTION OF LIFE

well known, if we have a salt in solution, e.g., sodium chloride, we have not only NaCl molecules in solution, but a certain number of NaCl molecules are split up into Na ions (Na atoms charged with a certain quantity of positive electricity) and Cl ions (Cl atoms charged with the same amount of negative electricity). When an egg is in sea-water, the various ions enter it in proportions determined by their osmotic pressure and the permeability of the protoplasm. It is probable that some of these ions are able to combine with the proteins of the protoplasm. At any rate, the physical qualities of the proteins of the protoplasm (their state of matter and power of binding water) are determined by the relative proportions of the various ions present in the protoplasm or in combination with the proteins. 1 By changing the relative proportions of these ions we change the physiological properties of the protoplasm, and thus are able to impart properties to a tissue which it does not possess ordinarily. I have found, for instance, that by changing the amount of sodium and calcium ions contained in the muscles of the skeleton we can make them contract rhythmically like the heart. It is only necessary to increase the number of sodium ions in the muscle or to reduce the number of calcium ions or do both simultaneously. 2 On the basis of this and similar observations I thought that by changing the constitution of the sea-water it might be possible to cause the eggs not only to show a beginning of development but to develop into living larvae, which were in every way similar to those produced by the fertilized egg.

There seemed to be three ways in which this might be accomplished. The first way was a simple change in the constitution of the sea-water without increasing its osmotic pressure. The second way was to increase the osmotic pressure

1 Loeb, J., "On lon-Proteid Compounds and Their Role in the Mechanics of Life-Phenomena," Amer. Journ. of Phys., Ill, 1900.

2 It is due to the Ca ions of our blood that the muscles of our skeleton do not beat rhythmically, like our heart

of the sea-water by adding a certain amount of a certain salt. The third way was by combining both of these methods. The first way did not lead to the result I desired. 1 All the various artificial solutions I prepared had only the one effect of causing the unfertilized egg to divide into a few cells, but I was not able to produce a blastula. I next tried the effects of an increase in the sea-water by adding a certain amount of magnesium chloride. In this case I had no better results than Morgan. Very few eggs began to divide, but these did not develop beyond the first stages of segmentation. I then tried the combination of both methods. The osmotic pressure of ordinary sea-water is roughly estimated to be the same as that of a fn NaCl solution or a -^-n MgCl 2 solution. I found, after a number of experiments, that by putting the unfertilized eggs of the sea-urchin into a solution of 60 c.c. of -^-n MgCl 2 solution and 40 c.c. of sea-water for two hours the eggs began to develop when put back into normal sea-water. Such eggs reached the blastula stage. I do not think that anybody has ever seen before such blastulae as resulted from these unfertilized eggs. As these eggs had no membrane, the amoeboid motions of the cleavage-cells led very frequently to a disconnection of the various parts of one and the same egg, and the outlines of the egg became extremely irregular. The blastulae showed, as a rule, the same outline as the egg had in the morula stage. It was, moreover, a rare thing that the whole mass of the egg developed into one blastula. The disconnection of the various cleavage-cells led, as a rule, to the formation of more than one embryo from one egg. The results were in a certain way similar to those I had obtained when I caused the fertilized eggs of sea-urchins to burst. In such cases a part of the protoplasm flowed out from the egg but was able to develop. These extraovates had no membrane, and of course showed some irregularity in their outlines, but the irregularity in this case

1 Later experiments gave, however, positive results. See next chapter.

120 THE MECHANISTIC CONCEPTION OF LIFE

was far less than that observed in the unfertilized eggs of my recent experiments. But although I had thus far satisfied my desire to see the unfertilized eggs of the sea-urchin reach the blastula stage, I was not able to keep these eggs alive long enough to see them grow into the pluteus stage. They developed more slowly than the normal eggs, and died, as a rule, on the second day.

It was my next task to find a solution which would allow the eggs to reach the pluteus stage. I found that this can be done by reducing the amount of magnesium chloride and increasing the amount of sea-water. By putting the unfertilized eggs for about two hours into a mixture of equal parts of 2 ¥ °-n MgCl 2 and sea-water, the eggs, after they were put back into normal sea-water, not only reached the blastula stage, but went into the gastrula and pluteus stages. The blastulae that originated from these eggs looked much healthier and more normal than those of the former solution with more MgCl 2 . Of course as these unfertilized eggs had no membrane it happened but rarely that the whole mass of an egg developed into one single embryo. Quadruplets, triplets, and twins were much more frequently produced than a single embryo. The outlines of each blastula were much more spherical than in the previous experiment. These eggs reached the pluteus stage on the second day (considerably later than the fertilized eggs do). Thus I had succeeded in raising the unfertilized eggs of sea-urchins to the same stage to which the fertilized eggs can be raised in the aquarium. I have not yet succeeded in raising the fertilized eggs in my laboratory dishes beyond the pluteus stage.

Though I do not wish to go into the technicalities of these experiments, I must mention a few of the precautions that I took in order to guard against the possible presence of spermatozoa in the sea-water. 1 The reader who is interested in this

1 Today it may seem strange that I had to meet such objections, but when my first papers on artificial parthenogenesis appeared, very few biologists were willing to accept the correctness of my statements. The most absurd sources of error were suggested.

technical side of the experiments will find all the necessary data in my publication in the American Journal of Physiology. 1 Here I wish only to mention the following points:

1. These experiments were made after the spawning season was practically over.

2. Bacteriological precautions were taken against the possibility of contamination of the hands, dishes, or instruments with spermatozoa.

3. The spermatozoa contained in the sea-water lose, according to the investigation of Gemmill, 2 their fertilizing power within five hours if distributed in large quantities of sea-water.

4. We have a criterion by which we can tell whether the egg is fertilized or not in the production of a membrane. The fertilized egg forms a membrane and the unfertilized egg has no distinct membrane. None of the unfertilized eggs that developed artificially had a membrane. 3

5. With each experiment a number of control experiments were made. Part of the unfertilized eggs were put into the same normal sea-water that was used for the eggs that did develop. None of these eggs that remained in normal sea-water formed a membrane or showed any development, except that a few of them were divided into two cells after about twenty-four hours.

6. I made another set of control experiments by putting a lot of eggs of the same female into a solution which differed less from the normal sea-water than the one which caused the formation of blastulae or plutei from the unfertilized eggs.

1 Loeb, J., "On the Artificial Production of Normal Larvae from the Unfertilized Egg of the Sea-Urchin," Amer. Journ. of Phys., III.

2 Gemmill, "The Vitality of the Ova and Spermatozoa of Certain Animals," Journ. of Anat. and Phys., 1900.

3 The method used in these experiments was primitive inasmuch as no fertilization membrane was formed. A few years later I found a method for the artificial production of a fertilization membrane, which is described in the next paper. In the earlier experiments in which no fertilization membrane was developed, nevertheless a change in the cortical layer of the egg was brought about by the combined action of the hydroxyl-ions of the solution, and the increased osmotic pressure.

122 THE MECHANISTIC CONCEPTION OF LIFE

In this case it was shown, that although these eggs received the same sea-water as the ones which developed, and although they were injured less than the ones which developed, yet not one single egg formed a membrane or reached the blastula stage. If the sea-water had contained any spermatozoa these eggs should have reached the blastula stage. 1 Hence, as in nine different series of experiments these results were confirmed, we may assume that by treating the eggs for two hours with a solution of equal parts of a -\° n MgCl 2 solution and sea-water we can cause them to develop parthenogenetically into plutei.

Ill

What conclusions may we draw from these results ? If we wish to avoid wild and sterile speculations, I think we should confine ourselves to the following question: What alterations can be produced in an egg by treating it for two hours with a solution of equal parts of \°-n MgCl 2 and of sea-water ? Even in this regard we can only give a very indefinite answer which, however, will have to be in the following direction: The bulk of our protoplasm consists of colloidal substances. This material easily changes its state of matter and its power of binding water. It seems probable that changes of these two qualities are mainly responsible for muscular contraction and perhaps amoeboid motions. Among the agencies that cause changes of these physical qualities we know of three that are especially powerful. The one is specific enzymes (trypsine, plasmase, etc.). The second is ions in definite concentration. The concentration varies for various ions. The third agency is temperature. In our experiments it is obvious that only the second possibility can have been active. I do not consider it advisable to enter into theoretical discussions beyond these

1 Through other control experiments I convinced myself that a treatment of eggs or spermatozoa with equal parts of a 2 g °n MgCl 2 solution and sea-water diminishes the impregnability of the eggs and annihilates the fertilizing power of spermatozoa in a very short time.

statements. The next question that should be raised would be whether the spermatozoa act in the same way. It is true that the spermatozoon contains a considerable proportion of salts, especially K 3 PO 4 , but it may contain enzymes or it may contain substances which have similar effects upon the physical qualities of the colloids, like the three agencies mentioned above. In the last volume of these lectures I pointed out that it is impossible to derive all the various elements that constitute heredity from one and the same condition of the egg. 1 Our recent experiments suggest the possibility that different constituents of the egg are responsible for the process of fertilization and for the transmission of the hereditary qualities of the male. While we are able to produce the process of fertilization by a treatment of the unfertilized egg with certain salts in certain concentrations, we cannot hope to bring about the transmission of the hereditary qualities of the male by any such treatment. Hence, the inference must be that the transmission of the hereditary qualities of the male and the agency that causes the process of fertilization are not necessarily one and the same thing. I consider the chief value of the experiments on artificial parthenogenesis to be the fact that they transfer the problem of fertilization from the realm of morphology into the realm of physical chemistry. 2

1 Loeb, J., " The Heredity of the Marking in Fish Embryos," Woods Hole Biol. Lect., Boston, 1899.

2 This paper was written immediately after I had succeeded in producing larvae from the unfertilized egg. In the following years the methods of artificial parthenogenesis were improved and this led to the unraveling of the mechanism by which the spermatozoon causes the egg to develop. An account of this work is given in the two following papers.

VII. ON THE NATURE OF FORMATIVE STIMULATION (ARTIFICIAL PARTHENOGENESIS)

ON THE NATURE OF FORMATIVE STIMULATION (ARTIFICIAL PARTHENOGENESIS) 1

PREFACE

The title of this paper was chosen in reference to Virchow's paper on "Stimulation and Irritability" (Virchow's Archiv, XIV, 1, 1858) in which he discriminates between three forms of stimulation: functional, nutritive, and formative. By formative stimuli he means those which give rise to nuclear and cellular division. He considers as the classic example for formative stimulation the fertilization of the egg and the parallel drawn by him between this process and the causation of a pathological process of growth is so characteristic that we may quote it in full:

If we admit the identity between the pathological and the embryonic neoformation, the egg will have to be considered as the analogue of the pathological mother cell and the act of impregnation as the analogue of pathological stimulation. This view is not essentially altered through the discovery of the entrance of the spermatozoon into the egg, since there is no reason to consider the spermatozoon as the direct morphological starting-point for the development of definite parts of the egg. If, as seems to be the case, the spermatozoa are dissolved in the egg, they carry into it only certain chemical substances, which serve as specific stimuli, by calling forth new chemical and morphological arrangements of the atoms. Each specific contagium offers the same possibilities.

The supposition prevalent at Virchow's time, that the spermatozoon is entirely dissolved in the egg was not correct; but his view, that the spermatozoon carries chemical substances into the egg, which form the stimulus for its development, is perfectly correct; and likewise the analogy between the causation of the development of the egg by a spermatozoon and the causation of a pathological growth seems correct. I therefore

i Address delivered at the International Medical Congress at Budapest, 1909.

127

128 THE MECHANISTIC CONCEPTION OF LIFE

believe that it may be of interest to the medical profession to follow me in a brief survey of my experiments on artificial parthenogenesis and the causation of the development of the egg by a spermatozoon.

Cellular physiology has shown that tissues and organs develop only from cells through nuclear and cellular division. The conditions which cause cells to divide and to develop into new normal or pathological tissues have, since Virchow, been called formative stimuli. It is the task of modern biology to ascertain first what is the nature of these stimuli, and second, which change occurs in the cell in the process of formative stimulation. Virchow already emphasized the fact that the fertilization of the egg is the model of all phenomena of formative stimulation and that the spermatozoon may be considered as the formative stimulus in this case.

Pathologists have not yet succeeded in determining what the physico-chemical nature of the formative stimulus in the case of a tumor is, or what changes a cell undergoes in such a process. This task has, however, been accomplished to a high degree in the animal egg, and it may therefore interest the pathologist and the physician in general to become familiar with the essential features of the data thus obtained.

It is known that aside from a few exceptions the animal egg can only develop if a spermatozoon enters into it. If no spermatozoon enters, as a rule no segmentation of the egg takes place and it perishes after a comparatively short period of time. The questions which I tried to solve were the following: By which physico-chemical agencies does the spermatozoon cause the egg to divide and to develop into an embryo; and second, which changes does the egg undergo in this formative stimulation by a spermatozoon ? Or in other words, what is the mechanism by which the unfertilized egg is caused to segment and to develop ?

Two ways were open to find an answer to this question: first to try to cause the development of the unfertilized egg with extracts from sperm. I have spent a good deal of time in trying to succeed in this task, but met at first with only negative results for the reason that I used at first only extracts from the sperm of the same species of animals from which the eggs were taken. Only recently have I found that the extract of sperm is effective only if it is taken from a foreign species. We shall return to this curious fact later on and show that it has a bearing upon the problem of the immunity of our cells to the lysins of our body.

The second way which could lead to a decision of the question concerning the nature of formative stimulation lay in the direction of artificial parthenogenesis, i.e., of the causation of the development of the animal egg, not by extracts of sperm but directly by physico-chemical agencies. This method of procedure has a special advantage. Since in this case we know the nature of the agencies we employ, it is easier to get an insight into the mechanism by which they cause the development of the egg; while if we work with extracts of sperm we are in the dark as to the chemical character of the active substances.

We will begin with a description of the method of artificial parthenogenesis in the egg of the Californian sea-urchin, since here this method has been worked out most completely. It may be mentioned that in the eggs of many animals the effect of the entrance of the spermatozoon manifests itself almost instantly by a characteristic change, namely, the formation of the so-called membrane of fertilization. Briefly stated this process may possibly consist in the entrance of sea-water between the surface film and the protoplasm of the egg, whereby the former is lifted up from the protoplasm of the egg and separated from it by a more or less wide, clear space. Figs. 1

130 THE MECHANISTIC CONCEPTION OF LIFE

and 2 (page 7) show these changes in the sea-urchin egg. Fig. 1 represents the unfertilized egg, Fig. 2 shows the same egg after the entrance of the spermatozoon.

In 1905 I succeeded in finding a method by which it is possible to call forth the formation of a membrane of fertilization without apparent injury to the egg. This method consists in putting the eggs for about two minutes (at a temperature of 15°) into a mixture of 50 c.c. of sea-water+3 c.c. of an n/10 lower monobasic fatty acid, e.g., acetic, propionic, butyric, or valerianic acid. In this mixture no membrane formation takes place; if, however, the eggs are transferred into normal sea-water all the eggs form a perfect fertilization membrane. The experiments showed that this process of membrane formation is the essential condition which causes the egg to develop. In all these eggs in the course of the next hours after the membrane formation those changes begin which lead to a cell-division. If the temperature is very low not only cell-divisions begin but the egg may develop into a swimming larva; it reaches the so-called blastula stage. At room temperature, however, the artificial production of a membrane in the egg by fatty acid only calls forth a nuclear and possibly a cell-division; after this the egg slowly begins to disintegrate.

We therefore see that the artificial membrane formation by a fatty acid induces the developmental process, but that at ordinary temperature the latter does not go far. In order to cause a complete development, a second influence is needed, as we shall see later.

Before we describe this second influence, another question has to be settled, namely, how we know that the membrane formation and not any other action of the acid, e.g., a catalytic, is the formative stimulus in this case. The answer is, that if we apply the acid but prevent the changes leading to a membrane formation, divisions of the nucleus and of the cell do not occur. On the other hand, we shall see later on that we can

call forth the membrane formation not alone by fatty acids but by a number of different agencies and that all these means act as formative stimuli.

The causation of the membrane formation by a fatty acid starts, therefore, the development in the sea-urchin egg, but this development is abnormal and the egg is sickly and perishes the more rapidly the higher the temperature. The question arises, how can we inhibit this sickliness and grant a normal development to the egg?

I found that two different means are at our disposal for this purpose. The one which never fails consists in putting the eggs about twenty minutes after the artificial membrane formation into hypertonic sea-water (or any other hypertonic solution, e.g., sugar solution), i.e., into sea-water or any other solution the osmotic pressure of which has been rendered 50 per cent higher than that of the sea-water. In this solution the eggs remain from twenty to sixty minutes—according to the temperature and the concentration of hydroxyl-ions in the solution. If after this time the eggs are transferred into normal sea-water they develop at room temperature in a way similar to the eggs which are fertilized by sperm. 1

The second method of causing the eggs to develop normally at room temperature after the artificial causation of the membrane formation consists in putting these eggs for three hours in sea-water free from oxygen or into sea-water to which a trace of KCN has been added. After the eggs are transferred into normal sea-water they develop often but not always. This method is, therefore, not quite as reliable as the other method mentioned previously.

We see, therefore, that the formative stimulus in the artificial activation of the egg of the sea-urchin consists of two phases,

1 The larvae originating from eggs fertilized by sperm live no longer than those originating from eggs which develop parthenogenetically, if the larvae are not fed. The feeding of these larvae is a tedious process and for this reason I have not undertaken the task. Delage has, however, raised two such larvae until they were sexually mature.

132 THE MECHANISTIC CONCEPTION OF LIFE

namely, first the artificial causation of the membrane formation and second the subsequent short treatment of the egg with a hypertonic solution; (or a longer treatment with an isotonic solution free from oxygen or containing KCN) .

We may add that these observations do not hold good for the sea-urchin egg only. Similar observations were made on the eggs of annelids (Polynoe) and of star-fish (Asterind). In Polynoe and star-fish the artificial membrane production is often sufficient to allow the eggs to develop into larvae. But the number of eggs which reach the larval stage and the type of segmentation is improved if the eggs are treated subsequently with one of the above-mentioned methods, as R. Lillie found for Asterias and I for Polynoe. The experiments on annelids and star-fish, therefore, confirm the fact, that the calling forth of the membrane is the essential feature in formative stimulation and that the subsequent treatment of the eggs with a hyper-tonic solution (or an isotonic solution free from oxygen) has merely a corrective effect; it probably counteracts a secondary detrimental effect connected with the membrane formation.

Ill

We will now try to gain some insight into the mechanism of these two agencies. How can the fatty acid cause the formation of a membrane? In order to get an answer to this question we must find out whether there are other agencies which act like fatty acids. It was noticed that all the agencies which cause cytolysis also cause membrane formation, namely, first the specifically cytolytic agencies like saponin, solanin, digitalin, bile salts, and soaps. Experiments with these agencies, especially with saponin, solanin, and digitalin, yielded a curious result. If the unfertilized eggs are put into a weak solution of saponin in sea-water we notice as the first effect on the eggs the formation of a fertilization membrane. Then ensues a pause of sometimes several minutes and after this pause a sudden

NATURE OF FORMATIVE STIMULATION

133

cytolysis of the whole egg follows. If we take the eggs during this pause (i.e., after the membrane is formed, but before the

FIG. 39

FIG. 40

FIG. 41

FIG. 42

FIG. 43

FIGS. 39-43.—Membrane formation and subsequent cytolysis of the sea-urchin egg in a weak solution of saponin in sea-water. Camera drawings from nature. Fig. 39, unfertilized egg at the beginning of the experiment. In this condition the egg was put into sea-water containing a small amount of saponin. The following figures show the changes it underwent in this solution. Fig. 40, membrane formation under the influence of saponin, eight minutes later. If the egg is taken out of the saponin-sea-water in this stage, washed and put into a hypertonic solution for about one half-hour, it will develop into a larva, after it is put back into normal sea-water. If, however, it is left in the saponin solution it undergoes the rapid cytolysis represented in Figs. 41, 42, and 43. In the above drawing of the egg, cytolysis began at G, Fig. 41, five minutes after the membrane formation. The stages represented in Figs. 42 and 43 were reached a few minutes later.

cytolysis of the egg occurs) out of the sea-water containing saponin and free them from all traces of saponin by washing them repeatedly with sea-water, they behave as if the

134 THE MECHANISTIC CONCEPTION OF LIFE

membrane formation had been called forth by a fatty acid. Such eggs begin to develop, but do not go beyond the first nuclear division at room temperature. If, however, the eggs are treated for half an hour with hypertonic sea-water they can develop to normal plutei, i.e., larvae with skeletons.

The second group of cytolytic agencies is formed by the specific fat solving hydrocarbons like amylen, benzol, toluol, and in a much lesser degree chloroform, etc. Hertwig had already observed that chloroform calls forth the membrane formation and Herbst had seen the same effect brought about by benzol and toluol. But these substances act so violently that the membrane formation is followed almost immediately by a cytolysis of the egg, and for this reason these authors could not notice that the membrane formation was followed by the development of the egg. I have, however, been able to convince myself that if amylen or benzol are allowed to act only for one moment and if the eggs are then quickly transferred into normal sea-water a membrane formation can be produced in some of them without subsequent cytolysis. If such eggs were afterward treated with hypertonic sea-water they developed into larvae.

A further group of cytolytic agencies is ether or alcohols. Cytolysis of the eggs by these agencies is also preceded by a membrane formation. If the eggs are taken out from such solutions immediately after membrane formation they can be saved from cytolytic destruction (Figs. 44-47).

Bases can also call forth membrane formation, but their action is rather slow and depends on the presence of free oxygen. One gains the impression as if the alkali acted in this case only as an accelerator of oxidations and as if a product of oxidation was the proper cause for the membrane formation. The membrane formation usually becomes manifest only if one treats the eggs afterward for a short time with a hypertonic solution; such a treatment causing them to develop into larvae.

NATURE OF FORMATIVE STIMULATION

135

An increase in temperature can also produce a cytolytic effect. I have observed that at 34° or 35° the eggs of Strongylo-centrotus purpuratus form often but not always a membrane

Fio. 44

FIG. 45

FIG. 46

FIG. 47

FIGS. 44-47.—Membrane formation and subsequent cytolysis of the egg under the influence of the addition of a minute quantity of salicylaldehyde to sea-water. Camera drawings. Fig. 44, unfertilized egg at the beginning of the experiment. Fig. 45, membrane formation in the salicylaldehyde-sea-water. Fig. 46, beginning of the cytolysis. Fig. 47, cytolysis completed. The cytolyzed egg has in this case an entirely different appearance from that of an egg cytolyzed in saponin.

of fertilization. Such a temperature kills these eggs almost instantly and consequently they are no longer able to develop after this treatment. The eggs of the star-fish Asterias for-besii are, however, not killed so rapidly after the membrane

136 THE MECHANISTIC CONCEPTION OF LIFE

formation, and R. Lillie was able to show that such eggs can develop into larvae if the membrane formation is called forth by raising the temperature. Von Knaffl has shown that if a high temperature acts for some time on these eggs they perish by cytolysis and are transformed into "ghosts."

We have been able to convince ourselves, therefore, that all the agencies which cause cytolysis also call forth the membrane formation; while the agencies which do not call forth cytolysis do not cause a membrane formation. We find in a$clition that the cytolytic power of these agencies runs parallel with their power of causing membrane formation.

From this we draw the inference that the membrane^orma-tion depends upon the cytolysis of the surface layer of the egg. We shall see later on that we must discriminate between a cortical layer and the core of the unfertilized egg. This superficial cortical layer of the egg is very thin. The essential feature of the developmental stimulus consists in the cytolysis of this cortical layer of the egg and this cytolysis is caused by the spermatozoon.

We have already mentioned that the cytolysis which underlies the membrane formation causes the development of the egg, but that the egg is as a rule sickly after this membrane formation. To fix our ideas provisionally we assume that through the membrane formation a substance is formed which must be abolished or destroyed before the egg is able to develop normally. If we permit the egg to begin its development while it still contains this hypothetical detrimental substance in a sufficient quantity it is sickly and dies prematurely. The destruction of this hypothetical substance can be brought about in two ways: first, by treating the egg for a short time with a hypertonic solution. When I discovered this fact there was no analogue known which allowed us to draw an inference concerning the mode of action of a hypertonic solution. I succeeded

in showing that such a solution is only effective in artificial parthenogenesis if it contains free oxygen. If the hypertonic solution is deprived of oxygen it remains without any effect. It remains also inefficient if a trace of KCN is added to it. Since KCN inhibits the oxidations in the cell it is obvious that the hypertonic solution only acts by a modification of the process of oxidation.

The second method of saving the life of the egg consists in putting it after the membrane formation for about three hours into sea-water which is practically free from oxygen, or contains a trace of KCN whereby the oxidations in the egg are suppressed. If these eggs are transferred after this time into normal sea-water containing free oxygen they are often able to develop normally. 1

Thus far we have dealt only with artificial parthenogenesis. We are now about to take up the causation of development by a spermatozoon. Is the formative stimulation of the egg by spermatozoon of the same character as that in artificial parthenogenesis? This question can be answered in the affirmative. It is possible to show that the spermatozoon also calls forth the normal development of the egg by at least two substances and that one of these substances acts like butyric acid or saponin in artificial parthenogenesis, inasmuch as it causes the cytolysis of the thin cortical layer of the egg; while the second substance has an effect similar to that of the hypertonic solution. The correctness for this view is proved by the fact that I succeeded in separating these two effects of the spermatozoon.

If we wish to bring about a separation of these two agencies in the spermatozoon we cannot use the spermatozoa of the same species of sea-urchins from which the egg is taken; for in this case the spermatozoon penetrates at once into the

* A further discussion of the facts in this chapter is contained in the next paper on " The Prevention of the Death of the Egg through the Act of Fertilization."

138 THE MECHANISTIC CONCEPTION OF LIFE

protoplasm of the egg as soon as it comes in contact with it. In this way almost simultaneously both substances of the spermatozoon become effective, the cytolytic substance, which causes the membrane formation, and the " corrective "substance. The experiments, however, result differently when we add the spermatozoa of a foreign species, e.g., star-fish, to the egg of the sea-urchin. Under ordinary conditions sperm of the star-fish cannot cause the egg of the sea-urchin to develop; it becomes effective, however, in sea-water which has been rendered a little more alkaline through the addition of some NaHO. If 0.6 c.c. n/10 NaHO is added to 50 c.c. of sea-water all the eggs of the sea-urchin form fertilization membranes in such a mixture if only a trace of living sperm of a star-fish (Asterias ochracea) is added. It takes, however, some time, mostly from ten to fifty minutes, until the living star-fish sperm brings about this effect; while after the addition of sea-urchin sperm this result is obtained in one minute.

If the sea-urchin eggs, all of which have formed membranes upon the addition of living star-fish sperm, are put back into normal sea-water and if we watch their further fate, we soon notice that we are dealing with two groups of eggs. The one group acts as if only one of the two agencies, namely, the cytolytic one, had taken effect. These eggs show at room temperature only the beginning of nuclear division and then disintegrate, while at a lower temperature they may develop a little farther. If we treat them, however, after the membrane formation by star-fish sperm for from thirty to fifty minutes with a hypertonic solution they all develop at room temperature mostly into normal larvae. The other eggs develop without any subsequent treatment with a hypertonic solution into normal larvae.

What causes this difference in the behavior of both groups of eggs ? A histological examination of these eggs decides this point. My assistant, Mr. Elder, found that a spermatozoon

had entered into those eggs which develop after the addition of star-fish sperm without subsequent treatment with a hyper-tonic solution into normal larvae; while the eggs which behave as if only an artificial membrane formation had taken place do not contain any spermatozoon.

This behavior of the eggs under the influence of foreign sperm is comprehensible under the assumption that the spermatozoon also causes the development of the egg through two agencies; one of these agencies is a cytolytic substance, a so-called lysin. This substance is probably situated at the surface of the spermatozoon. This lysin only calls forth the membrane formation and it acts like the butyric acid in the method of artificial parthenogenesis. The second agency seems to be more in the interior of the spermatozoon and it exercises an influence similar to the short treatment of the egg with a hypertonic solution. A normal development will result only if the spermatozoon enters the egg since in this case only both agencies, the cytolytic and the corrective, get into the egg. We have already mentioned that foreign spermatozoa penetrate only slowly into the egg. If a spermatozoon penetrates partially through the surface of the egg without entirely penetrating into the protoplasm, enough of the lysin sticking to the surface of the spermatozoon can be dissolved to cause the cytolysis of the surface film of the egg which gives rise to the membrane formation. Such eggs receive from the spermatozoon only the lysin, and they act therefore as if only the membrane formation had been called forth in them by the treatment with butyric acid, since in the formation of the membrane the spermatozoon is thrown out.

In the eggs of Strongylocentrotus purpuratus the membrane formation can in general only be called forth by living star-fish sperm while the extract of dead star-fish sperm in the same concentration remains without effect. This fact is of importance to disprove the possibility that the membrane formation

140 THE MECHANISTIC CONCEPTION OF LIFE

in these experiments was caused by star-fish blood which was added with the sperm.

That it is possible to separate a lysin from the sperm can be proved for the eggs of another species of sea-urchins, namely, Strongylocentrotus frandscanus, the eggs of which are very sensitive to lysins. In these eggs it is possible to call forth the membrane formation with a very dilute watery extract of the sperm of star-fish which was killed by heating it to 60° C., or more. Such eggs can be caused to develop into plutei by treating them after the membrane formation for a short time with hypertonic sea-water. In the place of star-fish sperm the sperm of other foreign species can be used. I have called forth the membrane formation in the sea-urchin egg with the living sperm of sharks or even roosters. Such eggs act as if only the membrane formation with the aid of butyric acid had been caused. At room temperature they begin to develop but they are sickly and soon perish. If, however, they are treated afterward with a hypertonic solution they develop into normal plutei. In this case only the lysin entered the egg but not the spermatozoon. It was, therefore, necessary to treat such eggs subsequently with hypertonic sea-water in order to cause them to undergo normal development at room temperature.

The idea that a lysin contained in the spermatozoon is the formative stimulus which causes the egg to develop can be tested experimentally. We know that blood contains lysins which destroy the blood corpuscles of foreign species, while it does not destroy the cells of the same species. If the idea is correct that the spermatozoon acts upon the egg through a lysin which calls forth the membrane formation it should be possible to call forth the membrane formation in the unfertilized egg of the sea-urchin by foreign blood and such is the case. I was able to show three years ago that the blood of certain

worms, namely Sipunculides, can call forth the membrane formation in the sea-urchin egg even if it is diluted a hundred times or more with sea-water. This effect is not produced in the eggs of every female sea-urchin but of only about 20 per cent of the females. I think the difference is caused by differences in the permeability of the eggs for lysins; and the degree of permeability seems to vary slightly for the eggs of different females.

Instead of wasting time on an examination of the effects of the blood of invertebrates 1 I examined the effects of the blood serum of warm-blooded animals. I succeeded in causing membrane formation in the sea-urchin egg (purpuratus) with the blood serum of cattle, sheep, pigs, and rabbits; and such eggs behaved like the eggs which had been treated with the living sperm of roosters or with butyric acid. They began to develop, but they became sickly at room temperature and soon disintegrated. If, however, they were treated after the membrane formation for a short time with a hypertonic solution they developed at room temperature. The blood, therefore, contains the lysin, but not the second substance necessary for the full development. It is, therefore, necessary to substitute for the action of the latter the treatment with a hypertonic solution if we wish to call forth a normal development of the egg treated with serum.

The lysin of the blood is like that of the spermatozoon relatively resistant to heat. The blood does not lose its power to call forth membrane formation by heating it for some time to 60° or 65° C. 2 It is curious that SrCl 2 and Babl 2 increase the membrane-forming power of the blood.

Not only blood but also the extracts of the organs of foreign

1 Since this was written the blood and the extracts of organs of a number of invertebrates were used successfully to produce the membrane formation and development of the egg of the sea-urchin.

2 The substance which causes membrane formation can be precipitated with acetone (Loeb, Pfliigers Archiv, CXXIV, 37, 1908).

142 THE MECHANISTIC CONCEPTION OF LIFE

species call forth membrane formation in the sea-urchin egg. An extract of the coecum of the star-fish was very effective.

We have already mentioned the fact that the extract of dead sperm of foreign species, e.g., of star-fish, certain mollusks, certain worms, sharks, fowl, causes membrane formation in the eggs of franciscanus. Experiments with the extract of dead sperm of their own species on the egg of franciscanus or purpura-tus fail; and the same is true for extracts from the tissues of these species. 1 What causes this difference in the action of the lysins from their own and a foreign species? We know that the lysins of our own blood do not hurt our cells while they hurt the cells of foreign species. There exists, therefore, an immunity of the eggs as well as of the rest of the cells against the lysins of their own blood or tissues.

Our experiments throw a light upon the nature of this immunity. If the lysins contained in our blood do not injure our cells it can only be due to one of two facts: The lysins of our own blood can either not diffuse into our cells, while they can diffuse into the cells of foreign forms, or the cells contain antibodies against the lysins of their own body, but not against those of foreign species. As far as the lysins of the blood are concerned we cannot decide between the two possibilities. We can, however, reach a decision for the lysins of the spermatozoa. The extract from the dead sperm of the sea-urchin is ineffective for the eggs of the sea-urchin solely for the reason that it cannot diffuse into the sea-urchin egg. For if the sea-urchin lysin is carried by the living sea-urchin spermatozoon (which acts as a motor for the lysin) into the sea-urchin egg, the lysin is very active and probably more active than the lysin of foreign species. If the sea-urchin egg contained an antibody against the lysin of the sea-urchin sperm, the sea-urchin sperm should not be able to call forth membrane formation when it enters the sea-urchin egg.

1 If eggs were sensitized with SrCl 2 they could be caused to develop by extracts from the coecum of the sea-urchin, though this was true only exceptionally.

We now understand the paradoxical fact, that by foreign sperm we can cause membrane formation and development of the sea-urchin egg in two different ways: namely, first by the living sperm and second by the extract from the dead sperm; while the sperm of the same species can only cause the eggs to develop when it is alive. We now understand the fact alluded to at the beginning of this chapter that my first experiments to cause the development of the egg with extract of sperm did not succeed, since I took it for granted that it was necessary to use the extract of the sperm of the same species from which the eggs were taken. The lysins in this case were not able to diffuse into the egg.

The further unraveling of the nature of the immunity of the egg-cell against the dissolved lysins of the blood and the tissues of the same species depends upon the explanation of the fact that the lysins of a species cannot diffuse into the egg of the same species. It would be of interest if the same principle formed for the immunity of the egg-cell would hold also for the immunity of the body-cells against the lysins in the blood of their own species.

We may, therefore, say that the substance to which the sperm owes its fertilizing power is a lysin and we may express the suspicion that the lysins which we have thus far known only as protective agencies against bacteria play a great physiological role in the mechanism of life phenomena. We may call our theory of the developmental action of the spermatozoon the lysin theory; thereby designating that the impulse for the development of the egg is given by a lysin contained in the spermatozoon. In artificial parthenogenesis we substitute for the natural lysin a cytolytic substance. Aside from the lysin action the normal development demands, as a rule (but not always), a second corrective influence which in artificial parthenogenesis may be given by a hypertonic solution.

VII

The experiments on the artificial parthenogenesis of other forms of animals show that the eggs of different animals possess a varying tendency for parthenogenetic development. There are eggs which can easily be induced to develop, so easily in fact, that the experimenter cannot always be sure whether he has caused the development by a substance applied by him or whether some accidental condition of the experiment was responsible. The eggs of the silkworm, of the star-fish, and of certain worms belong to this class. In working with starfish eggs we can observe that occasionally a few of them develop in normal sea-water, apparently without any demonstrable cause, into swimming larvae. The eggs of the Calif ornian sea-urchin Strongylocentrotus purpuratus, on the other hand, show not the slightest tendency to segment parthenogenetically; only the above-mentioned very specific and quantitative method causes them to develop. For this reason I selected these eggs for the investigation of the nature of the experimental stimulus, since I could always be sure that the same stimulus gave the same results; while, e.g., in the star-fish eggs we can never be perfectly certain that some internal condition in the egg or some overlooked unimportant secondary condition in the experiment may not have caused the development. Although eggs with such a strong tendency for spontaneous development as the star-fish eggs are not the best material for the study of the nature of the developmental stimulus yet we have to answer the question how it happens that some eggs have a greater tendency for parthenogenetic development than others.

Mathews has observed that by gently shaking the star-fish eggs the number of eggs which develop " spontaneously" can be increased. I made a similar observation in the eggs of Amphitrite, an annelid. In the eggs of the sea-urchin nobody has ever been able to obtain such a result. I am inclined to believe that if a sea-urchin should be found, the eggs of which

possess a greater tendency to develop spontaneously, it might also be found that the number of eggs developing spontaneously might be increased by agitation.

I tried whether it is possible to cause the eggs to cytolyze also mechanically. If we exercise only a slight pressure with a finger upon the ovary of a star-fish we find that many of the eggs which afterward leave the ovary are cytolyzed. This cytolysis is not caused by a bursting of the egg membrane; on the contrary, in this case the cytolysis of the egg is, as usual, preceded by the formation of a membrane of fertilization and this membrane remains intact in the star-fish egg which is caused to cytolyze by mechanical pressure. In the sea-urchin egg, however, it is impossible to produce cytolysis by a slight pressure.

The eggs of the star-fish which develop spontaneously first form a membrane. Shaking causes a development of the starfish eggs only if the shaking first leads to a membrane formation. The greater tendency of the star-fish to develop spontaneously is, therefore, due to the greater ease with which cytolysis can be produced in this egg.

How can mere agitation or pressure call forth membrane formation or cytolysis ? It seems to me that this fact is most easily understood under the assumption, first suggested by Butschli, that the cytoplasm is an emulsion. It would then follow that the membrane formation as well as the cytolysis depends upon the destruction of this emulsion. We know that different emulsions have a different degree of durability. The eggs which upon gentle pressure undergo cytolysis have an emulsion with a lesser degree of durability than the eggs in which pressure has no such effect. Let us assume that membrane formation as well as cytolysis depends upon the destruction of an emulsion; in this case the membrane formation depends upon the destruction of the emulsion in the cortical layer of the egg only. The lysin of the egg destroys only the emulsion in

146 THE MECHANISTIC CONCEPTION OF LIFE

the cortical layer of the egg and thereby causes development. The greater tendency of the eggs of certain animals for spontaneous parthenogenetic development thus depends upon the relatively small degree of durability of the emulsion which constitutes the cortical layer of the egg. But it should be stated that this hypothesis is not essential for the lysin theory of the activation of the egg.

VIII

The assumption that the membrane formation is only a superficial cytolysis of the egg presupposes that the cortical layer of the egg is different from the rest of the cytoplasm. Biitschli had already reached such a conclusion on the basis of histological observations. I am inclined to accept this view on the basis of my observations on the action of cytolytic agencies on the unfertilized egg. The action of these agencies on the unfertilized egg always occurs in two stages which are often separated from each other by a considerable interval of time. The first stage is the cytolysis of the superficial layer; the second stage is the cytolysis of the rest of the egg. This is most obvious in experiments with weak solutions of saponin or solanin in sea-water. In this case first a membrane formation occurs, then a pause ensues, often of several minutes, and then cytolysis of the whole egg follows. If instead of saponin benzol is used a pause can also be observed between membrane formation and cytolysis of the whole egg but this pause is short, often only a fraction of a second, or at the best a few seconds.

It can also be shown directly that there is a qualitative difference between the cortical layer of the protoplasm and the rest. If for the artificial membrane formation the lower fatty acids, from the formic to the capronic acid, are used, cytolysis of the cortical layer only is observed, i.e., membrane formation follows but no cytolysis of the whole egg. If, however, the higher fatty acids of the same series from the heptylic acid on

and upward are applied the membrane formation is always followed after a short pause by a cytolysis of the whole egg.

The lysins contained in the blood and the spermatozoon act according to my present experience only upon the cortical layer of the cytoplasm but not on the rest of the egg. We get a membrane formation and development but not a cytolysis of the whole egg.

If we go back to the idea of Biitschli that protoplasm has the structure of an emulsion we are led to the view that the emulsion of the cortical layer of the egg differs from that of the rest of the egg. There are certain cytolytic agencies which destroy only the cortical layer; while all general cytolytic agencies destroy the cortical layer as well as the rest of the egg.

How can the cytolysis of the cortical layer of the egg lead to a membrane formation? Von Knaffl has expressed the following view on this point: "Protoplasm is rich in lipoids, it is probably mainly an emulsion of these and of proteins. Every physical and chemical agency which is able to liquefy lipoids calls forth a cytolysis of the egg. The protein of the egg can only swell or be dissolved if the state of the lipoids is altered by chemical or physical means. The mechanism of cytolysis consists in the liquefaction of the lipoids and the subsequent swelling or liquefaction of proteins by absorption

of water This confirms Loeb's view that membrane

formation is caused by the liquefaction of lipoids."

We can accept this with a slight modification which refers to the nature of the emulsion. An emulsion requires not only two substances or phases as von Knaffl assumes but in addition a third substance. The third substance serves the purpose of making the emulsion more durable (Lord Rayleigh's theory). The droplets of the emulsion are surrounded by a thin layer of a substance which lessens the surface tension between the

148 THE MECHANISTIC CONCEPTION OF LIFE

droplet and the second phase of the emulsion. I assume that only this stabilizing substance consists of lipoids, especially cholesterin. The two other phases which constitute the emulsion need not be lipoids. To fix our ideas provisionally we may assume that these phases are first protein with little water and second water with little protein. The existence of these two phases has been established by Hardy. The emulsion at the surface of the egg consists, according to this view, of a system of protein droplets poor in water surrounded by a stabilizing film of a lipoid (cholesterin or lecithin). If the sea-urchin egg is treated with a lipoid solvent like benzol the stabilizing film of cholesterin is dissolved and the protein droplet can absorb water. If we use saponin the film is destroyed by the precipitation of cholesterin by saponin. The absorption of water leads to the lifting up of the surface film which surrounds the egg. 1

We wish to add a few remarks concerning the nature of this surface film, although this does not belong to our problem. According to Overton and Koeppe the surface film of cells consists of lipoids, and according to Koeppe cytolysis is determined by the solution or tearing of this film. This view is not tenable, since the surface film which is lifted off in the form of the fertilization membrane does not consist of a lipoid but of protein. This is suggested by the fact that this membrane is absolutely insoluble in any lipoid solvent. Moreover, this membrane remains perfectly intact when the egg is transformed into a " ghost."

Since we can cause the formation of a membrane of fertilization in the star-fish egg by gentle agitation or mere pressure,

1 We have assumed here that the fertilization membrane is preformed in the unfertilized egg and lifted up in consequence of the cytolysis of the layer beneath it. As I stated in my book on Die chemische Entwicklungserregung des tierischen Eies, it is also possible that the fertilization membrane is a membrane of precipitation formed through the reaction of a constituent of the liquefied cortical layer with a constituent of the sea-water (Ca?). It is immaterial for the problem discussed in this paper which view we adopt temporarily.

this membrane is apparently preformed in the unfertilized egg; and if this be true the process of membrane formation must consist in the lifting up of a preformed film from the underlying cytoplasm through the entrance of sea-water between this film and the cytoplasm. In this process the surface film undergoes a change, since the spermatozoon can enter into the egg before but not after the membrane formation. That merely a change in the nature of the surface film prevents the entrance of a spermatozoon into the egg after the membrane formation can be proved by the fact that if we tear the membrane mechanically a spermatozoon can penetrate into the egg. This proves that the surface film, even if it is already preformed in the unfertilized egg, has different qualities or a different structure when it is in close contact with the cytoplasm than when it is lifted off from the cytoplasm by a layer of sea-water.

We have assumed that the membrane formation is determined by the action of a lysin or cytolytic agency upon the cortical layer of the egg, whereby a protein in this layer absorbs sea-water, and is thereby dissolved. This assumption leads to two consequences: first it must be possible to show that the fertilization membrane is permeable for sea-water and crystalloid substances but impermeable for colloids. The correctness of this view can be proved. If we add to the sea-water, containing eggs with a fertilization membrane, a certain quantity of dissolved white of egg, tannin, or blood serum, the membrane collapses and closes tight around the cytoplasm. The reason is that almost all the liquid which existed between the membrane and the cytoplasm diffused into the surrounding sea-water. If the eggs are brought back into normal sea-water (free from protein) it diffuses again into the space between the membrane and the cytoplasm, and the fertilization membrane resumes its former distance from the cytoplasm and its round shape. The membrane is, therefore, impermeable for the colloids dissolved in sea-water.

150 THE MECHANISTIC CONCEPTION OF LIFE

If salts are added to the sea-water or if it is diluted by the addition of distilled water the tension and the diameter of the membrane do not change. This proves that the membrane is permeable for salts, but not for colloids, and that the lifting up of the fertilization membrane is determined by the swelling and subsequent liquefaction of a colloid. This dissolved colloid exercises an osmotic or colloidal pressure and sea-water must diffuse from the outside under the fertilization membrane of the egg until the tension of this membrane equals the osmotic or colloidal pressure of the dissolved colloid. This explains also why it is that the fertilization membrane as a rule assumes a spherical shape.

We now can understand why not in all cases of fertilization a distinct fertilization membrane is formed. This may be due to the fact that the degree of swelling of the colloid of the cortical layer varies under different conditions.

We now possess a pretty complete picture of what happens to the egg in the case of "formative stimulation," i.e., when it is caused to develop. Through a lysin or some other cytolytic agency a certain substance of the cortical layer, presumably a lipoid, is dissolved or precipitated, whereby a protein substance of that layer is able to absorb water and swell. Formerly it was thought that the spermatozoon caused the development of the egg by carrying a ferment or enzyme into it and that this ferment set the mechanism of development into action. Others expressed the opinion that the entrance of the sperm nucleus or of a centrosome was responsible for the development. We see, however, that it suffices to call forth the artificial membrane formation in the unfertilized sea-urchin egg, in order to observe after two or three hours the formation of normal astrospheres or spindles. This disproves the suggestion that the fusion of egg and sperm nucleus is essential for the development of the egg. 1

1 The fusion of the nuclei is of course of importance for the transmission of paternal qualities.

The ferment theory of the activation of the egg by the spermatozoon is also wrong. If it were correct the velocity of development should be accelerated if not doubled if two spermatozoa enter the egg instead of one; or if fertilization by sperm and artificial parthenogenesis are superposed in the same egg. But this is not the case. In neither case is a shortening of the time which elapses between two successive periods of segmentation observed. 1

The further development will be connected with the question how can the cytolysis of the cortical layer of the egg lead to its development? I may mention the possibility that the cytolysis of the cortical layer facilitates the diffusion of oxygen or of HO ions (bases) or other substances, necessary for the development, into the egg.

XII

Let us summarize our results concerning the activation or formative stimulation of the egg. For the normal development at least two agencies are required: the one is the cytolysis of the thin cortical layer of the egg. Any agency which causes this cytolysis (without causing the cytolysis of the rest of the egg) induces development. The spermatozoon as well as the blood and the tissues contain a substance (lysin) which causes only cytolysis of the cortical layer. The lower fatty acids, from formic to capronic, cause only the cytolysis of the cortical layer. Since most cytolytic agencies cause a cytolysis of the whole egg they can be used only if the eggs are withdrawn from their influence after the cortical layer is destroyed but before the rest of the egg has undergone destruction.

Cytolysis of the cortical layer leads often but not always to the formation of the membrane of fertilization.

Since all cytolytic substances are lipoid soluble (or destroy lipoids) it is probable, but not proved, that the formative

1 Another reason is that the velocity of segmentation is purely determined by the egg, no matter what is the nature of the spermatozoon.

152 THE MECHANISTIC CONCEPTION OF LIFE

stimulus in the activation of the egg consists in a liquefaction or precipitation or some other modification of the lipoids of the cortical layer of the egg which results in an imbibition or solution of a colloidal substance of the cortical layer. If the cytoplasm has the structure of an emulsion it is possible that lipoids form the stabilizing envelope for the droplets which, according to Lord Rayleigh, is necessary for the durability of the emulsion. The cytolysis of the cortical layer of the egg causes its development, but this development is often abnormal and comes prematurely to a standstill. In order to induce a more normal type of development a second agency is often required, the mode of action of which is not yet so clearly understood as that of the cytolytic agency, namely, a short treatment of the egg with a hypertonic solution containing oxygen or a longer inhibition of the development of the egg in normal sea-water which is free from oxygen. The spermatozoon carries in addition to the lysin a second substance into the egg, which acts similarly to the hypertonic solution in our method of artificial parthenogenesis.

VIII. THE PREVENTION OF THE DEATH OF THE EGG THROUGH THE ACT OF FERTILIZATION

THE PREVENTION OF THE DEATH OF THE EGG THROUGH THE ACT OF FERTILIZATION 1

The unfertilized egg dies in a comparatively short time, while the act of fertilization gives rise to a series of generations which, theoretically at least, is of infinite duration. The act of fertilization is, therefore, a life-saving act for the egg. The question arises, in which way can the spermatozoon save the life of the egg ?

If the ovaries of a star-fish are put into sea-water the eggs are shed. They are generally immature, and in this condition they cannot be fertilized, either by spermatozoa or by chemical means. If they remain, however, for some time in sea-water, all or a number of them gradually become mature; that is to say, their nuclear mass is diminished by the extrusion of the two so-called polar bodies. If immediately after the extrusion of the polar bodies sperm is added, the eggs develop. They can at that period likewise be caused to develop by certain chemical and physical agencies.

Ten years ago I made the following observations. If the eggs are not caused to develop by sperm or by physico-chemical agencies, they perish very rapidly. At summer temperature they may die in from four to six hours. The death of the egg manifests itself morphologically in a darkening and blackening of the otherwise clear egg. I found that the death of the egg can be prevented by withdrawing the oxygen, or by diminishing the rate of oxidations in the egg through the addition of a trace of potassium cyanide. The life-saving action of lack of

1 Reprinted from the Harvey Lectures, 1911, by courtesy of Messrs. J. B. Lippincott & Co.

155

156 THE MECHANISTIC CONCEPTION OF LIFE

oxygen can be shown in various ways. The maturation of the egg itself depends upon oxidations. If the oxygen is withheld from the immature eggs, or if the oxidations in the immature eggs are inhibited by potassium cyanide, the process of maturation does not take place. Maturation is, therefore, also a function of oxidations. The eggs of a female, which were unripe, were divided into two groups: the one group remained in sea-water in contact with oxygen; the other was put into sea-water whose oxygen had been removed by a current of hydrogen. The eggs of the second group remained alive; the eggs of the first group perished in a few hours.

It is not even necessary to drive out the air by hydrogen; the life of the unfertilized eggs can also be preserved by putting large masses of them into a narrow glass tube which is sealed at the bottom. The eggs sink to the bottom of the tube, and those which are lying near the bottom receive no oxygen, since the oxygen which diffuses from the air through the sea-water is consumed by the uppermost layer of the eggs. On account of this lack of oxygen the eggs at the bottom of the tube do not mature and do not perish; hence by withholding oxygen from the immature eggs their maturation and death are prevented.

If the oxygen is withheld from the eggs immediately after they become mature their life is also saved. A. P. Mathews has repeated this experiment and obtained the same results. This proves that the death of the mature but unfertilized egg is determined by oxidations. If these oxidations are inhibited death does not occur. When these experiments were first published they caused opposition. This opposition was based on the fact that potassium cyanide was used in part of the experiments. The objection was raised that the potassium cyanide in these experiments acted only by preventing the development of bacteria. The authors, however, who raised this objection, overlooked the fact that lack of oxygen acts in exactly the same way as the addition of potassium cyanide,

and that it is entirely immaterial how lack of oxygen is produced, whether the oxygen is driven out by carefully purified hydrogen or whether the eggs are put together in a large heap, whereby only those lying on the surface of the heap receive sufficient oxygen.

It is, however, easy to show directly that the above-mentioned objection is incorrect. The eggs of the star-fish can easily be put into sterilized sea-water without bacterial infection. The following experiment was tried. The eggs of a star-fish were separated into three parts: one part was put aseptically into a series of flasks with sterilized sea-water; the second part was put into ordinary sea-water without asepsis; the third part was put into sea-water to which a large quantity of a putrid culture of bacteria had been added that had developed on the dead eggs of the star-fish. It was found that in all three cases the mature eggs died within the same period of time. The sterilization of the eggs of the first group was complete, as was shown by the fact that the eggs although dead preserved their form for two months, while the dead eggs in the normal sea-water were completely destroyed in a few days by the action of the bacteria.

It is, therefore, certain that the death of the star-fish eggs which are not fertilized is not caused by bacteria, but by the process of oxidation in the egg. If no spermatozoon enters the egg, or if the egg is not caused to develop by chemical treatment it perishes very rapidly. If, however, a spermatozoon enters the egg, the latter remains alive in spite of the fact that the entrance of the spermatozoon causes an acceleration of the oxidations in the egg. Warburg found for the eggs of the sea-urchin at Naples that fertilization raises the velocity of the process of oxidations to six times their original value, while Wasteneys and I found that fertilization caused an increase in the velocity of oxidations of Arbacia in Woods Hole to three or four times the rate found in the unfertilized eggs.

158 THE MECHANISTIC CONCEPTION OF LIFE

How can we explain the fact that fertilization saves the life of the egg ? Let us make the following preliminary assumption: The unfertilized egg contains a poison, or some faulty combination of conditions which, if oxidations take place, causes the death of the egg. In the unfertilized but mature egg oxidations take place. The spermatozoon carries into the egg among other substances something which protects the egg against the fatal effects of the oxidations, and allows them even to carry on oxidations at an increased rate without suffering. We might say that the mature but unfertilized egg is comparable to an anaerobic being for which oxidations are fatal, and that the spermatozoon transforms the egg into an aerobic organism.

If we compare the eggs of different animals, we find great differences hi regard to the above-mentioned conditions. The eggs of certain annelids (Polynoe) also perish rapidly if they become mature without being caused to develop, while the eggs of the sea-urchin remain alive for a longer period of time after they have become mature. The problem as to what determines this difference has not yet been investigated.

The analysis of the process of fertilization by the spermatozoon shows that we must discriminate between two kinds of effects, the hereditary effect and the activating or developmental effect. The experiments on artificial parthenogenesis make it very probable that the two groups of substances, the substances which determine the heredity of paternal characters and the substances which cause the egg to develop, are entirely different. In this paper we are concerned • only with the second group of substances, namely, those which cause the development of the egg.

The analysis of the causation of development of the egg by a spermatozoon has shown that the latter acts by carrying at least two substances or groups of substances into the egg.

The first of these substances causes the formation of a membrane; the second serves the purpose of rendering the egg immune against the fatal action of oxidations.

I have shown in a number of papers that the essential feature in the causation of the development of the egg ic a

FIG. 50

FIGS. 48-50.—Disintegration of the sea-urchin egg after the membrane formation with butyric acid or with foreign serum or with the extract of sperm or of foreign cells; if the eggs are not treated after the membrane formation with a hypert9nic solution or a suppression of oxidations. A indicates the area where the disintegration begins.

modification of its surface, which in many cases leads to the formation of a membrane. If we cause membrane formation in an unfertilized sea-urchin egg by artificial means, it begins to develop, but very soon perishes; much more rapidly than if it is not exposed to any treatment. I was able to show that

160 THE MECHANISTIC CONCEPTION OF LIFE

this rapid death of the sea-urchin egg, after artificial membrane formation, can be prevented either by withdrawing the oxygen from the egg or by inhibiting the oxidations in the egg by the addition of a trace of potassium cyanide. The membrane formation, therefore, causes the rapid death of the egg through an acceleration of oxidations. Warburg has recently shown that the artificial membrane formation in the unfertilized sea-urchin egg causes the same increase in the rapidity of oxidations as the entrance of a spermatozoon.

If we wish to cause the unfertilized eggs to develop to the pluteus stage after the membrane formation, we have to subject them to a second treatment. This may consist in putting them about fifteen minutes after the membrane formation into a hypertonic solution of a certain osmotic pressure (for instance, 50 c.c. of sea-water+8 c.c. n/2| NaCl) for one-half to one hour. If, after this time, they are put back into normal sea-water they no longer perish, but develop into normal larvae. I ventured the hypothesis that the artificial membrane formation causes a rapid increase of the oxidations in the egg and in this way causes it to develop, but that these oxidations lead to the rapid decay of the eggs at room temperature for the reason that the egg contains a toxic substance, or a toxic complex of conditions, which in the presence of oxidations leads to the rapid death of the egg. The second treatment serves the purpose of rendering the egg immune against the toxic effects of the oxidations.

If we first cause the artificial membrane formation in the unfertilized egg by any of the various means which I have described in former papers, and if we afterward treat the eggs for a short time with a hypertonic solution, they develop after being transferred to normal sea-water in the same way as if a spermatozoon had entered them. They reach the successive larval stages, develop into a blastula, gastrula, and piuteus, and live as long as the larvae produced from eggs fertilized by a spermatozoon.

Hence the physico-chemical activation of the unfertilized egg of the sea-urchin consists of two kinds of treatment. The one is a change in the surface of the egg which may or may not result in the so-called formation of the membrane. This change causes the acceleration of oxidations which in my opinion is the essential feature of the process of fertilization. The second treatment consists in abolishing the faulty condition which makes oxidations fatal to the egg. This second treatment may consist in exposing the eggs for about half an hour or a little more to a hypertonic solution. We can substitute, however, for this treatment another treatment, namely, the deprivation of the egg for three hours from oxidations, either by removing the oxygen from the solution or by adding a trace of potassium cyanide to the solution. If, after the treatment with the hypertonic solution for half an hour, or the treatment with lack of oxygen for about three hours, the eggs are put back into normal sea-water they can develop into normal larvae.

We can show that the spermatozoon also causes the development of the egg by two different agencies comparable hi their action to the agencies used in the methods of chemical fertilization which we have just described.

For this purpose we must fertilize the egg of the sea-urchin with a sperm different from its own, and for the following reason: The spermatozoon of the sea-urchin enters so rapidly into the egg that it is impossible to show that it causes the development of the egg by two different substances.

If, however, we fertilize the sea-urchin egg with the sperm of star-fish, it takes from ten to fifty minutes to cause the membrane formation in the eggs, the reason being that the star-fish sperm can penetrate only very slowly into the egg of the sea-urchin.

It is, as a rule, not possible to fertilize the egg of the sea-urchin by star-fish sperm in normal sea-water. But I found

162 THE MECHANISTIC CONCEPTION OF LIFE

eight years ago that if we make the sea-water slightly more alkaline than it naturally is the eggs of the sea-urchin can be fertilized by the sperm of the star-fish. For the fertilization of the Californian sea-urchin, Strongylocentrotus purpuratus, with the sperm of Asterias, the best results were obtained when 0.6 c.c. of n/10 NaOH were added to 50 c.c. of sea-water. In this case, with active sperm, in about fifty minutes all the eggs form the typical fertilization membrane.

If we watch the further development of sea-urchin eggs fertilized by star-fish sperm we notice very soon that there are two different kinds of eggs present; the one kind of eggs behave as if they had been fertilized with sperm of their own kind. That is to say, they segment regularly and develop into swimming blastulae and gastrulae. The other kind of eggs, however, act as if they had been treated with one of the agencies which cause the membrane formation in the unfertilized sea-urchin egg; these eggs begin to segment, but at room temperature they slowly perish by cytolysis. If, however, these eggs are treated for half an hour with a hypertonic solution they develop into larvae.

If we examine the eggs of a sea-urchin which have been treated in an alkaline medium with the sperm of the star-fish, we find that only a certain percentage of these eggs contain the sperm nucleus, and this percentage seems to be identical with the percentage of the eggs which develop into larvae. As far as the other eggs are concerned, which form only a membrane and then disintegrate, no sperm nucleus can be found inside of them. I am inclined to draw the following conclusion from these observations: The spermatozoon of the star-fish penetrates very slowly through the surface film of the sea-urchin egg. When it lingers for some time partially imbedded in the surface film, one of the substances of the spermatozoon is dissolved in the superficial layer of the egg and causes the membrane formation. Through the act of

membrane formation the further entrance of the spermatozoon into the egg is prevented, since the fertilization membrane is impermeable to sperm. This membrane formation leads to an increase in the rate of oxidations and the beginning of the development of the egg. The latter, however, contains a toxic substance, or a faulty complex of conditions which has to be abolished, before the oxidations necessary for development can take place without the egg being destroyed by them. The spermatozoon carries a second substance into the egg which renders it immune against the fatal actions of the oxidations. While the membrane-forming substance of the spermatozoon may be situated at its surface, or superficially at least, the second substance which transforms the egg from an anaerobe into an aerobe must be situated in the interior of the spermatozoon; since it can only act if the spermatozoon penetrates into the egg. We see in these observations, concerning the fertilization of the sea-urchin egg by the star-fish sperm, a proof that the activation of the egg by the spermatozoon is also caused by two different substances, one of which causes the membrane formation, while the second renders the egg immune against the toxic action of the oxidations. These data support the assumption made above that the life-saving action of the spermatozoon is due to the fact that it carries a substance into the egg which renders the latter immune against the toxic action of oxidations.

Ill

Seven years ago I found that a number of agencies destroy the fertilized egg much more rapidly than the unfertilized egg. Thus, for instance, while in a pure sodium chloride solution the unfertilized egg of the Californian sea-urchin may be kept alive for several days, the fertilized egg is destroyed in such a solution in less than twenty-four hours. If we use slightly alkaline solutions of sodium chloride the greater resistance of the

164 THE MECHANISTIC CONCEPTION OF LIFE

unfertilized egg is perhaps still more striking. The egg of the Atlantic form of sea-urchin, Arbada, is cytolyzed in a neutral sodium chloride solution in a few hours, while the unfertilized egg may live for a considerably longer period of time. When we put fertilized and unfertilized eggs into hypertonic solutions, we find also that the fertilized eggs suffer much more than the unfertilized. What causes this difference of sensitiveness between fertilized and unfertilized eggs? It is possible that the permeability of the fertilized eggs is greater than that of the unfertilized. While this is probably to some extent true, yet it is not the whole explanation of the difference in the behavior of the two kinds of eggs. I have been able to show for a number of toxic solutions that their effect can be either completely annihilated or at least diminished if we take the oxygen away from the solution. Thus, for instance, fertilized eggs of the sea-urchin which perish very rapidly in pure salt solutions, or a solution of sodium+calcium, or a solution of sodium + barium, can be kept alive for a considerable period of time in the same solutions if we either carefully remove the oxygen from the solutions, or if we diminish the rate of the oxidations in the eggs by adding a trace of sodium cyanide. In this case we have the direct proof that solutions which are fatal for the egg when the oxidations are allowed to go on are rendered completely, or at least partially, harmless if we stop the oxidations in the egg. Not only the toxic action of salt solutions upon the fertilized egg could be inhibited by the suppression of the oxidations in the egg, but also the toxic action of sugar solutions, or of solutions of alcohol in the sea-water, or of a solution of chloral hydrate. 1

These observations prove directly that in the presence of certain toxic substances or mixtures of substances the oxidations in the egg lead to its rapid destruction; while a suppression of the oxidation saves the life of the egg.

1 Or of phenylurethane. This observation does not agree very well with the assumption that the narcotic action of these substances is due to a retardation of oxidation.

We therefore believe that we may conclude that the rapid death of the unfertilized egg of certain species is caused by the oxidations which take place in these eggs; and that the life-saving action of the spermatozoon consists in the fact that the latter, in addition to the membrane-forming substance, carries a second substance, or group of substances, into the egg which renders it immune against the harmful effect or consequences of oxidations.

OF LIFE

THE ROLE OF SALTS IN THE PRESERVATION OF LIFE 1

Less is known of the role of the salts in the animal body than of the role of the three other main food-stuffs, namely, carbohydrates, fats, and proteins. As far as the latter are concerned, we know at least that through oxidation they are capable of furnishing heat and other forms of energy. The neutral salts, however, are not oxidizable. Yet it seems to be a fact that no animal can live on an ash-free diet indefinitely, although no one can say why this should be so. We have a point of attack for the investigation of the role of the salts in the fact that the cells of our body live longest in a liquid which contains the three salts, NaCl, KC1, and CaCl 2 in a definite proportion, namely, 100 molecules NaCl, 2.2 molecules KC1, and 1.5 molecules of CaCl 2 . This proportion is identical with the proportion in which these salts are contained in sea-water; but the concentration of the three salts is not the same in both cases. It is about three times as high in the sea-water as in our blood serum.

Biologists have long been aware of the fact that the ocean has an incomparably richer fauna than fresh-water lakes or streams and it is often assumed that life on our planet originated in the ocean. The fact that the salts of Na, Ca, and K exist in about the same proportion in our blood serum as in the ocean has led some authors to the conclusion that our ancestors were marine animals, and that, as a kind of inheritance, we still carry diluted sea-water in our blood. Statements of this kind have

1 Carpenter lecture delivered at -the Academy of Medicine of New York, October 19, 1911. Reprinted from Science, N.S., XXXIV, No. 881, 653-65, November 17, 1911, by courtesy of Professor James McKeen Cattell.

169

170 THE MECHANISTIC CONCEPTION OF LIFE

mainly a metaphorical value, but they serve to emphasize the two facts, that the three salts, NaCl, KC1, and CaCl 2 , exist in our blood in the same relative proportion as in the ocean and that they seem to play an important role in the maintenance of life. I intend to put before you a series of experiments which seem to throw some light on the mechanism by which the solutions surrounding living cells influence their duration of life.

In order to give a picture of the extent to which the life of many animals depends upon the cooperation of the three salts I may mention experiments made on a small marine crustacean, Gammarus, of the Bay of San Francisco. If these animals are suddenly thrown into distilled water, their respiration stops (at a temperature of 20° C.) in about half an hour. If they are put back immediately after the cessation of respiration into sea-water, they can recuperate. If ten minutes or more are allowed to elapse before bringing them back into the sea-water, no recuperation is possible. Since in this case death is caused obviously through the entrance of distilled water into the tissues of the animals, one would expect that the deadly effect of distilled water would be inhibited if enough cane sugar were added to the distilled water to make the osmotic pressure of the solution equal to that of the sea-water. If, however, the animals are put into cane-sugar solution, the osmotic pressure of which is equal to that of sea-water, the animals die just about as rapidly as in distilled water. The same is true if the osmotic pressure of the sugar solution is higher or lower than that of the sea-water. The sugar solution is, therefore, about as toxic for these animals as the distilled water, although in the latter case water enters into the tissues of the animal, while in the former case it does not.

If the sea-water is diluted with an equal quantity of distilled water in one case, and of isotonic cane-sugar solution in the

other, in both cases the duration of life is shortened by practically the same amount.

If the crustaceans are brought into a pure solution of NaCl, of the same osmotic pressure as the sea-water, they also die in about half an hour. If to this solution a little calcium chloride be added in the proportion in which it is contained in the sea-water the animals die as rapidly as without it. If, however, both CaCl 2 and KC1 are added to the sodium chloride solution, the animals can live for several days. The addition of KC1 alone to the NaCl prolongs their life but little.

If KC1 and CaCl 2 are added to a cane-sugar solution isotonic with sea-water, the animals die as quickly or more so than in the pure cane-sugar solution.

If other salts be substituted for the three salts the animals die. The only substitution possible is that of SrCl 2 for CaCl 2 . We find also that the proportion in which the three salts of sodium, calcium, and potassium have to exist in the solution cannot be altered to any extent. All this leads us to the conclusion, that in order to preserve the life of the crustacean Gammarus, the solution must not only have a definite concentration or osmotic pressure but that this osmotic pressure must be furnished by definite salts, namely, sodium chloride, calcium chloride, and potassium chloride in the proportion in which these three salts exist in the sea-water (and in the blood); this fact could also be demonstrated for many other marine animals. The relative tolerance of various cells and animals for abnormal salt solutions is, however, not the same, a point which we shall discuss later on.

Ill

What is the role of the salts in these cases ? The botanists have always considered salt solutions as nutritive solutions. It is a well-known fact that plants require definite salts, e.g., nitrates and potassium salts, for their nutrition, and the question now arises whether the three salts NaCl, KC1, and CaCl 2 ,

which are needed for the preservation of animal life, play the role of nutritive salts. Experiments which I made on a small marine fish, Fundulus, proved beyond question that this is not the case. If the young, newly hatched fish are put into a pure solution of sodium chloride of the concentration in which this salt is contained in sea-water, the animals very soon die. If, however, KC1 and CaCl 2 be added to the solution in the right proportion, the animals can live indefinitely. These fish, therefore, behave in this respect like Gammarus and the tissues of the higher animals, but they differ from Gammarus and the majority of marine animals inasmuch as the fish can live long, and in some cases, indefinitely, in distilled and fresh water, and certainly in a very dilute solution of sodium chloride. From this fact I drew the conclusion that KC1 and CaCl 2 do not act as nutritive substances for these animals, that they only serve to render NaCl harmless if the concentration of the latter salt is too high. I succeeded in showing that as long as the sodium chloride solution is very dilute and does not exceed the concentration of m/8, the addition of KC1 and CaCl 2 is not required. Only when the solution of NaCl has a concentration above m/8 does it become harmful and require the addition of KC1 and CaCl 2 .

The experiments on Fundulus, therefore, prove that a mixture of NaCl-f KCl-fCaCl 2 does not act as a nutritive solution, but as a protective solution. KC1 and CaCl 2 are only necessary in order to prevent the harmful effects which NaCl produces if it is alone in solution and if its concentration is too high. We are dealing, in other words, with a case of antagonistic salt action; an antagonism between NaCl on the one hand and KC1 and CaCl 2 on the other. The discovery of antagonistic salt action was made by Ringer, who found that there is a certain antagonism between K and Ca in their action on the heart. When he put the heart of a frog into a mixture of NaCl+KCl he found that the contractions of the heart were not normal,

but they were rendered normal by the addition of a little CaCl 2 . A mixture of NaCl+CaCl 2 also caused abnormal contractions of the heart, but these were rendered normal by the addition of KC1. Ringer drew the conclusion that there existed an antagonism between potassium and calcium, similar to that which Schmiedeberg had found between different heart poisons, e.g., atropin and muscarin. Biedermann had found that alkaline salt solutions cause twitchings in the muscle and Ringer found that the addition of Ca inhibited these twitchings. Since these experiments were made many examples of the antagonistic action of salts have become known.

It had generally been assumed that the antagonistic action of two salts was based on the fact that each salt, when applied singly, acted in the opposite way from that of its antagonist. We shall see that in certain cases of antagonistic salt action at least this view is not supported by fact.

What is the mechanism of antagonistic salt action? I believe that an answer to this question lies in the following observations on the eggs of Fundulus. If these eggs are put immediately after fertilization into a pure sodium chloride solution which is isotonic with sea-water, they usually die without forming an embryo. If, however, only a trace of a calcium salt, or of any other salt with a bivalent metal (with the exception of Hg, Cu, or Ag) is added to the m/2 NaCl solution, the toxicity of the solution is diminished or even abolished. Even salts which are very poisonous, namely, salts of Ba, Zn, Pb, Ko, Ni, Mn, and other bivalent metals, are able to render the pure solution of sodium chloride harmless, at least to the extent that the eggs can live long enough to form an embryo. The fact that a substance as poisonous as Zn or lead can render harmless a substance as indifferent as sodium chloride seems so paradoxical that it demanded an explanation,

174 THE MECHANISTIC CONCEPTION OF LIFE

and this explanation casts light on the nature of the protective or antagonistic action of salts. For the antagonistic action of a salt of lead or zinc against the toxic action of sodium chloride can only consist in the lead salt protecting the embryo against the toxic action of the NaCl. But how is this protective action possible ?

We have mentioned that if we put the young fish, immediately after hatching, into a pure m/2 solution of sodium chloride the animals die very quickly, but that they live indefinitely in the sodium chloride solution if we add both CaCl 2 and KC1. How does it happen that for the embryo, as long as it is in the egg shell, the addition of CaC) 2 to the NaCl solution suffices, while if the fish is out of the shell the addition of CaCl 2 alone is no longer sufficient and the addition of KC1 also becomes necessary ? Moreover, if we try to preserve the life of the fish after it is taken out of the egg in an m/2 sodium chloride solution by adding ZnS0 4 , or lead acetate, to the solution we find that the fish die even much more quickly than without the addition. 1

If we look for the cause of this difference our attention is called to the fact that the fish, as long as it is in the egg, is separated from the surrounding solution by the egg membrane. This egg membrane possesses a small opening, the so-called micropyle, through which the spermatozoon enters into the egg. I have gained the impression that this micropyle is not closed as tightly immediately after fertilization as later on, since the newly fertilized egg is killed more rapidly by an m/2 solution of NaCl than it is killed by the same solution one or two days after fertilization. One can imagine that the micropyle contains a wad of a colloidal substance which is hardened gradually to a leathery consistency if the egg remains in the sea-water.

1 R. Lillle has found that in the larvae of Arenicola a slight antagonism between NaCl and ZnSO 4 can be proved. This shows that the general laws of antagonism between two salts differ in degree but not in principle in the living organism and the dead envelop of the fish egg.

With the process of hardening, or tanning, it becomes more impermeable for the NaCl solution. This process of hardening is brought about apparently very rapidly if we add to the m/2 NaCl solution a trace of a salt of a bivalent metal like Ca, Sr7 Ba, Zn, Pb, Mn, Ko, and Ni, etc. It is also possible that similar changes take place in the whole membrane. The process of rendering the m/2 Na solution harmless for the embryo of the fish, therefore, depends apparently upon the fact that the addition of the bivalent metals renders the micropyle or perhaps the whole membrane of the egg more impermeable to NaCl than was the case before.

But these are only one part of the facts which throw a light upon the protective or antagonistic action of salts. Further data are furnished by experiments which I made together with Professor Gies, also on the eggs of Fundulus. Gies and I were able to show that not only are the bivalent metals able to render the sodium chloride solution harmless, but that the reverse is also the case, namely, that NaCl is required to render the solutions of many of the bivalent metals, for instance ZnSO 4 , harmless. (That the SO 4 ion has nothing to do with the result was shown before by experiments with Na 2 SO 4 .)

If the eggs of Fundulus are put immediately after fertilization into distilled water, a large percentage of the eggs develop, often as many as 100 per cent, and the larvae and embryos formed in the distilled water are able to hatch. If we add, however, to 100 c.c. of distilled water that quantity of ZnSO 4 which is required to render the NaCl solution harmless, all the eggs are killed rapidly and not a single one is able to form an embryo. If we add varying amounts of NaCl we find that, beginning with a certain concentration of NaCl, this salt inhibits the toxic effects of ZnSO 4 and many eggs are able to form an embryo. This can be illustrated by the following table:

176 THE MECHANISTIC CONCEPTION OF LIFE

TABLE I

Percentage of

Nature of the Solution the Eggs Forming

an Embryo

100 c.c. distilled water 49

100 c.c. distilled water+8 c.c. m/32 ZnS0 4 0

100 c.c. m/64 NaCl+8 c.c. m/32 ZnS0 4 0

100 c.c. m/32 NaCl+8 c.c. m/32 ZnS0 4 3

100 c.c. m/16 NaCl+8 c.c. m/32 ZnS0 4 8

100 c.c. m/8 NaCl+8 c.c. m/32 ZnS0 4 44

100 c.c. m/4 NaCl+8 c.c. m/32 ZnS0 4 38

100 c.c. 3/8 NaCl+8 c.c. m/32 ZnS0 4 37

100 c.c. m/2 NaCl+8 c.c. m/32 ZnS0 4 34

100 c.c. 5/8 NaCl+8 c.c. m/32 ZnS0 4 29

100 c.c. 6/8 NaCl+8 c.c. m/32 ZnS0 4 8

100 c.c. 7/8 NaCl+8 c.c. m/32 ZnS0 4 6

100 c.c. m NaCl+8 c.c. m/32 ZnSO, 1

This table shows that the addition of NaCl, if its concentration exceeds a certain limit, namely, m/8, is able to render the ZnSO 4 in the solution comparatively harmless.

If we now assume that ZnS0 4 renders the 5/8 m NaCl solution harmless by rendering the egg membrane comparatively impermeable for NaCl we must also draw the opposite conclusion, namely, that NaCl renders the egg membrane comparatively impermeable for ZnSO 4 . We therefore arrive at a new conception of the mutual antagonism of two salts, namely, that this antagonism depends, in this case at least, upon a common, cooperative action of both salts on the egg membrane, by which action this membrane becomes completely or comparatively impermeable for both salts. And from this we must draw the further conclusion that the fact that each of these salts, if it is alone in the solution, is toxic, is due to its comparatively rapid diffusion through the membrane, so that it comes into direct contact with the protoplasm of the germ.

As long as we assumed that each of the two antagonistic salts acted, if applied singly, in the opposite way from its antagonist, it was impossible to understand these experiments

or find an analogue for them in colloid chemistry. But if we realize that NaCl alone is toxic because it is not able to render the egg membrane impermeable; and that ZnSO 4 if alone in solution is toxic for the same reason; while both combined are harmless (since for the "tanning" of the membrane the action of the two salts is required) these experiments become clear.

We may, for the sake of completeness, still mention that salts alone have such antagonistic effects; glycerin, urea, and alcohol have no such action. On the other hand, ZnSO 4 was not only able to render NaCl harmless, but also LiCl, NH 4 C1, CaCl 2 , and others; and vice versa.

These experiments on the egg of Fundulus are theoretically of importance, since they leave no doubt that in this case at least the " antagonistic " action of salts consists in a modification of the egg membrane by a combined action of two salts, whereby the membrane becomes less permeable for both salts.

It is not easy to find examples of experiments in the literature which are equally unequivocal in regard to the character of antagonistic salt action; but I think that some recent experiments by Osterhout satisfy this demand.

It has long been a question whether or not cells are at all permeable for salts. Nobody denies that salts diffuse much more slowly into the cells than water; but some authors, especially Overton and Hoeber, deny categorically that they can diffuse at all into the cells. Overton's view is based partly on experiments on plasmolysis in the cells of plants. If the cells of plants, for example, those of Spirogyra, are put into a solution of NaCl or some other salt of sufficiently high osmotic pressure, the volume of the contents of the cell decreases through loss of water and the protoplasm retracts, especially from corners of the rigid cellulose walls. Overton maintains that this plasmolysis is permanent, and concludes from this

178 THE MECHANISTIC CONCEPTION OF LIFE

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Text

Table of Contents

Title Page

Pages

Printed in the United States of America,

TO MY COLLABORATORS IN THESE RESEARCHES

DANIEL DE LA PAZ ALFRED T. SHOHL WADE 8. WRIGHT ARTHUR L. WASHBURN M^RY LYMAN LEONARD B. NICE CHARLES M. GRUBER HOWARD OSGOOD HORACE GRAY WALTER L. MENDENilALL

WITH PLEASANT MEMORIES OF OUR WORK TOGETHER

PREFACE

Fear, rage and pain, and the pangs of hunger are all primitive experiences which human beings share with the lower animals. These experiences are properly classed as among the most powerful that determine the action of men and beasts. A knowledge of the conditions which attend these experiences, therefore, is of general and fundamental importance in the interpretation of behavior.

During the past four years there has been conducted, in the Harvard Physiological Laboratory, a series of investigations concerned with the bodily changes which occur in conjunction with pain, hunger and the major emotions. A group of remarkable alterations in the bodily economy have been discovered, all of which can reasonably be regarded as responses that are nicely adapted to the individual's welfare and preservation. Because these physiological adaptations are interesting both in themselves and in their interpretation, not only to physiologists and psychologists, but to others as well, it has seemed worth while to gather together in convenient form the original accounts of the experiments, which have been published in various American medical and physiological journals. I have, however, attempted to arrange the results and discussions in an orderly and consecutive manner, and I have tried also to elim-

Vlll

PREFACE

mate or incidentally to explain the technical terms, so that the exposition will be easily understood by any intelligent reader even though not trained in the medical sciences.

My first interest in the conditions attending pain, hunger and strong emotional states was stimulated during the course of a previous series of researches on the motor activities of the alimentary canal. A summary of these researches appeared in 1911, under the title, "The Mechanical Factors of Digestion." The studies recorded in the present volume may be regarded as a natural sequence of observations on the influence of emotional states on the digestive process, which were reported in that volume.

W. B. CANNON.

Boston, Mass.

CONTENTS

CHAPTER I

PAGES

THE EFFECT OF THE EMOTIONS ON DIGESTION

Emotions favorable to normal secretion of the digestive juices—Emotions unfavorable to normal secretion of the digestive juices—Emotions favorable and unfavorable to contractions of the stomach and intestines—The disturbing effect of pain on digestion 1-21

CIIAPTEK II

THE GENERAL ORGANIZATION OF THE VIS-CERAt NERVES CONCERNED IN EMOTIONS

The outlying neurones—The three divisions of the outlying neurones—The extensive distribution of neurones of the "sympathetic" or thoracico-lumbar division and their arrangement for diffuse action—The arrangement of neurones of the cranial and sacral divisions for specific action—The cranial division a conserver of bodily resources—The sacral division a group of mechanisms for emptying—The sympathetic division antagonistic to both the cranial and the sacral—Neurones of the sympathetic division and adrenal secretion have the same action 22-39

CHAPTEE III

PAGES

METHODS OF DEMONSTRATING ADRENAL SECRETION AND ITS NERVOUS CONTROL

The evidence that splanchnic stimulation induces adrenal secretion—The question of adrenal secretion in emotional excitement—The method of securing blood from near the adrenal veins—The method of testing the blood for adrenin 40-51

CHAPTEE IV

ADRENAL SECRETION IN STRONG EMOTIONS AND PAIN

The evidence that adrenal secretion is increased in emotional excitement—The evidence that adrenal secretion is increased by "painful" stimulation—Confirmation of our results by other observers .... 52-65

CHAPTEE V

THE INCREASE OF BLOOD SUGAR IN PAIN AND GREAT EMOTION

Glycosuria from pain—Emotional glycosuria—The role of the adrenal glands in emotional glycosuria . 66-80

CHAPTEE VI

IMPROVED CONTRACTION OF FATIGUED MUSCLE AFTER SPLANCHNIC STIMULATION OF THE ADRENAL GLAND

The nerve-muscle preparation—The splanchnic preparation—The effects of splanchnic stimulation on the contraction of fatigued muscle—The first rise in the muscle record—The prolonged rise in the muscle record—The two factors: arterial pressure and adrenal secretion 81-94

CHAPTER VII

PAGES

THE EFFECTS ON CONTRACTION OF FATIGUED MUSCLE OF VARYING THE ARTERIAL BLOOD PRESSURE

The effect of increasing arterial pressure—The effect of decreasing arterial pressure—An explanation of the effects of varying the arterial pressure—The value of increased arterial pressure in pain and strong emotion 95-109

CHAPTER VIII

THE SPECIFIC R6LE OF ADRENIN IN COUNTERACTING THE EFFECTS OF FATIGUE

Variations of the threshold stimulus as a measure of irritability—The method of determining the threshold stimulus—The lessening of neuro-muscular irritability by fatigue—The slow restoration of fatigued muscle to normal irritability by rest—The quick restoration of fatigued muscle to normal irritability by adrenin—The evidence that the restorative action of adrenin is specific—The point of action of adrenin in muscle 110-134

CHAPTER IX

THE HASTENING OF THE COAGULATION OF BLOOD BY ADRENIN

The graphic method of measuring the coagulation time —The effects of subcutaneous injections of adrenin— The effects of intravenous injections—The hastening of coagulation by adrenin not a direct effect on the blood 135-160

CHAPTER X

THE HASTENING OF COAGULATION OF BLOOD IN PAIN AND GREAT EMOTION

Coagulation hastened by splanchnic stimulation—Coagulation not hastened by splanchnic stimulation if

PAGES

the adrenal glands are absent—Coagulation hastened by "painful" stimulation—Coagulation hastened

in emotional excitement 161-183

CHAPTEK XI

THE UTILITY OF THE BODILY CHANGES IN PAIN AND GREAT EMOTION

The reflex nature of bodily responses in pain and the major emotions, and the useful character of reflexes—The utility of the increased blood sugar as a source of muscular energy—The utility of increased adrenin in the blood as an antidote to the effects of fatigue—The question whether adrenin normally secreted inhibits the use of sugar in the body—The vascular changes produced by adrenin favorable to supreme muscular exertion—The changes in respiratory function also favorable to great effort —The effects produced in asphyxia similar to those produced in pain and excitement—The utility of rapid coagulation in preventing loss of blood . 184-214

CHAPTEK XII

THE ENERGIZING INFLUENCE OF EMOTIONAL EXCITEMENT

"Reservoirs of power"—The excitements and energies of competitive sports—Frenzy and endurance in ceremonial and other dances—The fierce emotions and struggles of battle—The stimulating influence of witnesses and of music—The feeling of power . 215-231

CHAPTER XIII THE NATURE OF HUNGER

Appetite and hunger—The sensation of hunger—The theory that hunger is a general sensation—Weakness of the assumptions underlying the theory that hunger is a general sensation—Body need may exist without hunger—The theory that hunger is of gen-

CONTENTS mi

. . PAGES

eral origin does not explain the quick onset and the periodicity of the sensation—The theory that hunger is of general origin does not explain the local reference—Hunger not due to emptiness of the stomach —Hunger not due to hydrochloric acid in the empty stomach—Hunger not due to turgescence of the gastric mucous membrane—Hunger the result of contractions—The "empty" stomach and intestines contract—Observations suggesting that contractions cause hunger—The concomitance of contractions and hunger in man 232-266

CHAPTER XIV THE INTERRELATIONS OF EMOTIONS

Antagonism between emotions expressed in the sympathetic and in the cranial divisions of the auto-nomic system—Antagonism between emotions expressed in the sympathetic and in the sacral divisions of the autonomic system—The function of hunger—The similarity of visceral effects in different strong emotions and suggestions as to its psychological significance 267-284

CHAPTER XV

ALTERNATIVE SATISFACTIONS FOR THE FIGHTING EMOTIONS

Support for the militarist estimate of the strength of the fighting emotions and instincts—Growing opposition to the fighting emotions and instincts as displayed in war—The desirability of preserving the martial virtues—Moral substitutes for warfare—Physical substitutes for warfare—The significance of international athletic competitions 285-301

A LIST OF PUBLISHED RESEARCHES FROM THE PHYSIOLOGICAL LABORATORY IN HARVARD UNIVERSITY 302-303

BODILY CHANGES IN PAIN, HUNGER, FEAR AND RAGE

CHAPTER I

THE EFFECT OF THE EMOTIONS ON DIGESTION

The doctrine of human development from subhuman, antecedents has done much to unravel the complex nature of man. As a means of interpretation this doctrine has been directed chiefly toward the solving of puzzles in the peculiarities of anatomical structure. Thus arrangements in the human body, which are without obvious utility, receive rational explanation as being vestiges of parts useful in or characteristic of remote ancestors—parts retained in man because of agelong racial inheritance. This mode of interpretation has proved applicable also in accounting for functional peculiarities. Expressive actions and gestures—the facial appearance in anger, for example—observed in children and in widely distinct races, are found to be innate, and are best explained as the retention in human beings of responses which are similar in character in lower animals.

From this point of view biology has contributed much to clarify our ideas regarding the motives of human behavior. The social philosophies ^hich prevailed during the past century either assumed that conduct was determined by a calculated search for pleasure and avoidance of pain or they ascribed it to a vague and undefined faculty named the conscience or the moral sense. Comparative study of the behavior of men and of lower animals under various circumstances, however, especially with the purpose of learning the source of prevailing impulses, is revealing the inadequacy of the theories of the older psychologists. More and more it is appearing that in men of all races and in most of the higher animals, the springs of action are to be found in the influence of certain emotions which express themselves in characteristic instinctive acts.

The role which these fundamental responses in the higher organisms play in the bodily economy has received little attention. As a realm for investigation the bodily changes in emotional excitement have been left by the physiologists to the philosophers and psychologists and to the students of natural history. These students, however, have usually had too slight experience in the detailed examination of bodily functions to permit them to follow the clues which superficial observation might present. In consequence our

knowledge of emotional states has been meagre. There are, of course, many surface manifestations of excitement. The contraction of blood vessels with resulting pallor, the pouring out of "cold sweat," the stopping of saliva-flow so that the "tongue cleaves to the roof of the mouth," the dilation of the pupils, the rising of the hairs, the rapid beating of the heart, the hurried respiration, the trembling and twitching of the muscles, especially those about the lips—all these bodily changes are well recognized accompaniments of pain and great emotional disturbance, such as fear, horror and deep disgust. But these disturbances of the even routine of life, which have been commonly noted, are mainly superficial and therefore readily observable. Even the increased rapidity of the heart beat is noted at the surface in the pulsing of the arteries. There are, however, other organs, hidden deep in the body, which do not reveal so obviously as the structures near or in the skin, the disturbances of action which attend states of intense feeling. Special methods must be used to determine whether these deep-lying organs also are included in the complex of an emotional* agitation.

* In the use of the term "emotion" the meaning here is not restricted to violent affective states, but includes "feelings" and other affective experiences. At times, also, in order to avoid awkward expressions, the term is used in the popular manner, as if the "feeling" caused the bodily change.

Among the organs that are affected to an important degree by feelings are those concerned with digestion. And the relations of feelings to the activities of the alimentary canal are of particular interest, because recent investigations have shown that not only are the first stages of the digestive process normally started by the pleasurable taste and smell and sight of food, but also that pain and great emotional excitement can seriously interfere with the starting of the process or its continuation after it has been started. Thus there may be a conflict of feelings and of their bodily accompaniments—a conflict the interesting bearing of which we shall consider later.

EMOTIONS FAVORABLE TO NORMAL SECRETION OF THE DIGESTIVE JUICES

The feelings or affective states favorable to the digestive functions have been studied fruitfully by Pawlow, 1 of Petrograd, through ingenious experiments on dogs. By the use of careful surgical methods he was able to make a side pouch of a part of the stomach, the cavity of which was wholly separate from the main cavity in which the food was received. This pouch was supplied in a normal manner with nerves and blood vessels, and as it opened to the surface of the body, the amount and character of the gastric juice secreted by it under various conditions

could be accurately determined. Secretion by that part of the stomach wall which was included in the pouch was representative of the secretory activities* of the entire stomach. The arrangement was particularly advantageous in providing the gastric juice unmixed with food. In some of the animals thus operated upon an opening was also made in the esophagus so that when the food was swallowed, it did not pass to the stomach but dropped out on the way. All the pleasures of eating were thus experienced, and there was no necessity of stopping because of a sense of fulness. This process was called "sham feeding." The well-being of these animals was carefully attended to, they lived the normal life of dogs, and in the course of months and years became the pets of the laboratory.

By means of sham feeding Pawlow showed that the chewing and swallowing of food which the dogs relished resulted, after a delay of about five minutes, in a flow of natural gastric juice from the side pouch of the stomach—a flow which persisted as long as the dog chewed and swallowed the food, and continued for some time after eating ceased. Evidently the presence of food in the stomach is not a prime condition for gastric secretion. And since the flow occurred only when the dogs had an appetite, and the material presented to them was agreeable, the conclusion

was justified that this was a true psychic secretion.

The mere sight or smell of a favorite food may start the pouring out of gastric juice, as was noted many years ago by Bidder and Schmidt 2 in a hungry dog which had a fistulous opening through the body wall into the stomach. This observation, reported in 1852, was confirmed later by Schiff and also still later by Pawlow. That the mouth "waters" with a flow of saliva when palatable food is seen or smelled has long been such common knowledge that the expression, "It makes my mouth water," is at once recognized as the highest testimony to the attractiveness of an appetizing dish. That the stomach also "waters" in preparation for digesting the food which is to be taken is clearly proved by the above cited observations on the dog.

The importance of the initial psychic secretion of saliva for further digestion is indicated when, in estimating the function of taste for the pleasures of appetite, we realize that materials can be tasted only when dissolved in the mouth and thereby brought into relation with the taste organs. The saliva which "waters" the mouth assures the dissolving of dry but soluble food even when it is taken in large amount.

The importance of the initial psychic secretion of gastric juice is made clear by the fact that con-

tinuance of the flow of this juice during digestion is provided by the action of its acid or its digestive products on the mucous membrane of the pyloric end of the stomach, and that secretion of the pancreatic juice and bile are called forth by the action of this same acid on the mucous membrane of the duodenum. The proper starting of the digestive process, therefore, is conditioned by the satisfactions of the palate, and the consequent flow of the first digestive fluids. The facts brought out experimentally in studies on lower animals are doubtless true also of man. Not very infrequently, because of the accidental swallowing of corrosive substances, the esophagus is so injured that, when it heals, the sides grow together and the tube is closed. Under these circumstances an opening has to be made into the stomach through the side of the body and then the individual chews his food in the usual manner, but ejects it from his mouth into a tube which is passed through the gastric opening. The food thus goes from mouth to stomach through a tube outside the chest instead of inside the chest. As long ago as 1878, Eichet, 3 who had occasion to study a girl whose esophagus was closed and who was fed through a gastric fistula, reported that whenever the girl chewed or tasted a highly sapid substance, such as sugar or lemon juice, while the stomach was empty, there flowed

from the fistula a considerable quantity of gastric juice. A number of later observers 4 have had similar cases in human beings, especially in children, and have reported in detail results which correspond remarkably with those obtained in the laboratory. Hornborg 4 found that when the little boy whom he studied chewed agreeable food a more or less active secretion of gastric juice invariably started, whereas the chewing of an indifferent substance, as gutta-percha, was followed by no secretion. All these observations clearly demonstrate that the normal flow of the first digestive fluids, the saliva and the gastric juice, is favored by the pleasurable feelings which accompany the taste and smell of food during mastication, or which are roused in anticipation of eating when choice morsels are seen or smelled.

These facts are of fundamental importance in the serving of food, especially when, through illness, the appetite is fickle. The degree of daintiness with which nourishment is served, the little attentions to esthetic details—the arrangement of the dishes, the small portions of food, the flower beside the plate—all may holp to render food pleasing to the eye and savory to the nostrils and may be the deciding factors in determining whether the restoration of strength is to begin or not.

EMOTIONS UNFAVORABLE TO THE NORMAL SECRETION OF THE DIGESTIVE JUICES

\The conditions favorable to proper digestion are wholly abolished when unpleasant feelings such as vexation and worry and anxiety, or great emotions such as anger and fear, are allowed to prevail. This fact, so far as the salivary secretion is concerned, has long been known. The dry mouth of the anxious person called upon to speak in public is a common instance; and the "ordeal of rice," as employed in India, was a practical utilization of the knowledge that excitement is capable of inhibiting the salivary flow. When several persons were suspected of crime, the consecrated rice was given to them all to chew, and after a short time it was spit out upon the leaf of the sacred fig tree. If anyone ejected it dry, that was taken as proof that fear of being discovered had stopped the secretion, and consequently he was adjudged guilty. 5

What has long been recognized as true of the secretion of saliva has been proved true also of the secretion of gastric juice. For example, Ilornborg was unable to confirm in his little patient with a gastric fistula the observation by Pawlow that when hunger is present the mere seeing of food results in a flow of gastric juice. Ilornborg explained the difference between his and Pawlow's results by the different ways in

which the boy and the dogs faced the situation. When food was shown, but withheld, the hungry dogs were all eagerness to secure it, and the juice very soon began to flow. The boy, on the contrary, became vexed when he could not eat at once, and began to cry; then no secretion appeared. Bogen also has reported the instance of a child with closed esophagus and gastric fistula, who sometimes fell into such a passion in consequence of vain hoping for food that the giving of the food, after the child was calmed, was not followed by any flow of the secretion.

The inhibitory influence of excitement has also been seen in lower animals under laboratory conditions. Le Conte 6 declares that in studying gastric secretion it is necessary to avoid all circumstances likely to provoke emotional reactions. In the fear which dogs manifest when first brought into strange surroundings he found that activity of the gastric glands may be completely suppressed. The suppression occurred even if the dog had eaten freely and was then disturbed —as, for example, by being tied to a table. When the animals became accustomed to the experimental procedure, it no longer had an inhibitory effect. The studies of Bickel and Sasaki 7 confirm and define more precisely this inhibitory effect of strong emotion on gastric secretion. They observed the inhibition on a dog with an

EMOTIONS AND DIGESTION 11

esophageal fistula, and with a side pouch of the stomach, which, as in Pawlow's experiments, opened only to the exterior. In this dog Bickel and Sasaki noted, as Pawlow had, that sham feeding was attended by a copious flow of gastric juice, a true psychic secretion, resulting from the pleasurable taste of the food. In a typical instance the sham feeding lasted five minutes, and the secretion continued for twenty minutes, during which time 66.7 cubic centimeters of pure gastric juice were produced.

On another day a cat was brought into the presence of the dog, whereupon the dog flew into a great fury. The cat was soon removed, and the dog pacified. Now the dog was again given the sham feeding for five minutes. In spite of the fact that the animal was hungry and ate eagerly, there was no secretion worthy of mention. During a period of twenty minutes, corresponding to the previous observation, only 9 cubic centimeters of acid fluid were produced, and this was rich in mucus. It is evident that in the dog, as in the boy observed by Bogen, strong emotions can so profoundly disarrange the mechanisms of secretion that the pleasurable excitation which accompanies the taking of food cannot cause the normal flow.

On another occasion Bickel and Sasaki started gastric secretion in the dog by sham feeding, and

when the flow of gastric juice had reached a certain height, the dog was infuriated for five minutes by the presence of the cat. During the next fifteen minutes there appeared only a few drops of a very mucous secretion. Evidently in this instance a physiological process, started as an accompaniment of a psychic state quietly pleasurable in character, was almost entirely stopped after another psychic state violent in character. It is noteworthy that in both the favorable and unfavorable results of the emotional excitement illustrated in Bickel and Sasaki's dog the effects persisted long after the removal of the exciting condition. This fact, in its favorable aspect, Bickel 8 was able to confirm in a girl with esophageal and gastric fistulas; the gastric secretion long outlasted the period of eating, although no food entered the stomach. The influences unfavorable to digestion, however, are stronger than those which promote it. And evidently, if the digestive process, because of emotional disturbance, is for some time inhibited, the swallowing of food which must lie stagnant in the stomach is a most irrational procedure. If a child has experienced an outburst of passion, it is well not to urge the taking of nourishment soon afterwards. Macbeth's advice that "good digestion wait on appetite and health on both," is now well-founded physiology.

EMOTIONS AND DIGESTION 13

Other digestive glands than the salivary and the gastric may be checked in emotional excitement. Kecently Oechsler 9 has reported that in such psychic disturbances as were shown by Bickel and Sasaki to be accompanied by suppressed secretion of the gastric juice, the secretion of pancreatic juice may be stopped, and the flow of bile definitely checked. All the means of bringing about chemical changes in the food may be thus temporarily abolished.

EMOTIONS FAVORABLE AND UNFAVORABLE TO THE CONTRACTIONS OF THE STOMACH AND INTESTINES

The secretions of the digestive glands and the chemical changes wrought by them are of little worth unless the food is carried onward through the alimentary canal into fresh regions of digestion and is thoroughly exposed to the intestinal wall for absorption. In. studying these mechanical aspects of digestion I was led to infer 10 that just as there is a psychic secretion, so likewise there is probably a "psychic tone" or "psychic contraction" of the gastro-intestinal muscles as a result of taking food. For if the vagus nerve supply to the stomach is cut immediately before an animal takes food, the usual contractions of the gastric wall, as seen by the Rontgen rays, do not occur; but if these nerves are cut after food has been eaten with relish, the contractions which

have started continue without cessation. The nerves in both conditions were severed under anesthesia, so that no element of pain entered into the experiments. In the absence of hunger, which in itself provides a contracted stomach, 11 the pleasurable taking of food may, therefore, be a primary condition for the appearance of natural contractions of the gastro-intestinal canal.

Again just as the secretory activities of the stomach are unfavorably influenced by strong emotions, so also are the movements of the stomach; and, indeed, the movements of almost the entire alimentary canal are wholly stopped during great excitement. In my earliest observations on the movements of the stomach 12 I had difficulty because in some animals the waves of contraction were perfectly evident, while in others there was no sign of activity. Several weeks passed before I discovered that this difference was associated with a difference of sex. In order to be observed with Kontgen rays the animals were restrained in a holder. Although the holder was comfortable, the male cats, particularly the young males, were restive and excited on being fastened to it, and under these circumstances gastric peristaltic waves were absent; the female cats, especially if elderly, usually submitted with calmness to the restraint, and in them the waves had their normal occurrence. Once a female with

EMOTIONS AND DIGESTION 15

kittens turned from her state of quiet contentment to one of apparent restless anxiety. The movements of the stomach immediately stopped, the gastric wall became wholly relaxed, and only after the animal had been petted and began to purr did the moving waves start again on their course. By covering the cat's mouth and nose with the fingers until a slight distress of breathing is produced, the stomach contractions can be stopped at will. In the cat, therefore, any sign of rage or fear, such as was seen in dogs by Lo Conte and by Bickel and Sasaki, was accompanied by a total abolition of the movements of the stomach. Even indications of slight anxiety may be attended by complete absence of the churning waves. In a vigorous young male cat I have watched the stomach for more than an hour by means of the Eontgen rays, and during that time not the slightest beginning of peristaltic activity appeared; yet the only visible indication of excitement in the animal was a continued quick twitching of the tail to and fro. What is true of the cat I have found true also of the rabbit, dog and guinea-pig 13 —very mild emotional disturbances are attended by abolition of peristalsis. The observations on the rabbit have been confirmed by Auer, 14 who found that the handling of the animal incidental to fastening it gently to a holder stopped gastric peristalsis for a

variable length of time. And if the animal was startled for any reason, or struggled excitedly, peristalsis was again abolished. The observations on the dog also have been confirmed; Lom-mel 15 found that small dogs in strange surroundings might have no contractions of the stomach for two or three hours. And whenever the animals showed any indications of being uncomfortable or distressed, the contractions were inhibited and the discharge of contents from the stomach checked.

Like the peristaltic waves in the stomach, the peristalsis and the kneading movements (segmentation) in the small intestine, and the reversed peristalsis in the large intestine all cease whenever the observed animal shows signs of emotional excitement.

There is no doubt that just as the secretory activity of the stomach is affected in a similar fashion in man and in lower animals, so likewise gastric and intestinal peristaltic waves are stopped in man as they are stopped in lower animals, by worry and anxiety and the stronger affective states. The conditions of mental discord may thus give rise to a sense of gastric inertia. For example, a patient described by Miiller 1G testified that anxiety was always accompanied by a feeling of weight, as if the food remained in the stomach. Every addition of food caused an

EMOTIONS AND DIGESTION 17

increase of the trouble. Strong emotional states in this instance led almost always to gastric distress, which persisted, according to the grade and the duration of the psychic disturbance, between a half-hour and several days. The patient was not hysterical or neurasthenic, but was a very sensitive woman deeply affected by moods.

The feeling of heaviness in the stomach, mentioned in the foregoing case, is not uncommonly complained of by nervous persons, and may be due to stagnation of the contents. That such stagnation occurs is shown by the following instance. A refined and sensitive woman, who had had digestive difficulties, came with her husband to Boston to be examined. They went to a hotel for the night. The next morning the woman appeared at the consultant's office an hour after having eaten a test meal. An examination of the gastric contents revealed no free acid, no digestion of the test breakfast, and the presence of a considerable amount of the supper of the previous evening. The explanation of this stagnation of the food in the stomach came from the family doctor, who reported that the husband had made the visit to the city an occasion for becoming uncontrollably drunk, and that he had by his escapades given his wife a night of turbulent anxiety. The second morning, after the woman had had a good rest, the gastric con-

tents were again examined; the proper acidity was found, and the test breakfast had been normally digested and discharged.

These cases are merely illustrative and doubtless can be many times duplicated in the experience of any physician concerned largely with digestive disorders. ( Indeed, the opinion has been expressed that a great majority of the cases of gastric indigestion that come for treatment are functional in character and of nervous origin. It is the emotional element that seems most characteristic of these cases. To so great an extent is this true that Rosenbach has suggested that as a term to characterize the cause of the disturbances, "emotional" dyspepsia is better than "nervous" dyspepsia. 17

THE DISTURBING EFFECT OF PAIN ON DIGESTION

(^The advocates of the theory of organic evolution early pointed out the similarity between the bodily disturbances in pain and in the major emotions. The alterations of function of internal organs they could not know about. The general statement, however, that pain evokes the same changes that are evoked by emotion, is true also of these deep-lying structures, j Wertheimer 18 proved many years since that stimulation of a sensory nerve in an anesthetized animal—such stimulation as in a conscious animal would in-

EMOTIONS AND DIGESTION 19

duce pain—quickly abolished the contractions of the stomach. And Netschaiev, working in Paw-low's 19 laboratory, showed that excitation of the sensory fibres in the sciatic nerve for two or three minutes resulted in an inhibition of the secretion of gastric juice that lasted for several hours. Similar effects from painful experience have been not uncommonly noted in human beings. 'Mantegazza, 20 in his account of the physiology of pain, has cited a number of such examples, and from them he has concluded that pain interferes with digestion by lessening appetite and by producing various forms of dyspepsia, with arrest of gastric digestion, and with vomiting and diarrhea. The expression, "sickening pain" is testimony to the power of strong sensory stimulation to upset the digestive processes profoundly. Vomiting is as likely to follow violent pain as it is to follow strong emotion. A "sick headache" may be, indeed, a sequence of events in which the pain from the headache is primary, and the nausea and other evidences of digestive disorder are secondary.

As the foregoing account has shown, emotional conditions or "feelings" may be accompanied by quite opposite effects in the alimentary canal, some highly favorable to good digestion, some highly disturbing. It is an interesting fact that the feelings having these antagonistic actions are

typically expressed through nerve supplies which are correspondingly opposed in their influence on the digestive organs. The antagonism between these nerve supplies is of fundamental importance in understanding not only the operation of conditions favorable or unfavorable to digestion but also in obtaining insight into the conflicts of emotional states. Since a consideration of the arrangement and mode of action of these nerves will establish a firm basis for later analysis and conclusions, they will next be considered.

REFERENCES

1 Pawlow: The Work of the Digestive Glands, London, 1902.

2 Bidder and Schmidt: Die Verdauungssafte und der Stoffwechsel, Leipzig, 1852, p. 35.

3 Richet: Journal de 1'Anatomic et de la Physiologic, 1878, xiv, p. 170.

* See Hornborg: Skandinavisches Archiv fur Physiologie, 1904, xv, p. 248. Cade and Latarjet: Journal de Physiologie et Pathologic Generale, 1905, vii, p. 221. Bogen: Archiv fur die gesammte Physiologie, 1907, cxvii, p. 156. Lavenson: Archives of Internal Medicine, 1909, iv, p. 271.

5 Lea: Superstition and Force, Philadelphia, 1892, p. 344.

6 Le Conte: La Cellule, 1900, xvii, p. 291.

7 Bickel and Sasaki: Deutsche medizinische Wochen-schrift, 1905, xxxi, p. 1829.

8 Bickel: Berliner klinische Wochenschrift, 1906, xliii, p. 845.

9 Oechsler: Internationelle Beitrage zur Pathologic und Therapie der Ernahrungstorungen, 1914, v, p. 1.

10 Cannon: The Mechanical Factors of Digestion, London and New York, 1911, p. 200.

11 Cannon and Washburn: American Journal of Physiology, 1912, xxix, p. 441.

12 Cannon: The American Journal of Physiology, 1898, i, p. 38.

13 Cannon: American Journal of Physiology, 1902, vii, p. xxii.

14 Auer: American Journal of Physiology, 1907, xviii, p. 356.

15 Lommel: Munchener mcdizinische Wochenschrift, 1903, i, p. 1634.

16 Miiller: Deutsches Archiv fur klinische Medicin, 1907, Ixxxix, p. 434.

17 Rosenbach: Berliner klinische Wochenschrift, 1897, xxxiv, p. 71

18 Wertheimer: Archives de Physiologic, 1892, xxiv, p. 379.

19 Pawlow: Loc. cit., p. 56.

20 Mantegazza: Fisiologia del Dolore, Florence, 1880, p. 123.

CHAPTER II

THE GENERAL ORGANIZATION OF THE VISCERAL NERVES CONCERNED IN EMOTIONS

The structures of the alimentary canal which are brought into activity during the satisfactions of appetite or are checked in their activity during pain and emotional excitement are either the secreting digestive glands or the smooth muscle which surrounds the canal. Both the gland cells and the smooth-muscle cells differ from other r cells which are subject to nervous influence— those of striated, or skeletal, muscle—in not being directly under voluntary control and in being slower in their response. The muscle connected with the skeleton responds to stimulation within two or three thousandths of a second; the delay with gland cells and with smooth muscle is more likely to be measured in seconds than in fractions of a second.

THE OUTLYING NEURONES

The skeletal muscles receive their nerve supply direct from the central nervous system, i. e., the

nerve fibres distributed to these muscles are parts of neurones whose cell bodies lie within the brain or spinal cord. The glands and smooth muscles of the viscera, on the contrary, are, so far as is now known, never innervated directly from the central nervous system.* The neurones reaching out from the brain or spinal cord never come into immediate relation with the gland or smooth-muscle cells; there are always interposed between the cerebrospinal neurones and the viscera extra neurones whose bodies and processes lie wholly outside the central nervous system. They are represented in dotted lines in Fig. 1. I have suggested that possibly these outlying neurones act as "transformers," modifying the impulses received from the central source (impulses suited to call forth the quick responses of skeletal muscle), and adapting these impulses to the peculiar, more slowly-acting tissues, the secreting cells and visceral muscle, to which they are distributed. 1

The outlying neurones typically have their cell bodies grouped in ganglia (G's, Fig. 1) which, in the trunk region, lie along either side of the spinal cord and in the head region and in the pelvic part of the abdominal cavity are disposed near the organs which the neurones supply. In some instances these neurones lie wholly within the

* The special case of the adrenal glands will be considered later.

Tear gland Dilator of pupil

Artery of salivary gland

Hair

Surface artery Sweat gland

Heart

Hair

Surface artery

Sweat gland

Liver

Stomach

tf Visceral artery Spleen

Intestine

Adrenal gland

Hair

Surface artery

Sweat gland

Colon

Bladder

Rectum

Artery of external genitals

FIGURE 1.—Diagram of the more important distributions of the autonomic nervous system. The brain and spinal cord are represented at the left. The nerves to skeletal muscles are not represented. The preganglionic fibres of the autonomic system are in solid lines, the post^anglionic in dash-lines. The nerves of the cranial and sacral divisions are distinguished from those of the thoracico-;lumbar or "sympathetic" division by broader lines. A + mark indicates an augmenting effect on the activity of the organ; a — mark, a depressive or inhibitory effect. For further description see text.

structure which they innervate (see e. g., the heart and the stomach, Fig. 1). In other instances the fibres passing out from the ganglia—the so-called "postganglionic fibres"—may traverse long distances before reaching their destination. The in-nervation of blood vessels in the foot by neurones whose cell bodies are in the lower trunk region is an example of this extensive distribution of the fibres.

THE THREE DIVISIONS OF THE OUTLYING NEURONES

As suggested above, the outlying neurones are connected with the brain and spinal cord by neurones whose cell bodies lie within the central nervous organs. These connecting neurones, represented by continuous lines in Fig. 1, do not pass out in an uninterrupted series all along the cere-bro-spinal axis. Where the nerves pass out from the spinal cord to the fore and hind limbs, fibres are not given off to the ganglia. Thus these connecting or "proganglionic" fibres are separated into three divisions. In front of the nerve roots for the fore limbs is the head or cranial division; between the nerve roots for the fore limbs and those for the hind limbs is the trunk division (or thorac-ico-lumbar division, or, in the older terminology, the "sympathetic system"); and after the nerve roots for the hind limbs the sacral division.

This system of outlying neurones, with post-

ganglionic fibres innervating the viscera, and with preganglionic fibres reaching out to them from the cerebrospinal system, has been called by Langley, to whom we are indebted for most of our knowledge of its organization, the autonomic nervous system. 2 This term indicates that the structures which the system supplies are not subject to voluntary control, but operate to a large degree independently. As we have seen, a highly potent mode of influencing these structures is through conditions of pain and emotional excitement. The parts of the autonomic system—the cranial, the sympathetic, and the sacral—have a number of peculiarities which are of prime importance in accounting for the bodily manifestations of such affective states.

THE EXTENSIVE DISTRIBUTION OF NEURONES OF THE "SYMPATHETIC" DIVISION AND THEIR ARRANGEMENT FOR DIFFUSE ACTION

The fibres of the sympathetic division differ from those of the other two divisions in being distributed through the body very widely. They go to the eyes, causing dilation of the pupils. They go to the heart and, when stimulated, they cause it to beat rapidly. They carry impulses to arteries and arterioles of the skin, the abdominal viscera, and other parts, keeping the smooth muscles of the vessel walls in a state of slight con-

traction or tone, and thus serving to maintain an arterial pressure sufficiently high to meet sudden demands in any special region; or, in times of special discharge of impulses, to increase the tone and thus also the arterial pressure. They are distributed extensively to the smooth muscle attached to the hairs; and when they cause this muscle to contract, the hairs are erected. They go to sweat glands, causing the outpouring of sweat. These fibres pass also to the entire length of the gastro-intestinal canal. And the inhibition of digestive activity which, as we have learned, occurs in pain and emotional states, is due to impulses which are conducted outward by the splanchnic nerves —the preganglionic fibres that reach to the great ganglia in the upper abdomen (see Fig. 1)—and thence are spread by post-ganglionic fibres all along the gut. 3 They innervate likewise the genito-urinary tracts, causing contraction of the smooth muscle of the internal genital organs, and usually relaxation of the bladder. Finally they affect the liver, releasing the storage of material there in a manner which may be of great service to the body in time of need. The extensiveness of the distribution of the fibres of the sympathetic division is one of its most prominent characteristics.

Another typical feature of the sympathetic division is an arrangement of neurones for diffuse

discharge of the nerve impulses. As shown dia-grammatically in Fig. 1, the preganglionic fibres from the central nervous system may extend through several of the sympathetic ganglia and give off in each of them connections to cell bodies of the outlying neurones. Although the neurones which transmit sensory impulses from the skin into spinal cord have similar relations to nerve cells lying at different levels of the cord, the operation in the two cases is quite different. In the spinal cord the sensory impulse produces directed and closely limited effects, as, for example, when reflexes are being evoked in a "spinal" animal (i. e., an animal with the spinal cord isolated from the rest of the central nervous system), the left hind limb is nicely lifted, in response to a harmful stimulus applied to the left foot, without widespread marked involvement of the rest of the body in the response. 4 In the action of the sympathetic division, on the contrary, the connection of single preganglionic fibres with numerous outlying neurones seems to be not at all arranged for specific effects in this or that particular region. There are, to be sure, in different circumstances variations in the degree of activity of different parts; for example, it is probable that dilation of the pupil in the cat occurs more readily than erection of the hairs. It may be in this instance, however, that specially direct

pathways to the eye are present for common use in non-emotional states (in dim light, e. g.), and that only slight general disturbance in the central nervous system, therefore, would be necessary to send impulses by these well-worn courses. Thus for local reasons (dust, e. g.) tears might flow from excitation of the tear glands by sympathetic impulses, although other parts innervated by this same division might be but little disturbed. AVe have no means of voluntarily wearing these pathways, however, and both from anatomical and physiological evidence the neurone relations in the sympathetic division of the autonomic system seem devised for widespread diffusion of nervous impulses.

THE ARRANGEMENT OF NEURONES OF THE CRANIAL AND SACRAL DIVISIONS FOR SPECIFIC ACTION

The cranial and sacral autonomic divisions differ from the sympathetic in having only restricted distribution (see Fig. 1). The third cranial nerves deliver impulses from the brain to ganglia in which lie the cell bodies of neurones innervating smooth muscle only in the front of the eyes. The vagus nerves are distributed to the lungs, heart, stomach, and small intestine. As shown diagrammatically in Fig. 1, the outlying neurones in the last three of these organs lie within the organs themselves. By this arrangement, although the preganglionic fibres of

the vagi are extended in various directions to structures of quite diverse functions, singleness and separateness of connection of the peripheral organs with the central nervous system is assured. The same specific relation between efferent fibres and the viscera is seen in the sacral autonomic. In this division the preganglionic fibres pass out from the spinal cord to ganglia lying in close proximity to the distal colon, the bladder, and the external genitals. And the post-ganglionic fibres deliver the nerve impulses only to the nearby organs. Besides these innervations the cranial and sacral divisions supply individual arteries with "dilator nerves"—nerves causing relaxation of the particular vessels. Quite typically, therefore, the efferent fibres of the two terminal divisions of the autonomic differ from those of the mid-division in having few of the diffuse connections characteristic of the mid-division, and in innervating distinctively the organs to which they are distributed. The cranial and sacral preganglionic fibres resemble thus the nerves to skeletal muscles, and their arrangement provides similar possibilities of specific and separate action in any part, without action in other parts.

THE CRANIAL DIVISION A CONSERVER OP BODILY KESOURCES

The cranial autonomic, represented by the

vagus nerves, is the part of the visceral nervous

system concerned in the psychic secretion of the gastric juice. Pawlow showed that when these nerves are severed psychic secretion is abolished. The cranial nerves to the salivary glands are similarly the agents for psychic secretion in these organs, and are known to cause also dilation of the arteries supplying the glands, so that during activity the glands receive a more abundant flow of blood. As previously stated (see p. 13), the evidence for a psychic tonus of the gastro-intestinal musculature rests on a failure of the normal contractions if the vagi are severed before food is taken, in contrast to the continuance of the contractions if the nerves are severed just afterwards. The vagi artificially excited are well-known as stimulators of increased tone in the smooth muscle of the alimentary canal. Aside from these positive effects on the muscles of the digestive tract and its accessory glands, cranial autonomic fibres cause contraction of the pupil of the eye, and slowing of the heart rate.

A glance at these various functions of the cranial division reveals at once that they serve for bodily conservation. By narrowing the pupil of the eye they shield the retina from excessive light. By slowing the heart rate, they give the cardiac muscle longer periods for rest and in-vigoration. And by providing for the flow of saliva and gastric juice and by supplying the mus-

cular tone necessary for contraction of the alimentary canal, they prove fundamentally essential to the processes of proper digestion and absorption by which energy-yielding material is taken into the body and stored. To the cranial division of the-visceral nerves, therefore, belongs the quiet service of building up reserves and fortifying the body against times of need or stress.

THE SACRAL DIVISION A GROUP OF MECHANISMS FOR EMPTYING

Sacral autonomic fibres cause contraction of the rectum and distal colon and also contraction of the bladder. In both instances the effects result reflexly from stretching of the tonically contracted viscera by their accumulating contents. No affective states precede this normal action of the sacral division and even those which accompany or follow are only mildly positive; a feeling of relief rather than of elation usually attends the completion of the act of defecation or micturition—though there is testimony to the contrary.

The sacral autonomic fibres also include, however, the nervi erigentes which bring about engorgement of erectile tissue in the external genitals. According to Langley and Anderson 5 the sacral nerves have no effect on the internal generative organs. The vasa deferentia and the seminal vesicles whose rhythmic contractions

mark the acme of sexual excitement in the male, and the uterus whose contractions in the female are probably analogous, are supplied only by lumbar branches—part of the sympathetic division. These branches also act in opposition to the nervi erigentes and cause constriction of the blood vessels of the external genitals. The sexual orgasm involves a high degree of emotional excitement; but it can be rightly considered as essentially a reflex mechanism; and, again in this instance, distention of tubules, vesicles, and blood vessels can be found at the beginning of the incident, and relief from this distension at the end. Although distention is the commonest occasion for bringing the sacral division into activity it is not the only occasion. Great emotion, such as is accompanied by nervous discharges via the sympathetic division, may also be accompanied by discharges via the sacral fibres. The involuntary voiding of the bladder and lower gut at times of violent mental stress is well-known. Veterans of wars testify that just before the beginning of a battle many of the men have to retire temporarily from the firing line. And the power of sights and smells and libidinous thoughts to disturb the regions controlled by the nervi erigentes proves that this part of the autonomic system also has its peculiar affective states. The fact that one part of the sacral division, e. g., the distribu-

tion to the bladder, may be in abeyance, while another part, e. g., the distribution to the rectum, is active, illustrates again the directive discharge of impulses which has been previously described as characteristic of the cranial and sacral portions of the autonomic system.

Like the cranial division, the sacral is engaged in internal service to the body, in the performance of acts leading immediately to greater comfort.

THE SYMPATHETIC DIVISION ANTAGONISTIC TO BOTH THE CRANIAL AND THE SACRAL

As indicated in the foregoing description many of the viscera are innervated both by the cranial or sacral part of the autonomic and by the sympathetic. When the mid-part meets either end-part in any viscus their effects are antagonistic. Thus the cranial supply to the eye contracts the pupil, the sympathetic dilates it; the cranial slows the heart, the sympathetic accelerates it; the sacral contracts the lower part of the large intestine, the sympathetic relaxes it; the sacral relaxes the exit from the bladder, the sympathetic contracts it. These opposed effects are indicated in Fig. 1 by 4- for contraction, acceleration or increased tone; and by - for inhibition, relaxation, or decreased tone.*

* The vagus nerve, when artificially stimulated, has a primary, brief inhibitory effect on the stomach and small intestine ; its main function, however, as already stated, is to pro-

Sherrington has demonstrated that the setting of skeletal muscles in opposed groups about a joint or system of joints—as in flexors and extensors—is associated with an internal organization of the central nervous system that provides for relaxation of one group of the opposed muscles when the other group is made to contract. This "reciprocal innervation of antagonistic muscles," as Sherrington has called it, 6 is thus a device for orderly action in the body. As the above description has shown, there are peripheral oppositions in the viscera corresponding to the oppositions between flexor and extensor muscles. In all probability these opposed innervations of the viscera have counterparts in the organization of neurones in the central nervous system. Sherrington has noticed, and I can confirm the observation, that even though the sympathetic supply to the eye is severed and is therefore incapable of causing dilation of the pupil, nevertheless the pupil dilates in a paroxysm of anger—due, no doubt (because the response is too rapid to be mediated by the blood stream), to central inhibition of the cranial nerve supply to the constrictor muscles—i. e., an inhibition of the muscles which naturally oppose the dilator action of the sympathetic. Pain, the major emotions—fear and

duce increased tone and contraction in these organs. This double action of the vagus is marked thus, T, in Fig. 1.

rage—and also intense excitement, are manifested in the activities of the sympathetic division. When in these states impulses rush out over the neurones of this division they produce all the changes typical of sympathetic excitation, such as dilating the pupils, inhibiting digestion, causing pallor, accelerating the heart, and various other well-known effects. The impulses of the sympathetic neurones, as indicated by their dominance over the digestive process, are capable of readily overwhelming the conditions established by neurones of the cranial division of the auto-nomic system.

NEURONES OF THE SYMPATHETIC DIVISION AND ADRENAL SECRETION HAVE THE SAME ACTION

Lying anterior to each kidney is a small body— the adrenal gland. It is composed of an external portion or cortex, and a central portion or medulla. From the medulla can be extracted a substance, called variously suprarenin, adrenin, epi-nephrin or "adrenalin,"* which, in extraordinarily minute amounts, affects the structures innervated by the sympathetic division of the autonomic sys-

* The name "adrenalin" is proprietary. "Epinephrin" and "adrenin" have been suggested as terms free from commercial suggestions. As adrenin is shorter and more clearly related to the common adjectival form, adrenal, I have followed Schafer in using adrenin to designate the substanoe produced physiologically by the adrenal glands.

tern precisely as if they were receiving nervous impulses. For example, when adrenin is injected into the blood, it will cause pupils to dilate, hairs to stand erect, blood vessels to be constricted, the activities of the alimentary canal to be inhibited, and sugar to be liberated from the liver. These effects are not produced by action of the substance on the central nervous system, but by direct action on the organ itself. 7 And the effects occur even after the structures have been removed from the body and kept alive artificially.

The adrenals are glands of internal secretion, i. e., like the thyroid, parathyroid, and pituitary glands, for example; they have no connection with the surface of the body, and they give out into the blood the material which they elaborate. The blood is carried away from each of them by the lumbo-adrenal vein which empties either into the renal vein or directly into the inferior vena cava just anterior to the openings of the renal veins. The adrenal glands are supplied by preganglionic fibres of the autonomic group, 8 shown in solid line in Fig. 1. This seems an exception to the general rule that gland cells have an outlying neurone between them and the neurones of the central nervous system. The medulla of the adrenal gland, however, is composed of modified nerve cells, and may therefore be regarded as offering exceptional conditions.

The foregoing brief sketch of the organization of the autonomic system brings out a number of points that should be of importance as bearing on the nature of the emotions which manifest themselves in the operations of this system. Thus it is highly probable that the sympathetic division, because arranged for diffuse discharge, is likely to be brought into activity as a whole, whereas the sacral and cranial divisions, arranged for particular action on separate organs, may operate in parts. Also, because antagonisms exist between the middle and either end division of the autonomic, affective states may be classified according to their expression in the middle or an end division and these states would be, like the nerves, antagonistic in character. And finally, since the adrenal glands are innervated by autonomic fibres of the mid-division, and since adrenal secretion stimulates the 'same activities that are stimulated nervously by this division, it is possible that disturbances in the realm of the sympathetic, although initiated by nervous discharge, are automatically augmented and prolonged through chemical effects of the adrenal secretion.

REFERENCES

1 Cannon: The American Journal of Psychology, 1914, xxv, p. 257.

2 For a summary of his studies of the organization of the autonomic system, see Langley: Ergebnisse der Physiologic, Wiesbaden, 1903, ii 2 , p. 818.

3 See Cannon: American Journal of Physiology, 1905, xiii, p. xxii.

4 See Sherrington: The Integrative Action of the Nervous System, New York, 1909, p. 19.

5 Langley and Anderson: Journal of Physiology, 1895, xix, see pp. 85, 122.

6 Sherrington: Loc. cit., p. 90.

7 Elliott: Journal of Physiology, 1905, xxxii, p. 426.

8 See Elliott: Journal of Physiology, 1913, xlvi, p. 289 ff.

CHAPTER III

METHODS OF DEMONSTRATING ADEENAL SECRETION AND ITS NERVOUS CONTROL

As stated in the first chapter, the inhibition of gastric secretion produced by great excitement long outlasts the presence of the object which evokes the excitement. The dog that was enraged by seeing a cat for five minutes secreted only a few drops of gastric juice during the next fifteen minutes. Why did the state of excitation persist so long after the period of stimulation had ended? This question, which presented itself to me while reading Bickel and Sasaki's paper, furnished the suggestion expressed at the close of the last chapter, that the excitement might provoke a flow of adrenal secretion, and that the changes originally induced in the digestive organs by nervous impulses might be continued by circulating adrenin. The prolongation of the effect might be thus explained. Whether that idea is correct or not has not been tested. Its chief service was in leading to an enquiry as to whether

the adrenal glands are in fact stimulated to action in emotional excitement. The preganglionic fibres passing to the glands are contained in the splanchnic nerves. What is the effect of splanchnic stimulation?

THE EVIDENCE THAT SPLANCHNIC STIMULATION INDUCES ADRENAL SECRETION

It was in 1891 that Jacobi l described nerve fibres derived from the splanchnic trunks which were distributed to the adrenal glands. Six years later Biedl 2 found that these nerves conveyed vaso-dilator impulses to the glands, and he suggested that they probably conveyed also secretory impulses. Evidence in support of this suggestion was presented the following year by Dreyer, 3 who demonstrated that electrical excitation of the splanchnic nerves produced in the blood taken from the adrenal veins an increased amount of a substance having the power of raising arterial blood pressure, and that this result was independent of accompanying changes in the blood supply to the glands. The conclusion drawn by Dreyer that this substance was adrenin has been confirmed in various ways by later observers. Tscheboksaroff 4 repeated Dreyer's procedure and found in blood taken from the veins after splanchnic stimulation evidences of the presence of adrenin that were previously absent. Asher 5

observed a rise of blood pressure when the glands were stimulated in such a manner as not to cause constriction of the arteries—the rise was therefore assumed to be due to secreted adrenin. Dilation of the pupil was used by Meltzer and Joseph 6 to prove secretory action of the splanch-nics on the adrenal glands; they found that stimulation of the distal portion of the cut splanchnic nerve caused the pupil to enlarge—an effect characteristic of adrenin circulating in the blood. Elliott 7 repeated this procedure, but made it a more rigorous proof of internal secretion of the adrenals by noting that the effect failed to appear if the gland on the stimulated side was removed. Additional proof was brought by myself and Lyman 8 when we found that the typical drop in arterial pressure produced in cats by injecting small amounts of adrenin could be exactly reproduced by stimulating the splanchnic nerves after the abdominal blood vessels, which contract when these nerves are excited, were tied so that no changes in them could occur to influence the rest of the circulation.

The problem of splanchnic influence on the adrenal glands Elliott attacked by a still different method. Using, as a measure, the graded effects of graded amounts of adrenin on blood pressure, he was able to assay the quantity of adrenin in adrenal glands after various conditions had been

allowed to prevail. The tests were made on cats. In these animals each adrenal gland is supplied only by the splanchnic fibres of its own side, and the two glands normally contain almost exactly the same amount of adrenin. Elliott 9 found that when the gland on one side was isolated by cutting its splanchnic supply, and then impulses were sent along the intact nerves of the other side, either by disturbing the animal or by artificial excitation of the nerves, the gland to which these fibres reached invariably contained less adrenin, often very much less, than the isolated gland. Kesults obtained by the method employed by Elliott have been confirmed with remarkable exactness in results obtained by Folin, Denis and myself, 10 using a highly sensitive color test after adding the gland extract to a solution of phosphotungstic acid.

All these observations, with a variety of methods, and by a respectable number of reliable investigators, are harmonious in bringing proof that artificial stimulation of the nerves leading to the adrenal glands will induce secretory activity in the adrenal medulla, and that in consequence adrenin will be increased in the blood. The fact is therefore securely established that in the body a mechanism exists by which these glands can be made to discharge this peculiar substance promptly into the circulation.

THE QUESTION OF ADRENAL SECRETION IN EMOTIONAL EXCITEMENT

As we have already seen, the phenomena of a great emotional disturbance in an animal indicate that sympathetic impulses dominate the viscera. When, for example, a cat becomes frightened, the pupils dilate, the activities of the stomach and intestines are inhibited, the heart beats rapidly, the hairs of the back and tail stand erect—from one end of the animal to the other there are abundant signs of nervous discharges along sympathetic courses. Do not the adrenal glands share in this widespread subjugation of the viscera to sympathetic control?

This question, whether the common excitements of an animal's life might be capable of evoking a discharge of adrenin, was taken up by D. de la Paz and myself in 1910. We made use of the natural enmity between two laboratory animals, the dog and the cat, to pursue pur experiments. In these experiments the cat, fastened in a comfortable holder (the holder already mentioned as being used in X-ray studies of the movements of the alimentary canal), was placed near a barking dog. Some cats when thus treated showed almost no signs of fear; others, with scarcely a movement of defence, presented the typical picture. In favorable cases the excitement was allowed to prevail for five or ten minutes, and in

a few cases longer. Samples of blood were taken within a few minutes before and after the period.

THE METHOD OF SECURING BLOOD FROM NEAR THE ADRENAL

VEINS

The blood was obtained from the inferior vena cava anterior to the opening of the adrenal veins, i. e., at a point inside the body near the level of the notch at the lower end of the sternum. To get the blood so far from the surface without disturbing the animal was at first a difficult problem. We found, however, that by making anesthetic with ethyl chloride the skin directly over the femoral vein high in the groin, the vein could be quickly bared, cleared of connective tissue, tied, and opened, without causing any general disturbance whatever. A long, fine, flexible catheter (2.4 millimeters in diameter) which had previously been coated with vaseline inside and out, to lubricate it and to delay the clotting of blood within it, was now introduced into the opening in the femoral vein, thence through the iliac and on into the inferior cava to a point near the level of the sternal notch. A thread tied around this tube where, after being inserted to the proper distance, it disappeared into the femoral vein, marked the extent of insertion, and permitted a later introduction to the same extent. This slight operation—a venesection, commonly practised on

onr ancestors—consumed only a few minutes, and as the only possibility of causing pain was guarded against by local anesthesia, the animal remained tranquil throughout. Occasionally it was necessary to stroke the cat's head gently to keep her quiet on the holder, and under such circumstances I have known her to purr during all the preparations for obtaining the blood, and while the blood was being taken.

The blood (3 or 4 cubic centimetres) was slowly drawn through the catheter into a clean glass syringe. Care was taken to avoid any marked suction such as might cause collapse of the vein near the inner opening of the tube. As soon as the blood was secured, the catheter was removed and the vein tied loosely, to prevent bleeding. The blood was at once emptied into a beaker, and the fibrin whipped from it by means of fringed rubber tubing fitted over a glass rod. Since this defibrinated blood was obtained while the animal was undisturbed, it was labelled "quiet blood."

The animal was then exposed to the barking dog, as already described, and immediately thereafter blood was again removed, from precisely the same region as before. This sample, after being defibrinated, was labelled "excited blood." The two samples, the "quiet" and the "excited," both obtained in the same manner and subse-

quently treated in the same manner, were now tested for their content of adrenin.

THE METHOD OF TESTING THE BLOOD FOR ADRENIN

It was desirable to use as a test tissues to which the blood was naturally related. As will be recalled, adrenin affects viscera even after they have been removed from the body, just as if they were receiving impulses via sympathetic fibres, and further, that sympathetic fibres normally deliver impulses which cause contraction of the internal genitals and relaxation of the stomach and intestines. The uterus has long been employed as a test for adrenin, the presence of which it indicates by increased contraction. That isolated strips of the longitudinal muscle of the intestine, which are contracting rhythmically, are characteristically inhibited by adrenin in dilutions of 1 part in 20 millions, had been shown by Magnus in 1905. Although, previous to our investigation in 1910, this extremely delicate reaction had not been used as a biological signal for adrenin, it possesses noteworthy advantages over other methods. The intestine is found in all animals and not in only half of them, as is the uterus; it is ready for the test within a few minutes, instead of the several hours said to be required for the best use of the uterus preparation; 11 and it responds by relaxing. This last characteristic

is especially important, for in deflbrinated blood there are, besides adrenin, other substances capable of causing contraction of smooth muscle, 12 and liable therefore to lead to erroneous conclusions when a structure which responds by contracting, such as uterus or artery, is used to prove whether adrenin is present. On the other hand, substances producing relaxation of smooth muscle are few, and are unusual in blood. 13

We used, therefore, the strip of intestinal muscle as an indicator. Later Hoskins 14 modified our procedure by taking, instead of the strip, a short segment of the rabbit intestine. The segment is not subjected to danger of injury during its preparation, and when fresh it is almost incredibly sensitive. It may be noticeably inhibited by adrenin, 1 part in 200 millions!

The strip, or the intestinal segment, was suspended between minute wire pincers (serrcs fines) in a cylindrical chamber 8 millimeters in diameter and 5 centimeters deep. By a thread attached to the lower serre fine the preparation was drawn into the chamber, and was held firmly; by the upper one it was attached to the short end of a writing lever (see Fig. 2). When not exposed to blood, the strip was immersed in a normal solution of the blood salts (Singer's). The blood or the salt solution could be quickly withdrawn from or introduced into the chamber, with-

ADRENAL SECRETION

out disturbing the muscle, by means of a fine pipette passed down along the inner surface. The chamber and its contents, the stock of Ringer's

FIGURE 2.—Diagram of the arrangements for recording contractions of the intestinal muscle.

solution, and the samples of "quiet" and "excited" blood were all surrounded by a large volume of water kept approximately at body temperature (37° C.). Through the blood or the salt solution in the chamber oxygen was passed in a slow but steady stream of bubbles. Under these circumstances the strip will live for hours, and will contract and relax in a beautifully regular rhythm, which may be recorded graphically by the writing lover.

The first effect of surrounding the muscle with blood, whether "quiet" or "excited," was to send it into a strong contraction which might persist, sometimes with slight oscillations, for a minute or two (see Figs. 4 and 5), After the initial shortening, the strip, if in quiet blood soon began to

contract and relax rhythmically and with each relaxation to lengthen more, until a fairly even base line appeared in the written record. At this stage the addition of fresh "quiet" blood usually had no effect, even though the strip were washed once with Einger's solution before the second portion of the blood was added. For comparison of the effects of "quiet" and "excited" blood on the contracting strip, the two samples were each added to the muscle immediately after the Ringer's solution had been removed, or they were applied to the muscle alternately and the differences in effect then noted. The results obtained by these methods are next to be presented.

REFERENCES

1 Jacobi: Archiv fiir experimentelle Pathologic und Phar-makologie, 1891, xxix, p. 185.

2 Biedl: Archiv f iir die gesammte Physiologic, 1897, Ixvii, pp. 456, 481.

8 Dreyer: American Journal of Physiology, 1898-99, ii, p. 219.

4 Tscheboksarof?: Archiv f iir die gesammte Physiologic, 1910, cxxxvii, p. 103.

5 Asher: Zcitschrif t f iir Biologic, 1912, Iviii, p. 274.

6 Meltzer and Joseph: American Journal of Physiology,

1912, xxix, p. xxxiv.

7 Elliott: Journal of Physiology, 1912, xliv, p. 400.

8 Cannon and Lyman: American Journal of Physiology,

1913, xxxi, p. 377.

9 Elliott: Journal of Physiology, 1912, xliv, p. 400.

10 Folin, Cannon and Denis: Journal of Biological Chemistry, 1913, xiii, p. 477.

11 Fraenkel: Archiv fiir experimentelle Pathologie und Pharmakologie, 1909, Ix, p. 399.

12 See O'Connor: Archiv f iir die experimentelle Pathologie und Pharmakologie, 1912, Ixvii, p. 206.

13 Grutzner: Ergebnisse der Physiologic, 1904, iii 2 , p. 66; Magnus: Loc. cit., p. 69.

14 IIoskins: Journal of Pharmacology and Experimental Therapeutics, 1911, iii, p. 95.

CHAPTER IV

ADKENAL SECKETION IN STRONG EMOTIONS AND PAIN

If the secretion of adrenin is increased in strong emotional states and in pain, that constitutes a fact of considerable significance, for, as already mentioned, adrenin is capable of producing many of the bodily changes which are characteristically manifested in emotional and painful experiences. It is a matter of prime importance for further discussion to determine whether the adrenal glands are in fact roused to special activity in times of stress.

THE EVIDENCE THAT ADRENAL SECRETION Is INCREASED IN EMOTIONAL EXCITEMENT

That blood from the adrenal veins causes the relaxation of intestinal muscle characteristic of adrenal extract or adrenin is shown in Fig. 3. The muscle was originally beating in blood which contained no demonstrable amount of adrenal secretion ; this inactive blood was replaced by blood

ADEENAL SECRETION IN EMOTIONS 53

from the adrenal veins, obtained after quick etherization. Etherization, it will be recalled, is accompanied by a "stage of excitement." Relaxation occurred almost immediately (at b), Then the rhythm was renewed in the former

FIGURE 3.—Intestinal muscle beating in inactive blood, which was withdrawn from the chamber at a. Blood from the adrenal vein of an animal excited by etherization was substituted at 6, and withdrawn at c. Contractions were restored in the original inactive blood which was removed at d. Blood from the renal vein (same ani-inal) was added at e.

In this and subsequent records time is marked in half minutes.

blood, and thereupon the muscle was surrounded with blood from the vein leading away from the left kidney, i. e., blood obtained from the same animal and under the same conditions as the adrenal blood, but from a neighboring vein. No relaxation occurred. l>y this and other similar tests tlie reliability of the method was proved.

In no instance did blood from the inferior vena cava of the quiet normal animal produce relaxation. On the other hand, blood from the animal after emotional excitement showed more or less promptly the typical relaxation. In Fig. 4 is

FIGURE 4.—Alternate application of " excited" blood (at 6 and/) and "quiet" blood (at d), from the same animal, to intestinal muscle initially beating in Ringer's solution.

represented the record of intestinal muscle which was beating regularly in Einger's solution. At a the Einger's solution was removed, and at & "excited" blood was added; after the preliminary shortening, which, as already stated, occurs at the first immersion in blood, the muscle lengthened gradually into complete inhibition. At c the "excited" blood was removed, and at d "quiet" blood was added in its place. The muscle at once began fairly regular rhythmic beats. At e the "quiet" blood was removed, and at / the "excited" blood was again applied. The muscle lengthened almost immediately into an inhibited state. In this instance the "excited" blood was taken after

ADEENAL SECRETION IN EMOTIONS 55

the cat had been barked at for about fifteen minutes.

The increase of effect with prolongation of the period of excitement is shown in Fig. 5. A is the

FIGURE 5.—The effect of prolonging the excitement. A. the record in "quiet" serum; B, in defibrinated blood after eleven minutes of excitement; and C, in serum after fifteen minutes of excitement.

record of contractions after the muscle was surrounded with "quiet" blood serum. B shows the gradual inhibition which occurred when the muscle was surrounded with defibrinated blood taken when the animal had been excited eleven minutes. And C is the record of rapid inhibition after fifteen minutes of excitement. In other instances the effect was manifested merely by a lowering of the tonus of the muscle, and a notable slowing of the beats, without, however, a total abolition of them.

The inference that this inhibition of contraction of the intestinal muscle is due to an increased amount of adrenal secretion in the "excited"

blood de la Paz and I justified on several grounds: (1) The inhibition was produced by "excited" blood from the inferior vena cava anterior to the mouths of the adrenal veins, when blood from the femoral vein, taken at the same time, had no inhibitory influence. Since blood from the femoral vein is typical of the cava blood below the entrance of the kidney veins, the conclusion is warranted that the difference of effect of the two samples of blood is not due to any agent below the kidneys. But that blood from the kidneys does not cause the relaxation is shown in Fig. 3.

FIGURE 6.—Failure of the cava blood (added at a) to produce inhibition when excitement has occurred after removal of the adrenal glands. The inn^-le later proved sensitive to adrenm in blood in the ratio 1:1,000,000.

The only other structures which could alter the blood between the two points at which it was taken are the adrenal glands, and the material

ADEENAL SECEETION IN EMOTIONS 57

secreted by them would produce precisely the inhibition of contraction which was in fact produced.

(2) If in ether anesthesia the blood vessels leading to and from the adrenal glands are first carefully tied, and then the glands are removed, ex-

FIGURE 7.—Effect of adding adrenin 1:1,000,000 (A), 1:2,000,000 (B), and 1:3,000,000 (C), to formerly inactive blood. In each case a marks the moment when the quiet blood was removed, and 6, the time when the blood with adrenin was added.

citement four or five hours later, before the weakness that follows the removal has become prominent, does not alter the blood so that the typical inhibition occurs (see Fig. 6). Thus, although the animal shows all the characteristic signs of sympathetic stimulation, the blood, in the absence of the adrenals, remains unchanged.

(3) As already shown, sometimes the effect pro-

duced by the "excited" blood was prompt inhibition, sometimes the inhibition followed only after several beats, and sometimes a slowing and shortening of contractions, with a lower tone, were the sole signs of the action of adrenin. All these degrees of relaxation can be duplicated by adding to inactive blood varying amounts of adrenin. Fig. 7 shows the effects, on a somewhat insensitive muscle preparation, of adding adrenin, 1:1,000,000 (A), 1:2,000,000 (B), and 1:3,000,000 (C), to different samples of blood previously without inhibitory influence. These effects of adrenin and the effects produced by blood taken near the opening of the adrenal veins are strikingly analogous.

(4) Emden and v. Furth 1 have reported that 0.1 gram of suprarenin chloride disappears almost completely in two hours if added to 200 cubic centimeters of defibrinated beef blood, and the mixture constantly aerated at body temperature. "Excited" blood which produces inhibition loses that power on standing in the cold for twenty-four hours, or on being kept warm and agitated with bubbling oxygen. This change is illustrated in Fig. 8; the power of the "excited" blood to inhibit the contractions of the intestinal muscle when record A was written was destroyed after three hours of exposure to bubbling oxygen, as shown by record B. The destruction of adrenin and

ADRENAL SECRETION IN EMOTIONS 59

the disappearance of tlie effect which adrenin would produce are thus closely parallel. All these considerations, taken with the proof

FIGURE 8.—The effect of bubbling oxygen through active blood. A, relaxation after active blood applied at a; B, failure of relaxation when the same blood, oxygenated three hours, was applied to a fresh strip at b,

that sympathetic impulses increase secretion of the adrenal glands, and taken also with the evidence that, during such emotional excitement as was employed in these experiments, signs of sympathetic discharges appeared throughout the animal from the dilated pupil of the eye to the standing hairs of the tail-tip, led us to the conclusions that the characteristic action of adrenin on intestinal muscle was in fact, in our experiments, due to secretion of the adrenal glands, and that that secretion is increased in great emotion.

THE EVIDENCE THAT ADRENAL SECRETION is INCREASED BY "PAINFUL" STIMULATION

As mentioned in the first chapter, stimulation of sensory fibres in one of the larger nerve trunks

is known to result in such, nervous discharges along sympathetic paths as to produce marked inhibition of digestive processes. Other manifestations of sympathetic innervations—e. g., contraction of arterioles, dilation of pupils, erection of hairs— are also demonstrable. And since the adrenal glands are stimulated to activity by sympathetic impulses, it was possible that they would be affected as are other structures supplied with sympathetic fibres, arid that they would secrete in greater abundance when sensory nerves were irritated.

The testing of this possibility was undertaken by Hoskins and myself in 1911. Since bodily changes from "painful" stimulation can in large degree be produced in an anesthetized animal, without, however, an experience of pain by the animal, it was possible to make the test quite simply. The sensory stimulus was a rapidly interrupted induced current applied to the sciatic nerve. The current was increased in strength as time passed, and thus the intensity of the effect, indicated by continuous dilation of the pupils, was maintained. There was no doubt that such stimulation would have caused very severe pain if the animal had not been anesthetized. Indeed, the stimulus used was probably much stronger than would be necessary to obtain a positive result in the absence of the anesthetic (urethane), which markedly lessens the irritabil-

ADRENAL SECRETION IN EMOTIONS 61

ity of visceral nerve fibres. 2 In different instances the stimulation lasted from three to six minutes. Throughout the period there was markedly increased rapidity and depth of breathing. As Fig. 9 shows, the normal blood, removed

FIGURE 9.—Intestinal muscle beating in normal vena cava blood, removed at 1 and renewed at 2. At 3 normal blood removed. At 4 contraction inhibited by vena cava blood drawn after sensory stimulation; at 5 removed. At 6 Rin-trpr's solution auhstitutpd.

from the vena cava before stimulation, caused no inhibition of the beating segment, whereas that removed afterwards produced a deep relaxation. Hoskins and I showed that the increased respiration which accompanies "painful" stimulation does not augment adrenal activity. We concluded, therefore, that when a sensory trunk is strongly excited the adrenal glands are reflexly stimulated, and that they pour into the blood stream an increased amount of adrenin.

CONFIRMATION OF OUR RESULTS BY OTHER OBSERVERS

The foregoing experiments and conclusions were reported in 1911. In 1912. Anrep 3 found that a denervated limb at first expands but later quickly contracts on sensory stimulation. The phase of contraction disappeared if the adrenal glands were removed. Since the limb was denervated, the only agency which could have caused contraction in the presence of increased blood pressure must have been brought by the blood stream. And, since the phenomenon disappeared on exclusion of the adrenals, the conclusion was drawn that adrenal secretions, poured out in consequence of reflex stimulation, produced the observed vaso-constric-tion. The following year, Hitchings, Sloan and Austin, 4 using our method, found that after great fear and rage had been induced in a cat, the adrenin reaction was clearly demonstrated. The reaction did not occur, however, if the splanchnic

ADEENAL SECEETION IN EMOTIONS 63

nerves had been previously severed. In 1913, also, Levy 5 reported that sciatic stimulation occasioned irregularity of the denervated heart, an effect likewise seen when a splanchnic nerve was stimulated, but lacking after adrenal extirpation in the stimulated side. Again the conclusion was drawn that the effect was due to adrenin discharged re-flexly. Similar evidence was reported in 1917 by Florovsky, 6 with reference to the denervated salivary gland. Furthermore, Eedfield noted (1917) 7 that nervous excitement causes a contraction of the melanophores in the denervated skin of the horned toad, a reaction which is absent after removal of the adrenal glands. Eecently I have myself 8 completely confirmed all our earlier work, by using the denervated heart as an indicator. The only opposition to all these positive results is that offered by Stewart and Eogoff, 0 who failed to demonstrate any effects of sensory stimulation in adrenal activity. Since they used a peculiar method, however, known to disturb profoundly the region innervated by the splanchnic nerves, their negative results cannot be regarded as offsetting the positive findings of all other observers.

The logic of all these experiments may be briefly summed up. That the adrenal glands are subject to splanchnic influence has been demonstrated anatomically and by the physiological effects of their secretion after artificial stimulation of the splanchnic nerves. Impulses are normally sent along these nerves, in the natural conditions of

life, when animals become greatly excited, as in fear and rage and pain. There is every probability, therefore, that these glands are stimulated to extra secretion at such times. Both by an exceedingly delicate biological test (intestinal muscle) and by an examination of the glands themselves, clear evidence has been secured that in pain and deep emotion the glands do, in fact, pour out an excess of adrenin into the circulating blood.

Here, then, is a remarkable group of phenomena —a pair of glands stimulated to activity in times of strong excitement and by such nerve impulses as themselves produce at such times profound changes in the viscera; and a secretion given forth into the blood stream by these glands, which is capable of inducing by itself, or of augmenting, the nervous influences which induce the very changes in the viscera which accompany suffering and the major emotions. What may be the significance of these changes, occurring when conditions of pain and great excitement—experiences common to animals of most diverse types and probably known to their ancestors for ages past —lay hold of the bodily functions and determine the instinctive responses?

Certain remarkable effects of injecting adrenin into the blood have for many years been more or less well recognized. For example, when injected it causes liberation of sugar from the liver into

ADRENAL SECRETION IN EMOTIONS 65

the blood stream. It relaxes the smooth muscle of the bronchioles. Some old experiments indicated that it acts as an antidote for muscular fatigue. It alters the distribution of the blood in the body, driving it from the abdominal viscera into the heart, lungs, central nervous system and limbs. And there was some evidence that it renders more rapid the coagulation of the blood. There may be other activities of adrenin not yet discovered—it may co-operate with the products of other glands of internal secretion. And other glands of internal secretion may be stimulated by sympathetic impulses. But we were not concerned with these possibilities. We wished to know whether the adrenin poured out in pain and emotional excitement produced or helped to produce the same effects that follow the injection of adrenin. Our later researches were directed towards securing answers to this question.

REFERENCES

1 Embden and v. Furth: Ilofmeister's Beitnige zur cliemi-scbeu Physiologie und Fathologie, 19O4, iv, p. 423.

2 Elliott: Journal of Physiology, 1005, xxxii, p. 448. s Anrep: Journal of Physiology, 1912, xiv, p. 307.

4 Hltchings, Sloan and Austin: Cleveland Medical Journal, 1913, xii, p. G86.

e Levy: Heart, 1913, iv, p. 342.

o Florovsky: Bulletin de I'AcadSmie Impgriale des Sciences, Petrograd, 1917, ix, p. 119.

TRedfield: Journal of Experimental Zoo'logy, 1918, xxvi, p. 295.

s Cannon: American Journal of Physiology, 1919, 1, p. 399.

9 Stewart and Rogoff: Journal of Experimental Medicine, 1917, xxvi, p. 637.

CHAPTER V

THE INCREASE OF BLOOD SUGAK IN PAIN AND GREAT EMOTION

Sugar is the form in which carbohydrate material is transported in organisms; starch is the storage form. In the bodies of animals that have been well fed the liver contains an abundance of glycogen or "animal starch," which may be called upon in times of need. At such times the glycogen is changed, and set free in the blood as sugar. Ordinarily there is a small percentage of sugar in the blood—from 0.06 to 0.1 per cent. When only this small amount is present the kidneys are capable of preventing its escape in any noteworthy amount. If the percentage rises to the neighborhood of 0.2-0.3 per cent, however, the sugar passes the obstacle set up by the kidneys, and is readily demonstrable in the urine by ordinary tests. The condition of "glycosuria," therefore, may properly be considered, in certain circumstances, as evidence of increased sugar in the blood. The injection of adrenin can liberate sugar from the

INCEEASE OF BLOOD SUGAE 67

liver to such an extent that glycosuria results. Does the adrenal secretion discharged in pain and strong emotional excitement play a role in producing glycosuria under such conditions?

In clinical literature scattered suggestions are to be found that conditions giving rise to emotional states may be the occasion also of more or less permanent glycosuria. Great grief and prolonged anxiety during a momentous crisis have been regarded as causes of individual instances of diabetes, and anger or fright has been followed by an increase in the sugar excreted by persons who already have the disease. Kleen 1 cites the instance of a German officer whose diabetes and whose Iron Cross for valor both came from a stressful experience in the Franco-Prussian War. The onset of the disease in a man directly after his wife was discovered in adultery is described by Naunyn; 2 and this author also mentions two cases in his own practice—one started during the bombardment of Strassburg (1870), the other started a few days after a companion had shot himself. In cases of mental disease, also, states of depression have been described accompanied by sugar in the urine. Schultze 3 has reported that in these cases the amount of glycosuria is dependent on the degree of depression, and that the greatest excretion of sugar occurs in the fear-psychoses. Eaimann 4 has reported that in both

melancholia and mania the assimilation limit of sugar may be lowered. Similar results in the insane have recently been presented by Mita, 5 and by Folin and Denis. 6 The latter investigators found glycosuria in 12 per cent of 192 insane patients, most of whom suffered from depression, apprehension, or excitement. And Arndt 7 has observed glycosuria appearing and disappearing as alcoholic delirium appeared and disappeared in his patients.

Although clinical evidence thus indicates an emotional origin of some cases of diabetes and glycosuria, the intricacies of existence and the complications of disease in human beings throw some doubt on the value of that evidence. Both Naunyn 8 and Hirsclifeld, although mentioning instances of diabetes apparently due to an emotional experience, urge a skeptical attitude toward such statements. It is desirable, therefore, that the question of an emotional glycosuria be tested under simpler and more controllable conditions. "Emotional glycosuria" in experimental animals has indeed been referred to by Waterman and Smit 9 and more recently by Henderson and Underbill. 10 Both these references, however, are based on the work of Bohm and Hoffmann, 11 reported in 1878.

INCEEASE OF BLOOD SUGAR 69

GLYCOSURIA FROM PAIN

Bohm and Hoffmann found that cats, when bound to an operating board, a tube inserted into the trachea (without anesthesia), and in some instances a catheter inserted into the urethra through an opening above the pubis, had in about half an hour an abundance of sugar in the urine. In three determinations sugar in the blood proved slightly above "normal" so long as sugar was appearing in the urine, but returned to "normal" as the glycosuria disappeared. Since they were able to produce the phenomenon by simply binding animals to the holder, they called it "Fes-selungsdiabetcs."

As possible causes of this glycosuria in bound animals, they considered opening the trachea, cooling, and pain. The first two they readily eliminated, and still they found sugar excreted. Pain they could not obviate, and since, without binding the animals, they caused glycosuria by merely stimulating the sciatic nerves, they concluded that painful confinement was itself a sufficient cause. Other factors, however, such as cooling and circulatory disturbances, probably cooperated with pain, they believed, to produce the result. Their observations on cats have been proved true also of rabbits; 12 and recently it has been shown that an operation involving some pain increases blood sugar in dogs. 13 Temporary gly-

cosuria has likewise been noted in association with intense pain in human beings.

Inasmuch as Bohm and Hoffmann did not mention the emotional element in discussing their results, and inasmuch as they admitted that they could not obviate from their experimental procedure pain, which they themselves proved was effective in causing glycosuria, designating what they called "Fesselungsdiabetes" as "emotional glycosuria" is not justified.

EMOTIONAL GLYCOSURIA

The discovery that during strong emotion adrenal secretion is increased, and the fact that injection of adrenin gives rise to glycosuria, suggested that glycosuria might be called forth by emotional excitement, and then that even without the painful element of Bohm and Hoffmann's experiments, sugar might be found in the urine. The testing of this possibility was undertaken by A. T. Shohl, W. S. Wright and myself in 1911.

Our first procedure was a repetition of Bohm and Hoffmann's experiments, freed from the factor of pain. The animals (cats) were bound to a comfortable holder, which left the head unfastened. This holder I had used hundreds of times in X-ray studies of digestion, with many different animals, without causing any signs of even so much as uneasiness. Just as in obser-

INCEEASE OF BLOOD SUGAR 71

vations on the movements of the alimentary canal, however, so here, the animals reacted differently to the experience of being confined. Young males usually became quite frantic, and with eyes wide, pupils dilated, pulse accelerated, hairs of the tail more or less erect, they struggled, snarling and growling, to free themselves. Females, on the contrary, especially if elderly, were as a rule much more calm, and resignedly accepted the novel situation.

According to differences in reaction the animals were left in the holder for periods varying in length from thirty minutes to five hours. In order to insure prompt urination, considerable quantities of water were given by stomach tube at the beginning of the experiment and in some cases again later. Arrangements were made for draining the urine promptly, when the animal was on the holder or when afterwards in a metal metabolism cage, into a glass receiver containing a few drops of chloroform to prevent fermentation. The diet in all cases consisted of customary raw meat and milk. In every instance the urine was proved free from sugar before the animal was excited.

In our series of observations twelve cats were used, and in every one a well-marked glycosuria was developed. The shortest periods of confinement to the holder which were effective were thirty

and forty minutes; the longest we employed, five hours. The average time required to bring about a glycosuria was less than an hour and a half; the average in seven of the twelve cases was less than forty minutes. In all cases no sugar was found in the urine passed on the day after the excitement.

The promptness with w^hich the glycosuria developed was directly related to the emotional state of the animal. Sugar was found early in animals which early showed signs of being frightened or in a rage, and much later in animals which took the experience more calmly.

As cooling may result in increased sugar in the blood, and consequent glycosuria, the rectal temperature was observed from time to time, and it was found to vary so slightly that in these experiments it was a wholly negligible factor. In one cat the rectal temperature fell to 36° C. while the animal was bound and placed in a cold room (about 2° C.) for fifty minutes, but no sugar appeared in the urine.

Further evidence that the appearance of sugar in the urine may arise purely from emotional excitement was obtained from three cats which gave negative results when bound in the holder for varying periods up to four hours. It was noteworthy that these animals remained calm and passive in their confinement. When, however,

INCREASE OF BLOOD SUGAR 73

they were placed, separately, in a small wire cage, and were barked at by an energetic little dog, that jumped at them and made signs of attack, the cats became much excited, they showed their teeth, humped their backs, and growled defiance. This sham fight was permitted to continue for a half hour in each of the three cases. In each case the animal, which after four hours of bondage had exhibited no glycosuria, now had sugar in the urine. Pain, cooling, and bondage were not factors in these experiments. The animal was either frightened or enraged by the barking dog, and that excitement was attended by glycosuria.

The sugar excreted in the twenty-four hours which included the period of excitement was determined by the Bertrand method. 14 It ranged from 0.024 gram to 1.93 grams, or from 0.008 gram to 0.62 gram per kilo body weight, for the twenty-four hours' quantity.

The presence of sugar in the urine may be used as an indication of increased sugar in the blood, for unless injury has been done to the cells of the kidneys, they do not permit sugar to escape until the percentage in the blood has risen to a considerable degree. Thus, though testing the urine reveals the instances of a high content of blood sugar, it does not show the fine variations that appear when the blood itself is examined. Recently Scott 15 has concluded a thorough in-

vestigation of the variations of blood sugar in cats, and has found that merely incidental conditions, producing even mild excitement, as indicated by crying or otherwise, result in a noticeable rise in the amount. Indeed, so sensitive is the sugar-liberating mechanism that all the early determinations of the "normal" content of sugar in blood which has been drawn from an artery or vein in the absence of anesthesia, are of very doubtful value. Certainly when care is taken to obtain blood suddenly from a tranquil animal, the percentage (0.069, Scott; 0.088, Pavy) is much less than when the blood is drawn without anesthesia (0.15, Bohm and Hoffmann), or after light narcosis (0.282, Eona and Takahashi 16 ).

Our observations on cats have since been found valid for rabbits. Eolly and Oppermann, Jacob-sen, and Hirsch and Eeinbach 17 have recently recorded that the mere handling of a rabbit preparatory to operating on it will increase the percentage of blood sugar (in some cases from 0.10 to 0.23 and 0.27 per cent). Dogs are said to be much less likely to be disturbed by the nature of their surroundings than are rabbits and cats. Nevertheless, pain and excitement are such fundamental experiences in animals that without much doubt the same mechanism is operative in all when these experiences occur. Probably, just as the digestion of dogs is disturbed by strong emotion,

INCEEASE OF BLOOD SUGAR 75

the blood sugar likewise is increased, for sympathetic impulses occasion both changes.* Gib has given an account of a bitch that became much agitated when shut up, and after such enforced seclusion, but never otherwise, she excreted small quantities of sugar in the urine. 18

The results noted in these lower animals have been confirmed in human beings. One of my former students, W. G. Smillie, found that four of nine medical students, all normally without sugar in their urine, had glycosuria after a hard examination, and only one of the nine had glycosuria after an easier examination. The tests, which were positive with Fehling's solution, Nylander's reagent, and also with phenyl-hydrazine, were made on the first urine passed after the examination. Furthermore, C. H. Fiske and I examined the urine of twenty-five members of the Harvard University football squad immediately after the final and most exciting contest of the season of 1913, and found sugar in twelve cases. Five of these positive cases were among substitutes not called upon to enter the game. The only excited spectator of the Har-

* Since the foregoing sentences were written Hirsch and Eeinbach have reported (Zeitschrift fiir physiologische Chemie, 1914, xci, p. 292) a "psychic hyperglycemia" in dogs, that resulted from fastening the animals to a table. The blood sugar rose in one instance from 0.11 to 0.14 per cent, and in another from 0.09 to 0.16 per cent.

vard victory whose urine was examined also had a marked glycosuria, which on the following day had disappeared.

Other tests made on students before and after important scholastic examinations have been published by Folin, Denis and Smillie. 19 Of thirty-four second-year medical students tested, one had sugar before the examination as well as afterwards. Of the remaining thirty-three, six, or 18 per cent, had small but unmistakable traces of sugar in the urine passed directly following the ordeal. A similar study was made on second-year students at a women's college. Of thirty-six students who had no sugar in the urine on the day before, six, or 17 per cent, eliminated sugar with the urine passed immediately after the examination.

From the foregoing results it is reasonable to conclude that just as in the cat, dog, and rabbit, so also in man, emotional excitement produces temporary increase of blood sugars

THE ROLE OP THE ADRENAL GLANDS IN EMOTIONAL GLYCOSURIA

Since artificial stimulation of the splanchnic nerves produces glycosuria, 20 and since major emotions, such as rage and fright, are attended by nervous discharges along splanchnic pathways, glycosuria as an accompaniment of emotional ex-

INCREASE OF BLOOD SUGAR 77

citement would naturally be expected to occur. To what extent the adrenal glands which, as already mentioned, are stimulated to increased secretion by excitement, might play a part in this process, has been in dispute. Removal of these glands or cutting of the nerve fibres supplying them, according to some observers, 21 prevents glycosuria after puncture of the fourth ventricle of the brain (the "sugar puncture," which typically induces glycosuria) and also after stimulation of the splanchnics. 22 On the other hand, Wert-heimer and Battez 23 have stated that removal of the glands does not abolish the effects of sugar puncture in the cat. It was questionable, therefore, whether removal of the adrenal glands would affect emotional glycosuria.

Evidence on this point I secured with Shohl and Wright in observations on three animals in which the adrenals were removed aseptically under ether. The animals selected had all become quickly excited on being bound to the holder, and had manifested glycosuria after about an hour of confinement. In the operation, to avoid discharge of adrenin by handling, the adrenal veins were first tied, and then the glands freed from their attachments and removed as quickly and with as little manipulation as possible. In one cat the entire operation was finished in twenty minutes. In two of the cats a small catheter was introduced into the

urethra through an incision, so that the bladder could be emptied at any time.

In all three cases urine that was free from sugar was obtained soon after the operation. Although the animals deprived of their adrenals manifested a general lessening of muscular tone, they still displayed much of their former rage or excitement when bound. Indeed, one was more excited after removal of the adrenals than before. That the animals might not be excessively cooled they were kept warm with coverings or an electric heating pad. Although they were now bound for periods from two to three times as long as the periods required formerly to cause glycosuria, no trace of sugar was found in the urine in any instance. The evidence thus secured tends, therefore, to support the view that the adrenal glands perform an important contributory role in the glycosuria resulting from splanchnic stimulation.

Possibly the emotional element is in part accountable for the glycosuria observed after painful stimulation, but conditions causing pain alone will reasonably explain it. As we have already seen, strong stimulation of sensory fibres causes the discharge of impulses along the splanchnic nerves, and incidentally calls forth an increased secretion of the adrenal glands. In glycosuria resulting from painful stimulation, as well as in emo-

INCEEASE OF BLOOD SUGAE 79

tional glycosuria, the adrenal glands may be essential factors.

Later the evidence will be given that sugar is the optimum source of muscular energy. In passing, we may note that the liberation of sugar at a time when great muscular exertion is likely to be demanded of the organism may be interpreted as a highly interesting instance of biological adaptation.

KEFEEENCES

1 Kleen: On Diabetes Mellitus and Glycosuria, Philadelphia, 1900, pp. 22, 37-39.

2 Naunyn: Der Diabetes Mellitus, Vienna, 1898, p. 72.

3 Schultze: Verhandlungen der Gesellschaft deutscher Naturforscher und Aerzte, Cologne, 1908, ii, p. 358.

4 Raimann: Zeitschrift fiir Heilkunde, 1902, xxiii, Ab-theilung iii, pp. 14, 19.

5 Mita: Monatshefte fiir Psychiatrie und Neurologic, 1912, xxxii, p. 159.

6 Folin, Denis and Smillie: Journal of Biological Chemistry, 1914, xvii, p. 519.

7 Arndt: Zeitschrift fur Nervenheilkunde, 1897, x. p. 436.

8 Naunyn: Loc. cit. f p. 73; Hirschfeld: Die Zuckerkrank-heit, Leipzig, 1902, p. 45.

9 Waterman and Smit: Archiv fiir die gesammte Physiologic, 1908, cxxiv, p. 205.

10 Henderson and Underbill: American Journal of Physiology, 1911, xxviii, p. 276.

11 Bohm and Hoffmann: Archiv fiir experimentelle Pa-thologie und Pharmakologie, 1878, viii, p. 295.

12 Eckhard: Zeitschrift fiir Biologic, 1903, xliv, p. 408.

18 Loewy and Rosenberg: Biochemische Zeitschrift, 1913, Ivi, p. 114.

14 See Abderhalden: Handbuch der biochemischen Ar-beitsmethoden, Berlin, 1910, ii, p. 181.

15 Scott: American Journal of Physiology, 1914, xxxiv, p. 283.

16 Cited by Scott: Loc. cit., p. 296.

17 Roily and Oppermann: Biochemischo Zeitschrift, 1913, xlix, p. 201. Jacobscn: Ibid., 1913, li, p. 449. Hirsch and Reinbach: Zeitschrift fur physiologische Chemie, 1913, Ixxxvii, p. 122.

18 Cited by Klecn: Loc. cit., p. 37.

19 Folin, Denis and Smillie: Loc. cit.,, p. 520.

20 See Macleod: American Journal of Physiology, 1907, xix, p. 405, also for other references to literature.

21 See Meyer: Comptes rend us de la Societe de Biologic, 1906, Iviii, p. 1123; Nishi: Archiv fur experimentelle Pathologic und Pharmakologie, 1909, Ixi, p. 416.

22 Gautrelct and Thomas: Comptes rcndus de la Societe de Biologic, 1909, Ixvii, p. 233; and Macleod: Proceedings of the Society for Experimental Biology and Medicine, 1911, viii, p. 110 (true for left adrenal and left splanchnic).

23 Wertheimer and Battez: Archives Internationales cle Physiologic, 1910, ix, p. 392.

CHAPTER VI

IMPEOVED CONTRACTION OF FATIGUED

MUSCLE AFTER SPLANCHNIC STIMULATION OF

THE ADRENAL GLAND

In the older literature on the adrenal glands the deleterious effect of their absence, or the beneficial effect of injected extracts, on the contraction of skeletal muscle was not infrequently noted. As evidence accumulated, however, tending to prove an important relation between the extract of the adrenal medulla (adrenin) and the sympathetic nervous system, the relations with the efficiency of skeletal muscle began to receive less consideration.

The muscular weakness of persons suffering from diseased adrenals (Addison's disease) was well recognized before experimental work on the glands was begun. Experiments on rabbits were reported in 1892 by Albanese, 1 who showed that muscles which were stimulated after removal of the glands were much more exhausted than when stimulated the same length of time in the same animal before the removal. Similarly Boi-

net 2 reported, in 1895, that rats recently deprived of their adrenals were much more quickly exhausted in a revolving cage than were normal animals.

That extract of the adrenal glands has the power of increasing and prolonging the contraction of normal resting skeletal muscle, was noted by Oliver and Schaefer, 3 in their classic original study of the action of adrenal substance. But a recent examination of this effect by Takayasu, 4 who employed adrenin alone, has failed to confirm the earlier observations. It should be understood that these observations, however, were made on resting and not on fatigued muscle. On fatigued muscle a beneficial effect of adrenal extract, even when applied to the solution in which the isolated muscle was contracting, was claimed by Dessy and Grandis, 5 who studied the phenomenon in a salamander.* Further evidence leading to the same conclusion was offered in a discriminat-

* These earlier investigations, in which an extract of the entire gland was used, made no distinction between the action of the medulla and that of the cortex. It may be that the weakness following removal or disease of the adrenals is due to absence of the cortex (see Hoskins and Wheelon: American Journal of Physiology, 1914, xxxiv, p. 184). Such a possible effect, however, should not be confused with the demonstrable influence of injected adrenin (derived from the adrenal medulla alone) and the similar effects from adrenal secretion caused by splanchnic stimulation.

CONTRACTION OF FATIGUED MUSCLE 83

ing paper by Panella. 6 He found that in coldblooded animals the active principle of the adrenal medulla notably reinforced skeletal muscle, prolonging its ability to do work, and improving its contraction when fatigued. In warmblooded animals the same effects were observed, but only after certain experimental procedures, such as anesthesia and section of the bulb, had changed them to a condition resembling the coldblooded.

The foregoing evidence indicates that removal of the adrenals has a debilitating effect on muscular power, and that injection of extracts of the glands has an invigorating effect. It seemed possible, therefore, that increased secretion of the adrenal glands, whether from direct stimulation of the splanchnic nerves or as a reflex result of pain or the major emotions, might act as a dyna-mogenic factor in the performance of muscular work. With this possibility in mind L. B. Nice and I 7 first concerned ourselves in a research which we conducted in 1912.

The general plan of the investigation consisted primarily in observing the effect of stimulating the splanchnic nerves, isolated from the spinal cord, on the contraction of a muscle whose nerve, also isolated from the spinal cord, was rhythmically and uniformly excited with break induction shocks. When a muscle is thus stimulated it

at first responds by strong contractions, but as time passes the contractions become weaker, the degree of shortening of the muscle becomes less, and in this state of lessened efficiency it may continue for a long period to do work. The tired muscle which is showing continuously and evenly its inability to respond as it did at first, is said to have reached the "fatigue level." This level serves as an excellent basis for testing influences that may have a beneficial effect on muscular performance, for the benefit is at once manifested in greater contraction.

In the experimental arrangement which we used, only a connection through the circulating blood existed between the splanchnic region and the muscle—all nervous relations were severed. Any change in muscular ability, therefore, occurring when the splanchnic nerve is stimulated, must be due to an alteration in the quantity or quality of the blood supplied to the laboring muscle.

Cats were used for most experiments, but results obtained with cats were confirmed on rabbits and dogs. To produce anesthesia in the cats and rabbits, and at the same time to avoid the fluctuating effects of ether, urethane (2 grams per kilo body-weight) was given by a stomach tube. The animals were fastened back downward, over an electric warming pad, to an animal holder.

CONTEACTION OF FATIGUED MUSCLE 85

Care was taken to maintain the body temperature at its normal level throughout each experiment.

THE NERVE-MUSCLE PREPARATION

The muscle selected to be fatigued was usually the extensor of the right hind foot (the tibialis anticus), though at times the common extensor muscle of the digits of the same foot was employed. The anterior tibial nerve which supplies these muscles was bared for about two centimeters, severed toward the body, and set in shielded electrodes, around which the skin was fastened by spring clips. Thus the nerve could be protected, kept moist, and stimulated without stimulation of neighboring structures. By a small slit in the skin the tendon of the muscle was uncovered, and after a strong thread was tied tightly about it, it was separated from its insertion. A nerve-muscle preparation was thereby made which was still connected with its proper blood supply. The preparation was fixed firmly to the animal holder by thongs looped around the hock and the foot, i. e., on either side of the slit through which the tendon emerged.

The thread tied to the tendon was passed over a pulley and down to a pivoted steel bar which bore a writing point. Both the pulley and this steel writing lever were supported in a rigid tripod. In the earliest experiments the contracting

muscle was made to lift weights (125 to 175 grams); in all the later observations, however, the muscle pulled against a spring attached below the steel bar. The tension of the spring as the muscle began to lift the lever away from the support was, in most of the experiments, 110 grams, with an increase of 10 grams as the writing point was raised 4.5 millimeters. The magnification of the lever was 3.8.

The stimuli delivered to the anterior tibial nerve were, in most experiments, single break shocks of a value barely maximal when applied to the fresh preparation. The rate of stimulation varied between 60 and 300 per minute, but was uniform in any single observation. A rate which was found generally serviceable was 180 per minute.

Since the anterior tibial nerve contains fibres affecting blood-vessels, as well as fibres causing contraction of skeletal muscle, the possibility had to be considered that stimuli applied to it might disturb the blood supply of the region. Constriction of the blood vessels would be likely to produce the most serious disturbance, by lessening the blood flow to the muscle. The observations of Bowditch and Warren, 8 that vasodilator rather than vasoconstrictor effects are produced by single induction shocks repeated at intervals of not more than five per second, reassured us as to the danger of diminishing the blood supply, for

CONTRACTION OF FATIGUED MUSCLE 87

the rate of stimulation in our experiments never exceeded five per second and was usually two or three. Furthermore, in using these different rates we have never noted any result which could reasonably be attributed to a diminished circulation.

THE SPLANCHNIC PREPARATION

The splanchnic nerves were stimulated in various ways. At first only the left splanchnics in the abdomen were prepared. The nerves, separated from the spinal cord, were placed upon shielded electrodes. The form of electrodes which was found most satisfactory was that illustrated

FIGURE 10.—The shielded electrodes used in stimulating the splanchnic nerves. For description see text.

in Fig. 10. The instrument was made of a round rod of hard wood, bevelled to a point at one end, and grooved on the two sides. Into the grooves were pressed insulated wires ending in platinum hooks, which projected beyond the bevelled surface. Around the rod was placed an insulating rubber tube which was cut out so as to leave the hooks uncovered when the tube was slipped downward.

In applying the electrodes the left splanchnic nerves were first freed from their surroundings and tightly ligatured as close as possible to their

origin. By means of strong compression the conductivity of the nerves was destroyed central to the ligature. The electrodes were now fixed in place by thrusting the sharp end of the wooden rod into the muscles of the back. This was so

done as to bring the platinum hooks a few milli-

meters above the nerves. With a small seeker the nerves were next gently lifted over the hooks, and then the rubber tube was slipped downward until it came in contact with the body wall. Absorbent cotton was packed about the lower end of the electrodes, to take up any fluid that might appear; and finally the belly wall was closed with spring clips. The rubber tube served to keep the platinum hooks from contact with the muscles of the back and the movable viscera, while still permitting access to the nerves which were to be stimulated. This stimulating apparatus could be quickly applied, and, once in -place, needed no further attention. In some of the experiments both splanchnic nerves were stimulated in the thorax. The rubber-covered electrode proved quite as serviceable there as in the abdomen.

The current delivered to the splanchnic nerves was a rapidly interrupted induced current of such strength that no effects of spreading were noticeable. That splanchnic stimulation causes secretion of the adrenal glands has been proved in

CONTRACTION OF FATIGUED MUSCLE 89

many different ways which' have already been described (see p. 41).

THE EFFECTS OF SPLANCHNIC STIMULATION ON THE CONTRACTION OF FATIGUED MUSCLE

When skeletal muscle is repeatedly stimulated by a long series of rapidly recurring electric shocks, its strong contractions gradually grow weaker until a fairly constant condition is reached. The record then has an even top—the muscle has reached the "fatigue level." The effect of splanchnic stimulation was tried when the muscle had been fatigued to this stage. The effect which was often obtained by stimulating the left splanchnic nerves is shown in Fig. 11. In this instance the muscle while relaxed supported no weight, and

FIGURE 11.—Upper record, contraction of the tibialis anticus, 80 times a minute, lifting a weight of 125 grams. Lower record, stimulation of the left splanchnic nerves, two minutes. Time, half minutes.

while contracting lifted a weight of 125 grams. The rate of stimulation was 80 per minute.

The muscle record shows a brief initial rise from the fatigue level, followed by a drop, and that in turn by another, prolonged rise. The maximum height of the record is 13.5 millimeters, an increase of 6 millimeters over the height recorded before splanchnic stimulation. Thus the muscle was performing for a short period 80 per cent more work than before splanchnic stimulation, and for a considerably longer period exhibited an intermediate betterment of its efficiency.

THE FIRST RISE IN THE MUSCLE EECORD

The brief first elevation in the muscle record when registered simultaneously with arterial blood pressure is observed to occur at the same time

FIGURE 12.—Top record, arterial blood pressure with membrane manometer. Middle record, contractions of tibialis anticus loaded with 125 grams and stimulated 80 times a minute. Bottom record, splanchnic stimulation (two minutes). Time, half minutes.

CONTEACTION OF FATIGUED MUSCLE 91

with the sharp initial rise in the blood-pressure curve (see Fig. 12). The first sharp rise in blood' pressure is due to contraction of the vessels in the area of distribution of the splanchnic nerves, for it does not appear if the alimentary canal is removed, or if the celiac axis and the superior and inferior mesenteric arteries are ligated. The betterment of the muscular contraction is probably due directly to the better blood supply resulting -from the increased pressure, for if the adrenal veins are clipped and the splanchnic nerves are stimulated, the blood pressure rises as before and at the same time there may be registered a higher contraction of the muscle.

THE PROLONGED KISE IN THE MUSCLE HECORD

As Fig. 12 shows, the initial quick uplift in the blood-pressure record is quickly checked by a drop. This rapid drop does not appear when the adrenal veins are obstructed. A similar difference in blood-pressure records has been noted before and after excision of the adrenal glands. As Elliott, 9 and as Lyman and 1 10 have shown, this sharp drop after the first rise, and also the subsequent elevation of blood pressure, are the consequences of liberation of adrenal secretion into the circulation. Fig. 12 demonstrates that the prolonged rise of the muscle record begins soon after this characteristic drop in blood pressure.

If after clips have been placed on the adrenal veins so that no blood passes from them, the splanchnic nerves are stimulated, and later the clips are removed, a slight but distinct improvement in the muscular contraction occurs. As in the experiments of Young and Lehinann, 1X in which the adrenal veins were tied for a time and then released, the release of the blood which had been pent in these veins was quickly followed by a rise of blood pressure. The volume of blood thus restored to circulation was too slight to account for the rise of pressure. In conjunction with the evidence that splanchnic stimulation calls forth adrenal secretion, the rise may reasonably be attributed to that secretion. The fact should be noted, however, that in this instance the prolonged improvement in muscular contraction did not appear until the adrenal secretion had been admitted to the general circulation.

Many variations in the improvement of activity in fatigued muscle after splanchnic stimulation were noted in the course of our investigation. The improvement varied in degree, as indicated by increased height of the record. In some instances the height of contraction was doubled—a betterment by 100 per cent; in other instances the contraction after splanchnic stimulation was only a small fraction higher than that preceding the stimulation; and in still other instances there was no

CONTRACTION OF FATIGUED MUSCLE 93

betterment whatever. Never, in our experience, were the augmented contractions equal to the original strong contractions of the fresh muscle. The improvement also varied in degree as indicated by persistence of effect. In some instances the muscle returned to its former working level within four or five minutes after splanchnic stimulation ceased (see Fig. 11); and in other cases the muscle continued working with greater efficiency for fifteen or twenty minutes after the stimulation.

THE Two FACTORS: ARTERIAL PRESSURE AND ADRENAL SECRETION

The evidence just presented has shown that splanchnic stimulation improves the contraction of fatigued muscle. Splanchnic stimulation, however, has two effects—it increases general arterial pressure and it also causes a discharge of adrenin from the adrenal glands. The questions now arise— Does splanchnic stimulation produce the improvement in muscular contraction by increasing the arterial blood pressure and thereby flushing the laboring muscles with fresh blood? Or does the adrenin liberated by splanchnic stimulation act itself, specifically, to improve the muscular contraction? Or may the two factors cooperate? These questions will be dealt with in the next two chapters.

REFERENCES

1 Albanese: Archives Italiennes de Biologie, 1892, xvii, p. 243.

2 Boinet: Comptes rendus, Societe de Biologie, 1895, xlvii, pp. 273, 498.

3 Oliver and Schafer: Journal of Physiology, 1895, xviii, p. 263. See also Radwanska, Anzeiger der Akademie, Krakau, 1910, pp. 728-736. Reviewed in Zentralblatt fur Biochemie und Biophysik, 1911, xi, p. 467.

^Takayasu: Quarterly Journal of Experimental Physiology, 1916, Ix, p. 347.

c Dessy and Grandis: Archives Italiennes de Biologie, 1904, xli, p. 231.

o Panella: Archives Italiennes de Biologie, 1907, xlviii, p. 462.

7 Cannon and Nice: American Journal of Physiology, 1913, xxxii, p. 44.

s Bowdftch and Warren: Journal of Physiology, 1886, vii, p. 438.

a Elliott: Journal of Physiology, 1912, xliv, p. 403.

10 Cannon and Lyman: American Journal of Physiology, 1913, xxxi, p. 376.

11 Young and Lehmann: Journal of Physiology, 1908, xxxvii, p. liv.

CHAPTEE VII

THE EFFECTS ON CONTRACTION OF FATIGUED

MUSCLE OF VARYING THE ARTERIAL

BLOOD PRESSURE

That great excitement is accompanied by sympathetic innervations which increase the contraction of the small arteries, render unusually forcible the heart beat, and consequently raise arterial pressure, has already been pointed out (see p. 26). Indeed, the counsel to avoid circumstances likely to lead to such excitement, which is given to persons with hardened arteries or with weak hearts, is based on the liability of serious consequences, either in the heart or in the vessels, that might arise from an emotional increase of pressure in these pathological conditions. That great muscular effort also is accompanied by heightened arterial pressure is equally well known, and is avoided by persons likely to be injured by it. Both in excitement and in strong exertion the blood is forced in large degree from the capacious vessels of the abdomen into other parts of the body. In excite-

ment the abdominal arteries and veins are contracted by impulses from the splanchnic nerves. In violent effort the diaphragm and the muscles of the belly wall are voluntarily and antagonistically contracted in order to stiffen the trunk as a support for the arms; and the increased abdominal pressure which results forces blood out of that region and does not permit reaccumulation. The general arterial pressure in man, as McCurdy l has shown, may suddenly rise during extreme physical effort, from approximately 110 millimeters to 180 millimeters of mercury.

THE EFFECT OF INCREASING ARTERIAL PRESSURE

What effect the increase of arterial pressure, resulting from excitement or physical strain, may have on muscular efficiency, has received only slight consideration. Nice and I found there was need of careful study of the relations between arterial pressure and muscular ability, and, in 1913, one of my students, C. M. Gruber, undertook to make clearer these relations.

The methods of anesthesia and stimulation used by Gruber were similar to those described in the last chapter. The arterial blood pressure was registered from the right carotid or the femoral artery by means of a mercury manometer. A time marker indicating half-minute intervals was placed at the atmospheric pressure level of thfc

FATIGUE AND BLOOD PEESSUEE 97

manometer. And since the blood-pressure style, the writing point of the muscle lever, and the time signal were all set in a vertical line on the surface of the recording drum, at any given muscular contraction the height of blood pressure was simultaneously registered.

To increase general arterial pressure two methods were used: the spinal cord was stimulated in the cervical region through platinum electrodes, or the left splanchnic nerves were stimulated after the left adrenal gland had been excluded from the circulation. This was done in order to avoid any influence which adrenal secretion might exert. It is assumed in these experiments that vessels supplying active muscles would be actively dilated, as Kaufmamx 2 has shown, and would, therefore, in case of a general increase of blood pressure, deliver a larger volume of blood to the area they supply. The effects of increased arterial pressure arc illustrated in Figs. 13, 14 and 15. In the experiment represented in Fig. 13, the rise of blood pressure was produced by stimulation of the cervical cord, and in Figs. 14 and 15 by stimulation of the left splanchnic nerves after the left adrenal gland had been tied off.

The original blood pressure in Fig. 13 was 120 millimeters of mercury. This was increased by 62 millimeters, with a rise of only 8.4 per cent in the height of contraction of the fatigued muscle.

BODILY CHANGES

FIGURE 13.—In this and the following records, the upper curve indicates the blood pressure, the middle line muscular contraction, and the lower line the time in 30 seconds (also zero blood pressure.) Between the arrows the exposed cervical spinal cord was stimulated.

In Fig. 14 the original blood pressure was 100 millimeters of mercury. By increasing this pres-

FATIGUE AND BLOOD PBESSURE 99

sure 32 millimeters there resulted simultaneous betterment of 9.8 per cent in the height of muscular contraction. In Fig. 14 B the arterial pressure was raised 26 millimeters and the height of

A B C

FIGURE 14.—Stimulation of the left splanchnic nerves (left adrenal gland tied off) during the periods indicated by the arrows.

contraction increased correspondingly 7 per cent. In Fig. 14 C no appreciable betterment can be seen although the blood pressure rose 18 millimeters. In Fig. 15 the original blood pressure was low —68 millimeters of mercury. This was increased in Fig. 15 A by 18 millimeters (the same as in

Fig. 14 C without effect), and there resulted an increase of 20 per cent in the height of contraction. In Fig. 15 B the pressure was raised 24 millime-

A B c

FIGURE 15.—During the periods indicated in the time line the left splanchnic nerves were stimulated. The vessels of the left adrenal gland were tied off.

ters with a corresponding increase of 90 per cent in the muscular contraction; and in Fig. 15 C 30 millimeters with a betterment of 125 per cent.

Comparison of Figs. 13, 14 and 15 reveals that the improvement of contraction of fatigued muscle is much greater when the blood pressure is raised, even slightly, from a low level, than when it is raised, perhaps to a very marked degree, from a high level. In one of the experiments performed by Nice and myself the arterial pressure

FATIGUE AND BLOOD PRESSURE 101

was increased by splanchnic stimulation from the low level of 48 millimeters of mercury to 110 millimeters, and the height of the muscular contractions was increased about sixfold (see Fig. 16).

FIGURE 16.—The bottom record (zero of blood pressure) shows stimulation of left splanchnics; between the arrows the pressure was kept from rising by compression of heart.

Results confirming those described above were obtained by Gruber in a study of the effects of splanchnic stimulation on the irritability of muscle when fatigued. In a series of eleven observations the average value of the barely effective stimulus (the "threshold" stimulus) had to be increased as the condition of fatigue developed. It

was increased for the nerve-muscle by 25 per cent and for the muscle by 75 per cent. The left splanchnic nerves, disconnected from the left adrenal gland, were now stimulated. The arterial pressure, which had varied between 90 and 100 millimeters of mercury, was raised at least 40 millimeters. As a result of splanchnic stimulation there was an average recovery of 42 per cent in the nerve-muscle and of 46 per cent in the muscle. The increased general blood pressure was effective, therefore, quite apart from any possible action of adrenal secretion, in largely restoring to the fatigued structures their normal irritability.

THE EFFECT OF DECREASING ARTERIAL PRESSURE

Inasmuch as an increase in arterial pressure produces an increase in the height of contraction of fatigued muscle, it is readily supposable that a decrease in the pressure would have the opposite effect. Such is the case only when the blood pressure falls below the region of 90 to 100 millimeters of mercury. Thus if the arterial pressure stands at 150 millimeters of mercury, it has to fall approximately 55 to 65 millimeters before causing a decrease in the height of contraction. Fig. 17 is the record of an experiment in which the blood pressure was lowered by lessening the output of blood from the heart by compressing the thorax. The record shows that when the pressure

FATIGUE AND BLOOD PKESSUKE 103

was lowered from 120 to 100 millimeters of mercury (A), there was no appreciable decrease in the height of contraction; when lowered to 90

FIGURE 17.—The arrows indicate the points at which the thorax began to be compressed in order to lessen the output of blood from the heart.

millimeters (B), there resulted a decrease of 2.4 per cent; when to 80 millimeters of mercury (C), a decrease of 7 per cent; and when to 70 millimeters (D), a decrease of 17.3 per cent. Eesults similar to those represented in Fig. 17 were obtained by pulling on a string looped about the

aorta just above its iliac branches, thus lessening the flow to the hind limbs.

The region of 90 to 100 millimeters of mercury may therefore be regarded as the critical region at which a falling blood pressure begins to be accompanied by a concurrent lessening of the efficiency of muscular contraction, when the muscle is kept in continued activity. It is at that region that the blood flow is dangerously near to being inadequate.

AN EXPLANATION OF THE EFFECTS OF VARYING THE ARTERIAL PRESSURE

How are these effects of increasing and decreasing the arterial blood pressure most reasonably explained? There is abundant evidence that fatigue products accumulate in a muscle which is doing work, and also that these metabolites interfere with efficient contraction. As Eanke 3 long ago demonstrated, if a muscle, deprived of circulating blood, is fatigued to a standstill, and then the circulation is restored, the muscle again responds for a short time to stimulation, because the waste has been neutralized or swept away by the fresh blood. When the blood pressure is at its normal height for warm-blooded animals (about 120 millimeters of mercury, see Fig. 13), the flow appears to be adequate to wash out the depressive metabolites, at least in the single muscle

FATIGUE AND BLOOD PRESSURE 105

used in these experiments, because a large rise of pressure produces but little change in the fatigue level. On the other hand, when the pressure is abnormally low, the flow is inadequate, and the waste products are permitted to accumulate and clog the action of the muscle. Under such circumstances a rise of pressure has a very striking beneficial effect.

It is noteworthy that the best results of adre-nin on fatigued muscle reported by previous observers were obtained from studies on cold-blooded animals. In these animals the circulation is maintained normally by an arterial pressure about one-third that of warm-blooded animals. Injection of adrenin in an amount which would not shut off the blood supply would, by greatly raising the arterial pressure, markedly increase the circulation of blood in the active muscle. In short, the conditions in cold-blooded animals are quite like those in tho pithed mammal with an arterial pressure of about 50 millimeters of mercury (see Fig, 1C). Under these conditions the improved circulation causes a remarkable recovery from fatigue. That notable results of adrenin on fatigue are observed in warm-blooded animals only when they are deeply anaesthetized or are deprived of the medulla was claimed by Panella. 4 He apparently believed that in normal mammalian conditions adrenin has little effect because quickly destroyed, whereas in

the cold-blooded animals, and in mammals whose respiratory, circulatory, and thermogenic states are made similar to the cold-blooded by anaesthesia or pithing, the contrary is true. In accordance with our observations of the effects of blood pressure on fatigued muscle, we would explain Panel-la's results not as he has done but as due to two factors. First, the efficiency of the muscle, when blood pressure is low, follows the ups and downs of pressure much more directly than when the pressure is high. And second, a given dose of adrenin always raises a low blood pressure in atonic vessels. The improvement of circulation is capable of explaining, therefore, the main results obtained in cold-blooded animals and in pithed mammals.

Oliver and Schafer reported unusually effective contractions in muscles removed from the body after adrenal extract had been injected. As shown in Fig. 16, however, the fact that the circulation had been improved results in continued greater efficiency of the contracting muscle. Oliver and Schii-fer's observation may perhaps be accounted for on this basis.

THE VALUE OF INCREASED ARTERIAL PRESSURE IN PAIN AND STRONG EMOTION

As stated in a previous paragraph, there is evidence that the vessels supplying a muscle dilate

FATIGUE AND BLOOD PRESSURE 107

when the muscle becomes' active. And although the normal blood pressure (about 120 millimeters of mercury) may be able to keep adequately supplied with blood the single muscle used in our investigation, a higher pressure might be required when more muscles are involved in activity, for a more widely spread dilation might then reduce the pressure to the point at which there would be insufficient circulation in active organs. Furthermore, with many muscles active, the amount of waste would be greatly augmented, and the need for abundant blood supply would thefeby to a like degree be increased. For both reasons a rise of general arterial pressure would prove advantageous. The high pressure developed in excitement and pain, therefore, might be specially serviceable in the muscular activities which are likely to accompany excitement and pain.

In connection with the foregoing considerations, the action of adrenin on the distribution of blood in the body is highly interesting. By measuring alterations in the volume of various viscera and the limbs, Oliver and Schafer 5 proved that the viscera of the splanchnic area—e.g., the spleen, the kidneys, and the intestines—suffer a considerable decrease of volume when adrenin is administered, whereas the limbs into which the blood is forced from the splanchnic region actually increase in size. Haskins, Gunning, and Berry 6

showed, and their work has been confirmed by others, 7 that with nerves intact adrenin causes active dilatation of the vessels in muscles and constriction of cutaneous vessels. This action of adrenin indicates differences in the degree or character of sympathetic innervations. In other words, at times of pain and excitement sym-x pathetic discharges, probably aided by the adrenal secretion simultaneously liberated, will drive the blood out of the vegetative organs of the interior, which serve the routine needs of the body, into the skeletal muscles which have to meet by extra action the urgent demands of struggle or escape. But there are exceptions to the general statement that by adrenin the viscera are emptied of their blood. It is well known that adrenin has a vasodilator, not a vasoconstrictor, action on the arteries of the heart; it is well known also that adrenin affects the vessels of the brain and the lungs only slightly if at all. From this evidence we may infer that sympathetic impulses, though causing constriction of the arteries of the abdominal viscera, have no effective influence on those of the pulmonary and intracranial areas and actually increase the blood supply to the heart. Thus the absolutely and immediately essential organs— those the ancients called the "tripod of life"—the heart, the lungs, the brain (as well as its instruments, the skeletal muscles)—are in times of ex-

FATIGUE AND BLOOD PRESSURE 109

citement abundantly supplied with blood taken from organs of less importance in critical moments. This shifting of the blood so that there is an assured adequate supply to structures essential for the preservation of the individual may reasonably be interpreted as a fact of prime biological significance. It will be placed in its proper setting when the other evidence of bodily changes in pain and excitement have been presented.

REFERENCES

1 McCurdy: American Journal of Physiology, 1901, v, p. 98.

2 Kaufmaiin: Archives de Physiologic, 1892, xxiv, p. 283.

3 Ranker Archiv fur Anatomic, 18G3, p. 446.

4 Panella: Archives Italiennes de Biologic, 1907, xlviii, p. 462.

5 Oliver and Schiifer: Journal of Physiology, 1895, xviii, p. 240.

«Hoskins, Gunning and Berry: American Journal of Physiology, 1916, xli, p. 513.

7 TIartman and Fraser: American Journal of Physiology, 1917, xliv, p. 353; Gruber: Ibid., 1918, xlv, p. 302; and Pearl-man and Vincent: Endocrinology, 1919, ill, p. 121.

CHAPTER VIII

THE SPECIFIC ROLE OF ADRENIN IN COUNTERACTING THE EFFECTS OF FATIGUE

As a muscle approaches its fatigue level, its contractions are decreased in height. Higher contractions will again be elicited if the stimulus is increased. Although these phenomena are well known, no adequate analysis of their causes has been advanced. A number of factors are probably operative in decreasing the height of contraction: (1) The using up of available energy-producing material; (2) the accumulation of metabolites in the fatigued muscle; (3) polarization of the nerve at the point of repeated electrical stimulation; and (4) a decrease of irritability. It may be that there are interactions between these factors within the muscle, e. g., the second may cause the fourth.

VARIATIONS OF THE THRESHOLD STIMULUS AS A MEASURE OF IRRITABILITY

The last of the factors mentioned above—the effect of fatigue on the irritability of the nerve-muscle combination, or on the muscle alone—can

be tested by determining variations in the least stimulus capable of causing the slightest contraction, the so-called "threshold stimulus." As the irritability lessens, the threshold stimulus must necessarily be higher. The height of the threshold is therefore a measure of irritability. How does fatigue affect the irritability of nerve-muscle and muscle ? How is the irritability of fatigued structures affected by rest? How is it influenced by adrenin or by adrenal secretion? Answers to these questions were sought in researches carried on by C. M. Gruber 1 in 1913.

THE METHOD OF DETERMINING THE THRESHOLD STIMULUS

The neuro-muscular arrangements used in these researches were in many respects similar to those already described in the account of experiments by Nice and myself. To avoid the influence of an anesthetic some of the animals were decerebrated under ether and then used as in the experiments in which urethane was the anesthetic. The nerve (the peroneus communis) supplying the tibialis an-ticus muscle was bared and severed; and near the cut end shielded platinum electrodes were applied. These electrodes were used in fatiguing the muscle. Between these electrodes and the muscle other platinum electrodes could be quickly applied to determine the threshold stimulus and the tissue resistance. These second electrodes were removed

except when in use, and when replaced were set always in the same position. Care was taken, before replacing them, to wipe off moisture on the

•

nerve or on the platinum points.

For determining the threshold stimulus of the muscle the skin and other overlying tissues were cut away from the tibialis anticus in two places about 5 centimeters apart. Through these openings platinum needle electrodes could be thrust into the muscle whenever readings were to be taken. Local polarization was avoided by reinserting the needles into fresh points on the exposed areas whenever new readings were to be taken.

The tendon of the tibialis anticus was attached, as in the previous experiments, by a strong thread passing about pulleys to a lever which when lifted stretched a spring. During the determination of the threshold the spring was detached from the lever, so that only the pull of the lever itself (about 15 grams) was exerted on the muscle.

The method of measuring the stimulating value of the electric current which was used in testing the threshold was that devised by E. G. Martin* of the Harvard Laboratory—a method by which the strength of an induced electric shock is calculable in definite units. If the tissue resistance enters

* For a full account of Dr. Martin's method of calculating the strength of electric stimuli, see Martin: The Measurement of Induction Shocks, New York, 1912.

into the calculation these are called 0 units. When the threshold of the nerve-muscle was taken, the apparatus for the determination was connected with the nerve through the electrodes nearer the muscle. They were separated from the fatiguing electrodes by more than 3 centimeters, and arranged so that the kathode was next the muscle. When the threshold of the muscle was taken directly the apparatus was connected with the muscle through platinum needle electrodes thrust into it. The position of the secondary coil of the inducto-rium, in every case, was read by moving it away from the primary coil until the very smallest possible contraction of the muscle was obtained. Four of these readings were made, one with tissue resistance, the others with 10,000, 20,000, and 30,000 ohms additional resistance in the secondary circuit. Only break shocks were employed—the make shocks were short-circuited. Immediately after the determination of the position of the secondary coil, and before the electrodes were removed or disconnected, three readings of the tissue resistance were made. From these data four values for ft were calculated.

The strength of the primary current for determining the threshold of the nerve-muscle was usually .01 ampere, but in a few cases .05 ampere was used. For normal muscle it was .05 ampere and for denervated muscle 1.0 ampere. The inducto-

rium, which was used throughout, had a secondary resistance of 1400 ohms. This was added to the average tissue resistance in making corrections— corrections were made also for core magnetization.

THE LESSENING OF NEURO-MUSCULAR IRRITABILITY BY FATIGUE The threshold for the peroneus communis nerve in decerebrate animals varied from 0.319 to 2.9G units, with an average in sixteen experiments of 1.179.* This average is the same as that found by E. L. Porter 2 for the radial nerve in the spinal cat. For animals under urethane anesthesia a higher average was obtained. In these it varied from .644 to 7.05, or an average in ten experiments of 3.081.

The threshold for the tibialis anticus muscle varied in the decerebrate animals from 6.75 units to 33.07, or an average in fifteen experiments of 18.8. Ten experiments were performed under urethane anesthesia and the threshold varied from 12.53 to 54.9, with an average of 29.84 ft units. From these results it is evident that anesthesia notably affects the threshold.

E. L. Porter proved, by experiments carried on in the Harvard Physiological Laboratory, that the threshold of an undisturbed nerve-muscle remains

* For the detailed data of these and other quantitative experiments, the reader should consult the tables in the original papers.

FATIGUE AND ADRENIN 115

constant for hours, and his observation was confirmed by Gruber (see Fig. 19). If, therefore, after fatigue, a change exists in the threshold, this change is necessarily the result of alterations set up by the fatigue process in the nerve-muscle or muscle.

After fatigue the threshold of the nerve-muscle, in sixteen decerebrate animals, increased from an average of 1.179 to 3.34—an increase of 183 per cent. In ten animals under urethane anesthesia the threshold after fatigue increased from a normal average of 3.08 to 9.408—an increase of 208 per cent.

An equal increase in the threshold stimulus was obtained from the normal muscle directly. In de-cerebrate animals the normal threshold of 18.8 units was increased by fatigue to 69.54, or an increase of 274 per cent. With urethane anesthesia the threshold increased from 29.849 to 66.238, or an increase of 122 per cent.

Fig. 18, plotted from the data of one of the many experiments, shows the relative heights of the threshold before and after fatigue. The correspondence of the two readings of the threshold, one from the nerve supplying the muscle and the other from the muscle directly, served as a check on the electrodes. The broken line in the figure represents the threshold (in units) of the nerve-muscle, and the continuous line that of the muscle. The

threshold values of the nerve-muscle have been magnified ten times in order to bring the two records close together. In this experiment the thresh-

FIGUBE 18.—A record plotted from the data of one experiment. The time intervals in minutes are registered on the abscissa; the value of the threshold in units is registered on the ordinate. The continuous line is the record of the muscle, the broken line that of the nerve-muscle. The values for the nerve-muscle have been magnified ten times, those for the muscle are normal.

(1) Normal values of the threshold.

(2) Fatigue thresholds after one hour's work, lifting 120 grams 240 times a minute.

(3 and 4) The threshold after rest.

old of the muscle after fatigue (i.e., at 2) is 167 per cent higher than the normal threshold (at 1), while that of the nerve-muscle after fatigue is 30.5 per cent higher than its normal.

Evidently a direct relation exists between the duration of work and the increase of threshold. For instance, the threshold is higher after a muscle is fatigued for two hours than it is at the end of

the first hour. The relation between the work done and the threshold is not so clear. In some animals the thresholds were higher after 120 grams had been lifted 120 times a minute for 30 minutes than they were in others in which 200 grams had been lifted 240 times a minute for the same period. The muscle in the latter instances did almost four times as much work, yet the threshold was lower. The difference may be due to the general condition of the animal.

A few experiments were performed on animals in which the nerve supplying the muscle was cut seven to fourteen days previous to the experiment. The muscle, therefore, had within it no living norve fibres. The average normal threshold for the denervatod muscle in G animals was 61.28 units. As in the normal muscle, the percentage increase due to fatigue was large.

THE SLOW RESTORATION OF FATIGUED MUSCLE TO NORMAL IRRITABILITY BY REST

That rest decreases the fatigue threshold of both nerve-muscle and muscle can be seen in Fig. 18. The time taken for total recovery, however, is dependent upon the amount of work done, but this change, like that of fatigue, varies widely with different individuals. In some animals the threshold returned to normal in 15 minutes; in others, in which the same amount of work was done, it was

still above normal even after 2 hours of rest. This may be due to the condition of the animals—in some the metabolites are probably eliminated more rapidly than in others. There were also variations in the rate of restoration of the normal threshold when tested on the nerve and when tested on the muscle in the same animal. In Fig. 18 (at 3) the nerve-muscle returned to normal in 30 minutes, whereas the muscle (at 4) after an hour's rest had not returned to normal by a few ft units. This, however, is not typical of all nerve-muscles and muscles. The opposite condition—that in which the muscle returned to normal before the nerve-muscle—occurred in as many cases as did the condition just cited. The failure of the two tissues to alter uniformly in the same direction may be explained as due to variations in the location of the electrodes when thrust into the muscle at different times (e. g., whether near nerve filaments or not). The results from observations made on the nerve are more likely to be uniform and reliable than are those from the muscle.

The time required for the restoration of the threshold from fatigue to normal, in denervated muscles, is approximately the same as that for the normal muscle.

THE QUICK KESTORATION OP FATIGUED MUSCLE TO NORMAL IRRITABILITY BY ADRENIN

The foregoing observations showed that fatigue raises the normal threshold of a muscle, on the average, between 100 and 200 per cent (it may be increased more than 600 per cent); that this increase is dependent on the time the muscle works, but also varies with the animal; that rest, 15 minutes to 2 hours, restores the normal irritability; and that this recovery of the threshold depends upon the time given to rest, the duration of the work, and also upon the condition of the animal. The problem which was next attacked by Gruber was that of learning whether the higher contractions of fatigued muscle after splanchnic stimulation could be attributed to any influence which adrenal secretion might have in restoring the normal irritability. To gain insight into the probabilities he tried first the effects of injecting slowly into the jugular vein physiological amounts of adrenin.*

The normal threshold of the peroneus communis nerve varied in the animals used in this series of observations from 0.35 to 5.45 units, with an average in nine experiments of 1.3, a figure close to the 1.179 found in the earlier series on the effect of fatigue. For the tibialis anticus muscle, in which the nerve-endings were intact, the threshold varied

* The form of adrenin used in these and in other injections was fresh adrenalin made by Parke, Davis & Co.

from 6.75 to 49.3 units, with an average in the nine experiments of 22.2. This is slightly higher than that cited for this same muscle in the earlier series. By fatigue the threshold of the nerve-muscle was increased from an average of 1.3 to an average of 3.3 units, an increase of 154 per cent. The muscle increased from an average of 22.2 to an average of 59.6, an increase of K>9 per cont. After an injection of 0.1 to 0.5 cubic centimeters of adrenin (1:100,000) the fatigue threshold was decreased ivithin five minutes in the nerve-muscle from an average of 3.3 to 1.8, a recovery of 75 per cent, and in the muscle from an average of 59.G to 42.4, a recovery of 46 per cent. To prove that this effect of adrenin is a counteraction of flic effects of fatigue, Gruber determined the threshold for muscle and nerve-muscle in non-fatigued animals before and after adrenin injection. He found that in these cases no lowering of threshold occurred, a result in marked contrast with the pronounced and prompt lowering induced by this agent in muscles when fatigued.

Figs. 19 and 20, plotted from the data of two of the experiments, show the relative heights of the threshold before and after an injection of adrenin. The close correspondence of the two readings of the threshold, one from the nerve supplying the muscle, the other from the muscle directly, served to show that there was no fault in the electrodes.

The continuous line in the Figures represents the threshold (in units) of the muscle, the broken line that of the nerve-muscle. The threshold of the nerve-muscle is magnified 100 times in Fig. 19 and 10 times in Fig. 20. In Fig. 19 (at 2 and 4) the threshold was taken after an intravenous injection of 0.1 and 0.2 cubic centimeter of adrenin respectively.

These examples show that adrenin does not affect the threshold of the normal non-fatigued muscle when tested either on the muscle directly or on the nerve-muscle. In Fig. 19 (at 3) the observation taken after two hours of rest illustrates the constancy of the threshold under these circumstances.

In Fig. 19 the normal threshold was increased by fatigue (at 5)—the muscle had been pulling 120 times a minute for one hour on a spring having an initial tension of 120 grams—from 30.0 to 51.G units, an increase of 72 per cent; and in the nerve-muscle from 0.62 to 0.89 units, an increase of 46 per cent. The threshold (at 6) was taken fire minutes after injecting 0.1 cubic centimeter of adrenin (1:100,000). The threshold of the muscle was lowered from 51.6 to 38.0 units, a recovery of 62 per cent; that of the nerve-muscle from 0.89 to 0.79 units, a recovery of 37 per cent. After another injection of 0.5 cubic centimeter of adrenin the thresholds (at 7) were

BODILY CHANGES

taken; that of the nerve-muscle dropped to normal —0.59 units—a recovery of 100 per cent, and that

90 80 70

3:30

FIGURE 19.—A record plotted from the data of one experiment. The time intervals in hours and minutes are represented on the abscissa; the values of the threshold in ft units are represented on the ordinate. The continuous line is the record of the muscle, the broken line that of the nerve-muscle. The nerve-muscle record is magnified 100 times; that of the muscle is normal.

(1) Normal threshold stimulus. (2) Threshold five minutes after an intravenous injection of 0.1 cubic centimeter of ad-renin (1:100,000) without previous fatigue.

(3) Threshold after a rest of two hours.

(4) Threshold five minutes after an injection of 0.2 cubic centimeter of adrenin (1:100,000) without previous fatigue. (5) Threshold after one hour's fatigue. The muscle contracted 120 times per minute against a spring having an initial tension of 120 grams. (6) Threshold five minutes after an injection (0.1 cubic centimeter) of adrenin (1:100,000). (7) Threshold five minutes after another injection of adrenin (0.5 cubic centimeter of a 1:100,000 solution).

of the muscle remained unaltered—26 per cent above its normal threshold. In Fig. 20 the threshold (at 5) was taken five

minutes after an injection of 0.1 cubic centimeter of adrenin. The drop here was as large as that shown in Fig. 19. The threshold taken from the

FIGURE 20.—A record plotted from the data of one experiment. The time intervals in hours and minutes are registered on the abscissa; the values of the threshold in units are registered on the ordinate. The continuous line is the record of the muscle, the broken line that of the nerve-muscle. The record of the nerve-muscle is magnified ten times; that of the muscle is normal.

(1) Normal threshold. (2) The threshold after one hour's fatigue. The muscle contracted 120 times per minute against a spring having an initial tension of 120 grams. (3 and 4) Thresholds after rest; after 60 minutes (3), and after 90 minutes (4). (5) Threshold five minutes after an injection of adrenin (0.1 cubic centimeter of a 1:100,000 solution). (6 and 7) Thresholds after rest; after 60 minutes (6), and after 90 minutes (7).

muscle directly was lowered from 30.6 to 18 units, a recovery of 61 per cent; the nerve-muscle from 1.08 to 0.87 units, a recovery of 51 per cent. That this sudden decrease cannot be due»to rest is shown in the same Figure (at 3 and 4). These readings were made after 60 and 90 minutes' rest respectively. The sharp decline in the record (at 5) indicates distinctly the remarkable restorative influ-

ence of adrenin in promptly lowering the high, fatigue threshold of neuro-muscular irritability.

THE EVIDENCE THAT THE KESTORATIVE ACTION OF ADRENIN is

SPECIFIC

As stated in describing the effects of arterial blood pressure, an increase of pressure is capable of causing a decided lowering of the neuro-muscular threshold after fatigue. Is it not possible that adrenin produces its beneficial effects by bettering the circulation ?

Nice and I had argued that the higher contractions of fatigued muscle, that follow stimulation or injection of adrenin, could not be wholly due to improved blood flow through the muscle, for when by traction on the aorta or compression of the thorax arterial pressure in the hind legs was prevented from rising, splanchnic stimulation still caused a distinct improvement, the initial appearance of which coincided with the point in the blood-pressure curve at which evidence of adrenal secretion appeared. And, furthermore, the improvement was seen also when adrenin was given intravenously in such weak solution (1:100,000) as to produce a fall instead of a rise of arterial pressure. Lyman and I had shown that this fall of pressure was due to a dilator effect of adrenin. Since the blood vessels of the fatigued muscle were dilated by severance of their nerves when the nerve trunk was

cut, and, besides, as previously stated (see p. 86), were being stimulated through their nerves at a rate favorable to relaxation, it seemed hardly prob-

FIGURE 21.—Top record, blood pressure with mercury manometer. Middle record, contractions of the tibialis anticus muscle 240 times per minute against a spring with an initial tension of 120 Drains. Bottom record (zero blood pressure)) injection of 0.4 cubic centimeter of adrcnin (1:100,-000). Time in half minutes.

able that adronin could produce its beneficial effect by further dilation of the vessels and by consequent flushing of the muscle with an extra supply of blood, 3 The lowering of blood pressure had

been proved to have no other effect than to impair the action of the muscle (see p. 103). Although the chances were thus against an interpretation of the beneficial influence of adrenin through action on the circulation, it was thought desirable to test the possibility by comparing its effect with that of another vasodilator—amyl nitrite.

Figs. 21 and 22 are curves obtained from the left tibialis anticus muscle. The rate of stimulation was 240 times a minute.

The muscle in Fig. 21 contracted against a spring having an initial tension of 120 grams, and that in Fig. 22 against an initial tension of 100 grams. In Fig. 21, at the point indicated on the base line, 0.4 cubic centimeter of adrenin (1:100,000) was injected into the left external jugular vein. There resulted a fall of 25 millimeters of mercury in the arterial pressure and a concurrent betterment of 15 per cent in the height of contraction, requiring two minutes and fifteen seconds of fatigue (about 540 contractions) before it returned to the former level. In Fig. 22, at the point indicated by the arrow, a solution of amyl nitrite was injected into the right external jugular vein. There resulted a fall of 70 millimeters of mercury in arterial pressure and a betterment of 4.1 per cent in the height of muscular contraction, requiring fifteen seconds of fatigue (about 60 contractions) to decrease the height of contraction to its former level. In

FATIGUE AND ADUENIN

127

FIGURE 22.—Top record, blood pressure with mercury manometer. Middle record, contractions of tibialis anticus muscle 240 per minute against a spring with an initial tension of 100 grams direct load. Bottom record (zero blood pressure), time in half minutes. The arrow indicates the point at which a solution of amyl nitrite was injected.

neither case did the blood pressure fall below the critical region (see p. 104).*

Although the fall in arterial pressure caused by dilation of the vessels due to amyl nitrite was almost three times as great as that produced by the adrenin,. yet the resultant betterment was only about one-fourth the percentage height and lasted but one-ninth the time. In all cases in which these solutions caused an equal fall in arterial pressure, adrenin caused higher contractions, whereas amyl nitrite caused no appreciable change.

THE POINT OF ACTION OF ADRENIN IN MUSCLE

From the evidence presented in the foregoing pages it is clear that adrenin somehow is able to bring about a rapid recovery of normal irritability of muscle after the irritability has been much lessened by fatigue, and that the higher contractions of a fatigued muscle after an injection of adrenin are due, certainly in part, to some specific action of this substance and not wholly to its influence on the circulation. Some of the earlier investigators

" x " In some cases after injection of amyl nitrite the normal blood pressure, which was high, dropped sharply to a point below the critical region. There resulted a primary increase in muscular contraction due to the betterment in circulation caused by the dilation of the vessels before the critical region was reached. During the time that the pressure was below the critical region the muscle contraction fell. As the blood pressure again rose to normal the muscle contraction increased comcidently.

of adrenal function, notably Albanese, 4 and also Abelous and Langlois, r> inferred from experiments on the removal of the glands that the role they played in the bodily economy was that of neutralizing, destroying or transforming toxic substances produced in tlie organism as a result of muscular or nervous work. It seemed possible that the metabolites might have a checking or blocking influence at the junction of the nerve fibres with the muscle fibres, and might thus, like curare, lessen the efficiency of the nerve impulses. Radwanska's observation 6 that the beneficial action of adrenin is far greater when the muscle is stimulated through its nerve than when stimulated directly, and Panel-la's discovery 7 that adrenin antagonizes the effect of curare, were favorable to the viow that adrenin improves the contraction of fatigued muscle by lessening or removing a block established by accumulated metabolites.

The high threshold of fatigued denervated muscle, however, Gruber found was quite as promptly lowered by adrenin as was that of normal muscles stimulated through their nerves. Fig. 23 shows that the height of contraction, also, of the fatigued muscle is increased when adrenin is administered. In this experiment the left tibialis anticus muscle was stimulated directly by thrusting platinum needle electrodes into it. The peroneus communis nerve supplying the muscle had been cut and two

centimeters of it removed nine days previous to the experiment. The rate of stimulation was 120 times per minute and the initial tension of the spring about 120 grams. At the point indicated

FIGURE 23.—Top record, blood pressure with mercury manometer. Middle record, contractions of a denervated muscle (tibialis anticus) 240 per per minute against a spring having an initial tension of 120 grams (peroneus comma nix nerve was cut nine days before this record was taken). Bottom record (zero blood pressure), time in half minutes. At the point indicated by an arrow 0.1 cubic centimeter of adreniri (1:100,000) was injected intravenously.

by the arrow an injection of 0.1 cubic centimeter of adrenin (1:100,000) was made into a jugular vein. A fall in arterial pressure from 110 to 86 millimeters of mercury and a simultaneous betterment of 20 per cent in the height of contraction

were obtained. It required four minutes of fatigue (about 480 contractions) to restore the muscle curve to its former level. Eesults similar to this were obtained from animals in which the nerve had been cut 7, 9, 12, 14, and 21 days. In all instances the nerve was inexcitable to strong f aradic stimulation.

In Kadwanska's experiments, mentioned above, the muscle was stimulated directly when the nerve endings were intact. It seems reasonable to suppose, therefore, that in all cases he was stimulating nerve tissue. Since a muscle is more irritable when stimulated through its nerve than when stimulated directly (nerve and muscle), a slight change in the irritability of the muscle by adrenin would naturally result in a greater contraction when the nerve was stimulated. Panella's results also are not inconsistent with the interpretation that the effect of adrenin is on the muscle substance rather than on the nerve endings. A method which has long been used to separate muscle from nerve is that of blocking the nervous impulses by the drug curare. Gruber found that when curare is injected the threshold of the normal muscle is increased, as was to be expected from the removal of the highly efficient nervous stimulations. And also, as was to be expected on that basis, curare did not increase the threshold in a muscle in which the nerve endings had degenerated. Adrenin antago-

nizes curare with great promptness, decreasing the heightened threshold of a curarized muscle, in five minutes or less, in some cases to normal. From this observation it might be supposed that curare and fatigue had the same effect, and that adrenin had the single action of opposing that effect. But fatigue raises the threshold of a curarized muscle, and adrenin then antagonizes this fatigue. Lang-ley 8 has argued that curare acts upon a hypothetical "receptive substance" in muscle. If so, probably curare acts upon a substance, or at a point, different from that upon which fatigue acts; for, as the foregoing evidence shows, fatigue increases the threshold of a muscle whether deprived of its nerve supply by nerve section and degeneration or by curare, whereas curare affects only the threshold of a muscle in which the nerve endings are normal. 9 And since adrenin can oppose the effects of both curare and fatigue, it may be said to have two actions, or to act on two different substances or at two different points in the muscle. Gruber 10 has recently shown that adrenin perfused through dying muscle, and through muscle rendered less efficient by the injection of fatigue products (lactic acid, and acid sodium and potassium phosphate), has a remarkable capacity to restore the contractile process after it has practically disappeared, or to augment it greatly after it has been much reduced.

The evidence adduced in the last chapter indicated that the greater "head" of arterial pressure produced by the more rapid heart beat and the stronger contraction of many arterioles in times of great excitement would be highly serviceable to the organism in any extensive muscular activity which the excitement might involve. By assuring an abundant flow of blood through the enlarged vessels of the working muscle, the waste products resulting from the wear and tear in contraction would be promptly swept away and thus would be prevented from impairing the muscular efficiency. The adrenin discharge at stich times would, as was pointed out, probably reinforce the effects of sympathetic impulses. The evidence presented in this chapter shows that adrenin has also another action, a very remarkable action, that of restoring to a muscle its original ability to respond to stimulation, after that has been largely lost by continued activity through a long period. What rest will do only after an hour or more, adrenin will do in five minutes or less. The bearing of this striking phenomenon on the functions of the organism in times of great need for muscular activity will be considered in a later discussion.

REFERENCES

1 Qruber: American Journal of Physiology, 1913, xxxii, p. 437.

2 E. L. Porter:' American Journal of Physiology, 1912, xxxi, p. 149.

3 Cannon and Nice: American Journal of Physiology, 1913, xxxii, p. 55.

4 Albanese: Archives Italiennes de Biologie, 1892, xvii, p. 239.

5 Abelous and Langlois: Archives de Physiologic, 1892, xxiv, pp. 269-278, 465-476.

6 Radw&nska: Anzeiger der Akademie, Krakau, 1910, pp. 728-736. Reviewed in the Centralblatt fur Biochemie und Biophysik, 1911, xi, p. 467.

7 Panella: Archives Italiennes de Biologie, 1907, xlvii, p. 30.

8 Langley: Proceedings of the Royal Society of London, 1906, Ixxviii, B, p. 181. Journal of Physiology, 1905-6, xxxiii, pp. 374-413.

9 See Gruber: American Journal of Physiology, 1914, xxxiv, p. 89.

10 Gruber: Ibid., 1918, xlvi, p. 472; 1918, xlvii, p. 178, 185.

CHAPTER IX

THE HASTENING OF COAGULATION OF BLOOD BY ADRENIN

The primary value of blood to the body must have been one of the earliest observations of reasoning beings. When we consider the variety of fundamental services which this circulating fluid performs—the conveyance of food and oxygen to all the tissues, the removal of waste, the delivery of the internal secretions, the protection of the body against toxins and bacterial invasion, and the distribution of heat from active to inactive regions— the view of the ancient Hebrews that the "life of the flesh is in the blood" is well justified. It is naturally of the utmost importance that this precious fluid shall be safeguarded against loss. And its property of turning to a jelly soon after escaping from its natural channels assures a closure of the opening through which the escape occurred, and thus protection of the body from further bleeding. The slight evidence that adrenin hastens the clotting process has already been hinted at. When we

found that adrenin is set free in pain and intense emotion, it seemed possible that there might exist in the body an arrangement for making doubly sure the assurance against loss of blood, a process that might nicely play its role precisely when the greatest need for it would be likely to arise. It was in 1903, while tracing in dogs the rise and fall of sugar in the blood after administering adrenin, that Vosburgh and Richards 1 first noted that simultaneously with the increase of blood sugar there occurred more rapid coagulation. In some cases the diminution was as much as four-fifths the coagulation time of the control. Since this result was obtained by painting "adrenalin" on the pancreas, as well as by injecting it into the abdominal cavity, they concluded that "the phenomenon appears to be due to the application of adrenalin to the pancreas." Six years later, during a study of the effect of adrenalin on internal hemorrhage, "Wiggers 2 examined incidentally the evidence presented by Vosburgh and Richards, and after many tests on five dogs found "never the slightest indication that adrenalin, either when injected or added to the blood, appreciably hastened the coagulation process." In 1911 von den Velden 3 reported that adrenin (about 0.007 milligram per kilo of body weight) decreased the coagulation time in man about one-half—an effect appearing 11 minutes after administration by

FASTER COAGULATION BY ADEENIN 137

mouth, and 85 minutes after subcutaneous injection. He affirmed also, but without describing the conditions or giving figures, that adrenin decreases coagulation time in vitro. He. did not attribute the coagulative effect of adrenin in patients to this direct action on the blood, however, but to vasoconstriction disturbing the normal circulation and thereby the normal equilibrium between blood and tissue. In consequence, the tissue juices with their coagulative properties enter the blood, so he assumed. In support of this theory he offered his observation that coagulation time is decreased after the nasal mucosa has been rendered anemic by adrenin pledgets. Von den Velden's claim 3 for adrenin given by mouth was subjected to a single test on man by Dale and Laidlaw, 4 but their result was completely negative.

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Notes

The Author

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Index

Prologue

There may be nothing new under the sun, tut

permutation of the old within complex systems

can do wonders.

STEPHEN JAY GOULD, 1977

THIS IS A BOOK about thought, memory, creativity, conscious-ness, narrative, talking to oneself, and even dreaming. In a book that parallels this one, How Brains Think, I explored

those subjects in a general way but here I treat them as some of the predicted outcomes of a detailed darwinian theory for how our cerebral cortex represents mental images — and occasionally recombines them, to create something new and different.

This book proposes how darwinian processes could operate in the brain to shape up mental images. Starting with shuffled memories no better than the jumble of our nighttime dreams, a mental image can evolve into something of quality, such as a sentence to speak aloud. Jung said that dreaming goes on contin-uously but you can't see it when you are awake, just as you can't see the stars in the daylight because the sky is too bright. Mine is a theory for what goes on, hidden from view by the glare of waking mental operations, that produces our peculiarly human type of consciousness with its versatile intelligence. As Piaget emphasized, intelligence is what we use when we don't know what to do, when we have to grope rather than using a standard response. In this book, I tackle a mechanism for doing this exploration and improvement offline, how we think before we act and how we practice the art of good guessing.

Surprisingly, the subtitle's mosaics of the mind is not just a liter-ary metaphor. It is a description of mechanism at what appears to be an appropriate level of explanation for many mental phenomena — that of hexagonal mosaics of electrical activity, competing for territory in the association cortex of the brain. This two-dimensional mosaic is predicted to grow and dissolve, much as the sugar crystals do in the bottom of a supersaturated glass of iced tea. Looking down on the cortical surface, with the right kind of imaging, ought to reveal a constantly changing patchwork quilt.

A closer look at each patch ought to reveal a hexagonal pattern that repeats every 0.5 mm. The pattern within each hexagon of this mosaic may be the representation of an item of our vocab-ulary: objects and actions such as the cat that sat on the mat, tunes such as Beethoven's dit-dit-dit-dah, images such as the profile of your grandmother, a high-order concept such as a Turing Machine

— even something for which you have no word, such as the face of someone whose name you haven't learned. If I am right, the spatiotemporal firing pattern within that hexagon is your cerebral code for a word or mental image.

THE OTHER PHRASE IN THE BOOK'S TITLE that is sure to be mistaken

for literary license is, of course, the cerebral code. The word "code" is often only a short way of saying "unlocking the secrets of and newspaper headline writers love such short words. Neurobiolog-ists also speak loosely about codes, as when we talk of "frequency codes" and "place codes," when we really mean only a simple mapping.

Real codes are phrase-based translation tables, such as those of bank wires and diplomatic telegrams. A code is a translation table whereby short abstract phrases are elaborated into the "real thing." If s similar to looking up ambivalence in a dictionary and getting an explanatory sentence back. In the genetic code, the RNA nucleotide sequence CUU is translated into leucine, the triplet GGA into glycine, and so on. The cerebral code, strictly speaking, would be what we use to convert thought into action, a translation table between the short-form cerebral pattern and its muscular implementation.

Informally, code is also used for the short-form pattern itself, for instance, a nucleotide chain such as GCACUUCUUGCACUU. In this book, cerebral code refers to the spatiotemporal firing pattern of neocortical neurons that is essential to represent a concept, word, or image, even a metaphor. One of my theoretical results is that a unique code could be contained within a unit hexagon about 0.5 mm across (though it is often redundantly repeated in many neighboring hexagons).

It was once thought that the genetic code was universal, that all organisms from bacteria to people used the same translation table. Now it turns out that mitochondria use a somewhat differ-ent translation table. Although the cerebral code is a true code, it surely isn't going to be universal; I doubt that the spatiotemporal firing pattern I use for dog (transposed to a musical scale, it would be a short melody, perhaps with some chords) is the same one that you use. Each person's cerebral codes are probably an accident of development and childhood experience. If we find some commonality, for example, that most people's brains innately use a particular subset of codes for animate objects (say, C minor chords) and another subset (like the D major chords) for inanimate objects, I will be pleasantly surprised.

An important consequence of my cerebral code candidate, fall-ing out of the way in which cortical pattern-copying mechanisms seem capable of generating new categories, is that ascending levels of abstraction become possible — even analogies can compete, to help you answer those multiple-choice questions such as "A is to B as C is to D,EF." With a darwinian

process operating in cerebral cortex, you can imagine using stratified stability to generate those strata of concepts that are inexpressible except by roundabout, inadequate means — as when we know things of which we cannot speak. Thaf s the topic of the book's penultimate chapter, "The Making of Metaphor."

AS A NEUROPHYSIOLOGY with long experience doing single neuron recordings in locales ranging from sea

slug ganglia in vitro to human cerebral cortex in situ, I undertook this theoretical venture about a decade ago. I didn't set out to

explain representations, or even the nature of working memory. Like most people in neurobiology, I considered such questions too big to be approached directly. One had to work on their found-ations instead.

Back then, I had a much more modest goal: to seek brain analogies to the darwinian mechanisms that create higher-order complex systems in nature, something that could handle Kenneth Craik's 1943 notion of simulating a possible course of action before actually acting. We know, after all, that the darwinian ratchet can create advanced capabilities in stages, that if s an algorithmic process that gradually creates quality — and gets around the usual presumption that fancy things require an even fancier designer. We even know a lot of the ins-and-outs of the process, such as how evolution speeds up in island settings and why it slows down in continental ones.

However attractive a top-down cognitive design process might be, we know that a bottom-up darwinian process can achieve sophisticated results, given enough time. Perhaps the brain has invented something even fancier than darwinism, but we first ought (so I reasoned) to try the darwinian algorithm out for size, as a foundation — and then look for shortcuts. In 1987,1 wrote a commentary in Nature, "The brain as a Darwin Machine/' propos-ing a term for any full-fledged darwinian process, in analogy to the Turing Machine.

Indeed, since William James first discussed the matter in the 1870s during Charles Darwin's lifetime, darwinian processes have been thought to be a possible basis for mental processes, a way to shape up a grammatically correct sentence or a more efficient plan for visiting the essential aisles of the grocery store. They're a way to explore the Piagetian maze, where you don't initially know what to do; standard neural decision trees for overlearned items may suffice for answering questions, but something creative is often needed when deciding what to do next — as when you pose a question.

When first discovered by Darwin and Wallace and used to explain the shaping up of new species over many millennia, the darwinian ratchet was naturally thought to operate slowly. Then it was discovered that a darwinian shaping up of antibodies also

occurs, during the days-to-weeks time course of the immune response to a novel antigen. You end up with a new type of antibody that is a hundred times more effective than the ones available at the time of infection — and is, of course, far more numerous as well. What would it take, one asks, for the brain to mimic this creative mechanism using still faster neural mechan-isms to run essentially the same process? Might some milliseconds-to-minutes darwinian ratchet form the foundation, atop which our sophisticated mental life is built?

As Wittgenstein once observed, you gain insights mostly through new arrangements of things you already know, not by acquiring new data. This is certainly true at the level of biological variation: despite the constant talk of "mutations," if s really the random shuffle of grandparent chromosomes during meiosis as sperm and ova are made, and the subsequent sexual recombinat-ion during fertilization, that generates the substantial new variations, such as all the differences between siblings. Novel mental images have also been thought to arise from recombinat-ions during brain activity. In our waking hours, most of these surely remain at subconscious levels—but many are probably the same sorts of juxtapositions that we experience in dreams every night. As the neurophysiologist J. Allan Hobson has noted:

Persons, places, and time change suddenly, without notice. There may be abrupt jumps, cuts, and interpolations. There may be fusions: impossible combinations of people, places, times, and activity abound.

Most such juxtapositions and chimeras are nonsense. But during our waking hours, they might be better shaped up in a darwinian manner. Only the more realistic ones might normally reach consciousness.

THE MECHANISTIC REQUIREMENTS for this kind of darwinian process are now better known than they were in the 1870s; they go well beyond the selective-survival summary of darwinism that so often trivializes the issue. Charles Darwin, alas, named his theory natural selection, thus leading many of his followers to focus on

only one of what are really a half-dozen essential aspects of the darwinian process. Thus far, most "darwinian" discussions of the brain's ontogeny, when examined, turn out to involve only several of the darwinian essentials — and not the whole creative loop that I discuss in later chapters.

I attempted to apply these six darwinian attributes to our mental processes in The Cerebral Symphony and in "Islands in the mind/7 published in Seminars in the Neurosciences in 1991, but at that time I hadn't yet found a specific neural mechanism that could turn the crank. Later in 1991,1 realized that two recent developments in neuroscience — emergent synchrony and standard-length intracortical axons — provided the essential elements needed for a darwinian process to operate in the super-ficial layers of our cerebral cortex. This neocortical Darwin Machine opens up a broad neurophysiological-level consideration of cortical operation. With it, you can address a range of cognitive issues, from recognition memory to higher intellectual function including language and plan-ahead mechanisms — even figuring out what goes with the leftovers in the refrigerator.

DESPITE THE HERITAGE from William James and Kenneth Craik, despite the recent interdisciplinary enthusiasm for fresh darwinian and complex adaptive systems approaches to long-standing problems, any such darwinian crank is going to seem new to those scientists who have little detailed knowledge of darwinian principles beyond the crude "survival of the fittest" caricature.

For one thing, you have to think about the statistical nature of the forest, as well as the characteristic properties of each type of tree. Population thinking is not an easily acquired habit but I hope that the first chapter will briefly illustrate how to use it to make a list of six essential features of the darwinian process — plus a few more features that serve as catalysts, to turn the ratchet faster. Next comes a dose of the local neural circuits of cerebral cortex, as that is where the triangular arrays of synchronized neurons are predicted, that will be needed for both the coding and creative complexity aspects. This is also where I introduce the hexagon as the smallest unit of the Hebbian cell-assembly and

estimate its size as about 100 minicolumns involving 10,000 neurons (ifs essentially the 0.5 mm macrocolumn of association cortex, about the same size as the ocular dominance columns of primary visual cortex but perhaps not anchored as permanently). This is where compressing the code is discussed and that puts us in a position to appreciate how long-term memory might work, both for encoding and retrieval.

About halfway through the book, we'll be finished with the circuitry of a neocortical Darwin Machine and ready to consider, in Act II, some of its surprising products: categories, cross-modality matching, sequences, analogies, and metaphors. Ifs just like the familiar distinction we make between the principles of evolution and the products of evolution. The products, in this case, are some of the most interesting ways that humans differ from our ape cousins: going beyond mere category formation to shape up further levels of complexity such as metaphor, narrative, and even agendas. I think that planning ahead, language, and musical abilities also fall out of this same set of neocortical mechanisms, as I've discussed (along with their "free lunch" aspects, thanks to common neural mechanisms) in my earlier books.

SOME READERS MAY HAVE NOTICED BY NOW that this book is not like

my previous ones. They were primarily for general readers and only secondarily for fellow scientists, but that order is reversed here. To help compensate, I've provided a glossary starting at page 203 (even the neuroscientists will need it for the brief tutorials in chaos theory and evolutionary biology). Consult it early and often.

And I had the general reader firmly in mind as I did the book design (ifs all my fault, even the page layout). The illustrations range from the serious to the sketchy. In Three Places in New England, the composer Charles Ives had a characteristic way of playing a popular tune such as "Yankee Doodle" and then dissolving it into his own melody; even a quote of only four notes can be sufficient to release a flood of associations in the listener (something that I tackle mechanistically in Act II, when warming up for metaphor mechanisms). As a matter of writer's technique,

I have tried to use captionless thumbnail illustrations as the briefest of scene-setting digressions, to mimic Ives. I have again enlisted the underground architect, Malcolm Wells, to help me out

— you won't have any trouble telling which illustrations are Mac's! Furthermore, a painting by the neurobiologist Mark Meyer adorns the cover. For some of my own illustrations, alas, I have had to cope with conveying spatiotemporal patterning in a spatial-only medium (further constrained by being grayscale-only and tree-based!). Although I've relied heavily on musical analogies, the material fairly begs for animations.

I have resisted the temptation to utilize computer simulations, mostly for reasons of clarity (in my own head — and perhaps also the reader's). Simulations, if they are to be more than mere animations of an idea, have hard-to-appreciate critical assumpt-ions. At this stage, simulations are simply not needed — one can comprehend the more obvious consequences of a neocortical Darwin Machine without them, both the modular circuits and the territorial competitions. Plane geometry fortunately suffices, essentially that discovered by the ancient Greeks as they contem-plated the hexagonal tile mosaics on the bathhouse floor.

Act I

Everyone knows that in 1859 Darwin demonstrated the occurrence of evolution with such overwhelming documentation tnat it was soon almost universally accepted. What not everyone knows, however, is tnat on tnat occasion Darwin introduced a number of otner scientific and philosophical concepts tkat nave been of far-reaching importance ever since. These concepts, population thinking and selection, owing to their total originality, had to overcome enormous resistance. One might think that among the many hundreds of philosophers who had developed ideas about change, beginning with the Ionians, Plato and Aristotle, the scholastics, the philosophers of the Enlightenment, Descartes, Locke, Hume, Leibniz, Kant, and the numerous philosophers of the first half of the nineteenth century, that there would have been at least one or two to have seen the enormous heuristic power of that combination of variation and selection. But the answer is no. To a modern, who sees the manifestations of variation and selection wherever he looks, this seems quite unbelievable, but it is a historical fact.

E R N S T MAYR, 1994

Looking back into the history of biology, it appears that wherever a phenomenon resembles learning, an instructive theory was first proposed to account for the underlying mechanisms. In every case, this was later replaced by a selective theory. Thus the species were thought to have developed by learning or by adaptation of individuals to the environment, until Darwin showed this to have been a selective process. Resistance of bacteria to antibacterial agents was thought to be acquired by adaptation, until Luria and Delbriick showed the mechanism to be a selective one. Adaptive enzymes were shown by Monod and his school to be inducible enzymes arising through the selection of preexisting genes. Finally, antibody formation that was thought to be based on instruction by the antigen is now found to result from the selection of already existing patterns. It thus remains to be asked if learning by the central nervous system might not also be a selective process, i.e., perhaps learning is not learning either.

N I E L S K J E R N E , 1967

T k e Representation Rroblem

and tke Copying Solution

Even in the small world of Drain science [in the 1860s], two camps were beginning to form. One held that psychological functions such as language or memory could never he traced to a particular region of the hrain. if one had to accept, reluctantly, that the hrain did produce the mind, it did so as a whole and not as a collection of parts with special functions. The

other camp held that, on the contrary, the hrain did

have specialized parts and those parts generated separate mind functions. The rift hetween the two camps was not merely indicative of the infancy of hrain research; the argument endured for another century and, to a certain extent, is still with us today.

A N T O N I O R . D A M A S I O , 1995

ONE CELL, ONE MEMORY may not be the way things work, but it seems to be the first way that people think about the problem of locating memories in cells. Even if you

aren't familiar with how computers store data, the take-home message of most introductions to the brain is that there are pigeonhole memories — highly specialized interneurons, the firing of which might constitute an item's memory evocation. On the perceptual side of neurophysiology, we call it the grandmother's face cell (a neuron that may fire only once a year, at Christmas dinner). On the movement side, if a single interneuron (thaf s an "insider neuron," neither sensory neuron nor motor

neuron) effectively triggers a particular response, it gets called a command neuron. In the simplest of arrangements, both would be the same neuron.

Indeed, the Mauthner cells that trigger the escape reflex of the fish are exactly such neurons. If the fish is attacked from one side, the appropriate Mauthner cell fires and a massive tail flip results, carrying the fish away from the nibbles of its predator. Fortunately these cells already had a proper name, so we were spared the nibble-detector tail-flip cell

But we know better than to generalize these special cases to the whole brain — it can't be one cell, one concept. Yet the reasoning that follows isn't as easily recalled as those pigeonhole memory examples that inadvertently become the take-home message from most introductions to the subject. A singular neuron for each concept is rendered implausible in most vertebrates by the neurophysiological evidence that has accum-ulated since 1928, when the first recordings from sensory nerves revealed a broad range of sensitivity. There were multiple types, with the sensitivity range of one type overlapping that of other types. This overlap, without pure specialties, had been suspected for a long time, at least by the physiologically inclined. Thomas

The three cone types

\ / X \ LI

h. Lh

A™

AOOnm

light wavelength

This combination is:

"Blue" "Green"

"YeHov/1

Ted"

Young formulated his trichromatic theory of colors in 1801; after Hermann von Helmholtz extended the theory in 1865, it was pretty obvious that each special color must be a particular pattern of response that was achievable in various ways, not a singular entity. More recently, taste has turned out the same way: bitter

is just a pattern of strong and weak responses in four types of taste buds, not the action of a particular type.

This isn't to say that a particular interneuron might not come to specialize in some unique combination — but it's so hard to find narrow specialists, insensitive to all else, that we talk of the expectation of finding one as the "Grandmother's face cell fallacy" The "command neuron" usually comes with scare quotes, too, as the Mauthner cell arrangement isn't a common one. While we seek out the specialized neurons in the hopes of finding a tractable experimental model, we usually recognize that committees are likely the irreducible basis of representations — certainly the more abstract ones we call schemas.

Because the unit of memory is likely to be closely related to sensory and motor schemas, pigeonhole schemes such as one-cell-one-memory had to be questioned. After Karl Lashley got through with his rat cortical lesions and found no crucial neocortical sites for maze memory traces, we had to suspect that a particular "memory trace" was a widespread patterning of some sort, one with considerable redundancy. You're left trying to imagine how a unit of memory could be spatially distributed in a redundant manner, overlapping with other memories.

One technological analogy is the hologram, but the brain seems unlikely to utilize phase information in the same way. A simpler and more familiar example of an ensemble representation is the pattern of lights on a message board. Individually, each light signifies nothing. Only in combination with other lights is there a meaning. More modern examples are the pixels of a computer screen or dot-matrix printer. Back in the 1940s, the physiological psychologist Donald Hebb postulated such an ensemble (which he called a cell-assembly) as the unit of perception — and therefore memory. I'll discuss the interesting history of the cell-assembly in the Intermission Notes but for now, just think of one committee-one concept, and that any one cell can serve on multiple committees.

Note that it is not merely the lights which are lit that contain the concept's characteristic pattern: it is just as important that other lights are off, those that might "fog" the desired pattern were they turned on. Fortunately, most neurons of association cortex fire so infrequently that we often take the shortcut of

talking only about "activating cells"; in other parts of the nervous system (especially the retina), there are background levels of activity that can be decreased as well as increased (just as gray backgrounds allow the textbook illustrator to use both black and white type) in an analog manner. But, as we shall see, neocortex also has some "digital" aspects.

A minor generalization to Hebb's cell-assembly would be moveable patterns, as when a message board scrolls: the pattern's the thing, irrespective of which cells are used to implement it. I cannot think of any cerebral examples equivalent to the moving patterns of Conway's Game of Life, such as flashers and gliders, but it is well to keep the free-floating patterns of automata in mind.

The important augmentation of the message board analogy is a pattern of twinkling lights: the possibility that the relevant memory pattern is a spatiotemporal one, not merely a spatial one. In looking for spatiotemporal patterns and trying to discern components, we are going to have the same problems as the child looking at a large Christmas tree, trying to see the independently flashing strings of lights that have been interwoven.

IN THE LONG RUN, however, a memory pattern cannot be a spatiotemporal one: long-term memories survive all sorts of temporary shutdowns in the brain's electricity, such as coma; they persist despite all sorts of fogging, such as those occurring with concussions and seizures. Hebb's dual trace memory said that there had to be major representational differences between long-term memory and the more current "working memories," which can be a distinctive pattern of neuron firings. As Hebb put it:

If some way can be found of supposing that a reverberatory [memory] trace might cooperate with the structural change, and

carry the memory until the growth change is made, we should be able

to recognize the theoretical value of the trace which is an activity only, without having to ascribe all memory to it.

We are familiar with this archival-versus-current, passive-versus-active distinction from phonograph records, where a spatial-only pattern holds the information in cold storage and a spatiotemporal pattern is recreated on occasion, a pattern almost identical to that which originally produced the spatial pattern. A sheet of music or a roll for a player piano also allows a spatial-only pattern to be converted to a spatiotemporal one. I will typically use musical performance as my spatiotemporal pattern analogy and sheet music as my analogy to a spatial-only underpinning.

At first glimpse, there appear to be some spatial-only sensat-ions, say, those produced by my wristwatch on my skin (if s not really static because I have the usual physiological tremor, and a radial pulse, to interact with its weight). But most of our sensat-ions are more obviously spatiotemporal, as when we finger the corner of the page in preparation for turning it. Even if the input appears static, as when we stare at the center of a checkerboard, some jitter is often introduced, as by the small micronystagmus of the eyeball (as I discuss further in the middle of my Intermission Notes, the nervous system gets a spatiotemporal pattern from the photoreceptors sweeping back and forth under the image). Whether timeless like a drawing of a comb or changing with time as when feeling a comb running through your hair, the active "working" representation is likely to be spatiotemporal, some-thing like the light sequence in a pinball machine or those winking light strings on the Christmas tree.

Certainly, all of our movements involve spatiotemporal patterns of muscle activation. Even in a static-seeming posture, physiological tremor moves things. In general, the implement-ation is a spatiotemporal pattern involving many motor neuron pools. Sometimes, as in the case of the fish's tail flip, the command for this starts at one point in time and space, but usually even the initiation of the movement schema is spatiotemporal, smeared out in both time and space.

The sensation need not funnel down to a point and then expand outwards to recruit the appropriate response sequence; rather, the spatiotemporal pattern of the sensation could create the appropriate spatiotemporal pattern for the response without ever having a locus. Spread out in both time and space, such ephemeral (and perhaps relocatable) ensembles are difficult to summarize in flow charts or metaphors. Think, perhaps, of two voices, one of which (the sensory code) starts the song, is answered by the other voice (movement code); the voices are then intertwined for awhile (and the movement eventually gets underway), and then the second voice finishes the song.

To my mind, the representation problem is which spatio-temporal pattern represents a mental object: surely recalling a memory is not a matter of recreating the firing patterns of every cell in the brain, so that they all mimic the activity at the time of input. Some subset must suffice. How big is it? Is it a synchron-ized ensemble like a chord, as some cortical theories would have it? Or is it more like a single note melody? Or with some chords mixed in? Does it repeat over and over, or does one repetition suffice for a while?

THOSE QUESTIONS WERE IN THE AIR, for the most part, even back in

my undergraduate days of the late 1950s, when I first met Hebb after reading his then-decade-old book, It is inaccurate — worse, it The Organization of Behavior. Hebb,

is mislea Jing — to call amazingly, guessed a solution in 1945, psyckology tke study of even before the first single neuron

Lekavior: It is tke study of

recordings from mammalian

cerebral

tke underlying processes,

cortex (glass microelectrodes

weren't

just as ckemistry is tke

invented until 1950). Although our data

study of tke atom ratker

have grown magnificently in recent

tkan pH values, spectro-

decades, we haven't improved much on

scopes, and test tukes.

Hebb's statement of the problem, or on

D. O. HEBB, 1980

his educated guess about where the

solution is likely to be found.

Multiple microelectrode techniques now allow the sampling of several dozen neurons in a neighborhood spanning a few square millimeters. In motor cortex, even a randomly sampled

ensemble can predict which movement, from a standard repertoire, that a trained monkey is about to make. For monkeys forced to wait before acting on a behavioral choice, sustained cell firing during the long hold is mostly up in premotor and prefrontal areas. In premotor and prefrontal cortex, some of the spatiotemporal patterns sampled by multiple microelectrodes are surprisingly precise and task-specific. With the fuzzier imaging techniques, we have recently seen some examples of where work-ing memory patterns might be located: for humans trying to remember telephone numbers long enough to dial them, it's the classical Broca and Wernicke language areas that light up in imaging techniques.

Because recall is so much more difficult than mere recognition (you can recognize an old phone number, even when you can't voluntarily recall it), we may need to distinguish between different representations for the same thing. The cryptographers make a similar distinction between a document and a hashed summary of that document (something like a checksum but capable of detecting even transposed letters). Such a 100-byte "message digest" is capable of recognizing a unique, multipage document ("I've seen that one before") but doesn't contain enough information to actually reconstruct it. So, too, we may have to distinguish between simple Hebbian cell-assemblies — ones that suffice for recognition — and the more detailed ones needed for abstracts and for complete recall.

Hebb's formulation imposes an important constraint on any possible explanation for the cerebral representation: if s got to explain both spatial-only and spatiotemporal patterns, their inter-conversions, their redundancy and spatial extent, their imperfect nature (and characteristic errors therefrom), and the links of assoc-iative memory (including how distortions of old memories are caused by new links). No present technology provides an analogy to help us think about the problem.

THE ROLE OF SIMILAR CONSTRAINTS on theorizing can be seen in how Kepler's three "laws" about planetary orbits posed the gravity problem that Newton went on to solve. Only a half century ago, molecular genetics had a similar all-important

constraint that set the stage for a solution. Biologists knew that, whatever the genetic material was, it had to fit inside the cell, be chemically stable — and, most significantly, it had to be capable of making very good copies of itself during cell "division." That posed the problem in a solvable way, as it turned out.

Most people thought that the gene would turn out to be a protein, its three-dimensional nooks and crannies serving as a template for another such giant molecule. The reason Crick and Watson's DNA helical-zipper model caused such excitement in 1953 was because it fit with the copying constraint. It wasn't until a few years later that it became obvious how a triplet of a 4-letter DNA code was translated into strings from the 20-letter amino acid alphabet, and so created enzymes and other proteins.

Looking for molecular copying ability led to the solution of the puzzle of how genes were decoded. Might looking for a neural copying mechanism provide an analogous way of approaching the cerebral code puzzle?

MEMES ARE THOSE THINGS that are copied from mind to mind. Richard Dawkins formulated this concept in 1976 in his book, The Selfish Gene. Cell division may copy genes, but minds mimic everything from words to dances. The cultural analog to the gene is the meme (as in mime or mimic); if s the unit of copying. An advertising jingle is a meme. The spread of a rumor is cloning a pattern from one mind to another, the metastasis of a representation.

Might, however, such cloning be seen inside one brain and not just between brains? Might seeing what was cloned lead us to the representation, the cerebral code? Copying of an ensemble pattern hasn't been observed yet, but there are reasons to expect it in any brain — at least, in any brain large enough to have a long-distance communications problem.

If the pattern's the thing, how is it transmitted from the left side of the brain to the right side? Or from front to back? We can't send it like a mail parcel, so consider the problems of telecopying, of making a distant copy of a local pattern. Is there a NeuroFax Principle at work?

When tracing techniques were crude, at a millimeter level of resolution, it seemed as if there were point-to-point mappings, an orderly topography for the major sensory pathways such that neighbors remained next to one another. One could imagine that

those

long corticocortical axon

bundles were like fiber optic bun-

Memes are not strung out along

dles

that

convey an

image by

linear chromosomes, ana it is

thousands

little light pipes.

not clear that they occupy and

But with finer resolution, topo-

compete for discrete "loci", or

graphic mappings turn out to be

tnat tney nave identifiable

only

approximately

point-to-

"alleles" . . . . The copying

point; instead, an axon breaks up

process is probably much less

into clumps of endings. For the

precise than in the case of

corticocortical axon terminations

genes. . . . Memes may partially

of the "interoffice mail," this fan-

blend with each other in a way

out

spans

macrocolumnar

that genes do not.

dimensions and sometimes many

RICHARD DAWKINS, 1982

millimeters. Exact point-to-point mapping doesn't occur.

So, at first glimpse, it appears that corticocortical bundles are considerably worse than those incoherent fiber optic bundles that are factory rejects — unless, of course, something else is going on. Perhaps it doesn't matter that the local spatiotemporal pattern is severely distorted at the far end; if codes are arbitrary, why should it matter that there are different codes for Apple in different parts of the brain? Just as there are two equally valid roots to a quad-ratic equation, just as isotopes have identical chemical properties despite different weights, so degenerate codes are quite common. For example, there are six different DNA triplets that all result in leucine being tacked on to a growing peptide.

The main drawback to a degenerate cortical code is that most corticocortical projections are reciprocal: six out of seven interareal pathways have a matching back projection. It might undo the distortion of the forward projection, in the manner of inverse transforms, but thaf s demanding a lot of careful tuning and regular recalibration. And it isn't simply a matter of each local region having two local codes for Apple, one for sending, the other

for receiving. Each region has multiple projection targets and thus many possible feedback codes that mean Apple.

There might, of course, be some sort of error-correction code that allows a single characteristic spatiotemporal pattern for Apple. It would have to remove any distortions caused by the spatial wanderings, plus those associated with temporal dispersions of corticocortical transmission. It would need, furthermore, to operate in both the forward and return paths. I originally dismissed this possibility, assuming that an error-correcting mechanism was too fancy for cerebral circuitry. But, as will become apparent by the end of the following chapter, such error correction is easier than it sounds, thanks to that fanout of the corticocortical axon's terminals contributing to standardization of a spatiotemporal pattern.

COPYING FOR A FAUX FAX is going to be needed for cerebral cortex, even if simpler nervous systems, without a long-distance problem, can operate without copying. Copying might also be handy for promoting redundancy. But there is a third reason why copying might have proved useful in a fancy brain: darwinism.

Perhaps it is only a matter of our impoverished knowledge of complex systems, but creativity seems to be a shaping-up process. During the evolution of new species and during the immune response's production of better and better antibodies, successive generations are shaped up, not especially the individual. Yes, the individual is plastic and it learns, but this modification during life is not typically incorporated into the genes that are passed on (learning and experience only change the chances of passing on the genes with which one was born — the propensity for learning such things, rather than the things themselves). Yes, culture itself passes along imitations, but memes are easily distorted and easily lost, compared to genuine genes.

Reproduction involves the copying of patterns, sometimes with small chance variations. Creativity may not always be a matter of copying errors and recombination, but it is reasonable to expect that the brain is going to make some use of this elementary darwinian mechanism for editing out the nonsense

and emphasizing variations on the better-fitting ones in a next generation.

NATURAL SELECTION ALONE isn't sufficient for evolution, and neither is copying alone — not even copying with selection will suffice. I can identify six essential aspects of the creative darwin-ian process that bootstraps quality.

There must be a reasonably complex pattern involved.

The pattern must be copied somehow (indeed, that which is copied may serve to define the pattern).

Variant patterns must sometimes be produced by chance.

The pattern and its variant must compete with one another for occupation of a limited work space. For example, bluegrass and crab grass compete for back yards.

The competition is biased by a multifaceted environment, for example, how often the grass is watered, cut, fertilized, and frozen, giving one pattern more of the lawn than another. That's natural selection.

There is a skewed survival to reproductive maturity (environmental selection is mostly juvenile mortality) or a skewed distribution of those adults who successfully mate (sexual selection), so new variants always preferentially occur around the more successful of the current patterns.

With only a few of the six essentials, one gets the more wide-spread "selective survival" process (which popular usage tends to call darwinian). You may get some changes (evolution, but only in the weakest sense of the word) but things soon settle, running out of steam without the full process to turn the darwinian ratchet.

Indeed, many things called darwinian turn out to have no copying process at all, such as the selective survival of some synaptic connections in the brain during pre- and postnatal development of a single individual. Selective survival, moreover, doesn't even require biology. For example, a shingle beach is one where the waves have carried away the smaller rocks and sand, much as a carving reflects the selective removal of some material to create a pattern. The copying-mutation-selection loop utilized

by the small-molecule chemists as they try to demonstrate the power of RNA-based evolution captures most of darwinism, as do "genetic" algorithms of computer science.

Not all of the essentials have to be at the same level of organiz-ation. Pattern, copying, and variation involve the genes, but selection is based on the bodies (the phenotypes that carry the genes) and their environment; inheritance, however, is back at the genotype level. In RNA-based evolution, the two levels are combined into one (the RNA serves as a catalyst in a way that affects its survival — but it is also what is copied).

BECAUSE NEURAL VERSIONS OF THE SIX ESSENTIALS are going to play

such a large role in the rest of this book, let me comment on the better-known versions for a moment.

The gene is a string of DNA base-pairs that, in turn, instructs the rest of the cell about how to make a protein, perhaps an enzyme that regulates the rate of tissue growth. We'll be looking back from neural implementations, such as movement comm-ands, and trying to see what patterns could have served as the cerebral code to get them going. Larger genetic patterns, such as whole chromosomes, are seldom copied exactly. So, too, we will have to delve below the larger movements to see what the smaller units might be.

While the biological variations seem random, unguided variation isn't really required for a darwinian process to operate. We tend to emphasize randomness for several reasons. First, randomness is the default assumption against which we test claims of guidance. And second, the process will work fine without guidance, without any foreknowledge of a desired result. That said, it might work faster, and in some restricted sense better, with some hints that bias the general direction of the variants; this need not involve anything as fancy as artificial selection. We will see neural versions of random copying errors and recombination, including (in the last chapter) some discussion about how a slow darwinian process might guide a faster one by biasing the general direction in which its variations are done.

Competition between variants depends on some limitation in resources (space in association cortex, in my upcoming examples)

or carrying capacity. During a wide-open population explosion, competition is minor because the space hasn't filled up yet.

For competition to be interesting, it must be based on a complex, multifaceted environment. Rather than the environment of grass, we'll be dealing with biases from sensation, feedback from our own movements, and even our moods. Most interestingly, there are both current versions of these environmental factors and memories of past ones.

Many of the offspring have variations that are "worse" than the successful parent pattern but a minority may possess a variant that is an even better fit to the particular multifaceted environment. This tendency to base most new variations on the more successful of the old ones is what Darwin called the principle of inheritance, his great insight and the founding principle of what became population biology.

It means that the darwinian process, as a whole loop, isn't truly random. Rather, it involves repeated exploratory steps where small chance variations are done on well-tested-by-the-environment versions. If s an enormously conservative process, because variations propagate from the base of the most successful adults — not the base of the population as born. Without this proviso, the process doesn't accumulate wisdom about what worked in the past. The neural version also needs exactly the same characteristic, where slight variations are done from an advanced position, not from the original center of the population.

AT LEAST FIVE OTHER FACTORS are known to be important to the evolution of species. The creative darwinian process will run without them, but they affect the stability of its outcome, or the rate of evolution, and will be important for my model of cognitive functions. Just like the catalysts and enzymes that speed chemical reactions without being consumed, they may make improbable outcomes into commonplace ones.

Stability may occur, as in getting stuck in a rut (a local peak or basin in the adaptational landscape). Variants occur but they backslide easily. Only particularly large variations can ever escape from a rut, but they are few, and

even more likely to produce nonsense (phenotypes that fail to develop properly, and so die young).

Systematic recombination generates many more variants than do copying errors and the far-rarer cosmic-ray mutations. Recombination usually occurs once during meiosis (the grandparent chromosomes are shuffled as haploid sperm and ova are made) and again at fertilization (as the haploid parent genomes are combined into diploid once again, at fertilization). Sex, in the sense of gamete dimorphism (going to the extremes of expensive ova and cheap sperm), was invented several billion years ago and greatly accelerated species evolution over the rate promot-ed by errors, bacterial conjugation, and retroviruses.

Fluctuating environments (seasons, climate changes, diseases) change the name of the game, shaping up more complex patterns capable of doing well in several environ-ments. For such jack-of-all-trades selection to occur, the environment must change much faster than efficiency adaptations can track it, or 'lean mean machine" special-ists will dominate the expensive generalists.

Parcellation, as when rising sea level converts the hilltops of one large island into an archipelago of small islands, typically speeds evolution. This is, in part, because more individuals then live on the margins of the habitat where selection pressure is greater. Also, there is no large central population to buffer change. When rising sea level con-verted part of the coastline of France into the island of Jersey, the red deer trapped there in the last interglaciation underwent a considerable dwarfing within only a few thousand years.

Local extinctions, as when an island population becomes too small to sustain itself, speed evolution because they create empty niches. When subsequent pioneers rediscov-er the unused resources, their descendants go through a series of generations where there is enough food — even for the more extreme variations that arise, the ones that would ordinarily lose out in the competition with the more optimally endowed, such as the survivors of a resident

population. When the environment again changes, some of those more extreme variants may be able to cope better with the third environment than the narrower range of variants that would reach reproductive age under the regime of a long-occupied niche.

Sexual selection also has the reputation of speeding evolution, and there are "catalysts" acting at several removes, as in Darwin's example of what introducing cats to an English village would do to enhance the bee-dependent flowers, via reducing the rodent populations that disrupt bee hives.

An example of how these catalysts work together is island biogeography, as in the differentiation of Darwin's finches unbuff-ered by large continental gene pools. Archipelagos allow for many parallel evolutionary experiments. Episodes that recombine the islands (as when sea level falls during an ice age) create winner-take-most tournaments. Most evolutionary change may occur in such isolation, in remote valleys or offshore islands, with major continental populations serving as slowly changing reservoirs that provide pioneers to the chancy periphery.

ALTHOUGH THE CREATIVE DARWINIAN PROCESS will run without

these catalysts, using darwinian creativity in a behavioral setting requires some optimization for speed, so that quality is achieved within the time span of thought and action. Accelerating factors are the problem in what the French call avoir Vesprit de I'escalier — finally thinking of a witty reply, but only after leaving the party.

I will not be surprised if some accelerating factors are almost essential in mental danvinism, simply because of the time windows created by fleeting opportunities.

The wheels of a machine

to play rapidly

must not fit with the utmost exactness

else the attrition diminishes the Impetus.

SIR WALTER SCOTT, discussing Lord Byron's mind

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Cloning in Ceretral Cortex

All scribes, however careful, are bound to make a few errors, and some are not above a little willful "improvement." If they all copied from a single master original, meaning would not be greatly perverted. But let copies be made from other copies, wbicb in their turn were made from other copies, and errors will start to become cumulative and serious. We tend to regard

erratic copying as a bad thing, and in tbe case of human

documents it is bard to think of examples wbere errors can be described as improvements. I suppose tbe scbolars of tbe Septuagint could at least be said to bave started something big wben tbey mistranslated tbe Hebrew word for "young woman" into tbe Greek word for "virgin," coming up witb tbe prophecy: "Behold a virgin sball conceive and bear a son. . . . " Anyway, as we sball see, erratic copying in biological replicators can in a real sense give rise to improvement, and it was essential for tbe progressive evolution of life that some errors were made.

RICHARD DAWKINS, The Selfish Gene, 1976

THIS is THE HARDEST CHAPTER in the whole book. In it, I have to delve into the neuroanatomy and neurophysiology of cortical neurons, importing lessons from such seemingly unrelated subjects as synchronously flashing fireflies. By the end of this chapter, I will have shown how copying could arise in neocortex. By the end of the sixth chapter, the cortical equivalents of all the darwinian essentials and all the accelerating factors will

have been examined. But it gets easier, not harder, starting with the fourth chapter.

Neurophysiologists distinguish between cell properties and circuit properties, much as biologists distinguish between genotype and phenotype. Some phenomena are clearly due to the circuit rather than the cells involved, to the wiring rather than the components — a new property "emerges" from the particular combination. You won't find it in any one neuron. The classical example of an emergent property involves lateral inhibition and it is the reason that Keffer Hartline got a Nobel Prize in 1967.

Thanks to local activity contributing to a ring of depression in surrounding neurons, lateral inhibition sharpens up fuzzy bound-aries. Compound eyes, the many narrow-angle photoreceptors of which provide an extreme case of fuzzy optics, have a series of inhibitory interconnections that are capable of recreating a light-dark boundary in the environment, restoring much of what was lost.

But lateral inhibition also has a tendency to produce features where none exist, illusions such as the Mach bands that you see if looking through a narrow slit between your fingers. Georg von Bekesy, whose studies of such sideways interactions in the cochlea were the subject of his 1961 Nobel Prize, also produced illusions from skin surfaces, to illustrate the generality of the lateral inhibition principles. Antagonistic surrounds ("Mexican hats")

are common in all the first half-dozen stages of the analysis of a visual image, though they become somewhat elongated and asymmetric ("Australian bush hats") in primary visual cortex. Because of the many axon collaterals that branch laterally in neocortex,

lateral inhibition extends several millimeters.

Both the sharpening of fuzzy boundaries and the illusions are emergent properties of a laterally inhibiting neural network. What might be the emergent consequences of lateral excitation?

THERE IS GOOD REASON to worry about recurrent excitation. It is potentially regenerative, in the same sense as a string of fire

3.0 mm

PyrwmUM neuron mama eond many

fPOGWVWtt GOmtCTtV VTWGnOB WtOIWty to neighboring areas of cortex, the hash for both lateral Inhibition and

crackers. It is also the most prominent wiring principle of mam-malian neocortex.

A few words about cerebral cortex, the icing on the brain's cake:. in this cake, it's the frosting that has the appearance of layering! Six layers are usually identified on the basis of cell size

or axon packing density, though we sometimes subdivide it further (in primary visual cortex, one talks about layers 4a, 4b, 4ca, and 4cP). At other times, we lump layers together: when I mention the "superficial layers/' I'm combining layers 1,2, and 3.

Part of the monkey superficial pyramidal

neuron reconstructed by McGuIre et al

(J. Comp. Neurol. 1991), showing axon

terminals to Immediate neighbors (thin

fcJ>

axons amidst dendritic tree) as well as

branches to cells a microcolumn away.

Furthermore, there are three functional groupings that have become apparent: on the analogy to the mail boxes stacked on many a desk, layer 4 could be said to be the IN box of neocortex, because most of the inputs from the thalamus terminate there. The deep layers could be called the OUT box, as pyramidal neurons of layers 5 and 6 send axons outside the cortex, back to thalamus or down to the spinal cord, and so forth. The neurons of the superficial layers seem to constitute the INTERNAL mailbox of the neocortex, specializing in the interoffice memos. Interactions among the superficial pyramidal neurons are what this book is mostly about, as these neurons seem capable of implementing a darwinian copying competition, one that can shape up quality from humble beginnings.

The axons of the superficial pyramidal cells are prominent in the corpus callosum and other long corticocortical paths, but also in the intrinsic horizontal connections: those axon branches that never leave the superficial layers because they run sideways. They preferentially terminate on other superficial pyramidal neu-rons — and in a patterned manner, too. Some axon branches go to near neighbors, but the ones that go further ignore a whole series of intermediate neurons before communicating with those about 0.5 mm distant.

Those sparsely populated gaps are something like the Sherlock Holmes story about the dog that didn't bark in the night. It took a long time before anyone noticed this fact. In 1975 came the first hint of these gap patterns. In 1982, when Jennifer Lund and Kathleen Rockland first studied the gaps in the superficial layers' intrinsic horizontal connections, it was in the visual cortex of the tree shrew. Though the gap distance varies, we now know that it is a common arrangement for many areas of neocortex, and for many animal species. Thanks to the detailed reconstructions of several HRP-injected superficial pyramidal neurons by Barbara McGuire and her colleagues, we also know that these synaptic connections are likely to be excitatory, probably using glutamate as their neurotransmitter, and that their predominant targets are other superficial pyramidal neurons.

Their axons have dozens of branches, going sideways in many radial directions, fanning out eventually into thousands of axon terminals. Although no single superficial pyramidal neuron has enough terminals to fill in a doughnut, we might expect a small minicolumn group of such neurons to produce a ring of excitation, as well as the central spot of excitation from the branches to immediate neighbors. Point-to-area is the more common arrangement for axon projections, such as those of the pyramidal neurons of the deep layers. Recurrent inhibition is also seen, but only the recurrent excitation of the superficial layers of neocortex has this Sherlock-Holmes feature of prominent silent gaps.

Optical imaging techniques that look down on the brain's surface are now capable of resolving a spread of activity in cortex. Stimulation of a restricted area of retina, of a type that classically would be expected to concentrate cortical activity in only one area

«ftM-Lonnt»<l«No

branching axon activating cortical loops

of the exposed cortical surface, is now seen to

contribute to multiple hot spots of activity at

4 #

macrocolumnar separations, much as predicted.

The neocortical versions of long-term potentiat-

ion (LTP) are also concentrated in the superficial

layers. We know that N-methyl-D-aspartate

(NMDA) types of postsynaptic receptors, which

I have the unusual characteristic of augmenting their strength when inputs arrive in clusters (such as quasi-synchronously from different sources), are especially

common in the superficial layers.

All of this raises the possibility of self-reexciting loops, not un-like the reverberating circuits postulated for the spinal cord by Rafael Lorente de N6 in 1938, in the very first volume of the Journal of Neurophysiology. If the synaptic strengths are high enough, and the paths long enough to escape the refractory periods that would otherwise limit re-excitation, closed loops of activity ought to be possible, impulses chasing their tails. Moshe Abeles, whose Jerusalem lab often observes more than a dozen cortical neurons at a time, has seen some precise impulse timing

of one neuron, relative to another, in premotor and prefrontal cortex neuron ensembles. It is unknown whether or not these firing patterns represent reverberation, in Lorente's original sense of recirculating loops. These long, precisely-timed firing patterns are important for the notion of spatiotemporal patterns that I will later develop.

EMERGENT SYNCHRONY is well known as a commonplace conseq-uence of recurrent excitation, one that ought to be seen with even weak connection strengths and short paths. In 1665, the Dutch physicist Christiaan Huygens noticed that two pendulum clocks hanging from a common support were synchronized. When he

disturbed the synchrony, it returned within a half hour. Harmonic oscillators are slower to entrain than nonlinear relaxation oscillators, which can take just a few cycles.

The most famous example of entrairunent is probably menstr-ual cycles in women's dormitories. More dramatic in appearance is a whole tree filled with little lights, flashing in unison. No, I don't mean a Christmas tree wired up, under the control of a single flasher — there's a natural, wireless example based on hundreds of independent oscillators. The little lights are hundreds of fireflies, and they have no leader to set the pace.

Imagine a tree thirty-five to forty feet high, apparently with a firefly on every leaf, and all the fireflies flashing in perfect unison at a rate of about three times in two seconds, the tree being in complete darkness between flashes. Imagine a tenth of a mile of river front with an unbroken line of mangrove trees with fireflies on every leaf flashing in synchronization, the insects on the trees at the ends of the line acting in perfect unison with those between. Then, if one's imagination is sufficiently vivid, he may form some conception of this amazing spectacle.

It doesn't require any elaborate notions of mimicry to account for the firefly entrainment; even small tendencies to advance to the next flash when stimulated with light will suffice to create a "rush hour." Furthermore, you usually do not see waves propagating through such a population, except perhaps when the flashing is just beginning or ending. Even in cortical simulations with prop-agation delays, near-synchrony is seen, in much the way (anomal-ous dispersion) that some velocities can exceed the speed of light.

Weak mutual re-excitation (a few percent of threshold) is quite sufficient to entrain; one need not postulate strong connection strengths in the manner needed for Lorente's recirculating chains. So long as the neurons (or fireflies) already have enough input to fire repeatedly, there will be an entrainment tendency if they mutually re-excite one another. And that is exactly what super-ficial pyramidal neurons, 0.5 mm apart, seem so likely to do. The triple combination — mutual re-excitation, silent gaps that focus it, and the resulting entrainment tendencies — is what gives the

superficial layers of neocortex the potential of being a Darwin Machine.

LOOKING DOWN FROM ON HIGH at the superficial layers of neocortex, in what the neuroanatomists call "tangential slices/' is like looking down on a forest from a balloon. Any one neuron is seen in a top-down perspective, orthogonal to that seen from the side in the usual surface-to-depth slice. Like the branches of any one tree, any one neuron has a dendritic tree, but also an axon tree, much as the foresf s tree has branching roots below ground.

The axon of a single superficial pyramidal neuron will be seen to spread in many directions. Though sensory neurons and motor neurons may vary, the average interneuron sends out as many synapses as it receives, usually between 2,000 and 10,000. Not enough radial plots have yet been done to know how symmetric the horizontal spread is, but it seems clear that the axon branches travel in many directions from the cell.

GIVEN standard length excitatory axons,

entrained

...recurrent excitation between some cell pairs produces entrained firing patterns.

An entrained pair tends to recruit additional cells

that are equidistant.

spot"

...and so create a

TRIANGULAR ARRAY.

The distance from the cell body to the center of the axon term-inal cluster, studied mostly in the side views, is not the same in all cortical areas. That "0.5 mm" mentioned earlier is really as small as 0.4 mm (in primary visual cortex of monkeys) or as large as 0.85 mm (in sensorimotor cortex). It scales with the width of the basal dendritic tree. I'll use 0.5 mm as my standard example of this local metric; it corresponds to a basal dendritic tree of about 0.25

mm spread, which is also about the spread of one cluster of axon terminals and the extent of one silent gap.

If two superficial pyramidal neurons, about 0.5 mm apart, are interested in the same features because of similar inputs and thresholds, their spike trains ought to start exhibiting occasional spike synchrony. It need not be all the spikes from each neuron for the following analysis to be relevant; only some of their spikes need synchronize via the recurrent excitation.

There should also be some minor tendency for two such cells, already firing repeatedly, to recruit another cell 0.5 mm away that is almost active. If that third superficial pyramidal neuron becomes active, we should see three often-synchronized neurons forming an equilateral triangle. But that is not the end of it: there is a second site receiving synchronous input from the

parent pair (this is exactly like that elementary exercise in plane geometry where a compass is used to bisect a line or drop a perpendicular). So a fourth neuron might join the chorus.

And because the third and fourth cells provide new annuli of excitation, either can combine with one of the first pair to bring a fifth point into synchrony. What we have, it is apparent, is a mechanism for forming up a triangular array of some size, nodes of synchronized activity 0.5 mm

from corresponding cells of this chorus. It could work either by synchronizing preexisting activity or by recruiting otherwise sub-threshold neurons at the nodes. Once a potential node is surround-ed by a few synchronous nodes exciting it, there ought to be a hot spot, an unusually effective con-vergence of simultaneous inputs.

This triangular array annexat-

ion tendency is not unlimited. (Regions with insufficiently excited neurons, as I discuss in the latter part of chapter 6, provide barriers to any further empire-building.) And the triangular array is surely ephemeral, here now and gone in seconds. When it is shut

down by enough inhibition (or reduction of excitation), it will be as if a blackboard had been erased.

Traces will linger, however, in much the way that blackboards retain ghostly images of former patterns. The synaptic strengths should remain changed for a while; indeed, the synchrony-sensitive long-term potentiation of the superficial neocortical layers suggests that synaptic strength can remain augmented for many minutes. This will make it easier to recreate the active form of the triangular array — perhaps not all of its spatial extent, but part of it.

THE LATTICE CONNEcnviTY seen in the anatomy, it should be said, does not fall into neat triangular arrays, measured by distance in the tangential plane of section. Though the neuroanatomists speak of "polka-dot" patterns and 'lattices" for the axon terminal clusters in the superficial layers, the spacing of the clusters is only roughly triangular. Of course, adjusting conduction velocity or synaptic delay during a tune-up period could make a triangular array, when replotted as "driving time" rather than distance.

But not even an equal conduction time, for converging simultaneously on a potential recruit, is actually required for the present theory. Though exact synchrony has been convenient for introducing the principles, all that triangular arrays require in the long run is a prenatal tune-up period that results in a good-enough self-organization, so that most of the six surrounding

nodes produce axon clusters that mutually overlap in a manner that aids entrainment. It may not matter to this self-organizing principle what an external observer would find "regular." I'll stick to triangular array terminology for the theory, but don't expect to find exact triangles in either the anatomy or physiology, only good-enough approximations.

FROM A PAIR OF LIKE-MINDED CELLS, we see the possibility of a large

chorus, all singing in synchrony. Furthermore, it's a chorus that can recruit additional members out on its edges. Like a choir standing on risers, these singers tend to space themselves so that each is standing in between two singers on the row below. The choir isn't as perfect a triangular array as the fruit displays at your corner grocery, but it's a good enough approximation to the familiar packing principle.

So far, this choir only chants in unison. It's monomaniacal, perhaps only interested in one feature of the stimulus. It's surely not the true Hebbian cell-assembly The choir corresponding to a concept representation would surely sing in parts, just as sopranos carry one melody and the altos another, each group having different interests. We will need polyphony for harmonious categories, not just chants.

A Compressed. Code Emerges

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probablespluyt · 3 years ago

Text

Table of Contents

Also by Steven Johnson

Title Page

Dedication

Contents

Introduction: Robot Historians and the Hummingbird’s Wing

1. Glass

2. Cold

3. Sound

4. Clean

5. Time

6. Light

Conclusion: The Time Travelers

Acknowledgments

Notes

Bibliography

Credits

Index

ALSO BY STEVEN JOHNSON

Interface Culture:

How New Technology Transforms the Way We Create and Communicate

Emergence:

The Connected Lives of Ants, Brains, Cities, and Software

Mind Wide Open:

Your Brain and the Neuroscience of Everyday Life

Everything Bad Is Good for You:

How Today’s Popular Culture Is Actually Making Us Smarter

The Ghost Map:

The Story of London’s Most Terrifying Epidemic—and How It Changed Science, Cities, and the Modern World

The Invention of Air:

A Story of Science, Faith, Revolution, and the Birth of America

Where Good Ideas Come From:

The Natural History of Innovation

Future Perfect:

The Case for Progress in a Networked Age

RIVERHEAD BOOKS

Published by the Penguin Group

Penguin Group (USA) LLC

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New York, New York 10014

USA • Canada • UK • Ireland • Australia • New Zealand • India • South Africa • China

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Penguin supports copyright. Copyright fuels creativity, encourages diverse voices, promotes free speech, and creates a vibrant culture. Thank you for buying an authorized edition of this book and for complying with copyright laws by not reproducing, scanning, or distributing any part of it in any form without permission. You are supporting writers and allowing Penguin to continue to publish books for every reader.

Library of Congress Cataloging-in-Publication Data

Johnson, Steven, date.

How we got to now : six innovations that made the modern world / Steven Johnson.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-698-15450-6

1. Technology—Social aspects. 2. Inventions—Social aspects. I. Title.

T14.5.J64 2014 2014018412

338'.064—dc23

Version_1

For Jane, who no doubt expected a three-volume treatise on nineteenth-century whaling

Contents

Also by Steven Johnson

Title Page

Dedication

Introduction: Robot Historians and the Hummingbird’s Wing

1. GLASS

2. COLD

3. SOUND

4. CLEAN

5. TIME

6. LIGHT

Conclusion: The Time Travelers

Acknowledgments

Notes

Bibliography

Credits

Index

Introduction

Robot Historians and the Hummingbird’s Wing

little more than two decades ago, the Mexican-American artist and philosopher Manuel De Landa published a strange and wonderful book called War in the Age of Intelligent Machines. The book was, technically speaking, a history of military technology, but it had nothing in common with what you might naturally expect from the genre. Instead of heroic accounts of submarine engineering written by some Naval Academy professor, De Landa’s book wove chaos theory, evolutionary biology, and French post-structuralist philosophy into histories of the conoidal bullet, radar, and other military innovations. I remember reading it as a grad student in my early twenties and thinking that it was one of those books that seemed completely sui generis, as though De Landa had arrived on Earth from some other intellectual planet. It seemed mesmerizing and deeply confusing at the same time.

De Landa began the book with a brilliant interpretative twist. Imagine, he suggested, a work of history written sometime in the future by some form of artificial intelligence, mapping out the history of the preceding millennium. “We could imagine,” De Landa argued, “that such a robot historian would write a different kind of history than would its human counterpart.” Events that loom large in human accounts—the European conquest of the Americas, the fall of the Roman Empire, the Magna Carta—would be footnotes from the robot’s perspective. Other events that seem marginal to traditional history—the toy automatons that pretended to play chess in the eighteenth century, the Jacquard loom that inspired the punch cards of early computing—would be watershed moments to the robot historian, turning points that trace a direct line to the present. “While a human historian might try to understand the way people assembled clockworks, motors and other physical contraptions,” De Landa explained, “a robot historian would likely place a stronger emphasis on the way these machines affected human evolution. The robot would stress the fact that when clockworks once represented the dominant technology on the planet, people imagined the world around them as a similar system of cogs and wheels.”

There are no intelligent robots in this book, alas. The innovations here belong to everyday life, not science fiction: lightbulbs, sound recordings, air-conditioning, a glass of clean tap water, a wristwatch, a glass lens. But I have tried to tell the story of these innovations from something like the perspective of De Landa’s robot historian. If the lightbulb could write a history of the past three hundred years, it too would look very different. We would see how much of our past was bound up in the pursuit of artificial light, how much ingenuity and struggle went into the battle against darkness, and how the inventions we came up with triggered changes that, at first glance, would seem to have nothing to do with lightbulbs.

This is a history worth telling, in part, because it allows us to see a world we generally take for granted with fresh eyes. Most of us in the developed world don’t pause to think how amazing it is that we drink water from a tap and never once worry about dying forty-eight hours later from cholera. Thanks to air-conditioning, many of us live comfortably in climates that would have been intolerable just fifty years ago. Our lives are surrounded and supported by a whole class of objects that are enchanted with the ideas and creativity of thousands of people who came before us: inventors and hobbyists and reformers who steadily hacked away at the problem of making artificial light or clean drinking water so that we can enjoy those luxuries today without a second thought, without even thinking of them as luxuries in the first place. As the robot historians would no doubt remind us, we are indebted to those people every bit as much as, if not more than, we are to the kings and conquerors and magnates of traditional history.

But the other reason to write this kind of history is that these innovations have set in motion a much wider array of changes in society than you might reasonably expect. Innovations usually begin life with an attempt to solve a specific problem, but once they get into circulation, they end up triggering other changes that would have been extremely difficult to predict. This is a pattern of change that appears constantly in evolutionary history. Think of the act of pollination: sometime during the Cretaceous age, flowers began to evolve colors and scents that signaled the presence of pollen to insects, who simultaneously evolved complex equipment to extract the pollen and, inadvertently, fertilize other flowers with pollen. Over time, the flowers supplemented the pollen with even more energy-rich nectar to lure the insects into the rituals of pollination. Bees and other insects evolved the sensory tools to see and be drawn to flowers, just as the flowers evolved the properties that attract bees. This is a different kind of survival of the fittest, not the usual zero-sum competitive story that we often hear in watered-down versions of Darwinism, but something more symbiotic: the insects and flowers succeed because they, physically, fit well with each other. (The technical term for this is coevolution.) The importance of this relationship was not lost on Charles Darwin, who followed up the publication of On the Origin of Species with an entire book on orchid pollination.

These coevolutionary interactions often lead to transformations in organisms that would seem to have no immediate connection to the original species. The symbiosis between flowering plants and insects that led to the production of nectar ultimately created an opportunity for much larger organisms—the hummingbirds—to extract nectar from plants, though to do that they evolved an extremely unusual form of flight mechanics that enables them to hover alongside the flower in a way that few birds can even come close to doing. Insects can stabilize themselves midflight because they have fundamental flexibility to their anatomy that vertebrates lack. Yet despite the restrictions placed on them by their skeletal structure, hummingbirds evolved a novel way of rotating their wings, giving power to the upstroke as well as the downstroke, enabling them to float midair while extracting nectar from a flower. These are the strange leaps that evolution makes constantly: the sexual reproduction strategies of plants end up shaping the design of a hummingbird’s wings. Had there been naturalists around to observe the insects first evolving pollination behavior alongside the flowering plants, they would have logically assumed that this strange new ritual had nothing to do with avian life. And yet it ended up precipitating one of the most astonishing physical transformations in the evolutionary history of birds.

The history of ideas and innovation unfolds the same way. Johannes Gutenberg’s printing press created a surge in demand for spectacles, as the new practice of reading made Europeans across the continent suddenly realize that they were farsighted; the market demand for spectacles encouraged a growing number of people to produce and experiment with lenses, which led to the invention of the microscope, which shortly thereafter enabled us to perceive that our bodies were made up of microscopic cells. You wouldn’t think that printing technology would have anything to do with the expansion of our vision down to the cellular scale, just as you wouldn’t have thought that the evolution of pollen would alter the design of a hummingbird’s wing. But that is the way change happens.

This may sound, at first blush, like a variation on the famous “butterfly effect” from chaos theory, where the flap of a butterfly’s wing in California ends up triggering a hurricane in the mid-Atlantic. But in fact, the two are fundamentally different. The extraordinary (and unsettling) property of the butterfly effect is that it involves a virtually unknowable chain of causality; you can’t map the link between the air molecules bouncing around the butterfly and the storm system brewing in the Atlantic. They may be connected, because everything is connected on some level, but it is beyond our capacity to parse those connections or, even harder, to predict them in advance. But something very different is at work with the flower and the hummingbird: while they are very different organisms, with very different needs and aptitudes, not to mention basic biological systems, the flower clearly influences the hummingbird’s physiognomy in direct, intelligible ways.

This book is then partially about these strange chains of influence, the “hummingbird effect.” An innovation, or cluster of innovations, in one field ends up triggering changes that seem to belong to a different domain altogether. Hummingbird effects come in a variety of forms. Some are intuitive enough: orders-of-magnitude increases in the sharing of energy or information tend to set in motion a chaotic wave of change that easily surges over intellectual and social boundaries. (Just look at the story of the Internet over the past thirty years.) But other hummingbird effects are more subtle; they leave behind less conspicuous causal fingerprints. Breakthroughs in our ability to measure a phenomenon—time, temperature, mass—often open up new opportunities that seem at first blush to be unrelated. (The pendulum clock helped enable the factory towns of the industrial revolution.) Sometimes, as in the story of Gutenberg and the lens, a new innovation creates a liability or weakness in our natural toolkit, that sets us out in a new direction, generating new tools to fix a “problem” that was itself a kind of invention. Sometimes new tools reduce natural barriers and limits to human growth, the way the invention of air-conditioning enabled humans to colonize the hotspots of the planet at a scale that would have startled our ancestors just three generations ago. Sometimes the new tools influence us metaphorically, as in the robot historian’s connection between the clock and the mechanistic view of early physics, the universe imagined as a system of “cogs and wheels.”

Observing hummingbird effects in history makes it clear that social transformations are not always the direct result of human agency and decision-making. Sometimes change comes about through the actions of political leaders or inventors or protest movements, who deliberately bring about some kind of new reality through their conscious planning. (We have an integrated national highway system in the United States in large part because our political leaders decided to pass the Federal-Aid Highway Act of 1956.) But in other cases, the ideas and innovations seem to have a life of their own, engendering changes in society that were not part of their creators’ vision. The inventors of air-conditioning were not trying to redraw the political map of America when they set about to cool down living rooms and office buildings, but, as we will see, the technology they unleashed on the world enabled dramatic changes in American settlement patterns, which in turn transformed the occupants of Congress and the White House.

I have resisted the understandable temptation to assess these changes with some kind of value judgment. Certainly this book is a celebration of our ingenuity, but just because an innovation happens, that doesn’t mean there aren’t, in the end, mixed consequences as it ripples through society. Most ideas that get “selected” by culture are demonstrably improvements in terms of local objectives: the cases where we have chosen an inferior technology or scientific principle over a more productive or accurate one are the exceptions that prove the rule. And even when we do briefly choose the inferior VHS over Betamax, before long we have DVDs that outperform either option. So when you look at the arc of history from that perspective, it does trend toward better tools, better energy sources, better ways to transmit information.

The problem lies with the externalities and unintended consequences. When Google launched its original search tool in 1999, it was a momentous improvement over any previous technique for exploring the Web’s vast archive. That was cause for celebration on almost every level: Google made the entire Web more useful, for free. But then Google started selling advertisements tied into the search requests it received, and within a few years, the efficiency of the searches (along with a few other online services like Craigslist) had hollowed out the advertising base of local newspapers around the United States. Almost no one saw that coming, not even the Google founders. You can make the argument—as it happens, I would probably make the argument—that the trade-off was worth it, and that the challenge from Google will ultimately unleash better forms of journalism, built around the unique opportunities of the Web instead of the printing press. But certainly there is a case to be made that the rise of Web advertising has been, all told, a negative development for the essential public resource of newspaper journalism. The same debate rages over just about every technological advance: Cars moved us more efficiently through space than did horses, but were they worth the cost to the environment or the walkable city? Air-conditioning allowed us to live in deserts, but at what cost to our water supplies?

This book is resolutely agnostic on these questions of value. Figuring out whether we think the change is better for us in the long run is not the same as figuring out how the change came about in the first place. Both kinds of figuring are essential if we are to make sense of history and to map our path into the future. We need to be able to understand how innovation happens in society; we need to be able to predict and understand, as best as we can, the hummingbird effects that will transform other fields after each innovation takes root. And at the same time we need a value system to decide which strains to encourage and which benefits aren’t worth the tangential costs. I have tried to spell out the full range of consequences with the innovations surveyed in this book, the good and the bad. The vacuum tube helped bring jazz to a mass audience, and it also helped amplify the Nuremberg rallies. How you ultimately feel about these transformations—Are we ultimately better off thanks to the invention of the vacuum tube?—will depend on your own belief systems about politics and social change.

I should mention one additional element of the book’s focus: The “we” in this book, and in its title, is largely the “we” of North Americans and Europeans. The story of how China or Brazil got to now would be a different one, and every bit as interesting. But the European/North American story, while finite in its scope, is nonetheless of wider relevance because certain critical experiences—the rise of the scientific method, industrialization—happened in Europe first, and have now spread across the world. (Why they happened in Europe first is of course one of the most interesting questions of all, but it’s not one this book tries to answer.) Those enchanted objects of everyday life—those lightbulbs and lenses and audio recordings—are now a part of life just about everywhere on the planet; telling the story of the past thousand years from their perspective should be of interest no matter where you happen to live. New innovations are shaped by geopolitical history; they cluster in cities and trading hubs. But in the long run, they don’t have a lot of patience for borders and national identities, never more so than now in our connected world.

I have tried to adhere to this focus because, within these boundaries, the history I’ve written here is in other respects as expansive as possible. Telling the story of our ability to capture and transmit the human voice, for instance, is not just a story about a few brilliant inventors, the Edisons and Bells whose names every schoolchild has already memorized. It’s also a story about eighteenth-century anatomical drawings of the human ear, the sinking of the Titanic, the civil rights movement, and the strange acoustic properties of a broken vacuum tube. This is an approach I have elsewhere called “long zoom” history: the attempt to explain historical change by simultaneously examining multiple scales of experience—from the vibrations of sound waves on the eardrum all the way out to mass political movements. It may be more intuitive to keep historical narratives on the scale of individuals or nations, but on some fundamental level, it is not accurate to remain between those boundaries. History happens on the level of atoms, the level of planetary climate change, and all the levels in between. If we are trying to get the story right, we need an interpretative approach that can do justice to all those different levels.

The physicist Richard Feynman once described the relationship between aesthetics and science in a similar vein:

I have a friend who’s an artist and has sometimes taken a view which I don’t agree with very well. He’ll hold up a flower and say “Look how beautiful it is,” and I’ll agree. Then he says “I as an artist can see how beautiful this is but you as a scientist take this all apart and it becomes a dull thing,” and I think that he’s kind of nutty. First of all, the beauty that he sees is available to other people and to me too, I believe. Although I may not be quite as refined aesthetically as he is . . . I can appreciate the beauty of a flower. At the same time, I see much more about the flower than he sees. I could imagine the cells in there, the complicated actions inside, which also have a beauty. I mean it’s not just beauty at this dimension, at one centimeter; there’s also beauty at smaller dimensions, the inner structure, also the processes. The fact that the colors in the flower evolved in order to attract insects to pollinate it is interesting; it means that insects can see the color. It adds a question: does this aesthetic sense also exist in the lower forms? Why is it aesthetic? All kinds of interesting questions which shows that a science knowledge only adds to the excitement, the mystery and the awe of a flower. It only adds. I don’t understand how it subtracts.

There is something undeniably appealing about the story of a great inventor or scientist—Galileo and his telescope, for instance—working his or her way toward a transformative idea. But there is another, deeper story that can be told as well: how the ability to make lenses also depended on the unique quantum mechanical properties of silicon dioxide and on the fall of Constantinople. Telling the story from that long-zoom perspective doesn’t subtract from the traditional account focused on Galileo’s genius. It only adds.

Marin County, California

February 2014

1. Glass

oughly 26 million years ago, something happened over the sands of the Libyan Desert, the bleak, impossibly dry landscape that marks the eastern edge of the Sahara. We don’t know exactly what it was, but we do know that it was hot. Grains of silica melted and fused under an intense heat that must have been at least a thousand degrees. The compounds of silicon dioxide they formed have a number of curious chemical traits. Like H2O, they form crystals in their solid state, and melt into a liquid when heated. But silicon dioxide has a much higher melting point than water; you need temperatures above 500 degrees Fahrenheit instead of 32. But the truly peculiar thing about silicon dioxide is what happens when it cools. Liquid water will happily re-form the crystals of ice if the temperature drops back down again. But silicon dioxide for some reason is incapable of rearranging itself back into the orderly structure of crystal. Instead, it forms a new substance that exists in a strange limbo between solid and liquid, a substance human beings have been obsessed with since the dawn of civilization. When those superheated grains of sand cooled down below their melting point, a vast stretch of the Libyan Desert was coated with a layer of what we now call glass.

About ten thousand years ago, give or take a few millennia, someone traveling through the desert stumbled across a large fragment of this glass. We don’t know anything more about that fragment, only that it must have impressed just about everyone who came into contact with it, because it circulated through the markets and social networks of early civilization, until it ended up as a centerpiece of a brooch, carved into the shape of a scarab beetle. It sat there undisturbed for four thousand years, until archeologists unearthed it in 1922 while exploring the tomb of an Egyptian ruler. Against all odds, that small sliver of silicon dioxide had found its way from the Libyan Desert into the burial chamber of Tutankhamun.

Glass first made the transition from ornament to advanced technology during the height of the Roman Empire, when glassmakers figured out ways to make the material sturdier and less cloudy than naturally forming glass like that of King Tut’s scarab. Glass windows were built during this period for the first time, laying the groundwork for the shimmering glass towers that now populate city skylines around the world. The visual aesthetics of drinking wine emerged as people consumed it in semitransparent glass vessels and stored it in glass bottles. But, in a way, the early history of glass is relatively predictable: craftsmen figured out how to melt the silica into drinking vessels or windowpanes, exactly the sort of typical uses we instinctively associate with glass today. It wasn’t until the next millennium, and the fall of another great empire, that glass became what it is today: one of the most versatile and transformative materials in all of human culture.

Pectoral in gold cloissoné with semiprecious stones and glass paste, with winged scarab, symbol of resurrection, in center, from the tomb of Pharaoh Tutankhamun

—

THE SACKING of Constantinople in 1204 was one of those historical quakes that send tremors of influence rippling across the globe. Dynasties fall, armies surge and retreat, the map of the world is redrawn. But the fall of Constantinople also triggered a seemingly minor event, lost in the midst of that vast reorganization of religious and geopolitical dominance and ignored by most historians of the time. A small community of glassmakers from Turkey sailed westward across the Mediterranean and settled in Venice, where they began practicing their trade in the prosperous new city growing out of the marshes on the shores of the Adriatic Sea.

Circa 1900: Roman civilization, first–second century AD glass containers for ointments

It was one of a thousand migrations set in motion by Constantinople’s fall, but looking back over the centuries, it turned out to be one of the most significant. As they settled into the canals and crooked streets of Venice, at that point arguably the most important hub of commercial trade in the world, their skills at blowing glass quickly created a new luxury good for the merchants of the city to sell around the globe. But lucrative as it was, glassmaking was not without its liabilities. The melting point of silicon dioxide required furnaces burning at temperatures near 1,000 degrees, and Venice was a city built almost entirely out of wooden structures. (The classic stone Venetian palaces would not be built for another few centuries.) The glassmakers had brought a new source of wealth to Venice, but they had also brought the less appealing habit of burning down the neighborhood.

In 1291, in an effort to both retain the skills of the glassmakers and protect public safety, the city government sent the glassmakers into exile once again, only this time their journey was a short one—a mile across the Venetian Lagoon to the island of Murano. Unwittingly, the Venetian doges had created an innovation hub: by concentrating the glassmakers on a single island the size of a small city neighborhood, they triggered a surge of creativity, giving birth to an environment that possessed what economists call “information spillover.” The density of Murano meant that new ideas were quick to flow through the entire population. The glassmakers were in part competitors, but their family lineages were heavily intertwined. There were individual masters in the group that had more talent or expertise than the others, but in general the genius of Murano was a collective affair: something created by sharing as much as by competitive pressures.

A section of a fifteenth-century map of Venice, showing the island of Murano

By the first years of the next century, Murano had become known as the Isle of Glass, and its ornate vases and other exquisite glassware became status symbols throughout Western Europe. (The glassmakers continue to work their trade today, many of them direct descendants of the original families that emigrated from Turkey.) It was not exactly a model that could be directly replicated in modern times: mayors looking to bring the creative class to their cities probably shouldn’t consider forced exile and borders armed with the death penalty. But somehow it worked. After years of trial and error, experimenting with different chemical compositions, the Murano glassmaker Angelo Barovier took seaweed rich in potassium oxide and manganese, burned it to create ash, and then added these ingredients to molten glass. When the mixture cooled, it created an extraordinarily clear type of glass. Struck by its resemblance to the clearest rock crystals of quartz, Barovier called it cristallo. This was the birth of modern glass.

—

WHILE GLASSMAKERS such as Barovier were brilliant at making glass transparent, we didn’t understand scientifically why glass is transparent until the twentieth century. Most materials absorb the energy of light. On a subatomic level, electrons orbiting the atoms that made up the material effectively “swallow” the energy of the incoming photon of light, causing those electrons to gain energy. But electrons can gain or lose energy only in discrete steps, known as “quanta.” But the size of the steps varies from material to material. Silicon dioxide happens to have very large steps, which means that the energy from a single photon of light is not sufficient to bump up the electrons to the higher level of energy. Instead, the light passes through the material. (Most ultraviolet light, however, does have enough energy to be absorbed, which is why you can’t get a suntan through a glass window.) But light doesn’t simply pass through glass; it can also be bent and distorted or even broken up into its component wavelengths. Glass could be used to change the look of the world, by bending light in precise ways. This turned out to be even more revolutionary than simple transparency.

In the monasteries of the twelfth and thirteenth centuries, monks laboring over religious manuscripts in candlelit rooms used curved chunks of glass as a reading aid. They would run what were effectively bulky magnifiers over the page, enlarging the Latin inscriptions. No one is sure exactly when or where it happened, but somewhere around this time in Northern Italy, glassmakers came up with an innovation that would change the way we see the world, or at least clarify it: shaping glass into small disks that bulge in the center, placing each one in a frame, and joining the frames together at the top, creating the world’s first spectacles.

Those early spectacles were called roidi da ogli, meaning “disks for the eyes.” Thanks to their resemblance to lentil beans—lentes in Latin—the disks themselves came to be called “lenses.” For several generations, these ingenious new devices were almost exclusively the province of monastic scholars. The condition of “hyperopia”—farsightedness—was widely distributed through the population, but most people didn’t notice that they suffered from it, because they didn’t read. For a monk, straining to translate Lucretius by the flickering light of a candle, the need for spectacles was all too apparent. But the general population—the vast majority of them illiterate—had almost no occasion to discern tiny shapes like letterforms as part of their daily routine. People were farsighted; they just didn’t have any real reason to notice that they were farsighted. And so spectacles remained rare and expensive objects.

The earliest image of a monk with glasses, 1342

What changed all of that, of course, was Gutenberg’s invention of the printing press in the 1440s. You could fill a small library with the amount of historical scholarship that has been published documenting the impact of the printing press, the creation of what Marshall McLuhan famously called “the Gutenberg galaxy.” Literacy rates rose dramatically; subversive scientific and religious theories routed around the official channels of orthodox belief; popular amusements like the novel and printed pornography became commonplace. But Gutenberg’s great breakthrough had another, less celebrated effect: it made a massive number of people aware for the first time that they were farsighted. And that revelation created a surge in demand for spectacles.

What followed was one of the most extraordinary cases of the hummingbird effect in modern history. Gutenberg made printed books relatively cheap and portable, which triggered a rise in literacy, which exposed a flaw in the visual acuity of a sizable part of the population, which then created a new market for the manufacture of spectacles. Within a hundred years of Gutenberg’s invention, thousands of spectacle makers around Europe were thriving, and glasses became the first piece of advanced technology—since the invention of clothing in Neolithic times—that ordinary people would regularly wear on their bodies.

But the coevolutionary dance did not stop there. Just as the nectar of flowering plants encouraged a new kind of flight in the hummingbird, the economic incentive created by the surging market for spectacles engendered a new pool of expertise. Europe was not just awash in lenses, but also in ideas about lenses. Thanks to the printing press, the Continent was suddenly populated by people who were experts at manipulating light through slightly convex pieces of glass. These were the hackers of the first optical revolution. Their experiments would inaugurate a whole new chapter in the history of vision.

Fifteenth-century glasses

In 1590 in the small town of Middleburg in the Netherlands, father and son spectacle makers Hans and Zacharias Janssen experimented with lining up two lenses, not side by side like spectacles, but in line with each other, magnifying the objects they observed, thereby inventing the microscope. Within seventy years, the British scientist Robert Hooke had published his groundbreaking illustrated volume Micrographia, with gorgeous hand-drawn images re-creating what Hooke had seen through his microscope. Hooke analyzed fleas, wood, leaves, even his own frozen urine. But his most influential discovery came by carving off a thin sheaf of cork and viewing it through the microscope lens. “I could exceeding plainly perceive it to be all perforated and porous, much like a Honey-comb,” Hooke wrote, “but that the pores of it were not regular; yet it was not unlike a Honey-comb in these particulars . . . these pores, or cells, were not very deep, but consisted of a great many little Boxes.” With that sentence, Hooke gave a name to one of life’s fundamental building blocks—the cell—leading the way to a revolution in science and medicine. Before long the microscope would reveal the invisible colonies of bacteria and viruses that both sustain and threaten human life, which in turn led to modern vaccines and antibiotics.

The Flea (engraving from Robert Hooke’s Micrographia, London)

The microscope took nearly three generations to produce truly transformative science, but for some reason the telescope generated its revolutions more quickly. Twenty years after the invention of the microscope, a cluster of Dutch lensmakers, including Zacharias Janssen, more or less simultaneously invented the telescope. (Legend has it that one of them, Hans Lippershey, stumbled upon the idea while watching his children playing with his lenses.) Lippershey was the first to apply for a patent, describing a device “for seeing things far away as if they were nearby.” Within a year, Galileo got word of this miraculous new device, and modified the Lippershey design to reach a magnification of ten times normal vision. In January of 1610, just two years after Lippershey had filed for his patent, Galileo used the telescope to observe that moons were orbiting Jupiter, the first real challenge to the Aristotelian paradigm that assumed all heavenly bodies circled the Earth.

This is the strange parallel history of Gutenberg’s invention. It has long been associated with the scientific revolution, for several reasons. Pamphlets and treatises from alleged heretics like Galileo could circulate ideas outside the censorious limits of the Church, ultimately undermining its authority; at the same time, the system of citation and reference that evolved in the decades after Gutenberg’s Bible became an essential tool in applying the scientific method. But Gutenberg’s creation advanced the march of science in another, less familiar way: it expanded possibilities of lens design, of glass itself. For the first time, the peculiar physical properties of silicon dioxide were not just being harnessed to let us see things that we could already see with our own eyes; we could now see things that transcended the natural limits of human vision.

The lens would go on to play a pivotal role in nineteenth- and twentieth-century media. It was first utilized by photographers to focus beams of light on specially treated paper that captured images, then by filmmakers to both record and subsequently project moving images for the first time. Starting in the 1940s, we began coating glass with phosphor and firing electrons at it, creating the hypnotic images of television. Within a few years, sociologists and media theorists were declaring that we had become a “society of the image,” the literate Gutenberg galaxy giving way to the blue glow of the TV screen and the Hollywood glamour shot. Those transformations emerged out of a wide range of innovations and materials, but all of them, in one way or another, depended on the unique ability of glass to transmit and manipulate light.

An early microscope designed by Robert Hooke, 1665

To be sure, the story of the modern lens and its impact on media is not terribly surprising. There’s an intuitive line that you can follow from the lenses of the first spectacles, to the lens of a microscope, to the lens of a camera. Yet glass would turn out to have another bizarre physical property, one that even the master glassblowers of Murano had failed to exploit.

—

AS PROFESSORS GO, the physicist Charles Vernon Boys was apparently a lousy one. H. G. Wells, who was briefly one of Boys’s students at London’s Royal College of Science, later described him as “one of the worst teachers who has ever turned his back on a restive audience. . . . [He] messed about with the blackboard, galloped through an hour of talk, and bolted back to the apparatus in his private room.”

But what Boys lacked in teaching ability he made up for in his gift for experimental physics, designing and building scientific instruments. In 1887, as part of his physics experiments, Boys wanted to create a very fine shard of glass to measure the effects of delicate physical forces on objects. He had an idea that he could use a thin fiber of glass as a balance arm. But first he had to make one.

Hummingbird effects sometimes happen when an innovation in one field exposes a flaw in some other technology (or in the case of the printed book, in our own anatomy) that can be corrected only by another discipline altogether. But sometimes the effect arrives thanks to a different kind of breakthrough: a dramatic increase in our ability to measure something, and an improvement in the tools we build for measuring. New ways of measuring almost always imply new ways of making. Such was the case with Boys’s balance arm. But what made Boys such an unusual figure in the annals of innovation is the decidedly unorthodox tool he used in pursuit of this new measuring device. To create his thin string of glass, Boys built a special crossbow in his laboratory, and created lightweight arrows (or bolts) for it. To one bolt he attached the end of a glass rod with sealing wax. Then he heated glass until it softened, and he fired the bolt. As the bolt hurtled toward its target, it pulled a tail of fiber from the molten glass clinging to the crossbow. In one of his shots, Boys produced a thread of glass that stretched almost ninety feet long.

Charles Vernon Boys standing in a laboratory, 1917

“If I had been promised by a good fairy for anything I desired, I would have asked for one thing with so many valuable properties as these fibres,” Boys would later write. Most astonishing, though, was how strong the fiber was: as durable, if not more so, than an equivalently sized strand of steel. For thousands of years, humans had employed glass for its beauty and transparency, and tolerated its chronic fragility. But Boys’s crossbow experiment suggested that there was one more twist in the story of this amazingly versatile material: using glass for its strength.

By the middle of the next century, glass fibers, now wound together in a miraculous new material called fiberglass, were everywhere: in home insulation, clothes, surfboards, megayachts, helmets, and the circuit boards that connected the chips of a modern computer. The fuselage of Airbus’s flagship jet, the A380—the largest commercial aircraft in the skies—is built with a composite of aluminum and fiberglass, making it much more resistant to fatigue and damage than traditional aluminum shells. Ironically, most of these applications ignored silicon dioxide’s strange capacity to transmit light waves: most objects made of fiberglass do not look to the untutored eye to be made of glass at all. During the first decades of innovation with glass fibers, this emphasis on nontransparency made sense. It was useful to allow light to pass through a windowpane or a lens, but why would you need to pass light through a fiber not much bigger than a human hair?

The transparency of glass fibers became an asset only once we began thinking of light as a way to encode digital information. In 1970, researchers at Corning Glassworks—the Murano of modern times—developed a type of glass that was so extraordinarily clear that if you created a block of it the length of a bus, it would be just as transparent as looking through a normal windowpane. (Today, after further refinements, the block could be a half-mile long with the same clarity.) Scientists at Bell Labs then took fibers of this super-clear glass and shot laser beams down the length of them, fluctuating optical signals that corresponded to the zeroes and ones of binary code. This hybrid of two seemingly unrelated inventions—the concentrated, orderly light of lasers, and the hyper-clear glass fibers—came to be known as fiber optics. Using fiber-optic cables was vastly more efficient than sending electrical signals over copper cables, particularly for long distances: light allows much more bandwidth and is far less susceptible to noise and interference than is electrical energy. Today, the backbone of the global Internet is built out of fiber-optic cables. Roughly ten distinct cables traverse the Atlantic Ocean, carrying almost all the voice and data communications between the continents. Each of those cables contains a collection of separate fibers, surrounded by layers of steel and insulation to keep them watertight and protected from fishing trawlers, anchors, and even sharks. Each individual fiber is thinner than a piece of straw. It seems impossible, but the fact is that you can hold the entire collection of all the voice and data traffic traveling between North America and Europe in the palm of one hand. A thousand innovations came together to make that miracle possible: we had to invent the idea of digital data itself, and laser beams, and computers at both ends that could transmit and receive those beams of information—not to mention the ships that lay and repair the cables. But those strange bonds of silicon dioxide, once again, turn out to be central to the story. The World Wide Web is woven together out of threads of glass.

Think of that iconic, early-twenty-first-century act: snapping a selfie on your phone as you stand in some exotic spot on vacation, and then uploading the image to Instagram or Twitter, where it circulates to other people’s phones and computers all around the world. We’re accustomed to celebrating the innovations that have made this act almost second nature to us now: the miniaturization of digital computers into handheld devices, the creation of the Internet and the Web, the interfaces of social-networking software. What we rarely do is recognize the way glass supports this entire network: we take pictures through glass lenses, store and manipulate them on circuit boards made of fiberglass, transmit them around the world via glass cables, and enjoy them on screens made of glass. It’s silicon dioxide all the way down the chain.

—

IT’S EASY TO MAKE FUN of our penchant for taking selfies, but in fact there is a long and storied tradition behind that form of self-expression. Some of the most revered works of art from the Renaissance and early modernism are self-portraits; from Dürer to Leonardo, to Rembrandt, all the way to van Gogh with his bandaged ear, painters have been obsessed with capturing detailed and varied images of themselves on the canvas. Rembrandt, for instance, painted around forty self-portraits over the course of his life. But the interesting thing about self-portraiture is that it effectively doesn’t exist as an artistic convention in Europe before 1400. People painted landscapes and royalty and religious scenes and a thousand other subjects. But they didn’t paint themselves.

The explosion of interest in self-portraiture was the direct result of yet another technological breakthrough in our ability to manipulate glass. Back in Murano, the glassmakers had figured out a way to combine their crystal-clear glass with a new innovation in metallurgy, coating the back of the glass with an amalgam of tin and mercury to create a shiny and highly reflective surface. For the first time, mirrors became part of the fabric of everyday life. This was a revelation on the most intimate of levels: before mirrors came along, the average person went through life without ever seeing a truly accurate representation of his or her face, just fragmentary, distorted glances in pools of water or polished metals.

Mirrors appeared so magical that they were quickly integrated into somewhat bizarre sacred rituals: During holy pilgrimages, it became common practice for well-off pilgrims to take a mirror with them. When visiting sacred relics, they would position themselves so that they could catch sight of the bones in the mirror’s reflection. Back home, they would then show off these mirrors to friends and relatives, boasting that they had brought back physical evidence of the relic by capturing the reflection of the sacred scene. Before turning to the printing press, Gutenberg had the start-up idea of manufacturing and selling small mirrors for departing pilgrims.

Las Meninas by Diego Rodríguez de Silva y Velázquez

But the mirror’s most significant impact would be secular, not sacred. Filippo Brunelleschi employed a mirror to invent linear perspective in painting, by drawing a reflection of the Florence Baptistry instead of his direct perception of it. The art of the late Renaissance is heavily populated by mirrors lurking inside paintings, most famously in Diego Velázquez’s inverted masterpiece, Las Meninas, which shows the artist (and the extended royal family) in the middle of painting King Philip IV and Queen Mariana of Spain. The entire image is captured from the point of view of two royal subjects sitting for their portrait; it is, in a very literal sense, a painting about the act of painting. The king and queen are visible only in one small fragment of the canvas, just to the right of Velázquez himself: two small, blurry images reflected back in a mirror.

As a tool, the mirror became an invaluable asset to painters who could now capture the world around them in a far more realistic fashion, including the detailed features of their own faces. Leonardo da Vinci observed the following in his notebooks (using mirrors, naturally, to write in his legendary backward script):

When you wish to see whether the general effect of your picture corresponds with that of the object represented after nature, take a mirror and set it so that it reflects the actual thing, and then compare the reflection with your picture, and consider carefully whether the subject of the two images is in conformity with both, studying especially the mirror. The mirror ought to be taken as a guide.

The historian Alan MacFarlane writes of the role of glass in shaping artistic vision, “It is as if all humans had some kind of systematic myopia, but one which made it impossible to see, and particularly to represent, the natural world with precision and clarity. Humans normally saw nature symbolically, as a set of signs. . . . What glass ironically did was to take away or compensate for the dark glass of human sight and the distortions of the mind, and hence to let in more light.”

At the exact moment that the glass lens was allowing us to extend our vision to the stars or microscopic cells, glass mirrors were allowing us to see ourselves for the first time. It set in motion a reorientation of society that was more subtle, but no less transformative, than the reorientation of our place in the universe that the telescope engendered. “The most powerful prince in the world created a vast hall of mirrors, and the mirror spread from one room to another in the bourgeois household,” Lewis Mumford writes in his Technics and Civilization. “Self-consciousness, introspection, mirror-conversation developed with the new object itself.” Social conventions as well as property rights and other legal customs began to revolve around the individual rather than the older, more collective units: the family, the tribe, the city, the kingdom. People began writing about their interior lives with far more scrutiny. Hamlet ruminated onstage; the novel emerged as a dominant form of storytelling, probing the inner mental lives of its characters with an unrivaled depth. Entering a novel, particularly a first-person narrative, was a kind of conceptual parlor trick: it let you swim through the consciousness, the thoughts and emotions, of other people more effectively than any aesthetic form yet invented. The psychological novel, in a sense, is the kind of story you start wanting to hear once you begin spending meaningful hours of your life staring at yourself in the mirror.

How much does this transformation owe to glass? Two things are undeniable: the mirror played a direct role in allowing artists to paint themselves and invent perspective as a formal device; and shortly thereafter a fundamental shift occurred in the consciousness of Europeans that oriented them around the self in a new way, a shift that would ripple across the world (and that is still rippling). No doubt many forces converged to make this shift possible: the self-centered world played well with the early forms of modern capitalism that were thriving in places like Venice and Holland (home to those masters of painterly introspection, Dürer and Rembrandt). Likely, these various forces complemented each other: glass mirrors were among the first high-tech furnishings for the home, and once we began gazing into those mirrors, we began to see ourselves differently, in ways that encouraged the market systems that would then happily sell us more mirrors. It’s not that the mirror made the Renaissance, exactly, but that it got caught up in a positive feedback loop with other social forces, and its unusual capacity to reflect light strengthened those forces. This is what the robot historian’s perspective allows us to see: the technology is not a single cause of a cultural transformation like the Renaissance, but it is, in many ways, just as important to the story as the human visionaries that we conventionally celebrate.

McFarlane has an artful way of describing this kind of causal relationship. The mirror doesn’t “force” the Renaissance to happen; it “allows” it to happen. The elaborate reproductive strategy of the pollinators didn’t force the hummingbird to evolve its spectacular aerodynamics; it created the conditions that allowed the hummingbird to take advantage of flower’s free sugars by evolving such a distinctive trait. The fact that the hummingbird is so unique in the avian kingdom suggests that, had the flowers not evolved their symbiotic dance with the insects, the hummingbird’s hovering skills would have never come into being. It’s easy to imagine a world with flowers but without hummingbirds. But it’s much harder to imagine a world without flowers but with hummingbirds.

The same holds true for technological advances like the mirror. Without a technology that enabled humans to see a clear reflection of reality, including their own faces, the particular constellation of ideas in art and philosophy and politics that we call the Renaissance would have had a much more difficult time coming into being. (Japanese culture had highly prized steel mirrors during roughly the same period, but never adopted them for the same introspective use that flourished in Europe—perhaps in part because steel reflected much less light than glass mirrors, and added unnatural coloring to the image.) Yet the mirror was not exclusively dictating the terms of the European revolution in the sense of self. A different culture, inventing the fine glass mirror at a different point in its historical development, might not have experienced the same intellectual revolution, because the rest of its social order differed from that of fifteenth-century Italian hill-towns. The Renaissance also benefited from a patronage system that enabled its artists and scientists to spend their days playing with mirrors instead of, say, foraging for nuts and berries. A Renaissance without the Medici—not the individual family, of course, but the economic class they represent—is as hard to imagine as the Renaissance without the mirror.

It should probably be said that the virtues of the society of the self are entirely debatable. Orienting laws around individuals led directly to an entire tradition of human rights and the prominence of individual liberty in legal codes. That has to count as progress. But reasonable people disagree about whether we have now tipped the scales too far in the direction of individualism, away from those collective organizations: the union, the community, the state. Resolving those disagreements requires a different set of arguments—and values—than the ones we need to explain where those disagreements came from. The mirror helped invent the modern self, in some real but unquantifiable way. That much we should agree on. Whether that was a good thing in the end is a separate question, one that may never be settled conclusively.

—

THE DORMANT VOLCANO of Mauna Kea on Hawaii’s Big Island rises almost fourteen thousand feet above sea level, though the mountain extends almost another twenty thousand feet down to the ocean floor below, making it significantly larger than Mount Everest in terms of base-to-peak height. It is one of the few places in the world where you can drive from sea level to fourteen thousand feet in a matter of hours. At the summit, the landscape is barren, almost Martian, in its rocky, lifeless expanse. An inversion layer generally keeps clouds several thousand feet below the volcano’s peak; the air is as dry as it is thin. Standing on the summit, you are as far from the continents of earth as you can be while standing on land, which means the atmosphere around Hawaii—undisturbed by the turbulence of the sun’s energy bouncing off or being absorbed by large, varied landmasses—is as stable as just about anywhere on the planet. All of these properties make the peak of Mauna Kea one of the most otherworldly places you can visit. Appropriately enough, they also make it a sublime location for stargazing.

Today, the summit of Mauna Kea is crowned by thirteen distinct observatories, massive white domes scattered across the red rocks like some gleaming outpost on a distant planet. Included in this group are the twin telescopes of the W. M. Keck Observatory, the most powerful optical telescopes on earth. The Keck telescopes would seem to be a direct descendant of Hans Lippershey’s creation, only they do not rely on lenses to do their magic. To capture light from distant corners of the universe, you would need lenses the size of a pickup truck; at that size, glass becomes difficult to physically support and introduces inevitable distortions into the image. And so, the scientists and engineers behind Keck employed another technique to capture extremely faint traces of light: the mirror.

Keck Observatory

Each telescope has thirty-six hexagonal mirrors that together become a twenty-foot-wide reflective canvas. That light is reflected up to a second mirror and then down to a set of instruments, where the images can then be processed and visualized on a computer screen. (There is no vantage point at Keck where one can gaze directly through the telescope the way Galileo and countless astronomers since have done.) But even in the thin, ultra-stable atmosphere above Mauna Kea, small disturbances can blur the images captured by Keck. And so the observatories employ an ingenious system called “adaptive optics” to correct the vision of the telescopes. Lasers are beamed into the night sky above Keck, effectively creating an artificial star in the heavens. That false star becomes a kind of reference point; because the scientists know exactly what the laser should look like in the heavens were there no atmospheric distortion, they are able to get a measurement of the existing distortion by comparing the “ideal” laser image and what the telescopes actually register. Guided by that map of atmospheric noise, computers instruct the mirrors of the telescope to flex slightly based on the exact distortions in the skies above Mauna Kea that night. The effect is almost exactly like putting spectacles on a nearsighted person: distant objects suddenly become significantly clearer.

Of course, with the Keck telescopes, those distant objects are galaxies and supernovas that are, in some cases, billions of light-years away. When we look through the mirrors of Keck, we are looking into the distant past. Once again, glass has extended our vision: not just down to the invisible world of cells and microbes, or the global connectivity of the cameraphone, but all the way back to the early days of the universe. Glass started out as trinkets and empty vessels. A few thousand years later, perched above the clouds at the top of Mauna Kea, it has become a time machine.

—

THE STORY OF GLASS reminds us how our ingenuity is both confined and empowered by the physical properties of the elements around us. When we think of the entities that made the modern world, we usually talk about the great visionaries of science and politics, or breakthrough inventions, or large collective movements. But there is a material element to our history as well: not the dialectical materialism that Marxism practiced, where “material” meant the class struggle and the ultimate primacy of economic explanations. Material history, instead, in the sense of history as shaped by the basic building blocks of matter, which are then connected to things like social movements or economic systems. Imagine you could rewrite the Big Bang (or play God, depending on your metaphor) and create a universe that was exactly like ours, with only one tiny change: those electrons on the silicon atom don’t behave quite the same way. In this alternate universe, the electrons absorb light like most materials, instead of letting the photons pass through them. Such a small adjustment might well have made no difference at all for the entire evolution of Homo sapiens until a few thousand years ago. But then, amazingly, everything changed. Humans began exploiting the quantum behavior of those silicon electrons in countless different ways. On some fundamental level, it is impossible to imagine the last millennium without transparent glass. We can now manipulate carbon (in the form of that defining twentieth-century compound, plastic) into durable transparent materials that can do the job of glass, but that expertise is less than a century old. Tweak those silicon electrons, and you rob the last thousand years of windows, spectacles, lenses, test tubes, lightbulbs. (High-quality mirrors might have been independently invented using other reflective materials, though it would likely have taken a few centuries longer.) A world without glass would not just transform the edifices of civilization, by removing all the stained-glass windows of the great cathedrals and the sleek, reflective surfaces of the modern cityscape. A world without glass would strike at the foundation of modern progress: the extended life spans that come from understanding the cell, the virus, and the bacterium; the genetic knowledge of what makes us human; the astronomer’s knowledge of our place in the universe. No material on Earth mattered more to those conceptual breakthroughs than glass.

In a letter to a friend about the book of natural history that he never got around to writing, René Descartes described how he had wanted to tell the story of glass: “How from these ashes, by the mere intensity of [heat’s] action, it formed glass: for as this transmutation of ashes into glass appeared to me as wonderful as any other nature, I took a special pleasure in describing it.” Descartes was close enough to the original glass revolution to perceive its magnitude. Today, we are too many steps away from the material’s original influence to appreciate just how important it was, and continues to be, to everyday existence.

This is one of those places where the long-zoom approach illuminates, allowing us to see things that we would have otherwise missed had we focused on the usual suspects of historical storytelling. Invoking the physical elements in discussing historical change is not unheard of, of course. Most of us accept the idea that carbon has played an essential role in human activity since the industrial revolution. But in a way, this is not really news: carbon has been essential to just about everything living organisms have done since the primordial soup. But humans didn’t have much use for silicon dioxide until the glassmakers began to tinker with its curious properties a thousand years ago. Today, if you look around the room you’re currently occupying, there might easily be a hundred objects within reach that depend on silicon dioxide for their existence, and even more that rely on the element silicon itself: the panes of glass in your windows or skylights, the lens in your cameraphone, the screen of your computer, everything with a microchip or a digital clock. If you were casting starring roles for the chemistry of daily life ten thousand years ago, the top billing would be the same as it is today: we’re heavy users of carbon, hydrogen, oxygen. But silicon wouldn’t likely have even received a credit. While silicon is abundant on Earth—more than 90 percent of the crust is made up of the element—it plays almost no role in the natural metabolisms of life-forms on the planet. Our bodies are dependent on carbon, and many of our technologies (fossil fuels and plastics) display the same dependence. But the need for silicon is a modern craving.

The question is: Why did it take so long? Why were the extraordinary properties of this substance effectively ignored by nature, and why did those properties suddenly become essential to human society starting roughly a thousand years ago? In trying to address these questions, of course, we can only speculate. But surely one answer has to do with another technology: the furnace. One reason that evolution didn’t find much use for silicon dioxide is that most of the really interesting things about the substance don’t appear until you get over 1,000 degrees Fahrenheit. Liquid water and carbon do wonderfully inventive things at the earth’s atmospheric temperature, but it’s hard to see the promise of silicon dioxide until you can melt it, and the earth’s environment—at least on the surface of the planet—simply doesn’t get that hot. This was the hummingbird effect that the furnace unleashed: by learning how to generate extreme heat in a controlled environment, we unlocked the molecular potential of silicon dioxide, which soon transformed the way we see the world, and ourselves.

In a strange way, glass was trying to extend our vision of the universe from the very beginning, way before we were smart enough to notice. Those glass fragments from the Libyan Desert that made it into King Tut’s tomb had puzzled archeologists, geologists, and astrophysicists alike for decades. The semiliquid molecules of silicon dioxide suggested that they had formed at temperatures that could only have been created by a direct meteor strike, and yet there was no evidence of an impact crater anywhere in the vicinity. So where had those extraordinary temperatures come from? Lightning can strike a small patch of silica with glassmaking heat, but it can’t strike acres of sand in a single blast. And so scientists began to explore the idea that the Libyan glass arose from a comet colliding with the earth’s atmosphere and exploding over the desert sands. In 2013, a South African geochemist named Jan Kramers analyzed a mysterious pebble from the site and determined that it had originated in the nucleus of a comet, the first such object to be discovered on Earth. Scientists and space agencies have spent billions of dollars searching for particles of comets because they offer such profound insight into the formation of solar systems. The pebble from the Libyan Desert now gives them direct access to the geochemistry of comets. And all the while, glass was pointing the way.

2. Cold

n the early summer months of 1834, a three-masted bark vessel named the Madagascar sailed into the port of Rio de Janeiro, its hull filled with the most implausible of cargo: a frozen New England lake. The Madagascar and her crew were in the service of an enterprising and dogged Boston businessman named Frederic Tudor. History now knows him as “the Ice King,” but for most of his early adulthood he was an abject failure, albeit one with remarkable tenacity.

“Ice is an interesting subject for contemplation,” Thoreau wrote in Walden, gazing out at the “beautifully blue” frozen expanse of his Massachusetts pond. Tudor had grown up contemplating the same scenery. As a well-to-do young Bostonian, his family had long enjoyed the frozen water from the pond on their country estate, Rockwood—not just for its aesthetics, but also for its enduring capacity to keep things cold. Like many wealthy families in northern climes, the Tudors stored blocks of frozen lake water in icehouses, two-hundred-pound ice cubes that would remain marvelously unmelted until the hot summer months arrived, and a new ritual began: chipping off slices from the blocks to freshen drinks, make ice cream, cool down a bath during a heat wave.

The idea of a block of ice surviving intact for months without the benefit of artificial refrigeration sounds unlikely to the modern ear. We are used to ice preserved indefinitely thanks to the many deep-freeze technologies of today’s world. But ice in the wild is another matter—other than the occasional glacier, we assume that a block of ice can’t survive longer than an hour in summer heat, much less months.

But Tudor knew from personal experience that a large block of ice could last well into the depths of summer if it was kept out of the sun—or at least it would last through the late spring of New England. And that knowledge would plant the seed of an idea in his mind, an idea that would ultimately cost him his sanity, his fortune, and his freedom—before it made him an immensely wealthy man.

At the age of seventeen, Tudor’s father sent him on a voyage to the Caribbean, accompanying his older brother John, who suffered from a knee ailment that had effectively rendered him an invalid. The idea was that the warm climates would improve John’s health, but in fact they had the opposite effect: arriving in Havana, the Tudor brothers were quickly overwhelmed by the muggy weather. They soon sailed north back to the mainland, stopping in Savannah and Charleston, but the early summer heat followed them, and John fell ill with what may have been tuberculosis. Six months later, he was dead at the age of twenty.

Frederic Tudor

As a medical intervention, the Tudor brothers’ Caribbean adventure was a complete disaster. But suffering through the inescapable humidity of the tropics in the full regalia of a nineteenth-century gentleman suggested a radical—some would say preposterous—idea to young Frederic Tudor: if he could somehow transport ice from the frozen north to the West Indies, there would be an immense market for it. The history of global trade had clearly demonstrated that vast fortunes could be made by transporting a commodity that was ubiquitous in one environment to a place where it was scarce. To the young Tudor, ice seemed to fit the equation perfectly: nearly worthless in Boston, ice would be priceless in Havana.

The ice trade was nothing more than a hunch, but for some reason Tudor kept it alive in his mind, through the grieving after his brother’s demise, through the aimless years of a young man of means in Boston society. Sometime during this period, two years after his brother’s death, he shared his implausible scheme with his brother William, and his future brother-in-law, the even wealthier Robert Gardiner. A few months after his sister’s wedding, Tudor began taking notes in a journal. As a frontispiece, he drew a sketch of the Rockwood building that had long enabled his family to escape the warmth of the summer sun. He called it the “Ice House Diary.” The first entry read: “Plan etc for transporting Ice to Tropical Climates. Boston Augst 1st 1805 William and myself have this day determined to get together what property we have and embark in the undertaking of carrying ice to the West Indies the ensuing winter.”

The entry was typical of Tudor’s whole demeanor: brisk, confident, almost comically ambitious. (Brother William was apparently less convinced of the scheme’s promise.) Tudor’s confidence in his scheme derived from the ultimate value of the ice once it made its way to the tropics: “In a country where at some seasons of the year the heat is almost unsupportable,” he wrote in a subsequent entry, “where at times the common necessary of life, water, cannot be had but in a tepid state—Ice must be considered as out doing most other luxuries.” The ice trade was destined to endow the Tudor brothers with “fortunes larger than we shall know what to do with.” He seems to have given less thought to the challenges of transporting the ice. In correspondence from the period, Tudor relays thirdhand stories—almost certainly apocryphal—of ice cream being shipped intact from England to Trinidad as prima facie evidence that his plan would work. Reading the “Ice House Diary” now, you can hear the voice of a young man in the full fever of conviction, closing the cognitive blinds against doubt and counterargument.

However deluded Frederic might have seemed, he had one thing in his favor: he had the means to put the broad strokes of his plan in motion. He had enough money to hire a ship, and an endless supply of ice, manufactured by Mother Nature each winter. And so, in November 1805, Tudor dispatched his brother and cousin off to Martinique as an advance guard, with instructions to negotiate exclusive rights to the ice that would follow several months later. While waiting for word from his envoys, Tudor bought a brig called the Favorite for $4,750 and began harvesting ice in preparation for the journey. In February, Tudor set sail from Boston Harbor, the Favorite loaded with a full cargo of Rockwood ice, bound for the West Indies. Tudor’s scheme was bold enough to attract the attentions of the press, though the tone left something to be desired. “No joke,” the Boston Gazette reported. “A vessel with a cargo of 80 tons of Ice has cleared out from this port for Martinique. We hope this will not prove to be a slippery speculation.”

The Gazette’s derision would turn out to be well founded, though not for the reasons one might expect. Despite a number of weather-related delays, the ice survived the journey in remarkably good shape. The problem proved to be one that Tudor had never contemplated. The residents of Martinique had no interest in his exotic frozen bounty. They simply had no idea what to do with it.

We take it for granted in the modern world that an ordinary day will involve exposure to a wide range of temperatures. We enjoy piping hot coffee in the morning and ice cream for dessert at the end of the day. Those of us who live in climates with hot summers expect to bounce back and forth between air-conditioned offices and brutal humidity; where winter rules, we bundle up and venture out into the frigid streets, and turn up the thermostat when we return home. But the overwhelming majority of humans living in equatorial climes in 1800 would have literally never once experienced anything cold. The idea of frozen water would have been as fanciful to the residents of Martinique as an iPhone.

The mysterious, almost magical, properties of ice would eventually appear in one of the great opening lines of twentieth-century literature, in Gabriel García Márquez’s One Hundred Years of Solitude: “Many years later, as he faced the firing squad, Colonel Aureliano Buendía was to remember that distant afternoon when his father took him to discover ice.” Buendía recalls a series of fairs put on by roving gypsies during his childhood, each showcasing some extraordinary new technology. The gypsies display magnetic ingots, telescopes, and microscopes; but none of these engineering achievements impress the residents of the imaginary South American town of Macondo as much as a simple block of ice.

But sometimes the sheer novelty of an object can make its utility hard to discern. This was Tudor’s first mistake. He assumed the absolute novelty of ice would be a point in his favor. He figured his blocks of ice would “out-do” all the other luxuries. Instead, they just received blank stares.

The indifference to ice’s magical powers had prevented Tudor’s brother William from lining up an exclusive buyer for the cargo. Even worse, William had failed to establish a suitable location to store the ice. Tudor had made it all the way to Martinique but found himself with no demand for a product that was melting in the tropical heat at an alarming rate. He posted handbills around town that included specific instructions on how to carry and preserve the ice, but found few takers. He did manage to make some ice cream, thereby impressing a few locals who believed the delicacy couldn’t be created so close to the equator. But the trip was ultimately a complete failure. In his diary, he estimated that he had lost nearly $4,000 with his tropical misadventure.

—

THE BLEAK PATTERN of the Martinique voyage would repeat itself in the years to come, with ever more catastrophic results. Tudor sent a series of ice ships to the Caribbean, with only a modest increase in demand for his product. In the meantime, his family fortunes collapsed, and the Tudors retreated to their Rockwood farm, which like most New England land had very poor agricultural prospects. Harvesting the ice was the family’s last best hope. But it was a hope that most of Boston openly ridiculed, and a series of shipwrecks and embargoes made that ridicule seem increasingly appropriate. In 1813, Tudor was thrown in debtor’s prison. He penned the following entry in his diary several days later:

On Monday the 9th instant I was arrested . . . and locked up as a debtor in Boston jail. . . . On this memorable day in my little annals I am 28 years 6 months and 5 days old. It is an event which I think I could not have avoided: but it is a climax which I did hope to have escaped as my affairs are looking well at last after a fearful struggle with adverse circumstances for seven years—but it has taken place and I have endeavoured to meet it as I would the tempest of heaven which should serve to strengthen rather than reduce the spirit of a true man.

Tudor’s fledgling business suffered from two primary liabilities. He had a demand problem, in that most of his potential customers didn’t understand why his product might be useful. And he had a storage problem: he was losing too much of his product to the heat, particularly once it arrived in the tropics. But his New England base gave him one crucial advantage, beyond the ice itself. Unlike the U.S. South, with its sugar plantations and cotton fields, the northeastern states were largely devoid of natural resources that could be sold elsewhere. This meant that ships tended to leave Boston harbor empty, heading off for the West Indies to fill their hulls with valuable cargo before returning to the wealthy markets of the eastern seaboard. Paying a crew to sail a ship with no cargo was effectively burning money. Any cargo was better than nothing, which meant that Tudor could negotiate cheaper rates for himself by loading his ice onto what would have otherwise been an empty ship, and thereby avoiding the need to buy and maintain his own vessels.

Part of the beauty of ice, of course, was that it was basically free: Tudor needed only to pay workers to carve blocks of it out of the frozen lakes. New England’s economy generated another product that was equally worthless: sawdust—the primary waste product of lumber mills. After years of experimenting with different solutions, Tudor discovered that sawdust made a brilliant insulator for his ice. Blocks layered on top of each other with sawdust separating them would last almost twice as long as unprotected ice. This was Tudor’s frugal genius: he took three things that the market had effectively priced at zero—ice, sawdust, and an empty vessel—and turned them into a flourishing business.

Tudor’s initial catastrophic trip to Martinique had made it clear that he needed on-site storage in the tropics that he could control; it was too dangerous to keep his rapidly melting product in buildings that weren’t specifically engineered to insulate ice from the summer heat. He tinkered with multiple icehouse designs, finally settling on a double-shelled structure that used the air between two stone walls to keep the interior cool.

Tudor didn’t understand the molecular chemistry of it, but both the sawdust and the double-shelled architecture revolved around the same principle. For ice to melt, it needs to pull heat from the surrounding environment to break the tetrahedral bonding of hydrogen atoms that gives ice its crystalline structure. (The extraction of heat from the surrounding atmosphere is what grants ice its miraculous capacity to cool us down.) The only place that heat exchange can happen is at the surface of the ice, which is why large blocks of ice survive for so long—all the interior hydrogen bonds are perfectly insulated from the exterior temperature. If you try to protect ice from external warmth with some kind of substance that conducts heat efficiently—metal for instance—the hydrogen bonds will break down quickly into water. But if you create a buffer between the external heat and the ice that conducts heat poorly, the ice will preserve its crystalline state for much longer. As a thermal conductor, air is about two thousand times less efficient than metal, and more than twenty times less efficient than glass. In his icehouses, Tudor’s double-shelled structure created a buffer of air that kept the summer heat away from the ice; his sawdust packaging on the ships ensured that there were countless pockets of air between the wood shavings to keep the ice insulated. Modern insulators such as Styrofoam rely on the same technique: the cooler you take on a picnic keeps your watermelon chilled because it is made of polystyrene chains interspersed with tiny pockets of gas.

By 1815, Tudor had finally assembled the key pieces of the ice puzzle: harvesting, insulation, transport, and storage. Still pursued by his creditors, he began making regular shipments to a state-of-the-art icehouse he had built in Havana, where an appetite for ice cream had been slowly maturing. Fifteen years after his original hunch, Tudor’s ice trade had finally turned a profit. By the 1820s, he had icehouses packed with frozen New England water all over the American South. By the 1830s, his ships were sailing to Rio and Bombay. (India would ultimately prove to be his most lucrative market.) By his death in 1864, Tudor had amassed a fortune worth more than $200 million in today’s dollars.

Three decades after his first failed voyage, Tudor wrote these lines in his journal:

This day I sailed from Boston thirty years ago in the Brig Favorite Capt Pearson for Martinique: with the first cargo of ice. Last year I shipped upwards of 30 cargoes of Ice and as much as 40 more were shipped by other persons. . . . The business is established. It cannot be given up now and does not depend upon a single life. Mankind will have the blessing for ever whether I die soon or live long.

Tudor’s triumphant (if long-delayed) success selling ice around the world seems implausible to us today not just because it’s hard to imagine blocks of ice surviving the passage from Boston to Bombay. There’s an additional, almost philosophical, curiosity to the ice business. Most of the trade in natural goods involves material that thrives in high-energy environments. Sugarcane, coffee, tea, cotton—all these staples of eighteenth- and nineteenth-century commerce were dependent on the blistering heat of tropical and subtropical climates; the fossil fuels that now circle the planet in tankers and pipelines are simply solar energy that was captured and stored by plants millions of years ago. You could make a fortune in 1800 by taking things that grew only in high-energy environments and shipping them off to low-energy climates. But the ice trade—arguably for the only time in the history of global commerce—reversed that pattern. What made ice valuable was precisely the low-energy state of a New England winter, and the peculiar capacity of ice to store that lack of energy for long periods of time. The cash crops of the tropics caused populations to swell in climates that could be unforgivingly hot, which in turn created a market for a product that allowed you to escape the heat. In the long history of human commerce, energy had always correlated with value: the more heat, the more solar energy, the more you could grow. But in a world that was tilting toward the productive heat of sugarcane and cotton plantations, cold could be an asset as well. That was Tudor’s great insight.

—

IN THE WINTER OF 1846, Henry Thoreau watched ice cutters employed by Frederic Tudor carve blocks out of Walden Pond with a horse-drawn plow. It might have been a scene out of Brueghel, men working in a wintry landscape with simple tools, far from the industrial age that thundered elsewhere. But Thoreau knew their labor was attached to a wider network. In his diaries, he wrote a lilting reverie on the global reach of the ice trade:

Thus it appears that the sweltering inhabitants of Charleston and New Orleans, of Madras and Bombay and Calcutta, drink at my well. . . . The pure Walden water is mingled with the sacred water of the Ganges. With favoring winds it is wafted past the site of the fabulous islands of Atlantis and the Hesperides, makes the periplus of Hanno, and, floating by Ternate and Tidore and the mouth of the Persian Gulf, melts in the tropic gales of the Indian seas, and is landed in ports of which Alexander only heard the names.

If anything, Thoreau was underestimating the scope of that global network—because the ice trade that Tudor created was about much more than frozen water. The blank stares that had confronted Tudor’s first shipment of ice to Martinique slowly but steadily gave way to an ever widening dependence on ice. Ice-chilled drinks became a staple of life in southern states. (Even today, Americans are far more likely to enjoy ice with their beverages than Europeans, a distant legacy of Tudor’s ambition.) By 1850, Tudor’s success had inspired countless imitators, and more than a hundred thousand tons of Boston ice were shipped around the world in a single year. By 1860, two out of three New York homes had daily deliveries of ice. One contemporary account describes how tightly bound ice had become to the rituals of daily life:

In workshops, composing rooms, counting houses, workmen, printers, clerks club to have their daily supply of ice. Every office, nook or cranny, illuminated by a human face, is also cooled by the presence of his crystal friend. . . . It is as good as oil to the wheel. It sets the whole human machinery in pleasant action, turns the wheels of commerce, and propels the energetic business engine.

Ice blocks being cut from a lake are floated in water, then up a runway to a storage house, 1950.

The dependence on natural ice became so severe that every decade or so an unusually warm winter would send the newspapers into a frenzy with speculation about an “ice famine.” As late as 1906, the New York Times was running alarming headlines: “Ice Up To 40 Cents And A Famine In Sight.” The paper went on to provide some historical context: “Not in sixteen years has New York faced such an iceless prospect as this year. In 1890 there was a great deal of trouble and the whole country had to be scoured for ice. Since then, however, the needs for ice have grown vastly, and a famine is a much more serious matter now than it was then.” In less than a century, ice had gone from a curiosity to a luxury to a necessity.

Ice-powered refrigeration changed the map of America, nowhere more so than in the transformation of Chicago. Chicago’s initial burst of growth had come after the nexus of canals and rail lines connected the city to both the Gulf of Mexico and the cities of the eastern seaboard. Its fortuitous location as a transportation hub—created both by nature and some of the most ambitious engineering of the century—enabled wheat to flow from the bountiful plains to the Northeast population centers. But meat couldn’t make the journey without spoiling. Chicago developed a large trade in preserved pork starting in the middle of the century, with the first stockyards slaughtering the hogs on the outskirts of the city before sending the goods east in barrels. But fresh beef remained largely a local delicacy.

But as the century progressed, a supply/demand imbalance developed between the hungry cities of the Northeast and the cattle of the Midwest. As immigration fueled the population of New York and Philadelphia and other urban centers in the 1840s and 1850s, the supply of local beef failed to keep up with the surging demand in the growing cities. Meanwhile, the conquest of the Great Plains had enabled ranchers to breed massive herds of cattle, without a corresponding population base of humans to feed. You could ship live cattle by train to the eastern states to be slaughtered locally, but transporting entire cows was expensive, and the animals were often malnourished or even injured en route. Almost half would be inedible by the time they arrived in New York or in Boston.

Two young boys watch two icemen make a delivery on a Harlem sidewalk, 1936.

It was ice that ultimately provided a way around this impasse. In 1868, the pork magnate Benjamin Hutchinson built a new packing plant, featuring “cooling rooms packed with natural ice that allowed them to pack pork year-round, one of the principal innovations in the industry,” according to Donald Miller, in his history of nineteenth-century Chicago, City of the Century. It was the beginning of a revolution that would transform not only Chicago but the entire natural landscape of middle America. In the years after the fire of 1871, Hutchinson’s cooling rooms would inspire other entrepreneurs to integrate ice-cooled facilities to the meatpacking trade. A few began transporting beef back east in open-air railcars during winter, relying on the ambient temperature to keep the steaks cold. In 1878, Gustavus Franklin Swift hired an engineer to build an advanced refrigerator car, designed from the ground up to transport beef to the eastern seaboard year round. Ice was placed in bins above the meat; at stops along the route, workers could swap in new blocks of ice from above, without disturbing the meat below. “It was this application of elementary physics,” Miller writes, “that transformed the ancient trade of beef slaughtering from a local to an international business, for refrigerator cars led naturally to refrigerator ships, which carried Chicago beef to four continents.” The success of that global trade transformed the natural landscape of the American plains in ways that are still visible today: the vast, shimmering grasslands replaced by industrial feedlots, creating, in Miller’s words, “a city-country [food] system that was the most powerful environmental force in transforming the American landscape since the Ice Age glaciers began their final retreat.”

The Chicago stockyards that emerged in the last two decades of the nineteenth century were, as Upton Sinclair wrote, “the greatest aggregation of labor and capital ever gathered in one place.” Fourteen million animals were slaughtered in an average year. In many ways, the industrial food complex held in such disdain by modern-day “slow food” advocates begins with the Chicago stockyards and the web of ice-cooled transport that extended out from those grim feedlots and slaughterhouses. Progressives like Upton Sinclair painted Chicago as a kind of Dante’s Inferno of industrialization, but in reality, most of the technology employed in the stockyards would have been recognizable to a medieval butcher. The most advanced form of technology in the whole chain was the refrigerated railcar. Theodore Dreiser got it right when he described the stockyard assembly line as “a direct sloping path to death, dissection, and the refrigerator.”

The conventional story about Chicago is that it was made possible thanks to the invention of the railroad and the building of the Erie Canal. But those accounts tell only part of the story. The runaway growth of Chicago would have never been possible without the peculiar chemical properties of water: its capacity for storing and slowly releasing cold with only the slightest of human interventions. If the chemical properties of liquid water had somehow turned out to be different, life on earth would have taken a radically different shape (or more likely, would not have evolved at all). But if water hadn’t also possessed its peculiar aptitude for freezing, the trajectory of nineteenth-century America would have almost certainly been different as well. You could send spices around the globe without the advantages of refrigeration, but you couldn’t send beef. Ice made a new kind of food network imaginable. We think of Chicago as a city of broad shoulders, of railroad empires and slaughterhouses. But it is just as true to say that it was built on the tetrahedral bonds of hydrogen.

—

IF YOU WIDEN YOUR FRAME of reference, and look at the ice trade in the context of technological history, there is something puzzling, almost anachronistic, about Tudor’s innovation. This was the middle of the nineteenth century, after all, an era of coal-powered factories, with railroads and telegraph wires connecting massive cities. And yet the state of the art in cold technology was still entirely based on cutting chunks of frozen water out of a lake. Humans had been experimenting with the technology of heat for at least a hundred thousand years, since the mastery of fire—arguably Homo sapiens’ first innovation. But the opposite end of the thermal spectrum was much more challenging. A century into the industrial revolution, artificial cold was still a fantasy.

But the commercial demand for ice—all those millions of dollars flowing upstream from the tropics to the ice barons of New England—sent a signal out across the world that there was money to be made from cold, which inevitably sent some inventive minds off in search of the next logical step of artificial cold. You might assume Tudor’s success would inspire a new generation of equally mercenary entrepreneur-inventors to create the revolution in man-made refrigeration. Yet, however much we may celebrate the start-up culture of today’s tech world, essential innovations don’t always come out of private-sector exploration. New ideas are not always motivated, like Tudor’s, by dreams of “fortunes larger than we shall know what to do with.” The art of human invention has more than one muse. While the ice trade began with a young man’s dream of untold riches, the story of artificial cold began with a more urgent and humanitarian need: a doctor trying to keep his patients alive.

It’s a story that begins at the scale of insects: in Apalachicola, Florida, a town of ten thousand people living alongside a swamp in a subtropical climate—the perfect environment for breeding mosquitoes. In 1842, abundant mosquitoes meant, inevitably, the risk of malaria. At the modest local hospital, a doctor named John Gorrie sat helpless as dozens of his patients burned up with fever.

Desperate for a way to reduce his patients’ fevers, Gorrie tried suspending blocks of ice from the hospital ceiling. It turned out to be an effective solution: the ice blocks cooled the air; the air cooled the patients. With fevers reduced, some of his patients survived their illnesses. But Gorrie’s clever hack, designed to combat the dangerous effects of subtropical climates, was ultimately undermined by another by-product of the environment. The tropical humidity that made Florida such a hospitable climate for mosquitoes also helped breed another threat: hurricanes. A string of shipwrecks delayed ice shipments from Tudor’s New England, which left Gorrie without his usual supply.

Dr. John Gorrie

And so the young doctor began mulling over a more radical solution for his hospital: making his own ice. Luckily for Gorrie, it happened to be the perfect time to have this idea. For thousands of years, the idea of making artificial cold had been almost unthinkable to human civilization. We invented agriculture and cities and aqueducts and the printing press, but cold was outside the boundaries of possibility for all those years. And yet somehow artificial cold became imaginable in the middle of the nineteenth century. To use the wonderful phrase of the complexity theorist Stuart Kauffman, cold became part of the “adjacent possible” of that period.

How do we explain this breakthrough? It’s not just a matter of a solitary genius coming up with a brilliant invention because he or she is smarter than everyone else. And that’s because ideas are fundamentally networks of other ideas. We take the tools and metaphors and concepts and scientific understanding of our time, and we remix them into something new. But if you don’t have the right building blocks, you can’t make the breakthrough, however brilliant you might be. The smartest mind in the world couldn’t invent a refrigerator in the middle of the seventeenth century. It simply wasn’t part of the adjacent possible at that moment. But by 1850, the pieces had come together.

The first thing that had to happen seems almost comical to us today: we had to discover that air was actually made of something, that it wasn’t just empty space between objects. In the 1600s, amateur scientists discovered a bizarre phenomenon: the vacuum, air that seemed actually to be composed of nothing and that behaved differently from normal air. Flames would be extinguished in a vacuum; a vacuum seal was so strong that two teams of horses could not pull it apart. In 1659, the English scientist Robert Boyle had placed a bird in a jar and sucked out the air with a vacuum pump. The bird died, as Boyle suspected it might, but curiously enough, it also froze. If a vacuum was so different from normal air that it could extinguish life, that meant there must be some invisible substance that normal air was made of. And it suggested that changing the volume or pressure of gases could change their temperature. Our knowledge expanded in the eighteenth century, as the steam engine forced engineers to figure out exactly how heat and energy are converted, inventing a whole science of thermodynamics. Tools for measuring heat and weight with increased precision were developed, along with standardized scales such as Celsius and Fahrenheit, and as is so often the case in the history of science and innovation, when you have a leap forward in the accuracy of measuring something, new possibilities emerge.

All of these building blocks were circulating through Gorrie’s mind, like molecules in a gas, bouncing off each other, forming new connections. In his spare time, he started to build a refrigeration machine. It would use energy from a pump to compress air. The compression heated the air. The machine then cooled down the compressed air by running it through pipes cooled with water. When the air expanded, it pulled heat from its environment, and just like the tetrahedral bonds of hydrogen dissolving into liquid water, that heat extraction cooled the surrounding air. It could even be used to create ice.

Amazingly, Gorrie’s machine worked. No longer dependent on ice shipped from a thousand miles away, Gorrie reduced his patients’ fevers with home-grown cold. He applied for a patent—correctly predicting a future where artificial cold, as he wrote, “might better serve mankind. . . . Fruits, vegetables, and meats will be preserved in transit by my refrigeration system and thereby enjoyed by all!”

And yet, despite his success as an inventor, Gorrie went nowhere as a businessman. Thanks to Tudor’s success, natural ice was abundant and cheap when the storms didn’t disrupt trade. To make things worse, Tudor himself launched a smear campaign about Gorrie’s invention—claiming the ice produced by his machine was infected with bacteria. It was a classic case of a dominant industry disparaging a much more powerful new technology, the way the first computers with graphic interfaces were dismissed by their rivals as “toys” and not “serious business machines.” John Gorrie died penniless, having failed to sell a single machine.

But the idea of artificial cold didn’t die with Gorrie. After thousands of years of neglect, suddenly the globe lit up with patents filed for some variation of artificial refrigeration. The idea was suddenly everywhere, not because people had stolen Gorrie’s idea, but because they’d independently hit upon the same basic architecture. The conceptual building blocks were finally in place, and so the idea of creating artificially cold air was suddenly “in the air.”

Those patents rippling across the planet are an example of one of the great curiosities in the history of innovation: what scholars now call “multiple invention.” Inventions and scientific discoveries tend to come in clusters, where a handful of geographically dispersed investigators stumble independently onto the very same discovery. The isolated genius coming up with an idea that no one else could even dream of is actually the exception, not the rule. Most discoveries become imaginable at a very specific moment in history, after which point multiple people start to imagine them. The electric battery, the telegraph, the steam engine, and the digital music library were all independently invented by multiple individuals in the space of a few years. In the early 1920s, two Columbia University scholars surveyed the history of invention in a wonderful paper called “Are Inventions Inevitable?” They found 148 instances of simultaneous invention, most of them occurring within the same decade. Hundreds more have since been discovered.

Refrigeration was no different: the knowledge of thermodynamics and the basic chemistry of air, combined with the economic fortunes being made in the ice trade, made artificial cold ripe for invention. One of those simultaneous inventors was the French engineer Ferdinand Carré, who independently designed a refrigeration machine that followed the same basic principles as Gorrie’s. He built prototypes for his refrigeration machine in Paris, but his idea would ultimately triumph because of events unfolding across the Atlantic: a different kind of ice famine in the American South. After the Civil War broke out in 1861, the Union blockaded the southern states to cripple the Confederate economy. The Union navy stopped the flow of ice more effectively than did the storms that churned up along the Gulf Stream. Having built up an economic and cultural dependence on the ice trade, the sweltering southern states suddenly found themselves in desperate need of artificial cold.

As the war raged, shipments of smuggled goods could sometimes make it through the blockade at night to land at beaches along the Atlantic and Gulf coasts. But the smugglers weren’t just carrying cargoes of gunpowder or weapons. Sometimes they carried goods that were far more novel: ice-making machines, based on Carré’s design. These new devices used ammonia as a refrigerant and could churn out four hundred pounds of ice per hour. Carré’s machines were smuggled all the way from France to Georgia, Louisiana, and Texas. A network of innovators tinkered with Carré’s machines, improving their efficiency. A handful of commercial ice plants opened, marking the debut on the main stage of industrialization. By 1870, the southern states made more artificial ice than anywhere else in the world.

In the decades after the Civil War, artificial refrigeration exploded, and the natural-ice trade began its slow decline into obsolescence. Refrigeration became a huge industry, measured not just by the cash that changed hands but also in the sheer size of the machines: steam-powered monster machines weighing hundreds of tons, maintained by a full-time army of engineers. At the turn of the twentieth century, New York’s Tribeca neighborhood—now home to some of the most expensive loft apartments in the world—was essentially a giant refrigerator, entire blocks of windowless buildings designed to chill the endless flood of produce from the nearby Washington food market.

Almost everything in the nineteenth-century story of cold was about making it bigger, more ambitious. But the next revolution in artificial cold would proceed in the exact opposite direction. Cold was about to get small: those block-long Tribeca refrigerators would soon shrink down to fit in every kitchen in America. But the smaller footprint of artificial cold would, ironically, end up triggering changes in human society that were so massive you could see them from space.

—

IN THE WINTER OF 1916, an eccentric naturalist and entrepreneur moved his young family up to the remote tundra of Labrador. He had spent several winters there on his own, starting a fur company breeding foxes and occasionally shipping animals and reports back to the U.S. Biological Survey. Five weeks after the birth of his son, his wife and child joined him. Labrador was, to say the least, not an ideal place for a newborn. The climate was unforgiving, with temperatures regularly hitting 30 degrees below Fahrenheit, and the region was entirely bereft of modern medical facilities. The food, too, left a great deal to be desired. The bleak climate in Labrador meant that everything you ate during the winter was either frozen or preserved: other than the fish, there were no sources of fresh food. A typical meal would be what locals called “brewis”: salted cod and hard tack, which is rock solid bread, boiled up and garnished with “scrunchions,” which were small, fried chunks of salted pork fat. Any meat or produce that had been frozen would be mushy and tasteless when thawed out.

But the naturalist was an adventurous eater, fascinated with the cuisines of different cultures. (In his journals, he recorded eating everything from rattlesnake to skunk.) And so he took up ice fishing with some of the local Inuits, carving holes in frozen lakes and casting a line for trout. With air temperatures so far below zero, a fish pulled out of the lake would freeze solid in a matter of seconds.

Advertisement for General Electric fridge and freezer, 1949

Unwittingly, the young naturalist had stumbled across a powerful scientific experiment as he sat down to eat with his family in Labrador. When they thawed out the frozen trout from the ice-fishing expeditions, they discovered it tasted far fresher than the usual grub. The difference was so striking that he became obsessed with trying to figure out why the frozen trout retained its flavor so much more effectively. And so Clarence Birdseye began an investigation that would ultimately put his name on packages of frozen peas and fish sticks in supermarkets around the world.

At first, Birdseye had assumed the trout had preserved its freshness simply because it had been caught more recently, but the more he studied the phenomenon, he began to think there was some other factor at work. For starters, ice-fished trout would retain its flavor for months, unlike other frozen fish. He began experimenting with frozen vegetables and discovered that produce frozen in the depths of winter somehow tasted better than produce frozen in late fall or early spring. He analyzed the food under a microscope and noticed a striking difference in the ice crystals that formed during the freezing process: the frozen produce that had lost its flavor had significantly larger crystals that seemed to be breaking down the molecular structure of the food itself.

Eventually, Birdseye hit upon a coherent explanation for the dramatic difference in taste: It was all about the speed of the freezing process. A slow freeze allowed the hydrogen bonds of ice to form larger crystalline shapes. But a freeze that happened in seconds—“flash freezing,” as we now call it—generated much smaller crystals that did less damage to the food itself. The Inuit fishermen hadn’t thought about it in terms of crystals and molecules, but they had been savoring the benefits of flash freezing for centuries by pulling live fish out of the water into shockingly cold air.

Clarence Birdseye in Labrador, Canada, 1912

As his experiments continued, an idea began to form in Birdseye’s mind: with artificial refrigeration becoming increasingly commonplace, the market for frozen food could be immense, assuming you could solve the quality problem. Like Tudor before him, Birdseye began taking notes on his experiments with cold. And like Tudor, the idea would linger in his mind for a decade before it turned into something commercially viable. It was not a sudden epiphany or lightbulb moment, but something much more leisurely, an idea taking shape piece by piece over time. It was what I like to call a “slow hunch”—the anti-“lightbulb moment,” the idea that comes into focus over decades, not seconds.

The first inspiration for Birdseye had been the very pinnacle of freshness: a trout pulled out of a frozen lake. But the second would be the exact opposite: a commercial fishing ship’s hull filled with rotting cod. After his Labrador adventure, Birdseye returned to his original home in New York and took a job with the Fisheries Association, where he saw firsthand the appalling conditions that characterized the commercial fishing business. “The inefficiency and lack of sanitation in the distribution of whole fresh fish so disgusted me,” Birdseye would later write, “that I set out to develop a method that would permit the removal of inedible waste from perishable foods at production points, packaging them in compact and convenient containers, and distributing them to the housewife with their intrinsic freshness intact.”

Clarence Birdseye is experimenting on chopped carrots to determine the effects of the various stirring speeds and air velocities on the food.

In the first decades of the twentieth century, the frozen-food business was considered to be the very bottom of the barrel. You could buy frozen fish or produce, but it was widely assumed to be inedible. (In fact, frozen food was so appalling that it was banned at New York State prisons for being below the culinary standards of the convicts.) One key problem was that the food was being frozen at relatively high temperatures, often just a few degrees below freezing. Yet scientific advances over the preceding decades had made it possible to artificially produce temperatures that were positively Labradorian. By the early 1920s, Birdseye had developed a flash-freezing process using stacked cartons of fish frozen at minus 40 degrees Fahrenheit. Inspired by the new industrial model of Henry Ford’s Model T factory, he created a “double-belt freezer” that ran the freezing process along a more efficient production line. He formed a company called General Seafood using these new production techniques. Birdseye found that just about anything he froze with this method—fruit, meat, vegetables—would be remarkably fresh after thawing.

Frozen food was still more than a decade away from becoming a staple of the American diet. (It required a critical mass of freezers—in supermarkets and home kitchens—that wouldn’t fully come into being until the postwar years.) But Birdseye’s experiments were so promising that in 1929, just months before the Black Friday crash, General Seafood was acquired by the Postum Cereal Company, which promptly changed its name to General Foods. Birdseye’s adventures in ice fishing had made him a multimillionaire. His name endures on packages of frozen fish filets to this day.

Birdseye’s frozen-food breakthrough took shape as a slow hunch, but it also emerged as a kind of collision between several very different geographic and intellectual spaces. To imagine a world of flash-frozen food, Birdseye needed to experience the challenges of feeding a family in an arctic climate surrounded by brutal cold; he needed to spend time with the Inuit fishermen; he needed to inspect the foul containers of cod-fishing trawlers in New York harbors; he needed the scientific knowledge of how to produce temperatures well below freezing; he needed the industrial knowledge of how to build a production line. Like every big idea, Birdseye’s breakthrough was not a single insight, but a network of other ideas, packaged together in a new configuration. What made Birdseye’s idea so powerful was not simply his individual genius, but the diversity of places and forms of expertise that he brought together.

Worker clad in overalls surveys boxes of Birds Eye frozen foods as they move along a conveyor. Undated photograph, circa 1922–1950.

In our age of locally sourced, artisanal food production, the frozen “TV dinners” that arose in the decades after Birdseye’s discovery have fallen out of favor. But in its original incarnation, frozen food had a positive impact on health, introducing more nutrition into the diets of Americans. Flash-frozen food extended the reach of the food network in both time and space: produce harvested in summer could be consumed months later; fish caught in the North Atlantic could be eaten in Denver or Dallas. It was better to eat frozen peas in January than it was to wait five months for fresh ones.

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BY THE 1950S, Americans had adopted a lifestyle that was profoundly shaped by artificial cold, buying frozen dinners purchased in the refrigerated aisles of the local supermarket, and stacking them up in the deep freeze of their new Frigidaires, featuring the latest in ice-making technology. Behind the scenes, the entire economy of cold was supported by a vast fleet of refrigerated trucks, transporting Birds Eye frozen peas (and their many imitations) around the country.

In that iconic 1950s American household, the most novel cold-producing device was not storing fish filets for dinner or making ice for the martinis. It was cooling down (and dehumidifying) the entire house. The first “apparatus for treating air” had been dreamed up by a young engineer named Willis Carrier in 1902. The story of Carrier’s invention is a classic in the annals of accidental discovery. As a twenty-five-year-old engineer, Carrier had been hired by a printing company in Brooklyn to devise a scheme that would help them keep the ink from smearing in the humid summer months. Carrier’s invention not only removed the humidity from the printing room; it also chilled the air. Carrier noticed that everyone suddenly wanted to have lunch next to the printing presses, and he began to design contraptions that would be deliberately built to regulate the humidity and temperature in an interior space. Within a few years, Carrier had formed a company—still one of the largest air-conditioning manufacturers in the world—that focused on industrial uses for the technology. But Carrier was convinced that air-conditioning should also belong to the masses.

A Carrier Corporation experimental lab test of their new $700, six-room capacity, central air-conditioning unit that diffuses cool air at floor level; smoke making cool air visible has risen to the three-foot-high level in this living room, 1945.

His first great test came over Memorial Day weekend of 1925, when Carrier debuted an experimental AC system in Paramount Pictures’ new flagship Manhattan movie theater, the Rivoli. Theaters had long been oppressive places to visit during the summer months. (In fact, a number of Manhattan playhouses had experimented with ice-based cooling during the nineteenth century, with predictably moist results.) Before AC, the whole idea of a summer blockbuster would have seemed preposterous: the last place you’d want to be on a warm day was a room filled with a thousand other perspiring bodies. And so Carrier had persuaded Adolph Zukor, the legendary chief of Paramount, that there was money to be made by investing in central air for his theaters.

Sackett & Wilhelms printing company air-conditioning system

Zukor himself showed up for the Memorial Day weekend test, sitting inconspicuously in the balcony seats. Carrier and his team had some technical difficulties getting the AC up and running; the room was filled with hand fans waving furiously before the picture started. Carrier later recalled the scene in his memoirs:

It takes time to pull down the temperature in a quickly filled theater on a hot day, and a still longer time for a packed house. Gradually, almost imperceptibly, the fans dropped into laps as the effects of the air conditioning system became evident. Only a few chronic fanners persisted, but soon they, too, ceased fanning. . . . We then went into the lobby and waited for Mr. Zukor to come downstairs. When he saw us, he did not wait for us to ask his opinion. He said tersely, “Yes, the people are going to like it.”

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BETWEEN 1925 AND 1950, most Americans experienced air-conditioning only in large commercial spaces such as movie theaters, department stores, hotels, or office buildings. Carrier knew that AC was headed for the domestic sphere, but the machines were simply too large and expensive for a middle-class home. The Carrier Corporation did offer a glimpse of this future in its 1939 World’s Fair attraction, “The Igloo of Tomorrow.” In a bizarre structure that looked something like a five-story helping of soft-serve vanilla ice cream, Carrier showcased the wonders of domestic air-conditioning, accompanied by a squadron of Rockettes-style “snow bunnies.”

But Carrier’s vision of domestic cool would be postponed by the outbreak of World War II. It wasn’t until the late 1940s, after almost fifty years of experimentation, that air-conditioning finally made its way to the home front, with the first in-window portable units appearing on the market. Within half a decade, Americans were installing more than a million units a year. When we think about twentieth-century miniaturization, our minds naturally gravitate to the transistor or the microchip, but the shrinking footprint of air-conditioning deserves its place in the annals of innovation as well: a machine that had once been larger than a flatbed truck reduced in size so that it could fit in a window.

That shrinking would quickly set off an extraordinary chain of events, in many ways rivaling the impact of the automobile on settlement patterns in the United States. Places that had been intolerably hot and humid—including some of the cities where Frederic Tudor had sweated out the summer as a young man—were suddenly tolerable to a much larger slice of the general public. By 1964, the historic flow of people from South to North that had characterized the post–Civil War era had been reversed. The Sun Belt expanded with new immigrants from colder states, who could put up with the tropical humidity or blazing desert climates thanks to domestic air-conditioning. Tucson rocketed from 45,000 people to 210,000 in just ten years; Houston expanded from 600,000 to 940,000 in the same decade. In the 1920s, when Willis Carrier was first demonstrating air-conditioning to Adolph Zukor at the Rivoli Theatre, Florida’s population stood at less than one million. Half a century later, the state was well on the way to becoming one of the four most populous in the country, with ten million people escaping the humid summer months in air-conditioned homes. Carrier’s invention circulated more than just molecules of oxygen and water. It ended up circulating people as well.

Irvin Theatre, 1920s

Broad changes in demography invariably have political effects. The migration to the Sun Belt changed the political map of America. Once a Democratic stronghold, the South was besieged by a massive influx of retirees who were more conservative in their political outlook. As the historian Nelson W. Polsby demonstrates in his book How Congress Evolves, Northern Republicans moving south in the post-AC era did as much to undo the “Dixiecrat” base as the rebellion against the civil rights movement. In Congress, this had the paradoxical effect of unleashing a wave of liberal reforms, as the congressional Democrats were no longer divided between conservative Southerners and progressives in the North. But air-conditioning arguably had the most significant impact on Presidential politics. Swelling populations in Florida, Texas, and Southern California shifted the electoral college toward the Sun Belt, with warm-climate states gaining twenty-nine electoral college votes between 1940 and 1980, while the colder states of the Northeast and Rust Belt lost thirty-one. In the first half of the twentieth century, only two presidents or vice presidents hailed from Sun Belt states. Starting in 1952, however, every single winning presidential ticket contained a Sun Belt candidate, until Barack Obama and Joe Biden broke the streak in 2008.

The “Igloo of Tomorrow.” Dr. Willis H. Carrier holds a thermometer inside an igloo display that demonstrates air-conditioning at the St. Louis World’s Fair. The temperature-controlled igloo remained at a steady 68 degrees Fahrenheit inside.

This is long-zoom history: almost a century after Willis Carrier began thinking about keeping the ink from smearing in Brooklyn, our ability to manipulate tiny molecules of air and moisture helped transform the geography of American politics. But the rise of the Sun Belt in the United States was just a dress rehearsal for what is now happening on a planetary scale. All around the world, the fastest growing megacities are predominantly in tropical climates: Chennai, Bangkok, Manila, Jakarta, Karachi, Lagos, Dubai, Rio de Janeiro. Demographers predict that these hot cities will have more than a billion new residents by 2025.

It goes without saying that many of these new immigrants don’t have air-conditioning in their homes, at least not yet, and it is an open question whether these cities are sustainable in the long run, particularly those based in desert climates. But the ability to control temperature and humidity in office buildings, stores, and wealthier homes allowed these urban centers to attract an economic base that has catapulted them to megacity status. It’s no accident that the world’s largest cities—London, Paris, New York, Tokyo—were almost exclusively in temperate climates until the second half of the twentieth century. What we are seeing now is arguably the largest mass migration in human history, and the first to be triggered by a home appliance.

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THE DREAMERS AND INVENTORS who ushered in the cold revolution didn’t have eureka moments, and their brilliant ideas rarely transformed the world immediately. Mostly they had hunches, but they were tenacious enough to keep those hunches alive for years, even decades, until the pieces came together. Some of those innovations can seem trivial to us today. All that collective ingenuity, focused over decades and decades—all to make the world safe for the TV dinner? But the frozen world that Tudor and Birdseye helped conjure into being would do more than just populate the world with fish sticks. It would also populate the world with people, thanks to the flash freezing and cryopreservation of human semen, eggs, and embryos. Millions of human beings around the world owe their existence to the technologies of artificial cold. Today, new techniques in oocyte cryopreservation are allowing women to store healthy eggs in their younger years, extending their fertility well into their forties and fifties in many cases. So much of the new freedom in the way we have children now—from lesbian couples or single mothers using sperm banks to conceive, to women giving themselves two decades in the workforce before thinking about kids—would have been impossible without the invention of flash freezing.

When we think about breakthrough ideas, we tend to be constrained by the scale of the original invention. We figure out a way to make artificial cold, and we assume that will just mean that our rooms will be cooler, we’ll sleep better on hot nights, or there will be a reliable supply of ice cubes for our sodas. That much is easy to understand. But if you tell the story of cold only in that way, you miss the epic scope of it. Just two centuries after Frederic Tudor started thinking about shipping ice to Savannah, our mastery of cold is helping to reorganize settlement patterns all over the planet and bring millions of new babies into the world. Ice seems at first glance like a trivial advance: a luxury item, not a necessity. Yet over the past two centuries its impact has been staggering, when you look at it from the long-zoom perspective: from the transformed landscape of the Great Plains; to the new lives and lifestyles brought into being via frozen embryos; all the way to vast cities blooming in the desert.

3. Sound

oughly one million years ago, the seas retreated from the basin that surrounds modern-day Paris, leaving a ring of limestone deposits that had once been active coral reefs. Over time, the River Cure in Burgundy slowly carved its way through some of those limestone blocks, creating a network of caves and tunnels that would eventually be festooned with stalactites and stalagmites formed by rainwater and carbon dioxide. Archeological findings suggest that Neanderthals and early modern humans used the caves for shelter and ceremony for tens of thousands of years. In the early 1990s, an immense collection of ancient paintings was discovered on the walls of the cave complex in Arcy-sur-Cure: over a hundred images of bison, woolly mammoths, birds, fish—even, most hauntingly, the imprint of a child’s hand. Radiometric dating determined that the images were thirty thousand years old. Only the paintings at Chauvet, in southern France, are believed to be older.

For understandable reasons, cave paintings are conventionally cited as evidence of the primordial drive to represent the world in images. Eons before the invention of cinema, our ancestors would gather together in the firelit caverns and stare at flickering images on the wall. But in recent years, a new theory has emerged about the primitive use of the Burgundy caves, one focused not on the images of these underground passages, but rather on the sounds.

A few years after the paintings in Arcy-sur-Cure were discovered, a music ethnographer from the University of Paris named Iegor Reznikoff began studying the caves the way a bat would: by listening to the echoes and reverberations created in different parts of the cave complex. It had long been apparent that the Neanderthal images were clustered in specific parts of the cave, with some of the most ornate and dense images appearing more than a kilometer deep. Reznikoff determined that the paintings were consistently placed at the most acoustically interesting parts of the cave, the places where the reverberation was the most profound. If you make a loud sound standing beneath the images of Paleolithic animals at the far end of the Arcy-sur-Cure caves, you hear seven distinct echoes of your voice. The reverberation takes almost five seconds to die down after your vocal chords stop vibrating. Acoustically, the effect is not unlike the famous “wall of sound” technique that Phil Spector used on the 1960s records he produced for artists such as the Ronettes and Ike and Tina Turner. In Spector’s system, recorded sound was routed through a basement room filled with speakers and microphones that created a massive artificial echo. In Arcy-sur-Cure, the effect comes courtesy of the natural environment of the cave itself.

Reznikoff’s theory is that Neanderthal communities gathered beside the images they had painted, and they chanted or sang in some kind of shamanic ritual, using the reverberations of the cave to magically widen the sound of their voices. (Reznikoff also discovered small red dots painted at other sonically rich parts of the cave.) Our ancestors couldn’t record the sounds they experienced the way they recorded their visual experience of the world in paintings. But if Reznikoff is correct, those early humans were experimenting with a primitive form of sound engineering—amplifying and enhancing that most intoxicating of sounds: the human voice.

Discovery of La grotte d’Arcy-sur-Cure, in France, September 1991

The drive to enhance—and, ultimately, reproduce—the human voice would in time pave the way for a series of social and technological breakthroughs: in communications and computation, politics and the arts. We readily accept the idea that science and technology have enhanced our vision to a remarkable extent: from spectacles to the Keck telescopes. But our vocal chords, vibrating in speech and in song, have also been massively augmented by artificial means. Our voices grew louder; they began traveling across wires laid on the ocean floor; they slipped the surly bonds of Earth and began bouncing off satellites. The essential revolutions in vision largely unfolded between the Renaissance and the Enlightenment: spectacles, microscopes, telescopes; seeing clearly, seeing very far, and seeing very close. The technologies of the voice did not arrive in full force until the late nineteenth century. When they did, they changed just about everything. But they didn’t begin with amplification. The first great breakthrough in our obsession with the human voice arrived in the simple act of writing it down.

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FOR THOUSANDS OF YEARS after those Neanderthal singers gathered in the reverberant sections of the Burgundy caves, the idea of recording sound was as fanciful as counting fairies. Yes, over that period we refined the art of designing acoustic spaces to amplify our voices and our instruments: medieval cathedral design, after all, was as much about sound engineering as it was about creating epic visual experiences. But no one even bothered to imagine capturing sound directly. Sound was ethereal, not tangible. The best you could do was imitate sound with your own voice and instruments.

The dream of recording the human voice entered the adjacent possible only after two key developments: one from physics, the other from anatomy. From about 1500 on, scientists began to work under the assumption that sound traveled through the air in invisible waves. (Shortly thereafter they discovered that these waves traveled four times faster through water, a curious fact that wouldn’t turn out to be useful for another four centuries.) By the time of the Enlightenment, detailed books of anatomy had mapped the basic structure of the human ear, documenting the way sound waves were funneled through the auditory canal, triggering vibrations in the eardrum. In the 1850s, a Parisian printer named Édouard-Léon Scott de Martinville happened to stumble across one of these anatomy books, triggering a hobbyist’s interest in the biology and physics of sound.

Human ear

Scott had also been a student of shorthand writing; he’d published a book on the history of stenography a few years before he began thinking about sound. At the time, stenography was the most advanced form of voice-recording technology in existence; no system could capture the spoken word with as much accuracy and speed as a trained stenographer. But as he looked at these detailed illustrations of the inner ear, a new thought began to take shape in Scott’s mind: perhaps the process of transcribing the human voice could be automated. Instead of a human writing down words, a machine could write sound waves.

In March 1857, two decades before Thomas Edison would invent the phonograph, the French patent office awarded Scott a patent for a machine that recorded sound. Scott’s contraption funneled sound waves through a hornlike apparatus that ended with a membrane of parchment. Sound waves would trigger vibrations in the parchment, which would then be transmitted to a stylus made of pig’s bristle. The stylus would etch out the waves on a page darkened by the carbon of lampblack. He called his invention the “phonautograph”: the self-writing of sound.

In the annals of invention, there may be no more curious mix of farsightedness and myopia than the story of the phonautograph. On the one hand, Scott had managed to make a critical conceptual leap—that sound waves could be pulled out of the air and etched onto a recording medium—more than a decade before other inventors and scientists got around to it. (When you’re two decades ahead of Edison, you can be pretty sure you’re doing well for yourself.) But Scott’s invention was hamstrung by one crucial—even comical—limitation. He had invented the first sound recording device in history. But he forgot to include playback.

Édouard-Léon Scott de Martinville, French writer and inventor of the phonautograph

Actually, “forgot” is too strong a word. It seems obvious to us now that a device for recording sound should also include a feature where you can actually hear the recording. Inventing the phonautograph without including playback seems a bit like inventing the automobile but forgetting to include the bit where the wheels rotate. But that is because we are judging Scott’s work from the other side of the divide. The idea that machines could convey sound waves that had originated elsewhere was not at all an intuitive one; it wasn’t until Alexander Graham Bell began reproducing sound waves at the end of a telephone that playback became an obvious leap. In a sense, Scott had to look around two significant blind spots, the idea that sound could be recorded and that those recordings could be converted back into sound waves. Scott managed to grasp the first, but he couldn’t make it all the way to the second. It wasn’t so much that he forgot or failed to make playback work; it was that the idea never even occurred to him.

Phonautograph, circa 1857

If playback was never part of Scott’s plan, it is fair to ask exactly why he bothered to build the phonautograph in the first place. What good is a record player that doesn’t play records? Here we confront the double-edged sword of relying on governing metaphors, of borrowing ideas from other fields and applying them in a new context. Scott got to the idea of recording audio through the metaphor of stenography: write waves instead of words. That structuring metaphor enabled him to make the first leap, years ahead of his peers, but it also may have prevented him from making the second. Once words have been converted into the code of shorthand, the information captured there is decoded by a reader who understands the code. Scott thought the same would happen with his phonautograph. The machine would etch waveforms into the lampblack, each twitch of the stylus corresponding to some phoneme uttered by a human voice. And humans would learn to “read” those squiggles the way they had learned to read the squiggles of shorthand. In a sense, Scott wasn’t trying to invent an audio-recording device at all. He was trying to invent the ultimate transcription service—only you had to learn a whole new language in order to read the transcript.

It wasn’t that crazy an idea, looking back on it. Humans had proven to be unusually good at learning to recognize visual patterns; we internalize our alphabets so well we don’t even have to think about reading once we’ve learned how to do it. Why would sound waves, once you could get them on the page, be any different?

Sadly, the neural toolkit of human beings doesn’t seem to include the capacity for reading sound waves by sight. A hundred and fifty years have passed since Scott’s invention, and we have mastered the art and science of sound to a degree that would have astonished Scott. But not a single person among us has learned to visually parse the spoken words embedded in printed sound waves. It was a brilliant gamble, but ultimately a losing one. If we were going to decode recorded audio, we needed to convert it back to sound so we could do our decoding via the eardrum, not the retina.

We may not be waveform readers, but we’re not exactly slackers, either: during the century and a half that followed Scott’s invention, we did manage to invent a machine that could “read” the visual image of a waveform and convert it back into sound: namely, computers. Just a few years ago, a team of sound historians named David Giovannoni, Patrick Feaster, Meagan Hennessey, and Richard Martin discovered a trove of Scott’s phonautographs in the Academy of Sciences in Paris, including one from April 1860 that had been marvelously preserved. Giovannoni and his colleagues scanned the faint, erratic lines that had been first scratched into the lampblack when Lincoln was still alive. They converted that image into a digital waveform, then played it back through computer speakers.

At first, they thought they were hearing a woman’s voice, singing the French folk song “Au clair de la lune,” but later they realized they had been playing back the audio at double its recorded speed. When they dropped it down to the right tempo, a man’s voice appeared out of the crackle and hiss: Édouard-Léon Scott de Martinville warbling from the grave.

Understandably, the recording was not of the highest quality, even played at the right speed. For most of the clip, the random noise of the recording apparatus overwhelms Scott’s voice. But even this apparent failing underscores the historic importance of the recording. The strange hisses and decay of degraded audio signals would become commonplace to the twentieth-century ear. But these are not sounds that occur in nature. Sound waves dampen and echo and compress in natural environments. But they don’t break up into the chaos of mechanical noise. The sound of static is a modern sound. Scott captured it first, even if it took a century and a half to hear it.

But Scott’s blind spot would not prove to be a complete dead end. Fifteen years after his patent, another inventor was experimenting with the phonautograph, modifying Scott’s original design to include an actual ear from a cadaver in order to understand the acoustics better. Through his tinkering, he hit upon a method for both capturing and transmitting sound. His name was Alexander Graham Bell.

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FOR SOME REASON, sound technology seems to induce a strange sort of deafness among its most advanced pioneers. Some new tool comes along to share or transmit sound in a new way, and again and again its inventor has a hard time imagining how the tool will eventually be used. When Thomas Edison completed Scott’s original project and invented the phonograph in 1877, he imagined it would regularly be used as a means of sending audio letters through the postal system. Individuals would record their missives on the phonograph’s wax scrolls, and then pop them into the mail, to be played back days later. Bell, in inventing the telephone, made what was effectively a mirror-image miscalculation: He envisioned one of the primary uses for the telephone to be as a medium for sharing live music. An orchestra or singer would sit on one end of the line, and listeners would sit back and enjoy the sound through the telephone speaker on the other. So, the two legendary inventors had it exactly reversed: people ended up using the phonograph to listen to music and using the telephone to communicate with friends.

As a form of media, the telephone most resembled the one-to-one networks of the postal service. In the age of mass media that would follow, new communications platforms would be inevitably drawn toward the model of big-media creators and a passive audience of consumers. The telephone system would be the one model for more intimate—one-to-one, not one-to-many—communications until e-mail arrived a hundred years later. The telephone’s consequences were immense and multifarious. International calls brought the world closer together, though the threads connecting us were thin until recently. The first transatlantic line that enabled ordinary citizens to call between North America and Europe was laid only in 1956. In the first configuration, the system allowed twenty-four simultaneous calls. That was the total bandwidth for a voice conversation between the two continents just fifty years ago: out of several hundred million voices, only two dozen conversations at a time. Interestingly, the most famous phone in the world—the “red phone” that provided a hotline between the White House and the Kremlin—was not a phone at all in its original incarnation. Created after the communications fiasco that almost brought us to nuclear war in the Cuban Missile Crisis, the hotline was actually a Teletype that enabled quick, secure messages to be sent between the powers. Voice calls were considered to be too risky, given the difficulties of real-time translation.

Inventor Alexander Graham Bell's laboratory in which he experimented with the transmission of sound by electricity, 1886.

The telephone enabled less obvious transformations as well. It popularized the modern meaning of the word “hello”—as a greeting that starts a conversation—transforming it into one of the most recognized words anywhere on earth. Telephone switchboards became one of the first inroads for women into the “professional” classes. (AT&T alone employed 250,000 women by the mid-forties.) An AT&T executive named John J. Carty argued in 1908 that the telephone had had as big of an impact on the building of skyscrapers as the elevator:

It may sound ridiculous to say that Bell and his successors were the fathers of modern commercial architecture—of the skyscraper. But wait a minute. Take the Singer Building, the Flatiron Building, the Broad Exchange, the Trinity, or any of the giant office buildings. How many messages do you suppose go in and out of those buildings every day? Suppose there was no telephone and every message had to be carried by a personal messenger? How much room do you think the necessary elevators would leave for offices? Such structures would be an economic impossibility.

But perhaps the most significant legacy of the telephone lay in a strange and marvelous organization that grew out of it: Bell Labs, an organization that would play a critical role in creating almost every major technology of the twentieth century. Radios, vacuum tubes, transistors, televisions, solar cells, coaxial cables, laser beams, microprocessors, computers, cell phones, fiber optics—all these essential tools of modern life descend from ideas originally generated at Bell Labs. Not for nothing was it known as “the idea factory.” The interesting question about Bell Labs is not what it invented. (The answer to that is simple: just about everything.) The real question is why Bell Labs was able to create so much of the twentieth century. The definitive history of Bell Labs, Jon Gertner’s The Idea Factory, reveals the secret to the labs’ unrivaled success. It was not just the diversity of talent, and the tolerance of failure, and the willingness to make big bets—all of which were traits that Bell Labs shared with Edison’s famous lab at Menlo Park as well as other research labs around the world. What made Bell Labs fundamentally different had as much to do with antitrust law as the geniuses it attracted.

Employees install the "red phone,” the legendary hotline that connected the White House to the Kremlin during the Cold War, in the White House, August 30, 1963, Washington, D.C.

From as early as 1913, AT&T had been battling the U.S. government over its monopoly control of the nation’s phone service. That it was, in fact, a monopoly was undeniable. If you were making a phone call in the United States at any point between 1930 and 1984, you were almost without exception using AT&T’s network. That monopoly power made the company immensely profitable, since it faced no significant competition. But for seventy years, AT&T managed to keep the regulators at bay by convincing them that the phone network was a “natural monopoly” and a necessary one. Analog phone circuits were simply too complicated to be run by a hodgepodge of competing firms; if Americans wanted to have a reliable phone network, it needed to be run by a single company. Eventually, the antitrust lawyers in the Justice Department worked out an intriguing compromise, settled officially in 1956. AT&T would be allowed to maintain its monopoly over phone service, but any patented invention that had originated in Bell Labs would have to be freely licensed to any American company that found it useful, and all new patents would have to be licensed for a modest fee. Effectively, the government said to AT&T that it could keep its profits, but it would have to give away its ideas in return.

It was a unique arrangement, one we are not likely to see again. The monopoly power gave the company a trust fund for research that was practically infinite, but every interesting idea that came out of that research could be immediately adopted by other firms. So much of the American success in postwar electronics—from transistors to computers to cell phones—ultimately dates back to that 1956 agreement. Thanks to the antitrust resolution, Bell Labs became one of the strangest hybrids in the history of capitalism: a vast profit machine generating new ideas that were, for all practical purposes, socialized. Americans had to pay a tithe to AT&T for their phone service, but the new innovations AT&T generated belonged to everyone.

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ONE OF THE MOST TRANSFORMATIVE breakthroughs in the history of Bell Labs emerged in the years leading up to the 1956 agreement. For understandable reasons, it received almost no attention at the time; the revolution it would ultimately enable was almost half a century in the future, and its very existence was a state secret, almost as closely guarded as the Manhattan Project. But it was a milestone nonetheless, and once again, it began with the sound of the human voice.

The innovation that had created Bell Labs in the first place—Bell’s telephone—had ushered us across a crucial threshold in the history of technology: for the first time, some component of the physical world had been represented in electrical energy in a direct way. (The telegraph had converted man-made symbols into electricity, but sound belonged to nature as well as culture.) Someone spoke into a receiver, generating sound waves that became pulses of electricity that became sound waves again on the other end. Sound, in a way, was the first of our senses to be electrified. (Electricity helped us see the world more clearly thanks to the lightbulb during the same period, but it wouldn’t record or transmit what we saw for decades.) And once those sound waves became electric, they could travel vast distances at astonishing speeds.

But as magical as those electrical signals were, they were not infallible. Traveling from city to city over copper wires, they were vulnerable to decay, signal loss, noise. Amplifiers, as we will see, helped combat the problem, boosting signals as they traveled down the line. But the ultimate goal was a pure signal, some kind of perfect representation of the voice that wouldn’t degrade as it wound its way through the telephone network. Interestingly, the path that ultimately led to that goal began with a different objective: not keeping our voices pure, but keeping them secret.

During World War II, the legendary mathematician Alan Turing and Bell Labs’ A. B. Clark collaborated on a secure communications line, code-named SIGSALY, that converted the sound waves of human speech into mathematical expressions. SIGSALY recorded the sound wave twenty thousand times a second, capturing the amplitude and frequency of the wave at that moment. But that recording was not done by converting the wave into an electrical signal or a groove in a wax cylinder. Instead, it turned the information into numbers, encoded it in the binary language of zeroes and ones. “Recording,” in fact, was the wrong word for it. Using a term that would become common parlance among hip-hop and electronic musicians fifty years later, they called this process “sampling.” Effectively, they were taking snapshots of the sound wave twenty thousand times a second, only those snapshots were written out in zeroes and ones: digital, not analog.

Working with digital samples made it much easier to transmit them securely: anyone looking for a traditional analog signal would just hear a blast of digital noise. (SIGSALY was code-named “Green Hornet” because the raw information sounded like a buzzing insect.) Digital signals could also be mathematically encrypted much more effectively than analog signals. While the Germans intercepted and recorded many hours of SIGSALY transmissions, they were never able to interpret them.

Developed by a special division of the Army Signal Corps, and overseen by Bell Labs researchers, SIGSALY went into operation on July 15, 1943, with a historic transatlantic phone call between the Pentagon and London. At the outset of the call, before the conversation turned to the more pressing issues of military strategy, the president of Bell Labs, Dr. O. E. Buckley, offered some introductory remarks on the technological breakthrough that SIGSALY represented:

We are assembled today in Washington and London to open a new service, secret telephony. It is an event of importance in the conduct of the war that others here can appraise better than I. As a technical achievement, I should like to point out that it must be counted among the major advances in the art of telephony. Not only does it represent the achievement of a goal long sought—complete secrecy in radiotelephone transmission—but it represents the first practical application of new methods of telephone transmission that promise to have far-reaching effects.

If anything, Buckley underestimated the significance of those “new methods.” SIGSALY was not just a milestone in telephony. It was a watershed moment in the history of media and communications more generally: for the first time, our experiences were being digitized. The technology behind SIGSALY would continue to be useful in supplying secure lines of communication. But the truly disruptive force that it unleashed would come from another strange and wonderful property it possessed: digital copies could be perfect copies. With the right equipment, digital samples of sound could be transmitted and copied with perfect fidelity. So much of the turbulence of the modern media landscape—the reinvention of the music business that began with file-sharing services such as Napster, the rise of streaming media, and the breakdown of traditional television networks—dates back to the digital buzz of the Green Hornet. If the robot historians of the future had to mark one moment where the “digital age” began—the computational equivalent of the Fourth of July or Bastille Day—that transatlantic phone call in July 1943 would certainly rank high on the list. Once again, our drive to reproduce the sound of the human voice had expanded the adjacent possible. For the first time, our experience of the world was becoming digital.

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THE DIGITAL SAMPLES OF SIGSALY traveled across the Atlantic courtesy of another communications breakthrough that Bell Labs helped create: radio. Interestingly, while radio would eventually become a medium saturated with the sound of people talking or singing, it did not begin that way. The first functioning radio transmissions—created by Guglielmo Marconi and a number of other more-or-less simultaneous inventors in the last decades of the nineteenth century—were almost exclusively devoted to sending Morse code. (Marconi called his invention “wireless telegraphy.”) But once information began flowing through the airwaves, it was not long before the tinkerers and research labs began thinking of how to make spoken word and song part of the mix.

One of those tinkerers was Lee De Forest, one of the most brilliant and erratic inventors of the twentieth century. Working out of his home lab in Chicago, De Forest dreamed of combining Marconi’s wireless telegraph with Bell’s telephone. He began a series of experiments with a spark-gap transmitter, a device that created a bright, monotone pulse of electromagnetic energy that can be detected by antennae miles away, perfect for sending Morse code. One night, while De Forest was triggering a series of pulses, he noticed something strange happening across the room: every time he created a spark, the flame in his gas lamp turned white and increased in size. Somehow, De Forest thought, the electromagnetic pulse was intensifying the flame. That flickering gaslight planted a seed in De Forest’s head: somehow a gas could be used to amplify weak radio reception, perhaps making it strong enough to carry the more information-rich signal of spoken words and not just the staccato pulses of Morse code. He would later write, with typical grandiosity: “I discovered an Invisible Empire of the Air, intangible, yet solid as granite.”

After a few years of trial and error, De Forest settled on a gas-filled bulb containing three precisely configured electrodes designed to amplify incoming wireless signals. He called it the Audion. As a transmission device for the spoken word, the Audion was just powerful enough to transmit intelligible signals. In 1910, De Forest used an Audion-equipped radio device to make the first ever ship-to-shore broadcast of the human voice. But De Forest had much more ambitious plans for his device. He had imagined a world in which his wireless technology was used not just for military and business communications but also for mass enjoyment—and in particular, to make his great passion, opera, available to everyone. “I look forward to the day when opera may be brought into every home,” he told the New York Times, adding, somewhat less romantically, “Someday even advertising will be sent out over the wireless.”

On January 13, 1910, during a performance of Tosca by New York’s Metropolitan Opera, De Forest hooked up a telephone microphone in the hall to a transmitter on the roof to create the first live public radio broadcast. Arguably the most poetic of modern inventors, De Forest would later describe his vision for the broadcast: “The ether wave passing over the tallest towers and those who stand between are unaware of the silent voices which pass them on either side. . . . And when it speaks to him, the strains of some well-loved earthly melody, his wonder grows.”

Alas, this first broadcast did not trigger quite as much wonder as it did derision. De Forest invited hordes of reporters and VIPs to listen to the broadcast on his radio receivers dotted around the city. The signal strength was terrible, and listeners heard something closer to the Green Hornet’s unintelligible buzz than the strains of a well-loved earthly melody. The Times declared the whole adventure “a disaster.” De Forest was even sued by the U.S. attorney for fraud, accused of overselling the value of the Audion in wireless technology, and briefly incarcerated. Needing cash to pay his legal bills, De Forest sold the Audion patent at a bargain price to AT&T.

When the researchers at Bell Labs began investigating the Audion, they discovered something extraordinary: from the very beginning Lee De Forest had been flat-out wrong about most of what he was inventing. The increase in the gas flame had nothing to do with electromagnetic radiation. It was caused by sound waves from the loud noise of the spark. Gas didn’t detect and amplify a radio signal at all; in fact, it made the device less effective.

But somehow, lurking behind all of De Forest’s accumulation of errors, a beautiful idea was waiting to emerge. Over the next decade, engineers at Bell Labs and elsewhere modified his basic three-electrode design, removing the gas from the bulb so that it sealed a perfect vacuum, transforming it into both a transmitter and a receiver. The result was the vacuum tube, the first great breakthrough of the electronics revolution, a device that would boost the electrical signal of just about any technology that needed it. Television, radar, sound recording, guitar amplifiers, X-rays, microwave ovens, the “secret telephony” of SIGSALY, the first digital computers—all would rely on vacuum tubes. But the first mainstream technology to bring the vacuum tube into the home was radio. In a way, it was the realization of De Forest’s dream: an empire of air transmitting well-loved melodies into living rooms everywhere. And yet, once again, De Forest’s vision would be frustrated by actual events. The melodies that started playing through those magical devices were well-loved by just about everyone except De Forest himself.

Lee De Forest, American inventor, at the end of the 1920s

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RADIO BEGAN ITS LIFE as a two-way medium, a practice that continues to this day as ham radio: individual hobbyists talking to one another over the airwaves, occasionally eavesdropping on other conversations. But by the early 1920s, the broadcast model that would come to dominate the technology had evolved. Professional stations began delivering packaged news and entertainment to consumers who listened on radio receivers in their homes. Almost immediately, something entirely unexpected happened: the existence of a mass medium for sound unleashed a new kind of music on the United States, a music that had until then belonged almost exclusively to New Orleans, to the river towns of the American South, and to African-American neighborhoods in New York and Chicago. Almost overnight, radio made jazz a national phenomenon. Musicians such as Duke Ellington and Louis Armstrong became household names. Ellington’s band performed weekly national broadcasts from the Cotton Club in Harlem starting in the late 1920s; Armstrong became the first African-American to host his own national radio show shortly thereafter.

All of this horrified Lee De Forest, who wrote a characteristically baroque denunciation to the National Association of Broadcasters: “What have you done with my child, the radio broadcast? You have debased this child, dressed him in rags of ragtime, tatters of jive and boogie-woogie.” In fact, the technology that De Forest had helped invent was intrinsically better suited to jazz than it was to classical performances. Jazz punched through the compressed, tinny sound of early AM radio speakers; the vast dynamic range of a symphony was largely lost in translation. The blast of Satchmo’s trumpet played better on the radio than the subtleties of Schubert.

Composer Duke Ellington performs onstage, circa 1935

The collision of jazz and radio created, in effect, the first surge of a series of cultural waves that would wash over twentieth-century society. A new sound that has been slowly incubating in some small section of the world—New Orleans, in the case of jazz—finds its way onto the mass medium of radio, offending the grown-ups and electrifying the kids. The channel first carved out by jazz would subsequently be filled by rock ’n’ roll from Memphis, British pop from Liverpool, rap and hip-hop from South Central and Brooklyn. Something about radio and music seems to have encouraged this pattern, in a way that television or film did not: almost immediately after a national medium emerged for sharing music, subcultures of sound began flourishing on that medium. There were “underground” artists before radio—impoverished poets and painters—but radio helped create a template that would become commonplace: the underground artist who becomes an overnight celebrity.

With jazz, of course, there was a crucial additional element. The overnight celebrities were, for the most part, African-Americans: Ellington, Armstrong, Ella Fitzgerald, Billie Holiday. It was a profound breakthrough: for the first time, white America welcomed African-American culture into its living room, albeit through the speakers of an AM radio. The jazz stars gave white America an example of African-Americans becoming famous and wealthy and admired for their skills as entertainers rather than advocates. Of course, many of those musicians also became powerful advocates, in songs such as Billie Holiday’s “Strange Fruit,” with its bitter tale of a southern lynching. Radio signals had a kind of freedom to them that proved to be liberating in the real world. Those radio waves ignored the way in which society was segmented at that time: between black and white worlds, between different economic classes. The radio signals were color-blind. Like the Internet, they didn’t break down barriers as much as live in a world separate from them.

The birth of the civil rights movement was intimately bound up in the spread of jazz music throughout the United States. It was, for many Americans, the first cultural common ground between black and white America that had been largely created by African-Americans. That in itself was a great blow to segregation. Martin Luther King Jr. made the connection explicit in remarks he delivered at the Berlin Jazz Festival in 1964:

It is no wonder that so much of the search for identity among American Negroes was championed by Jazz musicians. Long before the modern essayists and scholars wrote of “racial identity” as a problem for a multi-racial world, musicians were returning to their roots to affirm that which was stirring within their souls. Much of the power of our Freedom Movement in the United States has come from this music. It has strengthened us with its sweet rhythms when courage began to fail. It has calmed us with its rich harmonies when spirits were down. And now, Jazz is exported to the world.

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LIKE MANY POLITICAL FIGURES of the twentieth century, King was indebted to the vacuum tube for another reason. Shortly after De Forest and Bell Labs began using vacuum tubes to enable radio broadcasts, the technology was enlisted to amplify the human voice in more immediate settings: powering amplifiers attached to microphones, allowing people to speak or sing to massive crowds for the first time in history. Tube amplifiers finally allowed us to break free from the sound engineering that had prevailed since Neolithic times. We were no longer dependent on the reverberations of caves or cathedrals or opera houses to make our voices louder. Now electricity could do the work of echoes, but a thousand times more powerfully.

Amplification created an entirely new kind of political event: mass rallies oriented around individual speakers. Crowds had played a dominant role in political upheaval for the preceding century and a half; if there is an iconic image of revolution before the twentieth century, it’s the swarm of humanity taking the city streets in 1789 or 1848. But amplification took those teeming crowds and gave them a focal point: the voice of the leader reverberating through the plaza or stadium or park. Before tube amplifiers, the limits of our vocal chords made it difficult to speak to more than a thousand people at a time. (The elaborate vocal stylings of opera singing were in many ways designed to coax maximum projection out of the biological limitations of the voice.) But a microphone attached to multiple speakers extended the range of earshot by several orders of magnitude. No one recognized—and exploited—this new power more quickly than Adolf Hitler, whose Nuremberg rallies addressed more than a hundred thousand followers, all fixated on the amplified sound of the Führer’s voice. Remove the microphone and amplifier from the toolbox of twentieth-century technology and you remove one of that century’s defining forms of political organization, from Nuremberg to “I Have a Dream.”

Tube amplification enabled the musical equivalent of political rallies as well: the Beatles playing Shea Stadium, Woodstock, Live Aid. But the idiosyncrasies of vacuum-tube technology also had a more subtle effect on twentieth-century music—making it not just loud but also making it noisy.

It is hard for those of us who have lived in the postindustrial world our entire lives to understand just how much a shock the sound of industrialization was to human ears a century or two ago. An entirely new symphony of discord suddenly entered the realm of everyday life, particularly in large cities: the crashing, clanging of metal on metal; the white-noise blast of the steam engine. The noise was, in many ways, as shocking as the crowds and the smells of the big cities. By the 1920s, as electrically amplified sounds began roaring alongside the rest of the urban tumult, organizations such as Manhattan’s Noise Abatement Society began advocating for a quieter metropolis. Sympathetic to the society’s mission, a Bell Labs engineer named Harvey Fletcher created a truck loaded with state-of-the-art sound equipment and Bell engineers who drove slowly around New York City noise hot spots taking sound measurements. (The unit of measurement for sound volume—the decibel—came out of Fletcher’s research.) Fletcher and his team found that some city sounds—riveting and drilling in construction, the roar of the subway—were at the decibel threshold for auditory pain. At Cortlandt Street, known as “Radio Row,” the noise of storefronts showcasing the latest radio speakers was so loud it even drowned out the elevated train.

But while noise-abatement groups battled modern noise through regulations and public campaigns, another reaction emerged. Instead of being repelled by the sound, our ears began to find something beautiful in it. The routine experiences of everyday life had been effectively a training session for the aesthetics of noise since the early nineteenth century. But it was the vacuum tube that finally brought noise to the masses.

Starting in the 1950s, guitarists playing through tube amplifiers noticed that they could make an intriguing new kind of sound by overdriving the amp: a crunchy layer of noise on top of the notes generated by strumming the strings of the guitar itself. This was, technically speaking, the sound of the amplifier malfunctioning, distorting the sound it had been designed to reproduce. To most ears it sounded like something was broken with the equipment, but a small group of musicians began to hear something appealing in the sound. A handful of early rock ’n’ roll recordings in the 1950s features a modest amount of distortion on the guitar tracks, but the art of noise wouldn’t really take off until the sixties. In July 1960, a bassist named Grady Martin was recording a riff for a Marty Robbins song called “Don’t Worry” when his amplifier malfunctioned, creating a heavily distorted sound that we now call a “fuzz tone.” Initially Robbins wanted it removed from the song, but the producer persuaded him to keep it. “No one could figure out the sound because it sounded like a saxophone,” Robbins would say years later. “It sounded like a jet engine taking off. It had many different sounds.” Inspired by the strange, unplaceable noise of Martin’s riff, another band called the Ventures asked a friend to hack together a device that could add the fuzz effect deliberately. Within a year, there were commercial distortion boxes on the market; within three years Keith Richards was saturating the opening riff of “Satisfaction” with distortion, and the trademark sound of the sixties was born.

A similar pattern developed with a novel—and initially unpleasant—sound that occurs when amplified speakers and microphones share the same physical space: the swirling, screeching noise of feedback. Distortion was a sound that had at least some aural similarity to those industrial sounds that had first emerged in the eighteenth century. (Hence the “jet engine” tone of Grady Martin’s bass line.) But feedback was an entirely new creature; it did not exist in any form until the invention of speakers and microphones roughly a century ago. Sound engineers would go to great lengths to eliminate feedback from recordings or concert settings, positioning microphones so they didn’t pick up signal from the speakers, and thus cause the infinite-loop screech of feedback. Yet once again, one man’s malfunction turned out to be another man’s music, as artists such as Jimi Hendrix or Led Zeppelin—and later punk experimentalists like Sonic Youth—embraced the sound in their recordings and performances. In a real sense, Hendrix was not just playing the guitar on those feedback-soaked recordings in the late 1960s, he was creating a new sound that drew upon the vibration of the guitar strings, the microphone-like pickups on the guitar itself, and the speakers, building on the complex and unpredictable interactions between those three technologies.

Sometimes cultural innovations come from using new technologies in unexpected ways. De Forest and Bell Labs weren’t trying to invent the mass rally when they came up with the first sketches of a vacuum tube, but it turned out to be easy to assemble mass rallies once you had amplification to share a single voice with that many people. But sometimes the innovation comes from a less likely approach: by deliberately exploiting the malfunctions, turning noise and error into a useful signal. Every genuinely new technology has a genuinely new way of breaking—and every now and then, those malfunctions open a new door in the adjacent possible. In the case of the vacuum tube, it trained our ears to enjoy a sound that would no doubt have made Lee De Forest recoil in horror. Sometimes the way a new technology breaks is almost as interesting as the way it works.

Taxonomy of sound diagram featured in the book City Noise

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FROM THE NEANDERTHALS chanting in the Burgundy caves, to Édouard-Léon Scott de Martinville warbling into his phonautograph, to Duke Ellington broadcasting from the Cotton Club, the story of sound technology had always been about extending the range and intensity of our voices and our ears. But the most surprising twist of all would come just a century ago, when humans first realized that sound could be harnessed for something else: to help us see.

The use of light to signal the presence of dangerous shorelines to sailors is an ancient practice; the Lighthouse of Alexandria, constructed several centuries before the birth of Christ, was one of the original seven wonders of the world. But lighthouses perform poorly at precisely the point where they are needed the most: in stormy weather, where the light they transmit is obscured by fog and rain. Many lighthouses employed warning bells as an additional signal, but those too could be easily drowned out by the sound of a roaring sea. Yet sound waves turn out to have an intriguing physical property: under water, they travel four times faster than they do through the air, and they are largely undisturbed by the sonic chaos above sea level.

In 1901, a Boston-based firm called the Submarine Signal Company began manufacturing a system of communications tools that exploited this property of aquatic sound waves: underwater bells that chimed at regular intervals, and microphones specially designed for underwater reception called “hydrophones.” The SSC established more than a hundred stations around the world at particularly treacherous harbors or channels, where the underwater bells would warn vessels, equipped with the company’s hydrophones, that steered too close to the rocks or shoals. It was an ingenious system, but it had its limits. To begin with, it worked only in places where the SSC had installed warning bells. And it was entirely useless at detecting less predictable dangers: other ships, or icebergs.

The threat posed by icebergs to maritime travel became vividly apparent to the world in April 1912, when the Titanic foundered in the North Atlantic. Just a few days before the sinking, the Canadian inventor Reginald Fessenden had run across an engineer from the SSC at a train station, and after a quick chat, the two men agreed that Fessenden should come by the office to see the latest underwater signaling technologies. Fessenden had been a pioneer of wireless radio, responsible for both the first radio transmission of human speech and the first transatlantic two-way radio transmission of Morse code. That expertise had led the SSC to ask him to help them design their hydrophone system to better filter out the background noise of underwater acoustics. When news of the Titanic broke, just four days after his visit to the SSC, Fessenden was as shocked as the rest of the world, but unlike the rest of the world, he had an idea about how to prevent these tragedies in the future.

Fessenden’s first suggestion had been to replace the bells with a continuous, electric-powered tone that could also be used to transmit Morse code, borrowing from his experiences with wireless telegraphy. But as he tinkered with the possibilities, he realized the system could be much more ambitious. Instead of merely listening to sounds generated by specifically designed and installed warning posts, Fessenden’s device would generate its own sounds onboard the ship and listen to the echoes created as those new sounds bounced off objects in the water, much as dolphins use echolocation to navigate their way around the ocean. Borrowing the same principles that had attracted the cave chanters to the unusually reverberant sections of the Arcy-sur-Cure caves, Fessenden tuned the device so that it would resonate with only a small section of the frequency spectrum, right around 540hz, allowing it to ignore all the background noise of the aquatic environment. After calling it, somewhat disturbingly, his “vibrator” for a few months, he ultimately dubbed it the “Fessenden Oscillator.” It was a system for both sending and receiving underwater telegraphy, and the world’s first functional sonar device.

Once again, the timing of world-historical events underscored the need for Fessenden’s contraption. Just a year after he completed his first working prototype, World War I erupted. The German U-boats roaming the North Atlantic now posed an even greater threat to maritime travel than the Titanic’s iceberg. The threat was particularly acute for Fessenden, who as a Canadian citizen was a fervent patriot of the British Empire. (He also seems to have been a borderline racist, later advancing a theory in his memoirs about why “blond-haired men of English extraction” had been so central to modern innovation.) But the United States was still two years away from joining the war, and the executives at the SSC didn’t share his allegiance to the Union Jack. Faced with the financial risk of developing two revolutionary new technologies, the company decided to build and market the oscillator as a wireless telegraphy device exclusively.

Fessenden ultimately traveled on his own dollar all the way to Portsmouth, England, to try to persuade the Royal Navy to invest in his oscillator, but they too were dubious of this miracle invention. Fessenden would later write: “I pleaded with them to just let us open the box and show them what the apparatus was like.” But his pleas were ultimately ignored. Sonar would not become a standard component of naval warfare until World War II. By the armistice in 1918, upward of ten thousand lives had been lost to the U-boats. The British and, eventually, the Americans had experimented with countless offensive and defensive measures to ward off these submarine predators. But, ironically, the most valuable defensive weapon would have been a simple 540hz sound wave, bouncing off the hull of the attacker.

Radio developer Reginald Fessenden testing his invention, 1906

In the second half of the twentieth century, the principles of echolocation would be employed to do far more than detect icebergs and submarines. Fishing vessels—and amateur fishers—used variations of Fessenden’s oscillator to detect their catch. Scientists used sonar to explore the last great mysteries of our oceans, revealing hidden landscapes, natural resources, and fault lines. Eighty years after the sinking of the Titanic inspired Reginald Fessenden to dream up the first sonar, a team of American and French researchers used sonar to discover the vessel on the Atlantic seabed, twelve thousand feet below the surface.

But Fessenden’s innovation had the most transformative effect on dry land, where ultrasound devices, using sound to see into a mother’s womb, revolutionized prenatal care, allowing today’s babies and their mothers to be routinely saved from complications that had been fatal less than a century ago. Fessenden had hoped his idea—using sound to see—might save lives; while he couldn’t persuade the authorities to put it to use in detecting U-boats, the oscillator did end up saving millions of lives, both at sea and in a place Fessenden would never have expected: the hospital.

Of course, ultrasound’s most familiar use involves determining the sex of a baby early in a pregnancy. We are accustomed now to think of information in binary terms: a zero or a one, a circuit connected or broken. But in all of life’s experiences, there are few binary crossroads like the sex of your unborn child. Are you going to have a girl or a boy? How many life-changing consequences flow out of that simple unit of information? Like many of us, my wife and I learned the gender of our children using ultrasound. We now have other, more accurate, means of determining the sex of a fetus, but we found our way to that knowledge first by bouncing sound waves off the growing body of our unborn child. Like the Neanderthals navigating the caves of Arcy-sur-Cure, echoes led the way.

There is, however, a dark side to that innovation. The introduction of ultrasound in countries such as China with a strong cultural preference for male offspring has led to a growing practice of sex-selective abortions. An extensive supply of ultrasound machines was introduced throughout China in the early 1980s, and while the government shortly thereafter officially banned the use of ultrasound to determine sex, the “back-door” use of the technology for sex selection is widespread. By the end of the decade, the sex ratio at birth in hospitals throughout China was almost 110 boys to every 100 girls, with some provinces reporting ratios as high as 118:100. This may be one of the most astonishing, and tragic, hummingbird effects in all of twentieth-century technology: someone builds a machine to listen to sound waves bouncing off icebergs, and a few generations later, millions of female fetuses are aborted thanks to that very same technology.

The skewed sex ratios of modern China contain several important lessons, setting aside the question of abortion itself, much less gender-based abortion. First, they are a reminder that no technological advance is purely positive in its effects: for every ship saved from an iceberg, there are countless pregnancies terminated because of a missing Y chromosome. The march of technology has its own internal logic, but the moral application of that technology is up to us. We can decide to use ultrasound to save lives or terminate them. (Even more challenging, we can use ultrasound to blur the very boundaries of life, detecting a heartbeat in a fetus that is only weeks old.) For the most part, the adjacencies of technological and scientific progress dictate what we can invent next. However smart you might be, you can’t invent an ultrasound before the discovery of sound waves. But what we decide to do with those inventions? That is a more complicated question, one that requires a different set of skills to answer.

But there’s another, more hopeful lesson in the story of sonar and ultrasound, which is how quickly our ingenuity is able to leap boundaries of conventional influence. Our ancestors first noticed the power of echo and reverberation to change the sonic properties of the human voice tens of thousands of years ago; for centuries we have used those properties to enhance the range and power of our vocal chords, from cathedrals to the Wall of Sound. But it’s hard to imagine anyone studying the physics of sound two hundred years ago predicting that those echoes would be used to track undersea weapons or determine the sex of an unborn child. What began with the most moving and intuitive sound to the human ear—the sound of our voices in song, in laughter, sharing news or gossip—has been transformed into the tools of both war and peace, death and life. Like those distorted wails of the tube amp, it is not always a happy sound. Yet, again and again, it turns out to have unsuspected resonance.

4. Clean

n December 1856, a middle-aged Chicago engineer named Ellis Chesbrough traveled across the Atlantic to take in the monuments of the European continent. He visited London, Paris, Hamburg, Amsterdam, and a half dozen other towns—the classic Grand Tour. Only Chesbrough hadn’t made his pilgrimage to study the architecture of the Louvre or Big Ben. He was there, instead, to study the invisible achievements of European engineering. He was there to study the sewers.

Chicago, in the middle of the nineteenth century, was a city in dire need of expertise about waste removal. Thanks to its growing role as a transit hub bringing wheat and preserved pork from the Great Plains to the coastal cities, the city had gone from hamlet to metropolis in a matter of decades. But unlike other cities that had grown at prodigious rates during this period (such as New York and London), Chicago had one crippling attribute, the legacy of a glacier’s crawl thousands of years before the first humans settled there: it was unforgivingly flat. During the Pleistocene era, vast ice fields crept down from Greenland, covering present-day Chicago with glaciers that were more than a mile high. As the ice melted, it formed a massive body of water that geologists now call Lake Chicago. As that lake slowly drained down to form Lake Michigan, it flattened the clay deposits left behind by the glacier. Most cities enjoy a reliable descending grade down to the rivers or harbors they evolved around. Chicago, by comparison, is an ironing board—appropriately enough, for the great city of the American plains.

Building a city on perfectly flat land would seem like a good problem to have; you would think hilly, mountainous terrain like that of San Francisco, Cape Town, or Rio would pose more engineering problems, for buildings and for transportation. But flat topographies don’t drain. And in the middle of the nineteenth century, gravity-based drainage was key to urban sewer systems. Chicago’s terrain also suffered from being unusually nonporous; with nowhere for the water to go, heavy summer rainstorms could turn the topsoil into a murky marshland in a matter of minutes. When William Butler Ogden, who would later become Chicago’s inaugural mayor, first waded through the rain-soaked town, he found himself “sinking knee deep in the mud.” He wrote to his brother-in-law, who had purchased land in the frontier town in a bold bet on its future potential: “You have been guilty of an act of great folly in making [this] purchase.” In the late 1840s, roadways made out of wood planks had been erected over the mud; one contemporary noted that every now and then one of the planks would give way, and “green and black slime [would] gush up between the cracks.” The primary system for sanitation removal was scavenging pigs roaming the streets, devouring the refuse that the humans left behind.

With its rail and shipping network expanding at extraordinary speed, Chicago more than tripled in size during the 1850s. That rate of growth posed challenges for the city’s housing and transportation resources, but the biggest strain of all came from something more scatological: when almost a hundred thousand new residents arrive in your city, they generate a lot of excrement. One local editorial declared: “The gutters are running with filth at which the very swine turn up their noses in supreme disgust.” We rarely think about it, but the growth and vitality of cities have always been dependent on our ability to manage the flow of human waste that emerges when people crowd together. From the very beginnings of human settlements, figuring out where to put all the excrement has been just as important as figuring out how to build shelter or town squares or marketplaces.

The problem is particularly acute in cities experiencing runaway growth, as we see today in the favelas and shantytowns of megacities. Nineteenth-century Chicago, of course, had both human and animal waste to deal with, the horses in the streets, the pigs and cattle awaiting slaughter in the stockyards. (“The river is positively red with blood under the Rush Street Bridge and past down our factory,” one industrialist wrote. “What pestilence may result from it I don’t know.”) The effects of all this filth were not just offensive to the senses; they were deadly. Epidemics of cholera and dysentery erupted regularly in the 1850s. Sixty people died a day during the outbreak of cholera in the summer of 1854. The authorities at the time didn’t fully understand the connection between waste and disease. Many of them subscribed to the then-prevailing “miasma” theory, contending that epidemic disease arose from poisonous vapors, sometimes called “death fogs,” that people inhaled in dense cities. The true transmission route—invisible bacteria carried in fecal matter polluting the water supply—would not become conventional wisdom for another decade.

But while their bacteriology wasn’t well developed, the Chicago authorities were right to make the essential connection between cleaning up the city and fighting disease. On February 14, 1855, a Chicago Board of Sewerage Commissioners was created to address the problem; their first act was to announce a search for “the most competent engineer of the time who was available for the position of chief engineer.” Within a few months, they had found their man, Ellis Chesbrough, the son of a railway officer who had worked on canal and rail projects, and who was currently employed as chief engineer of the Boston Water Works.

It was a wise choice: Chesbrough’s background in railway and canal engineering turned out to be decisive in solving the problem of Chicago’s flat, nonporous terrain. Creating an artificial grade by building sewers deep underground was deemed too expensive: tunneling that far below the surface was difficult work using nineteenth-century equipment, and the whole scheme required pumping the waste back to the surface at the end of the process. But here Chesbrough’s unique history helped him come up with an alternate scenario, reminding him of a tool he had seen as a young man working the railway: the jackscrew, a device used to lift multiton locomotives onto the tracks. If you couldn’t dig down to create a proper grade for drainage, why not use jackscrews to lift the city up?

Ellis Chesbrough, Chicago, circa 1870

Aided by the young George Pullman, who would later make a fortune building railway cars, Chesbrough launched one of the most ambitious engineering projects of the nineteenth century. Building by building, Chicago was lifted by an army of men with jackscrews. As the jackscrews raised the buildings inch by inch, workmen would dig holes under the building foundations and install thick timbers to support them, while masons scrambled to build a new footing under the structure. Sewer lines were inserted beneath buildings with main lines running down the center of streets, which were then buried in landfill that had been dredged out of the Chicago River, raising the entire city almost ten feet on average. Tourists walking around downtown Chicago today regularly marvel at the engineering prowess on display in the city’s spectacular skyline; what they don’t realize is that the ground beneath their feet is also the product of brilliant engineering. (Not surprisingly, having participated in such a Herculean undertaking, when George Pullman set out to build his model factory town of Pullman, Illinois, several decades later, his first step was to install sewer and water lines before breaking ground on any of the buildings.)

Amazingly, life went on largely undisturbed as Chesbrough’s team raised the city’s buildings. One British visitor observed a 750-ton hotel being lifted, and described the surreal experience in a letter: “The people were in [the hotel] all the time coming and going, eating and sleeping—the whole business of the hotel proceeding without interruption.” As the project advanced, Chesbrough and his team became ever more daring in the structures they attempted to raise. In 1860, engineers raised half a city block: almost an acre of five-story buildings weighing an estimated thirty-five thousand tons was lifted by more than six thousand jackscrews. Other structures had to be moved as well as lifted to make way for the sewers: “Never a day passed during my stay in the city,” one visitor recalled, “that I did not meet one or more houses shifting their quarters. One day I met nine. Going out on Great Madison Street in the horse cars we had to stop twice to let houses get across.”

The result was the first comprehensive sewer system in any American city. Within three decades, more than twenty cities around the country followed Chicago’s lead, planning and installing their own underground networks of sewer tunnels. These massive underground engineering projects created a template that would come to define the twentieth-century metropolis: the idea of a city as a system supported by an invisible network of subterranean services. The first steam train traveled through underground tunnels beneath London in 1863. The Paris metro opened in 1900 followed shortly by the New York subway. Pedestrian walkways, automobile freeways, electrical and fiber-optic cabling coiled their way beneath city streets. Today, entire parallel worlds exist underground, powering and supporting the cities that rise above them. We think of cities intuitively now in terms of skylines, that epic reach toward the heavens. But the grandeur of those urban cathedrals would be impossible without the hidden world below grade.

Raising the Briggs House—a brick hotel in Chicago— circa 1857.

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OF ALL THOSE ACHIEVEMENTS, more than the underground trains and high-speed Internet cables, the most essential and the most easily overlooked is the small miracle that sewer systems in part make possible: enjoying a glass of clean drinking water from a tap. Just a hundred and fifty years ago, in cities around the world, drinking water was effectively playing Russian roulette. When we think of the defining killers of nineteenth-century urbanism, our minds naturally turn to Jack the Ripper haunting the streets of London. But the real killers of the Victorian city were the diseases bred by contaminated water supplies.

This was the—literally—fatal flaw in Chesbrough’s plan for the sewers of Chicago. He had brilliantly conceived a strategy to get the waste away from the streets and the privies and the cellars of everyday life, but almost all of his sewer pipes drained into the Chicago River, which emptied directly into Lake Michigan, the primary source of the city’s drinking water. By the early 1870s, the city’s water supply was so appalling that a sink or tub would regularly be filled with dead fish, poisoned by the human filth and then hoovered up into the city’s water pipes. In summer months, according to one observer, the fish “came out cooked and one’s bathtub was apt to be filled with what squeamish citizens called chowder.”

Workmen make progress on the Metropolitan Line underground railway works at King’s Cross, London.

Upton Sinclair’s novel The Jungle is generally considered to be the most influential literary work in the muckraking tradition of political activism. Part of the power of the book came from its literal muckraking, describing the filth of turn-of-the-century Chicago in excruciating detail, as in this description of the wonderfully named Bubbly Creek, an offshoot of the Chicago River:

The grease and chemicals that are poured into it undergo all sorts of strange transformations, which are the cause of its name; it is constantly in motion, as if huge fish were feeding in it, or great leviathans disporting themselves in its depths. Bubbles of carbonic gas will rise to the surface and burst, and make rings two or three feet wide. Here and there the grease and filth have caked solid, and the creek looks like a bed of lava; chickens walk about on it, feeding, and many times an unwary stranger has started to stroll across, and vanished temporarily.

Chicago’s experience was replicated around the world: sewers removed human waste from people’s basements and backyards, but more often than not they simply poured it into the drinking water supply, either directly, as in the case of Chicago, or indirectly during heavy rainstorms. Drawing plans for sewer lines and water pipes on the scale of the city itself would not be sufficient for the task of keeping the big city clean and healthy. We also needed to understand what was happening on the scale of microorganisms. We needed both a germ theory of disease—and a way to keep those germs from harming us.

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WHEN YOU GO BACK to look at the initial reaction from the medical community to the germ theory, the response seems beyond comical; it simply doesn’t compute. It is a well-known story that the Hungarian physician Ignaz Semmelweis was roundly mocked and criticized by the medical establishment when he first proposed, in 1847, that doctors and surgeons wash their hands before attending to their patients. (It took almost half a century for basic antiseptic behaviors to take hold among the medical community, well after Semmelweis himself lost his job and died in an insane asylum.) Less commonly known is that Semmelweis based his initial argument on studies of puerperal (or “childbed”) fever, where new mothers died shortly after childbirth. Working in Vienna’s General Hospital, Semmelweis stumbled across an alarming natural experiment: the hospital contained two maternity wards, one for the well-to-do, attended by physicians and medical students, the other for the working class who received their care from midwives. For some reason, the death rates from puerperal fever were much lower in the working-class ward. After investigating both environments, Semmelweis discovered that the elite physicians and students were switching back and forth between delivering babies and doing research with cadavers in the morgue. Clearly some kind of infectious agent was being transmitted from the corpses to the new mothers; with a simple application of a disinfectant such as chlorinated lime, the cycle of infection could be stopped in its tracks.

There may be no more startling example of how much things have changed in our understanding of cleanliness over the past century and a half: Semmelweis was derided and dismissed not just for daring to propose that doctors wash their hands; he was derided and dismissed for proposing that doctors wash their hands if they wanted to deliver babies and dissect corpses in the same afternoon.

This is one of those places where our basic sensibilities deviate from the sensibilities of our nineteenth-century ancestors. They look and act like modern people in many ways: they take trains and schedule meetings and eat in restaurants. But every now and then, strange gaps open between us and them, not just the obvious gaps in technological sophistication, but more subtle, conceptual gaps. In today’s world, we think of hygiene in fundamentally different ways. The concept of bathing, for instance, was alien to most nineteenth-century Europeans and Americans. You might naturally assume that taking a bath was a foreign concept simply because people didn’t have access to running water and indoor plumbing and showers the way most of us in the developed world do today. But, in fact, the story is much more complicated than that. In Europe, starting in the Middle Ages and running almost all the way to the twentieth century, the prevailing wisdom on hygiene maintained that submerging the body in water was a distinctly unhealthy, even dangerous thing. Clogging one’s pores with dirt and oil allegedly protected you from disease. “Bathing fills the head with vapors,” a French doctor advised in 1655. “It is the enemy of the nerves and ligaments, which it loosens, in such a way that many a man never suffers from gout except after bathing.”

You can see the force of this prejudice most clearly in the accounts of royalty during the 1600s and 1700s—in other words, the very people who could afford to have baths constructed and drawn for them without a second thought. Elizabeth I bothered to take a bath only once a month, and she was a veritable clean freak compared to her peers. As a child, Louis XIII was not bathed once until he was seven years old. Sitting naked in a pool of water was simply not something civilized Europeans did; it belonged to the barbaric traditions of Middle Eastern bathhouses, not the aristocracy of Paris or London.

Slowly, starting in the early nineteenth century, the attitudes began to shift, most notably in England and America. Charles Dickens built an elaborate cold-water shower in his London home, and was a great advocate for the energizing and hygienic virtues of a daily shower. A minor genre of self-help books and pamphlets emerged, teaching people how to take a bath, with detailed instructions that seem today as if they are training someone to land a 747. One of the first steps Professor Higgins takes in reforming Eliza Doolittle in George Bernard Shaw’s Pygmalion is getting her into a tub. (“You expect me to get into that and wet myself all over?” she protests. “Not me. I should catch my death.”) Harriet Beecher Stowe and her sister Catharine Beecher advocated a daily wash in their influential handbook, The American Woman’s Home, published in 1869. Reformers began building public baths and showers in urban slums around the country. “By the last decades of the century,” the historian Katherine Ashenburg writes, “cleanliness had become firmly linked not only to godliness but also to the American way.”

Poster issued by the Central Council for Health Education (1927–1969), 1955

The virtues of washing oneself were not self-evident, the way we think of them today. They had to be discovered and promoted, largely through the vehicles of social reform and word of mouth. Interestingly, there is very little discussion of soap in the popular embrace of bathing in the nineteenth century. It was hard enough just to convince people that the water wasn’t going to kill them. (As we will see, when soap finally hit the mainstream in the twentieth century, it would be propelled by another new convention: advertising.) But the evangelists for bathing were supported by the convergence of several important scientific and technological developments. Advances of public infrastructure meant that people were much more likely to have running water in their homes to fill their bathtubs; that the water was cleaner than it had been a few decades earlier; and, most important, that the germ theory of disease had gone from fringe idea to scientific consensus.

This new paradigm had been achieved through two parallel investigations. First, there was the epidemiological detective work of John Snow in London, who first proved that cholera was caused by contaminated water and not miasmatic smells, by mapping the deaths of a Soho epidemic. Snow never managed to see the bacteria that caused cholera directly; the technology of microscopy at the time made it almost impossible to see organisms (Snow called them “animalcules”) that were so small. But he was able to detect the organisms indirectly, in the patterns of death on the streets of London. Snow’s waterborne theory of disease would ultimately deliver the first decisive blow to the miasma paradigm, though Snow himself didn’t live to see his theory triumph. After his untimely death in 1858, The Lancet ran a terse obituary that made no reference whatsoever to his groundbreaking epidemiological work. In 2014, the publication ran a somewhat belated “correction” to the obit, detailing the London doctor’s seminal contributions to public health.

John Snow’s cholera map of Soho

The modern synthesis that would come to replace the miasma hypothesis—that diseases such as cholera and typhoid are caused not by smells but by invisible organisms that thrive in contaminated water—was ultimately dependent, once again, on an innovation in glass. The German lens crafters Zeiss Optical Works began producing new microscopes in the early 1870s—devices that for the first time had been constructed around mathematical formulas that described the behavior of light. These new lenses enabled the microbiological work of scientists such as Robert Koch, one of the first scientists to identify the cholera bacterium. (After receiving the Nobel Prize for his work in 1905, Koch wrote to Carl Zeiss, “A large part of my success I owe to your excellent microscopes.”) With his great rival Louis Pasteur, Koch and his microscopes helped develop and evangelize the germ theory of disease. From a technological standpoint, the great nineteenth-century breakthrough in public health—the knowledge that invisible germs can kill—was a kind of team effort between maps and microscopes.

Today, Koch is rightly celebrated for the numerous microorganisms that he identified through those Zeiss lenses. But his research also led to a related breakthrough that was every bit as important, though less widely appreciated. Koch didn’t just see the bacteria; he also developed sophisticated tools to measure the density of bacteria in a given quantity of water. He mixed contaminated water with transparent gelatin, and viewed the growing bacterial colonies on a glass plate. Koch established a unit of measure that could be applied to any quantity of water—below 100 colonies per milliliter was considered to be safe to drink.

New ways of measuring create new ways of making. The ability to measure bacterial content allowed a completely new set of approaches to the challenges of public health. Before the adoption of these units of measurement, you had to test improvements to the water system the old-fashioned way: you built a new sewer or reservoir or pipe, and you sat around and waited to see if fewer people would die. But being able to take a sample of water and determine empirically whether it was free of contamination meant that cycles of experimentation could be tremendously accelerated.

Microscopes and measurement quickly opened a new front in the war on germs: instead of fighting them indirectly, by routing the waste away from the drinking water, new chemicals could be used to attack the germs directly. One of the key soldiers on this second front was a New Jersey doctor named John Leal. Like John Snow before him, Leal was a doctor who treated patients but who also had a passionate interest in wider issues of public health, particularly those concerning contaminated water supplies. It was an interest born of a personal tragedy: his father had suffered a slow and painful death from drinking bacteria-infested water during the Civil War. His father’s experience in the war gives us a compelling statistical portrait of the threat posed by contaminated water and other health risks during this period. Nineteen men in the 144th Regiment died in combat, while 178 died of disease during the war.

Leal experimented with many techniques for killing bacteria, but one poison in particular began to pique his interest as early as 1898: calcium hypochlorite, the potentially lethal chemical that is better known as chlorine, also known at the time as “chloride of lime.” The chemical had already been in wide circulation as a public health remedy: houses and neighborhoods that had suffered an outbreak of typhoid or cholera were routinely disinfected with the chemical, an intervention that did nothing to combat waterborne disease. But the idea of putting chlorine in water had not yet taken hold. The sharp, acrid smell of chloride of lime was indelibly associated with epidemic disease in the minds of city dwellers throughout the United States and Europe. It was certainly not a smell that one wanted to detect in one’s drinking water. Most doctors and public health authorities rejected the approach. One noted chemist protested: “The idea itself of chemical disinfection is repellent.” But armed with tools that enabled him to both see the pathogens behind diseases such as typhoid and dysentery and measure their overall presence in the water, Leal became convinced that chlorine—at the right dosage—could rid water of dangerous bacteria more effectively than any other means, without any threat to the humans drinking it.

Eventually, Leal landed a job with the Jersey City Water Supply Company, giving him oversight of seven billion gallons of drinking water in the Passaic River watershed. This new job set the stage for one of the most bizarre and daring interventions in the history of public health. In 1908, the company was immersed in a prolonged legal battle over contracts (worth hundreds of millions of dollars in today’s money) for reservoirs and water-supply pipes they had recently completed. The judge in the case had criticized the firm for not supplying waste that was “pure and wholesome” and ordered them to construct expensive additional sewer lines designed to keep pathogens out of the city’s drinking water. But Leal knew the sewer lines would be limited in their effectiveness, particularly during big storms. And so he decided to put his recent experiments with chlorine to the ultimate test.

In almost complete secrecy, without any permission from government authorities (and no notice to the general public), Leal decided to add chlorine to the Jersey City reservoirs. With the help of engineer George Warren Fuller, Leal built and installed a “chloride of lime feed facility” at the Boonton Reservoir outside Jersey City. It was a staggering risk, given the popular opposition to chemical filtering at the time. But the court rulings had severely limited his timeline, and he knew that lab tests would be meaningless to a lay audience. “Leal did not have time for a pilot study. He certainly did not have time to build a demonstration-scale facility to test the new technology,” Michael J. McGuire writes in his account, The Chlorine Revolution. “If the chlorine of lime feed system lost control of the amount of chemical being fed and a slug of high chlorine residual was delivered to Jersey City, Leal knew that would define the failure of the process.”

Cholera victim

It was the first mass chlorination of a city’s water supply in history. Once word got out, however, it initially seemed as though Leal was a madman or some kind terrorist. Drinking a few glasses of calcium hypochlorite could kill you, after all. But Leal had done enough experiments to know that very small quantities of the compound were harmless to humans but lethal to many forms of bacteria. Three months after his experiment, Leal was called to appear in court to defend his actions. Throughout his interrogation, he stood strong in defense of his public health innovation:

Q: Doctor, what other places in the world can you mention in which this experiment has been tried of putting this bleaching powder in the same way in the drinking water of a city of 200,000 inhabitants?

A: 200,000 inhabitants? There is no such place in the world, it has never been tried.

Q: It never has been.

A: Not under such conditions or under such circumstances but it will be used many times in the future, however.

Q: Jersey City is the first one?

A: The first to profit by it.

Q: Jersey City is the first one used to prove whether your experiment is good or bad?

A: No, sir, to profit by it. The experiment is over.

Q: Did you notify the city that you were going to try this experiment?

A: I did not.

Q: Do you drink this water?

A: Yes sir.

Q: Would you have any hesitation about giving it to your wife and family?

A: I believe it is the safest water in the world.

Cholera warning, 1866

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ULTIMATELY THE COURT CASE was settled with near complete victory for Leal. “I do there find and report,” the special master in the case wrote, “that this device is capable of rendering the water delivered to Jersey City, pure and wholesome . . . and is effective in removing from the water . . . dangerous germs.” Within a few years, the data supporting Leal’s daring move had become incontrovertible: communities such as Jersey City that enjoyed chlorinated drinking water saw dramatic decreases in waterborne diseases like typhoid fever.

At one point in Leal’s cross-examination during the Jersey City trial, the prosecuting attorney accused John Leal of seeking vast financial rewards from his chlorine innovation. “And if the experiment turned out well,” he sneered, “why, you made a fortune.” Leal interrupted him from the witness box with a shrug, “I don’t know where the fortune comes in; it is all the same to me.” Unlike others, Leal made no attempt to patent the chlorination technique that he had pioneered at the Boonton Reservoir. His idea was free to be adopted by any water company that wished to provide its customers with “pure and wholesome” water. Unencumbered by patent restrictions and licensing fees, municipalities quickly adopted chlorination as a standard practice, across the United States and eventually around the world.

About a decade ago, two Harvard professors, David Cutler and Grant Miller, set out to ascertain the impact of chlorination (and other water filtration techniques) between 1900 and 1930, the period when they were implemented across the United States. Because extensive data existed for rates of disease and particularly infant mortality in different communities around the country, and because chlorination systems were rolled out in a staggered fashion, Cutler and Miller were able to get an extremely accurate portrait of chlorine’s effect on public health. They found that clean drinking water led to a 43 percent reduction in total mortality in the average American city. Even more impressive, chlorine and filtration systems reduced infant mortality by 74 percent, and child mortality by almost as much.

It is important to pause for a second to reflect on the significance of those numbers, to take them out of the dry domain of public health statistics and into the realm of lived experience. Until the twentieth century, one of the givens of being a parent was that you faced a very high likelihood that at least one of your children would die at an early age. What may well be the most excruciating experience that we can confront—the loss of a child—was simply a routine fact of existence. Today, in the developed world at least, that routine fact has been turned into a rarity. One of the most fundamental challenges of being alive—keeping your children safe from harm—was dramatically lessened, in part through massive engineering projects, and in part through the invisible collision between compounds of calcium hypochlorite and microscopic bacteria. The people behind that revolution didn’t become rich, and very few of them became famous. But they left an imprint on our lives that is in many ways more profound than the legacy of Edison or Rockefeller or Ford.

Chlorination wasn’t just about saving lives, though. It was also about having fun. After World War I, ten thousand chlorinated public baths and pools opened across America; learning how to swim became a rite of passage. These new aquatic public spaces were the leading edge in challenges to the old rules of public decency during the period between the wars. Before the rise of municipal pools, women bathers generally dressed as though they were bundled up for a sleigh ride. By the mid-1920s, women began exposing their legs below the knee; one-piece suits with lower necklines emerged a few years later. Open-backed suits, followed by two-piece outfits, followed quickly in the 1930s. “In total, a woman’s thighs, hip line, shoulders, stomach, back and breast line all become publicly exposed between 1920 and 1940,” the historian Jeff Wiltse writes in his social history of swimming, Contested Waters. We can measure the transformation in terms of simple material: at the turn of the century, the average woman’s bathing suit required ten yards of fabric; by the end of the 1930s, one yard was sufficient. We tend to think of the 1960s as the period when shifting cultural attitudes led to the most dramatic change in everyday fashion, but it is hard to rival the rapid-fire unveiling of the female body that occurred between the wars. Of course, it is likely that women’s fashion would have found another route to exposure without the rise of swimming pools, but it seems unlikely that it would have happened as quickly as it did. No doubt exposing the thighs of female bathers was not in the forefront of John Leal’s mind as he dumped his chlorine into the Jersey City reservoir, but like the hummingbird’s wing, a change in one field triggers a seemingly unrelated change at a different order of existence: a trillion bacteria die at the hands of calcium hypochlorite, and somehow, twenty years later, basic attitudes toward exposing the female body are reinvented. As with so many cultural changes, it’s not that the practice of chlorination single-handedly transformed women’s fashion; many social and technological forces converged to make those bathing suits smaller: various strands of early feminism, the fetishizing gaze of the Hollywood camera, not to mention individual stars who wore those more revealing suits. But without the mass adoption of swimming as a leisure activity, those fashions would have been deprived of one of their key showcases. What’s more, those other explanations—as valid as they are—usually get all the press. Ask your average person on the street what factors drive women’s fashion, and they’ll inevitably point to Hollywood or glossy magazines. But they won’t often mention calcium hypochlorite.

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THROUGH THE NINETEENTH CENTURY, the march of clean technologies had largely unfolded on the terrain of public health: big engineering projects, mass filtration systems. But the story of hygiene in the twentieth century is a much more intimate affair. Just a few years after Leal’s bold experiment, five San Francisco entrepreneurs invested a hundred dollars each to launch a chlorine-based product. It seems with hindsight to have been a good idea, but their bleach business had been aimed at big industry, and sales didn’t develop as quickly as they had hoped. But the wife of one of the investors, Annie Murray, a shop owner in Oakland, California, had an idea: that chlorine bleach could be a revolutionary product for people’s homes as well as factories. At Murray’s insistence, the company created a weaker version of the chemical and packaged it in smaller bottles. Murray was so convinced of the product’s promise that she gave out free samples to all her shop customers. Within months, bottles were selling like crazy. Murray didn’t realize it at that time, but she was helping to invent an entirely new industry. Annie Murray had created America’s first commercial bleach for the home, and the first in a wave of cleaning brands that would become ubiquitous in the new century: Clorox.

Clorox bottles became so commonplace that the remnants our grandparents left behind are used by archaeologists to date dig sites today. (The pint-glass chlorine bleach bottle is to the early twentieth century what spear tips are to the iron age or colonial pottery is to the eighteenth century.) It was accompanied by other bestselling hygiene products for the home: Palmolive soap, Listerine, a popular antiperspirant named Odorono. Hygiene products like these were among the first to be promoted in full-page advertisements in magazines and newspapers. By the 1920s, Americans were being bombarded by commercial messages convincing them that they were facing certain humiliation if they didn’t do something about the germs on their bodies or in their homes. (The phrase “often a bridesmaid, never a bride” originated with a 1925 Listerine advertisement.) When radio and television began experimenting with storytelling, it was the personal-hygiene companies that once again led the way in pioneering new forms of advertising, a brilliant marketing move that still lingers with us today in the phrase “soap opera.” This is one of the stranger hummingbird effects of contemporary culture: the germ theory of disease may have reduced infant mortality to a fraction of its nineteenth-century levels, and made surgery and childbirth far safer than it had been in Semmelweis’s day. But it also played a crucial role in inventing the modern advertising business.

Today the cleaning business is worth an estimated $80 billion. Walk into a big-box supermarket or drugstore, and you will find hundreds, if not thousands, of products devoted to ridding our households of dangerous germs: cleaning our sinks and our toilets and floors and silverware, our teeth and our feet. These stores are effectively giant munitions depots for the war on bacteria. Naturally, there are some who feel that our obsession with cleanliness may now have gone too far. Some research suggests that our ever cleaner world may actually be linked to increasing rates of asthma and allergies, as our childhood immune systems now develop without being exposed to the full diversity of germs.

Clorox advertisement

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THE CONFLICT BETWEEN MAN and bacteria that played out over the past two centuries has had far-reaching consequences: from the trivial pursuits of swimwear fashion all the way to the existential improvements of lowered infant mortality rates. Our growing understanding of the microbial routes of disease enabled cities to burst through the population ceilings that had constrained them for the entirety of human civilization. As of 1800, no society had successfully built and sustained a city of more than two million people. The first cities to challenge that barrier (London and Paris, followed shortly by New York) had suffered mightily from the diseases that erupted when that many people shared such a small amount of real estate. Many reasonable observers of urban life in the middle of the nineteenth century were convinced that cities were not meant to be built on this scale, and that London would inevitably collapse back to a more manageable size, as Rome had done almost two thousand years before. But solving the problems of clean drinking water and reliable waste removal changed all of that. A hundred and fifty years after Ellis Chesbrough first took his grand tour of European sewage, cities such as London and New York were approaching ten million residents, with life expectancies and infectious disease rates that were far lower than their Victorian antecedents.

Of course, the problem now is not cities of two million or ten million; it’s megacities such as Mumbai or São Paulo that will soon embrace thirty million human beings or more, many of them living in improvised communities—shantytowns, favelas—that are closer to the Chicago that Chesbrough had to raise than a contemporary city in the developed world. If you look only at today’s Chicago or London, the story of the past century and a half seems to be one of incontrovertible progress: the water is cleaner; the mortality rates are much lower; epidemic disease is effectively nonexistent. And yet today there are more than three billion people around the world who lack access to clean drinking water and basic sanitation systems. In absolute numbers, we have gone backward as a species. (There were only a billion people alive in 1850.) So the question before us now is how we bring the clean revolution to the favelas, and not just Michigan Avenue. The conventional assumption has been that these communities need to follow the same path charted by Snow, Chesbrough, Leal, and all the other unsung heroes of our public health infrastructure: they need toilets connected to massive sewer systems that dispose of waste without contaminating reservoirs that pump out filtered water, delivered through an equally elaborate system direct to the home. But increasingly, these new megacities’ citizens—and other global development innovators—have begun to think that history need not repeat itself.

However bold and determined John Leal was, if he had been born just a generation earlier, he would have never had the opportunity to chlorinate the Jersey City water, because the science and the technology that made chlorination possible simply hadn’t been invented yet. The maps and lenses and chemistry and units of measure that converged in the second half of the nineteenth century gave him a platform for the experiment, so much so that it is probably fair to assume that if Leal hadn’t brought chlorination to the mainstream, someone else would have done it within a decade, if not sooner. All of which leads to the question: If new ideas and new technology can make a new solution imaginable, the way the germ theory and the microscope triggered the idea of chemically treating water, then has there not been a sufficient supply of new ideas since Leal’s day that might trigger a new paradigm for keeping our cities clean, one that would bypass the big-engineering phase altogether? And perhaps that paradigm might be a leading indicator of a future that we’re all destined to share. The developing world has famously bypassed some of the laborious infrastructure of wired telephone lines, jumping ahead of more “advanced” economies by basing their communications around wireless connections instead. Could the same pattern play out with sewers?

In 2011, the Bill and Melinda Gates Foundation announced a competition to help spur a paradigm shift in the way we think about basic sanitation services. Memorably called the “Reinvent the Toilet Challenge,” the competition solicited designs for toilets that do not require a sewer connection or electricity and cost less than five cents per user per day. The winning entry was a toilet system from Caltech that uses photovoltaic cells to power an electrochemical reactor that treats human waste, producing clean water for flushing or irrigation and hydrogen that can be stored in fuel cells. The system is entirely self-contained; it has no need for an electrical grid, a sewer line, or a treatment facility. The only input the toilet requires, beyond sunlight and human waste, is simple table salt, which is oxidized to make chlorine to disinfect the water.

Those chlorine molecules might well be the only part of the toilet that John Leal would recognize, were he around to see it today. And that’s because the toilet depends on new ideas and technology that have become part of the adjacent possible in the twentieth century, tools that hopefully can allow us to bypass the costly, labor-intensive work of building giant infrastructure projects. Leal needed microscopes and chemistry and the germ theory to clean the water supply in Jersey City; the Caltech toilet needs hydrogen fuel cells, solar panels, and even lightweight, inexpensive computer chips to monitor and regulate the system.

Ironically, those microprocessors are themselves, in part, the by-product of the clean revolution. Computer chips are fantastically intricate creations—despite the fact that they are ultimately the product of human intelligence, their microscopic detail is almost impossible for us to comprehend. To measure them, we need to zoom down to the scale of micrometers, or microns: one-millionth of a meter. The width of a human hair is about a hundred microns. A single cell of your skin is about thirty microns. A cholera bacterium is about three microns across. The pathways and transistors through which electricity flows on a microchip—carrying those signals that represent the zeroes and ones of binary code—can be as small as one-tenth of a single micron. Manufacturing at this scale requires extraordinary robotics and laser tools; there’s no such thing as a hand-crafted microprocessor. But chip factories also require another kind of technology, one we don’t normally associate with the high-tech world: they need to be preposterously clean. A spec of household dust landing on one of these delicate silicon wafers would be comparable to Mount Everest landing in the streets of Manhattan.

Bill Gates inspects the winning entry in the 2011 “Reinvent the Toilet Challenge.”

Environments such as the Texas Instruments microchip plant outside Austin, Texas, are some of the cleanest places on the planet. To even enter into the space, you have to don a full clean suit, your body covered head-to-toe with sterile materials that don’t shed. There’s something strangely inverted about the process. Normally when you find yourself dressing in such extreme protective outfits, you’re guarding yourself against some kind of hostile environment: severe cold, pathogens, the vacuum of space. But in the clean room, the suit is designed to protect the space from you. You are the pathogen, threatening the valuable resources of computer chips waiting to be born: your hair follicles and your epidermal layers and the mucus swarming around you. From the microchip’s point of view, every human being is Pig Pen, a dust cloud of filth. Washing up before entering the clean room, you’re not even allowed to use soap, because most soaps have fragrances that give off potential contaminants. Even soap is too dirty for the clean room.

There is a strange symmetry to the clean room as well, one that brings us back to those first pioneers struggling to purify the drinking water of their cities: to Ellis Chesbrough, John Snow, John Leal. Producing microchips also requires large quantities of water, only this water is radically different from the water you drink from the tap. To avoid impurities, chip plants create pure H2O, water that has been filtered not only of any bacterial contaminants but also of all the minerals, salts, and random ions that make up normal filtered water. Stripped of all those extra “contaminants,” ultrapure water, as it is called, is the ideal solvent for microchips. But those missing elements also make ultrapure water undrinkable for humans; chug a glass of the stuff and it will start leeching minerals out of your body. This is the full circle of clean: some of the most brilliant ideas in science and engineering in the nineteenth century helped us purify water that was too dirty to drink. And now, a hundred and fifty years later, we’ve created water that’s too clean to drink.

The interior of Texas Instruments

Standing in the clean room, the mind naturally drifts back to the sewers that lie beneath our city streets, the two polar extremes of the history of clean. To build the modern world, we had to create an unimaginably repellent space, an underground river of filth, and cordon it off from everyday life. And at the same time, to make the digital revolution, we had to create a hyper-clean environment, and once again, cordon it off from everyday life. We never get to visit these environments, and so they retreat from our consciousness. We celebrate the things they make possible—towering skyscrapers and ever-more-powerful computers—but we don’t celebrate the sewers and the clean rooms themselves. Yet their achievements are everywhere around us.

5. Time

n October 1967, a group of scientists from around the world gathered in Paris for a conference with the unassuming name “The General Conference on Weights and Measures.” If you’ve had the questionable fortune to attend an academic conference before, you probably have some sense of how these affairs go: papers are presented, along with an interminable series of panel discussions, broken up by casual networking over coffee; there’s gossip and infighting at the hotel bar at night; everyone has a tolerably good time, and not a whole lot gets done. But the General Conference on Weights and Measures broke from that venerable tradition. On October 13, 1967, the attendees agreed to change the very definition of time.

For almost the entire span of human history, time had been calculated by tracking the heavenly rhythms of solar bodies. Like the earth itself, our sense of time revolved around the sun. Days were defined by the cycle of sunrise and sunset, months by the cycles of the moon, years by the slow but predictable rhythms of the seasons. For most of that stretch, of course, we misunderstood what was causing those patterns, assuming that the sun was revolving around the earth, and not the reverse. Slowly, we built tools to measure the flow of time more predictably: sundials to track the passage of the day; celestial observatories such as Stonehenge to track seasonal milestones like the summer solstice. We began dividing up time into shorter units—seconds, minutes, hours—with many of those units relying on a base-12 counting system passed down from the ancient Egyptians and Sumerians. Time was defined by grade-school division: a minute was one-sixtieth of an hour, an hour was one-twenty-fourth of a day. And a day was simply the time that passed between the two moments when the sun was highest in the sky.

But starting about sixty years ago, as our tools of measuring time increased in precision, we began to notice flaws in that celestial metronome. The clockwork of the heavens turned out to be, well, a bit wobbly. And that’s what the General Conference on Weights and Measures set out to address in 1967. If we were going to be truly accurate with our measurements of time, we needed to trade the largest entity in the solar system for one of the smallest.

Nundinal calendar, Rome. The ancient Etruscans developed an eight-day market week, known as the nundinal cycle, around the eighth or seventh century BC.

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MEASURED PURELY BY TOURIST ATTENTION, the Duomo of Pisa is generally overshadowed by its famous leaning neighbor next door, but the thousand-year-old cathedral, with its brilliant white stone and marble façade, is in many ways a more impressive structure than the tilted bell tower beside it. Stand at the base of the nave and gaze up toward the fourteenth-century apse mosaic, and you can re-create a moment of absentminded distraction that would ultimately transform our relationship to time. Suspended from the ceiling is a collection of altar lamps. They are motionless now, but legend has it that in 1583, a nineteen-year-old student at the University of Pisa attended prayers at the cathedral and, while daydreaming in the pews, noticed one of the altar lamps swaying back and forth. While his companions dutifully recited the Nicene Creed around him, the student became almost hypnotized by the lamp’s regular motion. No matter how large the arc, the lamp appeared to take the same amount of time to swing back and forth. As the arc decreased in length, the speed of the lamp decreased as well. To confirm his observations, the student measured the lamp’s swing against the only reliable clock he could find: his own pulse.

Most nineteen-year-olds figure out less scientific ways to be distracted while attending mass, but this college freshman happened to be Galileo Galilei. That Galileo was daydreaming about time and rhythm shouldn’t surprise us: his father was a music theorist and played the lute. In the middle of the sixteenth century, playing music would have been one of the most temporally precise activities in everyday culture. (The musical term “tempo” comes from the Italian word for time.) But machines that could keep a reliable beat didn’t exist in Galileo’s age; the metronome wouldn’t be invented for another few centuries. So watching the altar lamp sway back and forth with such regularity planted the seed of an idea in Galileo’s young mind. As is so often the case, however, it would take decades before the seed would blossom into something useful.

Galileo spent the next twenty years becoming a professor of mathematics, experimenting with telescopes, and more or less inventing modern science, but he managed to keep the memory of that swinging altar lamp alive in his mind. Increasingly obsessed with the science of dynamics, the study of how objects move through space, he decided to build a pendulum that would re-create what he had observed in the Duomo of Pisa so many years before. He discovered that the time it takes a pendulum to swing is not dependent on the size of the arc or the mass of the object swinging, but only on the length of the string. “The marvelous property of the pendulum,” he wrote to fellow scientist Giovanni Battista Baliani, “is that it makes all its vibrations, large or small, in equal times.”

In equal times. In Galileo’s age, any natural phenomenon or mechanical device that displayed this rhythmic precision seemed miraculous. Most Italian towns in that period had large, unwieldy mechanical clocks that kept a loose version of the correct time, but they had to be corrected by sundial readings constantly or they would lose as much as twenty minutes a day. In other words, the state of the art in timekeeping technology was challenged by just staying accurate on the scale of days. The idea of a timepiece that might be accurate to the second was preposterous.

The swinging altar lamp inside Duomo of Pisa

Preposterous, and seemingly unnecessary. Just like Frederic Tudor’s ice trade, it was an innovation that had no natural market. You couldn’t keep accurate time in the middle of the sixteenth century, but no one really noticed, because there was no need for split-second accuracy. There were no buses to catch, or TV shows to watch, or conference calls to join. If you knew roughly what hour of the day it was, you could get by just fine.

The need for split-second accuracy would emerge not from the calendar but from the map. This was the first great age of global navigation, after all. Inspired by Columbus, ships were sailing to the Far East and the newly discovered Americas, with vast fortunes awaiting those who navigated the oceans successfully. (And almost certain death awaiting those who got lost.) But sailors lacked any way to determine longitude at sea. Latitude you could gauge just by looking up at the sky. But before modern navigation technology, the only way to figure out a ship’s longitude involved two clocks. One clock was set to the exact time of your origin point (assuming you knew the longitude of that location). The other clock recorded the current time at your location at sea. The difference between the two times told you your longitudinal position: every four minutes of difference translated to one degree of longitude, or sixty-eight miles at the equator.

Galileo Galilei

In clear weather, you could easily reset the ship clock through accurate readings of the sun’s position. The problem was the home-port clock. With timekeeping technology losing or gaining up to twenty minutes a day, it was practically useless on day two of the journey. All across Europe, bounties were offered for anyone who could solve the problem of determining longitude at sea: Philip III of Spain offered a life pension in ducats, while the famous Longitude Prize in England promised more than a million dollars in today’s currency. The urgency of the problem—and the economic rewards for solving it—brought Galileo’s mind back to the pursuit of “equal time” that had first captured his imagination at the age of nineteen. His astronomical observations had suggested that the regular eclipses of Jupiter’s moons might be useful for navigators keeping time at sea, but the method he devised was too complicated (and not as accurate as he had hoped). And so he returned, one last time, to the pendulum.

Fifty-eight years in the making, his slow hunch about the pendulum’s “magical property” had finally begun to take shape. The idea lay at the intersection point of multiple disciplines and interests: Galileo’s memory of the altar lamp, his studies of motion and the moons of Jupiter, the rise of a global shipping industry, and its new demand for clocks that would be accurate to the second. Physics, astronomy, maritime navigation, and the daydreams of a college student: all these different strains converged in Galileo’s mind. Aided by his son, he began drawing up plans for the first pendulum clock.

By the end of the next century, the pendulum clock had become a regular sight throughout Europe, particularly in England—in workplaces, town squares, even well-to-do homes. The British historian E. P. Thompson, in a brilliant essay on time and industrialization published in the late 1960s, noted that in the literature of the period, one of the telltale signs that a character has raised himself a rung or two up the socioeconomic ladder is the acquisition of a pocket watch. But these new timepieces were not just fashion accessories. A hundred times more accurate than its predecessors—losing or gaining only a minute or so a week—the pendulum clock brought about a change in the perception of time that we still live with today.

Drawing of the pendulum clock designed by Italian physicist, mathematician, astronomer, and philosopher Galileo Galilei, 1638–1659.

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WHEN WE THINK ABOUT the technology that created the industrial revolution, we naturally conjure up the thunderous steam engines and steam-powered looms. But beneath the cacophony of the mills, a softer but equally important sound was everywhere: the ticking of pendulum clocks, quietly keeping time.

Imagine some alternative history where, for whatever reason, timekeeping technology lags behind the development of the other machines that catalyzed the industrial age. Would the industrial revolution have even happened? You can make a reasonably good case that the answer is no. Without clocks, the industrial takeoff that began in England in the middle of the eighteenth century would, at the very least, have taken much longer to reach escape velocity—for several reasons. Accurate clocks, thanks to their unrivaled ability to determine longitude at sea, greatly reduced the risks of global shipping networks, which gave the first industrialists a constant supply of raw materials and access to overseas markets. In the late 1600s and early 1700s, the most reliable watches in the world were manufactured in England, which created a pool of expertise with fine-tool manufacture that would prove to be incredibly handy when the demands of industrial innovation arrived, just as the glassmaking expertise producing spectacles opened the door for telescopes and microscopes. The watchmakers were the advance guard of what would become industrial engineering.

Marine chronometer, from the Clockmakers’ Museum at the city’s Guildhall, London

More than anything else, though, industrial life needed clock time to regulate the new working day. In older agrarian or feudal economies, units of time were likely to be described in terms of the time required to complete a task. The day was divided not into abstract, mathematical units, but into a series of activities: instead of fifteen minutes, time was described as how long it would take to milk the cow or nail soles to a new pair of shoes. Instead of being paid by the hour, craftsmen were conventionally paid by the piece produced—what was commonly called “taken-work”—and their daily schedules were almost comically unregulated. Thompson cites the diary of one farming weaver from 1782 or 1783 as an example of scattered routines of pre-industrial work:

On a rainy day, he might weave 8½ yards; on October 14th he carried his finished piece, and so wove only 4¾ yards; on the 23rd he worked out till 3 o’clock, wove two yards before the sun set. . . . Apart from harvesting and threshing, churning, ditching and gardening, we have these entries: “Wove 2½ yards the Cow having calved she required much attendance.” On January 25th he wove 2 yards, walked to a nearby village, and did “sundry jobbs [sic] about the lathe and in the yard and wrote a letter in the evening.” Other occupations include jobbing with a horse and cart, picking cherries, working on a mill dam, attending a Baptist association, and a public hanging.

Try showing up for work in a modern office on that kind of clock. (Not even famously laid-back Google could tolerate that level of eccentricity.) For an industrialist trying to synchronize the actions of hundreds of workers with the mechanical tempo of the first factories, this kind of desultory work life was unmanageable. And so the creation of a viable industrial workforce required a profound reshaping of the human perception of time. The pottery manufacturer Josiah Wedgwood, whose Birmingham mills mark the very beginnings of industrial England, first implemented the convention of “clocking in” to work each day. (The lovely double entendre of “punching the clock” would have been meaningless to anyone born before 1700.) The whole idea of an “hourly wage”—now practically universal in the modern world—came out of the time regimen of the industrial age. In such a system, Thompson writes, “the employer must use the time of his labour, and see it is not wasted. . . . Time is now currency: it is not passed but spent.”

For the first generations living through this transformation, the invention of “time discipline” was deeply disorienting. Today, most of us in the developed world—and increasingly in the developing world—have been acclimated to the strict regimen of clock time from an early age. (Sit in on your average kindergarten classroom and you’ll see the extensive focus on explaining and reinforcing the day’s schedule.) The natural rhythms of tasks and leisure had to be forcibly replaced with an abstract grid. When you spend your whole life inside that grid, it seems like second nature, but when you are experiencing it for the first time, as the laborers of industrial England did in the second half of the eighteenth century, it arrives as a shock to the system. Timepieces were not just tools to help you coordinate the day’s events, but something more ominous: the “deadly statistical clock,” in Dickens’s Hard Times, “which measured every second with a beat like a rap upon a coffin lid.”

Workers punching the time clock at the Rouge Plant of the Ford Motor Company.

Naturally, that new regimen provoked a backlash. Not so much from the working classes—who began operating within the dictates of clock time by demanding overtime wages or shorter workdays—but rather from the aesthetes. To be a Romantic at the turn of the nineteenth century was in part to break from the growing tyranny of clock time: to sleep late, ramble aimlessly through the city, refuse to live by the “statistical clocks” that governed economic life. In The Prelude, Wordsworth announces his break from the “keepers of our time”:

The guides, the wardens of our faculties

And stewards of our labour, watchful men

And skillful in the usury of time

Sages, who in their prescience would control

all accidents, and to the very road

which they have fashioned would confine us down

like engines . . .

The time discipline of the pendulum clock took the informal flow of experience and nailed it to a mathematical grid. If time is a river, the pendulum clock turned it into a canal of evenly spaced locks, engineered for the rhythms of industry. Once again, an increase in our ability to measure things turned out to be as important as our ability to make them.

Potrait of Aaron Lufkin Dennison

That power to measure time was not distributed evenly through society: pocket watches remained luxury items until the middle of the nineteenth century, when a Massachusetts cobbler’s son named Aaron Dennison borrowed the new process of manufacturing armaments using standardized, interchangeable parts and applied the same techniques to watchmaking. At the time, the production of advanced watches involved more than a hundred distinct jobs: one person would make individual flea-sized screws, by turning a piece of steel on a thread; another would inscribe watch cases; and so on. Dennison had a vision of machines mass-producing identical tiny screws that could then be put into any watch of the same model, and machines that would engrave cases at precision speed. His vision took him through a bankruptcy or two, and earned him the nickname “the Lunatic of Boston” in the local press. But eventually, in the early 1860s, he hit on the idea of making a cheaper watch, without the conventional jeweled ornamentation that traditionally adorned pocket watches. It would be the first watch targeted at the mass market, not just the well-to-do.

Dennison’s “Wm. Ellery” watch—named after one of the signers of the Declaration of Independence, William Ellery—became a breakout hit, particularly with the soldiers of the Civil War. More than 160,000 watches were sold; even Abraham Lincoln owned and carried a “Wm. Ellery” watch. Dennison turned a luxury item into a must-have commodity. In 1850, the average pocket watch cost $40; by 1878, a Dennison unjeweled watch cost just $3.50.

With watches spiking in popularity across the country, a Minnesota railroad agent named Richard Warren Sears stumbled across a box of unwanted watches from a local jeweler, and turned a tidy profit selling them to other station agents. Inspired by his success, he partnered with a Chicago businessman named Alvah Roebuck, and together they launched a mail-order publication showcasing a range of watch designs: the Sears, Roebuck catalog. Those fifteen pounds of mail-order catalogs currently weighing down your mailbox? They all started with the must-have gadget of the late nineteenth century: the consumer-grade pocket watch.

Unknown soldier with pocket watch, 1860s (Library of Congress)

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WHEN DENNISON FIRST STARTED thinking about democratizing time in America, in one key respect the clocks of the period remained woefully irregular. Local time—in cities and towns across the United States—was now accurate to the second, if you consulted a public clock in a place where time discipline was particularly crucial. But there were literally thousands of distinct local times. Clock time had been democratized, but it had not yet been standardized. Thanks to Dennison, watches were spreading quickly through the system, but they were all running at different times. In the United States, each town and village ran at its own independent pace—with clocks synced to the sun’s position in the sky. As you moved west or east, even a few miles, the shifting relationship to the sun would produce a different time on a sundial. You could be standing in one city at 6:00 p.m., but just three towns over, the correct time would be 6:05. If you asked what time it was 150 years ago, you would have received at least twenty-three different answers in the state of Indiana, twenty-seven in Michigan, and thirty-eight in Wisconsin.

The strangest thing about this irregularity is the fact that no one noticed it. You couldn’t talk directly to someone three towns over, and it took an hour or two to get there by unreliable roads at low speeds. So a few minutes of fuzziness in the respective clocks of each town didn’t even register. But once people (and information) began to travel faster, the lack of standardization suddenly became a massive problem. Telegraphs and railroads exposed the hidden blurriness of nonstandardized clock time, just as, centuries before, the invention of the book had exposed the need for spectacles among the first generation of European readers.

The rewinding of a big Dennison watch (operation done once a year) in the district of Holborn, London.

Trains moving east or west—longitudinally—travel faster than the sun moves through the sky. So for every hour you traveled on a train, you needed to adjust your watch by four minutes. In addition, each railroad was running on its own clock, which meant that making a journey in the nineteenth century took some formidable number crunching. You’d leave New York at 8:00 a.m. New York time, catching the 8:05 on Columbia Railroad time, and arrive in Baltimore three hours later later, at 10:54 Baltimore time, which was, technically speaking, 11:05 Columbia Rail time, where you would wait ten minutes and then catch the 11:01 B&O train to Wheeling, West Virgina, which was, technically speaking again, the 10:49 train if you were on Wheeling time, and 11:10 if your watch was still keeping New York time. And the funny thing is, all those different times were the right ones, at least measured by the sun’s position in the sky. What made time easily measured by sundial made it infuriating by railroad.

The British had dealt with this problem by standardizing the entire country on Greenwich Mean Time in the late 1840s, synchronizing railroad clocks by telegraph. (To this day, clocks in every air traffic control center and cockpit around the world report Greenwich time; GMT is the single time zone of the sky.) But the United States was too sprawling to run off of one clock, particularly after the transcontinental railroad opened in 1869. With eight thousand towns across the country, each on its own clock, and over a hundred thousand miles of railroad track connecting them, the need for some kind of standardized system became overwhelming. For several decades, various proposals circulated for standardizing U.S. time, but nothing solidified. The logistical hurdles of coordinating schedules and clocks were immense, and somehow standardized time seemed to spark a strange feeling of resentment among ordinary citizens, as though it were an act against nature itself. A Cincinnati paper editorialized against standard time: “It is simply preposterous. . . . Let the people of Cincinnati stick to the truth as it is written by the sun, moon and stars.”

The United States remained temporally challenged until the early 1880s, when a railroad engineer named William F. Allen took on the cause. As the editor of a guide to railroad timetables, Allen knew firsthand how Byzantine the existing time system was. At a railroad convention in St. Louis in 1883, Allen presented a map that proposed a shift from fifty distinct railroad times to the four time zones that are still in use, more than a century later: Eastern, Central, Mountain, and Pacific. Allen designed the map so that the divisions between time zones zigzagged slightly to correspond to the points where the major railroad lines connected, instead of having the divisions run straight down meridian lines.

Persuaded by Allen’s plan, the railroad bosses gave him just nine months to make his idea a reality. He launched an energetic campaign of letter-writing and arm-twisting to convince observatories and city councils. It was an extraordinarily challenging campaign, but somehow Allen managed to pull it off. On November 18, 1883, the United States experienced one of the strangest days in the history of clock time, what became known as “the day of two noons.” Eastern Standard Time, as Allen had defined it, ran exactly four minutes behind local New York time. On that November day, the Manhattan church bells rang out the old New York noon, and then four minutes later, a second noon was announced by a second ringing: the very first 12:00 p.m., EST. The second noon was broadcast out across the country via telegraph, allowing railroad lines and town squares all the way to the Pacific to synchronize their clocks.

The very next year, GMT was set as the international clock (based on Greenwich being located on the prime meridian), and the whole globe was divided into time zones. The world had begun to break free from the celestial rhythms of the solar system. Consulting the sun was no longer the most accurate way to tell the time. Instead, pulses of electricity traveling by telegraph wire from distant cities kept our clocks in sync.

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ONE OF THE STRANGE PROPERTIES of the measurement of time is that it doesn’t belong neatly to a single scientific discipline. In fact, each leap forward in our ability to measure time has involved a handoff from one discipline to another. The shift from sundials to pendulum clocks relied on a shift from astronomy to dynamics, the physics of motion. The next revolution in time would depend on electromechanics. With each revolution, though, the general pattern remained the same: scientists discover some natural phenomenon that displays the propensity for keeping “equal time” that Galileo had observed in the altar lamps, and before long a wave of inventors and engineers begin using that new tempo to synchronize their devices. In the 1880s, Pierre and Jacques Curie first detected a curious property of certain crystals, including quartz, the very same material that had been so revolutionary for the glassmakers of Murano: under pressure, these crystals could be made to vibrate at a remarkably stable frequency. (This property came to be known as “piezoelectricity.”) The effect was even more pronounced when an alternating current was applied to the crystal.

The quartz crystal’s remarkable ability to expand and contract in “equal time” was first exploited by radio engineers in the 1920s, who used it to lock radio transmissions to consistent frequencies. In 1928, W. A. Marrison of Bell Labs built the first clock that kept time from the regular vibrations of a quartz crystal. Quartz clocks lost or gained only a thousandth of a second per day, and were far less vulnerable to atmospheric changes in temperature or humidity, not to mention movement, than pendulum clocks. Once again, the accuracy with which we measured time had increased by several orders of magnitude.

For the first few decades after Marrison’s invention, quartz clocks became the de facto timekeeping devices for scientific or industrial use; standard U.S. time was kept by quartz clocks starting in the 1930s. But by the 1970s, the technology had gotten cheap enough for a mass market, with the emergence of the first quartz-based wristwatches. Today, just about every consumer appliance that has a clock on it—microwaves, alarm clocks, wristwatches, automobile clocks—all run on the equal time of quartz piezoelectricity. That transformation was predictable enough. Someone invents a better clock, and the first iterations are too expensive for consumer use. But eventually the price falls, and the new clock enters mainstream life. No surprise there. Once again, the surprise comes from somewhere else, from some other field that wouldn’t initially seem to be all that dependent on time. New ways of measuring create new possibilities for making. With quartz time, that new possibility was computation.

A microprocessor is an extraordinary technological achievement on many levels, but few are as essential as this: computer chips are masters of time discipline. Think of the coordination needs of the industrial factory: thousands of short, repetitive tasks performed in proper sequence by hundreds of individuals. A microprocessor requires the same kind of time discipline, only the units being coordinated are bits of information instead of the hands and bodies of millworkers. (When Charles Babbage first invented a programmable computer in the middle of the Victorian Age, he called the CPU “the mill” for a reason.) And instead of thousands of operations per minute, the microprocessor is executing billions of calculations per second, while shuffling information in and out of other microchips on the circuit board. Those operations are all coordinated by a master clock, now almost without exception made of quartz. (This is why tinkering with your computer to make it go faster than it was engineered to run is called “overclocking.”) A modern computer is the assemblage of many different technologies and modes of knowledge: the symbolic logic of programming languages, the electrical engineering of the circuit board, the visual language of interface design. But without the microsecond accuracy of a quartz clock, modern computers would be useless.

The accuracy of the quartz clock made its pendulum predecessors seem hopelessly erratic. But it had a similar effect on the ultimate timekeepers: the earth and the sun. Once we started measuring days with quartz clocks, we discovered that the length of the day was not as reliable as we had thought. Days shortened or lengthened in semi-chaotic ways thanks to the drag of the tides on the surface of the planet, wind blowing over mountain ranges, or the inner motion of the earth’s molten core. If we really wanted to keep exact time, we couldn’t rely on the earth’s rotation. We needed a better timepiece. Quartz let us “see” that the seemingly equal times of a solar day weren’t nearly as equal as we had assumed. It was, in a way, the deathblow to the pre-Copernican universe. Not only was the earth not the center of the universe, but its rotation wasn’t even consistent enough to define a day accurately. A block of vibrating sand could do the job much better.

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KEEPING PROPER TIME IS ULTIMATELY all about finding—or making—things that oscillate in consistent rhythms: the sun rising in the sky, the moon waxing and waning, the altar lamp, the quartz crystal. The discovery of the atom in the early days of the twentieth century—led by scientists such as Niels Bohr and Werner Heisenberg—set in motion a series of spectacular and deadly innovations in energy and weaponry: nuclear power plants, hydrogen bombs. But the new science of the atom also revealed a less celebrated, but equally significant, discovery: the most consistent oscillator known to man. Studying the behavior of electrons orbiting within a cesium atom, Bohr noticed that they moved with an astonishing regularity. Untroubled by the chaotic drag of mountain ranges or tides, the electrons tapped out a rhythm that was several orders of magnitude more reliable than the earth’s rotation.

The first atomic clocks were built in the mid-1950s, and immediately set a new standard of accuracy: we were now capable of measuring nanoseconds, a thousand times more accurate than the microseconds of quartz. That leap forward was what ultimately enabled the International Conference of Weights and Measures in 1967 to declare that it was time to reinvent time. In the new era, the master time for the planet would be measured in atomic seconds: “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.” A day was no longer the time it took the earth to complete one rotation. A day became 86,400 atomic seconds, ticked off on 270 synchronized atomic clocks around the world.

The old timekeepers didn’t die off completely, though. Modern atomic clocks actually tick off the seconds using a quartz mechanism, relying on the cesium atom and its electrons to correct any random aberrations in the quartz timekeeping. And the world’s atomic clocks are reset every year based on the chaotic drift of the earth’s orbit, adding or gaining a second so that the atomic and solar rhythms don’t get too far out of sync. The multiple scientific fields of time discipline—astronomy, electromechanics, subatomic physics—are all embedded within the master clock.

The rise of the nanosecond might seem like an arcane shift, interesting only to the sort of person who attends a conference on weights and measures. And yet everyday life has been radically transformed by the rise of atomic time. Global air travel, telephone networks, financial markets—all rely on the nanosecond accuracy of the atomic clock. (Rid the world of these modern clocks, and the much vilified practice of high-frequency trading would disappear in a nanosecond.) Every time you glance down at your smartphone to check your location, you are unwittingly consulting a network of twenty-four atomic clocks housed in satellites in low-earth orbit above you. Those satellites are sending out the most elemental of signals, again and again, in perpetuity: the time is 11:48:25.084738 . . . the time is 11:48:25.084739. . . . When your phone tries to figure out its location, it pulls down at least three of these time stamps from satellites, each reporting a slightly different time thanks to the duration it takes the signal to travel from satellite to the GPS receiver in your hand. A satellite reporting a later time is closer than one reporting an earlier time. Since the satellites have perfectly predictable locations, the phone can calculate its exact position by triangulating among the three different time stamps. Like the naval navigators of the eighteenth century, GPS determines your location by comparing clocks. This is in fact one of the recurring stories of the history of the clock: each new advance in timekeeping enables a corresponding advance in our mastery of geography—from ships, to railroads, to air traffic, to GPS. It’s an idea that Einstein would have appreciated: measuring time turns out to be key to measuring space.

Professor Charles H. Townes, executive of the physics department at Columbia University, is shown with the “atomic clock” in the university’s physics department. Date released: January 25, 1955.

The next time you glance down at your phone to check what time it is or where you are, the way you might have glanced at a watch or a map just two decades ago, think about the immense, layered network of human ingenuity that has been put in place to make that gesture possible. Embedded in your ability to tell the time is the understanding of how electrons circulate within cesium atoms; the knowledge of how to send microwave signals from satellites and how to measure the exact speed with which they travel; the ability to position satellites in reliable orbits above the earth, and of course the actual rocket science needed to get them off the ground; the ability to trigger steady vibrations in a block of silicon dioxide—not to mention all the advances in computation and microelectronics and network science necessary to process and represent that information on your phone. You don’t need to know any of these things to tell the time now, but that’s the way progress works: the more we build up these vast repositories of scientific and technological understanding, the more we conceal them. Your mind is silently assisted by all that knowledge each time you check your phone to see what time it is, but the knowledge itself is hidden from view. That is a great convenience, of course, but it can obscure just how far we’ve come since Galileo’s altar-lamp daydreams in the Duomo of Pisa.

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AT FIRST GLANCE, THE STORY of time’s measurement would seem to be all about acceleration, dividing up the day into smaller and smaller increments so that we can move things faster: bodies, dollars, bits. But time in the atomic age has also moved in the exact opposite direction: slowing things down, not speeding them up; measuring in eons, not microseconds. In the 1890s, while working on her doctoral thesis in Paris, Marie Curie proposed for the first time that radiation was not some kind of chemical reaction between molecules, but something intrinsic to the atom—a discovery so critical to the development of physics, in fact, that she would become the first woman ever to win a Nobel Prize. Her research quickly drew the attention of her husband, Pierre Curie, who abandoned his own research into crystals to focus on radiation. Together they discovered that radioactive elements decayed at constant rates. The half-life of carbon 14, for instance, is 5,730 years. Leave some carbon 14 lying around for five thousand years or so, and you’ll find that half of it is gone.

Once again, science had discovered a new source of “equal time”—only this clock wasn’t ticking out the microseconds of quartz oscillations, or the nanoseconds of cesium electrons. Radiocarbon decay was ticking on the scale of centuries or millennia. Pierre Curie had surmised that the decay rate of certain elements might be used as a “clock” to determine the age of rocks. But the technique, now popularly known as carbon dating, wasn’t perfected until the late 1940s. Most clocks focus on measuring the present: What time is it right now? But radiocarbon clocks are all about the past. Different elements decay at wildly different rates, which means that they are like clocks running at different time scales. Carbon 14 “ticks” every five thousand years, but potassium 40 “ticks” every 1.3 billion years. That makes radiocarbon dating an ideal clock for the deep time of human history, while potassium 40 measures geologic time, the history of the planet itself. Radiometric dating has been critical in determining the age of the earth itself, establishing the most convincing scientific evidence that the biblical story of the earth being six thousand years old is just that: a story, not fact. We have immense knowledge about the prehistoric migrations of humans across the globe in large part thanks to carbon dating. In a sense, the “equal time” of radioactive decay has turned prehistoric time into history. When Homo sapiens first crossed the Bering Land Bridge into the Americas more than ten thousand years ago, there were no historians capable of writing down a narrative account of their journey. Yet their story was nonetheless captured by the carbon in their bones and the charcoal deposits they left behind at campsites. It was a story written in the language of atomic physics. But we couldn’t read that story without a new kind of clock. Without radiometric dating, “the deep time” of human migrations or geologic change would be like a history book where all the pages have been randomly shuffled: teeming with facts but lacking chronology and causation. Knowing what time it was turned that raw data into meaning.

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HIGH IN THE SOUTHERN SNAKE MOUNTAINS in eastern Nevada, a grove of bristlecone pines grows in the dry, alkaline soil. The pines are small trees for conifers, rarely more than thirty feet high, gnarled by the constant winds rolling across the desert range. We know from carbon dating (and tree rings) that some of them are more than five thousand years old—the oldest living things on the planet.

At some point, several years from now, a clock will be buried in the soil beneath those pines, a clock designed to measure time on the scale of civilizations, not seconds. It will be—as its primary designer, the computer scientist Danny Hillis, puts it—“a clock that ticks once a year. The century hand advances once every 100 years, and the cuckoo comes out on the millennium.” It is being engineered to keep time for at least ten thousand years, roughly the length of human civilization to date. It is an exercise in a different kind of time discipline: the discipline of avoiding short-term thinking, of forcing yourself to think about our actions and their consequences on the scale of centuries and millennia. Borrowing a wonderful phrase from the musician and artist Brian Eno, the device is called “the Clock of the Long Now.”

The Clock of the Long Now

The organization behind this device, the Long Now Foundation—cofounded by Hillis, Eno, Stewart Brand, and a few other visionaries—aims to build a number of ten-thousand-year clocks. (The first one is being constructed for a mountainside location in West Texas.) Why go to such extravagant lengths to build a clock that might tick only once in your lifetime? Because new modes of measuring force us to think about the world in a new light. Just as the microseconds of quartz and cesium opened up new ideas that transformed everyday life in countless ways, the slow time of the Long Now clock helps us think in new ways about the future. As Long Now board member Kevin Kelly puts it:

If you have a Clock ticking for 10,000 years what kinds of generational-scale questions and projects will it suggest? If a Clock can keep going for ten millennia, shouldn’t we make sure our civilization does as well? If the Clock keeps going after we are personally long dead, why not attempt other projects that require future generations to finish? The larger question is, as virologist Jonas Salk once asked, “Are we being good ancestors?”

This is the strange paradox of time in the atomic age: we live in ever shorter increments, guided by clocks that tick invisibly with immaculate precision; we have short attention spans and have surrendered our natural rhythms to the abstract grid of clock time. And yet simultaneously, we have the capacity to imagine and record histories that are thousands or millions of years old, to trace chains of cause and effect that span dozens of generations. We can wonder what time it is and glance down at our phone and get an answer that is accurate to the split-second, but we can also appreciate that the answer was, in a sense, five hundred years in the making: from Galileo’s altar lamp to Niels Bohr’s cesium, from the chronometer to Sputnik. Compared to an ordinary human being from Galileo’s age, our time horizons have expanded in both directions: from the microsecond to the millennium.

Which measure of time will win out in the end: our narrow focus on the short term, or our gift for the long now? Will we be high-frequency traders or good ancestors? For that question, only time will tell.

6. Light

magine some alien civilization viewing Earth from across the galaxies, looking for signs of intelligent life. For millions of years, there would be almost nothing to report: the daily flux of weather moving across the planet, the creep of glaciers spreading and retreating every hundred thousand years or so, the incremental drift of continents. But starting about a century ago, a momentous change would suddenly be visible: at night, the planet’s surface would glow with the streetlights of cities, first in the United States and Europe, then spreading steadily across the globe, growing in intensity. Viewed from space, the emergence of artificial lighting would arguably have been the single most significant change in the planet’s history since the Chicxulub asteroid collided with Earth sixty-five million years ago, coating the planet in a cloud of superheated ash and dust. From space, all the transformations that marked the rise of human civilization would be an afterthought: opposable thumbs, written language, the printing press—all these would pale beside the brilliance of Homo lumens.

Viewed from the surface of the earth, of course, the invention of artificial light had more rivals in terms of visible innovations, but its arrival marked a threshold point in human society. Today’s night sky now shines six thousand times brighter than it did just 150 years ago. Artificial light has transformed the way we work and sleep, helped create global networks of communication, and may soon enable radical breakthroughs in energy production. The lightbulb is so bound up in the popular sense of innovation that it has become a metaphor for new ideas themselves: the “lightbulb” moment has replaced Archimedes’s eureka as the expression most likely to be invoked to celebrate a sudden conceptual leap.

One of the odd things about artificial light is how stagnant it was as a technology for centuries. This is particularly striking given that artificial light arrived via the very first technology, when humans originally mastered the controlled fire more than a hundred thousand years ago. The Babylonians and Romans developed oil-based lamps, but that technology virtually disappeared during the (appropriately named) Dark Ages. For almost two thousand years, all the way to the dawn of the industrial age, the candle was the reigning solution for indoor lighting. Candles made from beeswax were highly prized but too expensive for anyone but the clergy or the aristocracy. Most people made do with tallow candles, which burned animal fat to produce a tolerable flicker, accompanied by a foul odor and thick smoke.

As our nursery rhymes remind us, candle-making was a popular vocation during this period. Parisian tax rolls from 1292 listed seventy-two “chandlers,” as they were called, doing business in the city. But most ordinary households made their own tallow candles, an arduous process that could go on for days: heating up containers of animal fat, and dipping wicks into them. In a diary entry from 1743, the president of Harvard noted that he had produced seventy-eight pounds of tallow candles in two days of work, a quantity that he managed to burn through two months later.

Chalice-shaped lamp from the tomb of Tutankhamun. The cup was intended to be filled with oil and when the wick was lit, then the scene of Tutankhamun and Ankhesenamun was visible. Ancient Egyptian, New Kingdom, Eighteenth Dynasty, 1333–1323 BC.

It’s not hard to imagine why people were willing to spend so much time manufacturing candles at home. Consider what life would have been like for a farmer in New England in 1700. In the winter months the sun goes down at five, followed by fifteen hours of darkness before it gets light again. And when that sun goes down, it’s pitch-black: there are no streetlights, flashlights, lightbulbs, fluorescents—even kerosene lamps haven’t been invented yet. There’s just a flickering glow of a fireplace, and the smoky burn of the tallow candle.

Those nights were so oppressive that scientists now believe our sleep patterns were radically different in the ages before ubiquitous night lighting. In 2001, the historian Roger Ekirch published a remarkable study that drew upon hundreds of diaries and instructional manuals to convincingly argue that humans had historically divided their long nights into two distinct sleep periods. When darkness fell, they would drift into “first sleep,” waking after four hours to snack, relieve themselves, have sex, or chat by the fire, before heading back for another four hours of “second sleep.” The lighting of the nineteenth century disrupted this ancient rhythm, by opening up a whole array of modern activities that could be performed after sunset: everything from theaters and restaurants to factory labor. Ekirch documents the way the ideal of a single, eight-hour block of continuous sleep was constructed by nineteenth-century customs, an adaptation to a dramatic change in the lighting environment of human settlements. Like all adaptations, its benefits carried inevitable costs: the middle-of-the-night insomnia that plagues millions of people around the world is not, technically speaking, a disorder, but rather the body’s natural sleep rhythms asserting themselves over the prescriptions of nineteenth-century convention. Those waking moments at three a.m. are a kind of jet lag caused by artificial light instead of air travel.

The flicker of the tallow candle had not been strong enough to transform our sleep patterns. To make a cultural change that momentous, you needed the steady bright glow of nineteenth-century lighting. By the end of the century, that light would come from the burning filaments of the electric lightbulb. But the first great advance in the century of light came from a source that seems macabre to us today: the skull of a fifty-ton marine mammal.

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IT’S A STORY THAT BEGINS with a storm. Legend has it that sometime around 1712 a powerful nor’easter off the coast of Nantucket blew a ship captain named Hussey far out to sea. In the deep waters of the North Atlantic, he encountered one of Mother Nature’s most bizarre and intimidating creations: the sperm whale.

Hussey managed to harpoon the beast—though some skeptics think it simply washed ashore in the storm. Either way, when locals dissected the giant mammal, they discovered something utterly bizarre: inside the creature’s massive head, they found a cavity above the brain, filled with a white, oily substance. Thanks to its resemblance to seminal fluid, the whale oil came to be called “spermaceti.”

To this day, scientists are not entirely sure why sperm whales produce spermaceti in such vast quantities. (A mature sperm whale holds as much as five hundred gallons inside its skull.) Some believe the whales use the spermaceti for buoyancy; others believe it helps with the mammal’s echolocation system. New Englanders, however, quickly discovered another use for spermaceti: candles made from the substance produce a much stronger, whiter light than tallow candles, without the offensive smoke. By the second half of the eighteenth century, spermaceti candles had become the most prized form of artificial light in America and Europe.

In a 1751 letter, Ben Franklin described how much he enjoyed the way the new candles “afford a clear white Light; may be held in the Hand, even in hot Weather, without softening; that their Drops do not make Grease Spots like those from common Candles; that they last much longer, and need little or no Snuffing.” Spermaceti light quickly became an expensive habit for the well-to-do. George Washington estimated that he spent $15,000 a year in today’s currency burning spermaceti candles. The candle business became so lucrative that a group of manufacturers formed an organization called United Company of Spermaceti Chandlers, conventionally known as the “Spermaceti Trust,” designed to keep competitors out of the business and force the whalers to keep their prices in check.

Despite the candle-making monopoly, significant economic rewards awaited anyone who managed to harpoon a sperm whale. The artificial light of the spermaceti candle triggered an explosion in the whaling industry, building out the beautiful seaside towns of Nantucket and Edgartown. But as elegant as these streets seem today, whaling was a dangerous and repulsive business. Thousands of lives were lost at sea chasing these majestic creatures, including from the notorious sinking of the Essex, which ultimately inspired Herman Melville’s masterpiece, Moby-Dick.

Extracting the spermaceti was almost as difficult as harpooning the whale itself. A hole would be carved in the side of the whale’s head, and men would crawl into the cavity above the brain—spending days inside the rotting carcass, scraping spermaceti out of the brain of the beast. It’s remarkable to think that only two hundred years ago, this was the reality of artificial light: if your great-great-great-grandfather wanted to read his book after dark, some poor soul had to crawl around in a whale’s head for an afternoon.

Spermaceti whale of the Southern Ocean. Hand-colored engraving from The Naturalist’s Libray, Mammalia, Vol. 12, 1833–1843, by Sir William Jardine.

Somewhere on the order of three hundred thousand sperm whales were slaughtered in just a little more than a century. It is likely that the entire population would have been killed off had we not found a new source of oil for artificial light in the ground, introducing petroleum-based solutions such as the kerosene lamp and the gaslight. This is one of the stranger twists in the history of extinction: because humans discovered deposits of ancient plants buried deep below the surface of the earth, one of the ocean’s most extraordinary creatures was spared.

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FOSSIL FUELS WOULD BECOME CENTRAL to almost all aspects of twentieth-century life, but their first commercial use revolved around light. These new lamps were twenty times brighter than any candle had ever been, and their superior brightness helped spark an explosion in magazine and newspaper publishing in the second half of the nineteenth century, as the dark hours after work became increasingly compatible with reading. But they also sparked literal explosions: thousands of people died each year in the fiery eruption of a reading light.

Despite these advances, artificial light remained extremely expensive by modern standards. In today’s society, light is comparatively cheap and abundant; 150 years ago, reading after dark was a luxury. The steady march of artificial light since then, from a rare and feeble technology to a ubiquitous and powerful one, gives us one map for the path of progress over that period. In the late 1990s, the Yale historian William D. Nordhaus published an ingenious study that charted that path in extraordinary detail, analyzing the true costs of artificial light over thousands of years of innovation.

When economic historians try to gauge the overall health of economies over time, average wages are usually one of the first places they start. Are people today making more money than they did in 1850? Of course, inflation makes those comparisons tricky: someone making ten dollars a day was upper-middle-class in nineteenth-century dollars. That’s why we have inflation tables that help us understand that ten dollars then is worth $160 in today’s currency. But inflation covers only part of the story. “During periods of major technological change,” Nordhaus argued, “the construction of accurate price indexes that capture the impact of new technologies on living standards is beyond the practical capability of official statistical agencies. The essential difficulty arises for the obvious but usually overlooked reason that most of the goods we consume today were not produced a century ago.” Even if you had $160 in 1850, you couldn’t buy a wax phonograph, not to mention an iPod. Economists and historians needed to factor not only the general value of a currency, but also some sense of what that currency could buy.

This is where Nordhaus proposed using the history of artificial light to illuminate the true purchasing power of wages over the centuries. The vehicles of artificial light vary dramatically over the years: from candles to LEDs. But the light they produce is a constant, a kind of anchor in the storm of rapid technological innovation. So Nordhaus proposed as his unit of measure the cost of producing one thousand “lumen-hours” of artificial light.

A tallow candle in 1800 would cost roughly forty cents per thousand lumen-hours. A fluorescent bulb in 1992, when Nordhaus originally compiled his research, cost a tenth of a cent for the same amount of light. That’s a four-hundred-fold increase in efficiency. But the story is even more dramatic when you compare those costs to the average wages from the period. If you worked for an hour at the average wage of 1800, you could buy yourself ten minutes of artificial light. With kerosene in 1880, the same hour of work would give you three hours of reading at night. Today, you can buy three hundred days of artificial light with an hour of wages.

Something extraordinary obviously happened between the days of tallow candles or kerosene lamps and today’s illuminated wonderland. That something was the electric lightbulb.

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THE STRANGE THING about the electric lightbulb is that it has come to be synonymous with the “genius” theory of innovation—the single inventor inventing a single thing, in a moment of sudden inspiration—while the true story behind its creation actually makes the case for a completely different explanatory framework: the network/systems model of innovation. Yes, the lightbulb marked a threshold in the history of innovation, but for entirely different reasons. It would be pushing things to claim that the lightbulb was crowdsourced, but it is even more of a distortion to claim that a single man named Thomas Edison invented it.

The canonical story goes something like this: after a triumphant start to his career inventing the phonograph and the stock ticker, a thirty-one-year-old Edison takes a few months off to tour the American West—perhaps not coincidentally, a region that was significantly darker at night than the gaslit streets of New York and New Jersey. Two days after returning to his lab in Menlo Park, in August 1878, he draws three diagrams in his notebook and titles them “Electric Light.” By 1879, he files a patent application for an “electric lamp” that displays all the main characteristics of the lightbulb we know today. By the end of 1882, Edison’s company is powering electric light for the entire Pearl Street district in Lower Manhattan.

Thomas Edison

It’s a thrilling story of invention: the young wizard of Menlo Park has a flash of inspiration, and within a few years his idea is lighting up the world. The problem with this story is that people had been inventing incandescent light for eighty years before Edison turned his mind to it. A lightbulb involves three fundamental elements: some kind of filament that glows when an electric current runs through it, some mechanism to keep the filament from burning out too quickly, and a means of supplying electric power to start the reaction in the first place. In 1802, the British chemist Humphry Davy had attached a platinum filament to an early electric battery, causing it to burn brightly for a few minutes. By the 1840s, dozens of separate inventors were working on variations of the lightbulb. The first patent was issued in 1841 to an Englishman named Frederick de Moleyns. The historian Arthur A. Bright compiled a list of the lightbulb’s partial inventors, leading up to Edison’s ultimate triumph in the late 1870s.

At least half of the men had hit upon the basic formula that Edison ultimately arrived at: a carbon filament, suspended in a vacuum to prevent oxidation, thus keeping the filament from burning up too quickly. In fact, when Edison finally began tinkering with electric light, he spent months working on a feedback system for regulating the flow of electricity to prevent melting, before finally abandoning that approach in favor of the vacuum—despite the fact that nearly half of his predecessors had already embraced the vacuum as the best environment for a sustained glow. The lightbulb was the kind of innovation that comes together over decades, in pieces. There was no lightbulb moment in the story of the lightbulb. By the time Edison flipped the switch at the Pearl Street station, a handful of other firms were already selling their own models of incandescent electric lamps. The British inventor Joseph Swan had begun lighting homes and theaters a year earlier. Edison invented the lightbulb the way Steve Jobs invented the MP3 player: he wasn’t the first, but he was the first to make something that took off in the marketplace.

So why does Edison get all the credit? It’s tempting to use the same backhanded compliment that many leveled against Steve Jobs: that he was a master of marketing and PR. It is true that Edison had a very tight relationship with the press at this point of his career. (On at least one occasion, he gave shares in his company to a journalist in exchange for better coverage.) Edison was also a master of what we would now call “vaporware”: He announced nonexistent products to scare off competitors. Just a few months after he had started work on electric light, he began telling reporters from New York papers that the problem had been solved, and that he was on the verge of launching a national system of magical electrical light. A system so simple, he says, “that a bootblack might understand it.”

Despite this bravado, the fact remained that the finest specimen of electric light in the Edison lab couldn’t last five minutes. But that didn’t stop him from inviting the press out to Menlo Park lab to see his revolutionary lightbulb. Edison would bring each reporter in one at a time, flick the switch on a bulb, and let the reporter enjoy the light for three or four minutes before ushering him from the room. When he asked how long his lightbulbs would last, he answered confidently: “Forever, almost.”

But for all this bluffing, Edison and his team did manage to ship a revolutionary and magical product, as the Apple marketing might have called the Edison lightbulb. Publicity and marketing will only get you so far. By 1882, Edison had produced a lightbulb that decisively outperformed its competitors, just as the iPod outperformed its MP3-player rivals in its early years.

In part, Edison’s “invention” of the lightbulb was less about a single big idea and more about sweating the details. (His famous quip about invention being one percent inspiration and ninety-nine percent perspiration certainly holds true for his adventures in artificial light.) Edison’s single most significant contribution to the electric lightbulb itself was arguably the carbonized bamboo filament he eventually settled on. Edison wasted at least a year trying to make platinum work as a filament, but it was too expensive and prone to melting. Once he abandoned platinum, Edison and his team tore through a veritable botanic garden of different materials: “celluloid, wood shavings (from boxwood, spruce, hickory, baywood, cedar, rosewood, and maple), punk, cork, flax, coconut hair and shell, and a variety of papers.” After a year of experimentation, bamboo emerged as the most durable substance, which set off one of the strangest chapters in the history of global commerce. Edison dispatched a series of Menlo Park emissaries to scour the globe for the most incandescent bamboo in the natural world. One representative paddled down two thousand miles of river in Brazil. Another headed to Cuba, where he was promptly struck down with yellow fever and died. A third representative named William Moore ventured to China and Japan, where he struck a deal with a local farmer for the strongest bamboo the Menlo Park wizards had encountered. The arrangement remained intact for many years, supplying the filaments that would illuminate rooms all over the world. Edison may not have invented the lightbulb, but he did inaugurate a tradition that would turn out to be vital to modern innovation: American electronics companies importing their component parts from Asia. The only difference is that, in Edison’s time, the Asian factory was a forest.

The other key ingredient to Edison’s success lay in the team he had assembled around him in Menlo Park, memorably known as the “muckers.” The muckers were strikingly diverse both in terms of professional expertise and nationality: the British mechanic Charles Batchelor, the Swiss machinist John Kruesi, the physicist and mathematician Francis Upton, and a dozen or so other draftsmen, chemists, and metalworkers. Because the Edison lightbulb was not so much a single invention as a bricolage of small improvements, the diversity of the team turned out to be an essential advantage for Edison. Solving the problem of the filament, for instance, required a scientific understanding of electrical resistance and oxidation that Upton provided, complementing Edison’s more untutored, intuitive style; and it was Batchelor’s mechanical improvisations that enabled them to test so many different candidates for the filament itself. Menlo Park marked the beginning of an organizational form that would come to prominence in the twentieth century: the cross-disciplinary research-and-development lab. In this sense, the transformative ideas and technologies that came out of places such as Bell Labs and Xerox-PARC have their roots in Edison’s workshop. Edison didn’t just invent technology; he invented an entire system for inventing, a system that would come to dominate twentieth-century industry.

Edison also helped inaugurate another tradition that would become vital to contemporary high-tech innovation: paying his employees in equity rather than just cash. In 1879, in the middle of the most frenetic research into the lightbulb, Edison offered Francis Upton stock worth 5 percent of the Edison Electric Light Company—though Upton would have to forswear his salary of $600 a year. Upton struggled over the decision, but ultimately decided to take the stock grant, over the objections of his more fiscally conservative father. By the end of the year, the ballooning value of Edison stock meant that his holdings were already worth $10,000, more than a million dollars in today’s currency. Not entirely graciously, Upton wrote to his father, “I cannot help laughing when I think how timid you were at home.”

By any measure, Edison was a true genius, a towering figure in nineteenth-century innovation. But as the story of the lightbulb makes clear, we have historically misunderstood that genius. His greatest achievement may have been the way he figured out how to make teams creative: assembling diverse skills in a work environment that valued experimentation and accepted failure, incentivizing the group with financial rewards that were aligned with the overall success of the organization, and building on ideas that originated elsewhere. “I am not overly impressed by the great names and reputations of those who might be trying to beat me to an invention. . . . It’s their ‘ideas’ that appeal to me,” Edison famously said. “I am quite correctly described as ‘more of a sponge than an inventor.’”

Early Edison carbon filament lamp, 1897

The lightbulb was the product of networked innovation, and so it is probably fitting that the reality of electric light ultimately turned out to be more of a network or system than a single entity. The true victory lap for Edison didn’t come with that bamboo filament glowing in a vacuum; it came with the lighting of the Pearl Street district two years later. To make that happen, you needed to invent lightbulbs, yes, but you also needed a reliable source of electric current, a system for distributing that current through a neighborhood, a mechanism for connecting individual lightbulbs to the grid, and a meter to gauge how much electricity each household was using. A lightbulb on its own is a curiosity piece, something to dazzle reporters with. What Edison and the muckers created was much bigger than that: a network of multiple innovations, all linked together to make the magic of electric light safe and affordable.

New York: Adapting the Brush Electric Light to the Illumination of the Streets, a Scene Near the Fifth Avenue Hotel.

Why should we care whether Edison invented the lightbulb as a lone genius or as part of a wider network? For starters, if the invention of the lightbulb is going to be a canonical story of how new technologies come into being, we might as well tell an accurate story. But it’s more than just a matter of getting the facts right, because there are social and political implications to these kinds of stories. We know that one key driver of progress and standards of living is technological innovation. We know that we want to encourage the trends that took us from ten minutes of artificial light on one hour’s wage to three hundred days. If we think that innovation comes from a lone genius inventing a new technology from scratch, that model naturally steers us toward certain policy decisions, like stronger patent protection. But if we think that innovation comes out of collaborative networks, then we want to support different policies and organizational forms: less rigid patent laws, open standards, employee participation in stock plans, cross-disciplinary connections. The lightbulb shines light on more than just our bedside reading; it helps us see more clearly the way new ideas come into being, and how to cultivate them as a society.

Artificial light turns out to have an even deeper connection to political values. Just six years after Edison lit the Pearl Street district, another maverick would push the envelope of light in a new direction, while walking the streets just a few blocks north of Edison’s illuminated wonderland. The muckers might have invented the system of electric light, but the next breakthrough in artificial light would come from a muckraker.

—

BURIED DEEP NEAR THE CENTER of the Great Pyramid of Giza lies a granite-faced cavity known as “the King’s Chamber.” The room contains only one object: an open rectangular box, sometimes called a “coffer,” carved out of red Aswan granite, chipped on one corner. The chamber’s name derives from the assumption that the coffer had been a sarcophagus that once contained the body of Khufu, the pharaoh who built the pyramid more than four thousand years ago. But a long line of maverick Egyptologists have suggested that the coffer had other uses. One still-circulating theory notes that the coffer possesses the exact dimensions that the Bible attributes to the original Ark of the Covenant, suggesting to some that the coffer once housed the legendary Ark itself.

In the fall of 1861, a visitor came to the King’s Chamber in the throes of an equally outlandish theory, this one revolving around a different Old Testament ark. The visitor was Charles Piazzi Smyth, who for the preceding fifteen years had served as the Royal Astronomer of Scotland, though he was a classic Victorian polymath with dozens of eclectic interests. Smyth had recently read a bizarre tome that contended that the pyramids had been originally built by the biblical Noah. Long an armchair Egyptologist, Smyth had grown so obsessed with the theory that he left his armchair in Edinburgh and headed off to Giza to do his own investigations firsthand. His detective work would ultimately lead to a bizarre stew of numerology and ancient history, published in a series of books and pamphlets over the coming years. Smyth’s detailed analyses of the pyramid’s structure convinced him that the builders had relied on a unit of measurement that was almost exactly equivalent to the modern British inch. Smyth interpreted this correspondence to be a sign that the inch itself was a holy measure, passed directly from God to Noah himself. This in turn gave Smyth the artillery he needed to attack the metric system that had begun creeping across the English Channel. The revelation of the Egyptian inch made it clear that the metric system was not just a symptom of malevolent French influence. It was also a betrayal of divine will.

Smyth’s scientific discoveries in the Great Pyramid may not have stood the test of time, or even kept Britain from going metric. Yet he still managed to make history in the King’s Chamber. Smyth brought the bulky and fragile tools of wet-plate photography (then state of the art) to Giza to document his findings. But the collodion-treated glass plates couldn’t capture a legible image in the King’s Chamber, even when the room was lit by torchlight. Photographers had tinkered with artificial lighting since the first daguerreotypes were printed in the 1830s, but almost all the solutions to date had produced unsatisfactory results. (Candles and gaslight were useless, obviously.) Early experiments heated a ball of calcium carbonate—the “limelight” that would illuminate theater productions until the dawn of electric light—but limelit photographs suffered from harsh contrasts and ghostly white faces.

The failed experiments with artificial lighting meant that by the time Smyth set up his gear in the King’s Chamber, more than thirty years after the invention of the daguerreotype, the art of photography was still entirely dependent on natural sunlight, a resource that was not exactly abundant in the inner core of a massive pyramid. But Smyth had heard of recent experiments using wire made of magnesium—photographers who twisted the wire into a bow and set it ablaze before capturing their low-light image. The technique was promising, but the light was unstable and generated an unpleasant amount of dense fumes. Burning magnesium wire in a closed environment had a tendency to make ordinary portraits look as though they were composed in dense fog.

Smyth realized that what he needed in the King’s Chamber was something closer to a flash than a slow burn. And so—for the first time in history, as far as we know—he mixed magnesium with ordinary gunpowder, creating a controlled mini-explosion that illuminated the walls of the King’s Chamber for a split second, allowing him to record its secrets on his glass plates. Today, the tourists that pass through the Great Pyramid encounter signs that forbid the use of flash photography inside the vast structure. They do not mention that the Great Pyramid also marks the site where flash photography was invented.

Or at least, one of the sites where flash photography was invented. Just as with Edison’s lightbulb, the true story of flash photography’s origins is a more complicated, more networked affair. Big ideas coalesce out of smaller, incremental breakthroughs. Smyth may have been the first to conceive of the idea of combining magnesium with an oxygen-rich, combustible element, but flash photography itself didn’t become a mainstream practice for another two decades, when two German scientists, Adolf Miethe and Johannes Gaedicke, mixed fine magnesium powder with potassium chlorate, creating a much more stable concoction that allowed high-shutter-speed photographs in low-light conditions. They called it Blitzlicht—literally, “flash light.”

Word of Miethe and Gaedicke’s invention soon trickled out of Germany. In October 1887, a New York paper ran a four-line dispatch about Blitzlicht. It was hardly a front-page story; the vast majority of New Yorkers ignored it altogether. But the idea of flash photography set off a chain of associations in the mind of one reader—a police reporter and amateur photographer who stumbled across the article while having breakfast with his wife in Brooklyn. His name was Jacob Riis.

Charles Piazzi Smyth

Then a twenty-eight-year-old Danish immigrant, Riis would ultimately enter the history books as one of the original muckrakers of the late nineteenth century, the man who did more to expose the squalor of tenement life—and inspire a progressive reform movement—than any other figure of the era. But until that breakfast in 1887, Riis’s attempts to shine light on the appalling conditions in the slums of Manhattan had failed to change public opinion in any meaningful way. A close confidant of then police commissioner Teddy Roosevelt, Riis had been exploring the depths of Five Points and other Manhattan hovels for years. With over half a million people living in only fifteen thousand tenements, sections of Manhattan were the most densely populated places on the planet. Riis was fond of taking late-night walks through the bleak alleyways on his way back home to Brooklyn from the police headquarters on Mulberry Street. “We used to go in the small hours of the morning,” he later recalled, “into the worst tenements to count noses and see if the law against overcrowding was violated, and the sights I saw there gripped my heart until I felt that I must tell of them, or burst, or turn anarchist, or something.”

Appalled by what he had discovered on his expeditions, Riis began writing about the mass tragedy of the tenements for local papers and national magazines such as Scribner’s and Harper’s Weekly. His written accounts of the shame of the cities belonged to a long tradition, dating back at least to Dickens’s horrified visit to New York in 1840. A number of exhaustive surveys of tenement depravity had been published over the years, with titles like “The Report of the Council of Hygiene and Public Health.” An entire genre of “sunshine and shadow” guidebooks to Five Points and its ilk flourished after the Civil War, offering curious visitors tips on exploring the seedy underbelly of big-city life, or at least exploring it vicariously from the safety of a small-town oasis. (The phrase “slumming it” originates with these tourist expeditions.) But despite stylistic differences, these texts shared one attribute: they had almost no effect on improving the actual living conditions of those slum dwellers.

Jacob Riis, 1900s

Riis had long suspected that the problem with tenement reform—and urban poverty initiatives generally—was ultimately a problem of imagination. Unless you walked through the streets of Five Points after midnight, or descended into the dark recesses of interior apartments populated by multiple families at a time, you simply couldn’t imagine the conditions; they were too far removed from the day-to-day experience of most Americans, or at least most voting Americans. And so the political mandate to clean up the cities never quite amassed enough support to overcome the barriers of remote indifference.

Like other chroniclers of urban blight before him, Riis had experimented with illustrations that dramatized the devastating human cost of the tenements. But the line drawings invariably aestheticized the suffering; even the bleakest underground hovel looked almost quaint as an etching. Only photographs seemed to capture the reality with sufficient resolution to change hearts, but whenever Riis experimented with photography, he ran into the same impasse. Almost everything he wanted to photograph involved environments with minimal amounts of light. Indeed, the lack of even indirect sunlight in so many of the tenement flats was part of what made them so objectionable. This was Riis’s great stumbling block: as far as photography was concerned, the most important environments in the city—in fact, some of the most important new living quarters in the world—were literally invisible. They couldn’t be seen.

All of which should explain Jacob Riis’s epiphany at the breakfast table in 1887. Why trifle with line drawings when Blitzlicht could shine light in the darkness?

Within two weeks of that breakfast discovery, Riis assembled a team of amateur photographers (and a few curious police officers) to set off into the bowels of the darkened city—literally armed with Blitzlicht. (The flash is produced by firing a cartridge of the substance from a revolver.) More than a few denizens of Five Points found the shooting party hard to comprehend. As Riis would later put it: “The spectacle of half a dozen strange men invading a house in the midnight hour armed with big pistols which they shot off recklessly was hardly reassuring, however sugary our speech, and it was not to be wondered at if the tenants bolted through windows and down fire-escapes wherever we went.”

Before long, Riis replaced the revolver with a frying pan. The apparatus seemed more “home-like,” he claimed, and made his subjects feel more comfortable encountering the baffling new technology. (The simple act of being photographed was novelty enough for most of them.) It was still dangerous work; one small explosion in the frying pan nearly blinded Riis, and twice he set fire to his house while experimenting with the flash. But the images that emerged from those urban expeditions would ultimately change history. Using new halftone printing techniques, Riis published the photographs in his runaway bestseller, How the Other Half Lives, and traveled across the country giving lectures that were accompanied by magic-lantern images of Five Points and its previously invisible poverty. The convention of gathering together in a darkened room and watching illuminated images on a screen would become a ritual of fantasy and wish fulfillment in the twentieth century. But for many Americans, the first images they saw in those environments were ones of squalor and human suffering.

Riis’s books and lectures—and the riveting images they contained—helped create a massive shift in public opinion, and set the stage for one of the great periods of social reform in American history. Within a decade of their publication, Riis’s images built support for the New York State Tenement House Act of 1901, one of the first great reforms of the Progressive Era, which eliminated much of the appalling living conditions that Riis had documented. His work ignited a new tradition of muckraking that would ultimately improve the working conditions of factory floors as well. In a literal sense, illuminating the dark squalor of the tenements changed the map of urban centers around the world.

New York City: A shelter for immigrants in a Bayard Street tenement. Photo taken by Jacob Riis, 1888.

Here again we see the strange leaps of the hummingbird’s wing at play in social history, new inventions leading to consequences their creators never dreamed of. The utility of mixing magnesium and potassium chlorate seems straightforward enough: Blitzlicht meant that human beings could record images in dark environments more accurately than ever before. But that new capability also expanded the space of possibility for other ways of seeing. This is what Riis understood almost immediately. If you could see in the dark, if you could share that vision with strangers around the world thanks to the magic of photography, then the underworld of Five Points could, at long last, be seen in all its tragic reality. The dry, statistical accounts of “The Report of the Council of Hygiene and Public Health” would be replaced with actual human beings sharing physical space of devastating squalor.

The network of minds that invented flash photography—from the first tinkerers with limelight to Smyth to Miethe and Gaedicke—had deliberately set out with a clearly defined goal: to build a tool that would allow photographs to be taken in darkness. But like almost every important innovation in human history, that breakthrough created a platform that allowed other innovations in radically different fields. We like to organize the world into neat categories: photography goes here, politics there. But the history of Blitzlicht reminds us that ideas always travel in networks. They come into being through networks of collaboration, and once unleashed on the world, they set into motion changes that are rarely confined to single disciplines. One century’s attempt to invent flash photography transformed the lives of millions of city dwellers in the next century.

Riis’s vision should also serve as a corrective to the excesses of crude techno-determinism. It was virtually inevitable that someone would invent flash photography in the nineteenth century. (The simple fact that it was invented multiple times shows us that the time was ripe for the idea.) But there was nothing intrinsic to the technology that suggested it be used to illuminate the lives of the very people who could least afford to enjoy it. You could have reasonably predicted that the problem of photographing in low light would be “solved” be 1900. But no one would have predicted that its very first mainstream use would come in the form of a crusade against urban poverty. That twist belongs to Riis alone. The march of technology expands the space of possibility around us, but how we explore that space is up to us.

—

IN THE FALL OF 1968, the sixteen members of a graduate studio at the Yale School of Art and Architecture—three faculty and thirteen students—set off on a ten-day expedition to study urban design in the streets of an actual city. This in itself was nothing new: architecture students had been touring the ruins and the monuments of Rome or Paris or Brasília for as long as there have been architecture students. What made this group unusual is that they were leaving behind the Gothic charm of New Haven for a very different kind of city, one that happened to be growing faster than any of the old relics: Las Vegas. It was a city that looked nothing like the dense, concentrated tenements of Riis’s Manhattan. But like Riis, the Yale studio sensed that something new and significant was happening on the Vegas strip. Led by Robert Venturi and Denise Scott Brown, the husband-and-wife team who would become founders of postmodern architecture, the Yale studio had been drawn to the desert frontier by the novelty of Vegas, by the shock value they could elicit by taking it seriously, and by the sense that they were watching the future being born. But as much as anything, they had come to Vegas to see a new kind of light. They were drawn, postmodern moths to the flame, to neon.

1960s night scene in downtown Las Vegas, Nevada

While neon is technically considered one of the “rare gases,” it is actually ubiquitous in the earth’s atmosphere, just in very small quantities. Each time you take a breath, you are inhaling a tiny amount of neon, mixed in with all the nitrogen and oxygen that saturate breathable air. In the first years of the twentieth century, a French scientist named Georges Claude created a system for liquefying air, which enabled the production of large quantities of liquid nitrogen and oxygen. Processing these elements at industrial scale created an intriguing waste product: neon. Even though neon appears as only one part per 66,000 in ordinary air, Claude’s apparatus could produce one hundred liters of neon in a day’s work.

With so much neon lying around, Claude decided to see if it was good for anything, and so in proper mad-scientist fashion, he isolated the gas and passed an electrical current through it. Exposed to an electric charge, the gas glowed a vivid shade of red. (The technical term for this process is ionization.) Further experiments revealed that other rare gases such as argon and mercury vapor would produce different colors when electrified, and they were more than five times brighter than conventional incandescent light. Claude quickly patented his neon lights, and set up a display showcasing the invention in front of the Grand Palais in Paris. When demand surged for his product, he established a franchise business for his innovation, not unlike the model employed by McDonald’s and Kentucky Fried Chicken years later, and neon lights began to spread across the urban landscapes of Europe and the United States.

In the early 1920s, the electric glow of neon found its way to Tom Young, a British immigrant living in Utah who had started a small business hand-lettering signs. Young recognized that neon could be used for more than just colored light; with the gas enclosed in glass tubes, neon signs could spell out words much more easily than collections of lightbulbs. Licensing Claude’s invention, he set up a new business covering the American Southwest. Young realized that the soon-to-be-completed Hoover Dam would bring a vast new source of electricity to the desert, providing a current that could ionize an entire city of neon lights. He formed a new venture, the Young Electric Sign Company, or YESCO. Before long, he found himself building a sign for a new casino and hotel, The Boulders, that was opening in an obscure Nevada town named Las Vegas.

It was a chance collision—a new technology from France finding its way to a sign letterer in Utah—that would create one of the most iconic of twentieth-century urban experiences. Neon advertisements would become a defining feature of big-city centers around the world—think Times Square or Tokyo’s Shibuya Crossing. But no city embraced neon with the same unchecked enthusiasm that Las Vegas did, and most of those neon extravaganzas were designed, erected, and maintained by YESCO. “Las Vegas is the only city in the world whose skyline is made not of buildings . . . but signs,” Tom Wolfe wrote in the middle of the 1960s. “One can look at Las Vegas from a mile away on route 91 and see no buildings, no trees, only signs. But such signs! They tower. They revolve, they oscillate, they soar in shapes before which the existing vocabulary of art history is helpless.”

It was precisely that helplessness that brought Venturi and Brown to Vegas with their retinue of architecture students in the fall of 1968. Brown and Venturi had sensed that there was a new visual language emerging in that glittering desert oasis, one that didn’t fit well with the existing languages of modernist design. To begin with, Vegas had oriented itself around the vantage point of the automobile driver, cruising down Fremont Street or the strip: shop windows and sidewalk displays had given way to sixty-foot neon cowboys. The geometric seriousness of the Seagram Building or Brasília had given way to a playful anarchy: the Wild West of the gold rush thrust up against Olde English feudal designs, sitting next to cartoon arabesques, fronted by an endless stream of wedding chapels. “Allusion and comment, on the past or present or on our great commonplaces or old clichés, and inclusion of the everyday in the environment, sacred and profane—these are what are lacking in present-day Modern architecture,” Brown and Venturi wrote. “We can learn about them from Las Vegas as have other artists from their own profane and stylistic sources.”

That language of allusion and comment and cliché was written in neon. Brown and Venturi went so far as to map every single illuminated word visible on Fremont Street. “In the seventeenth century,” they wrote, “Rubens created a painting ‘factory’ wherein different workers specialized in drapery, foliage, or nudes. In Las Vegas, there is just such a sign ‘factory,’ the Young Electric Sign Company.” Until then, the symbolic frenzy of Vegas had belonged purely to the world of lowbrow commerce: garish signs pointing the way to gambling dens, or worse. But Brown and Venturi had seen something more interesting in all that detritus. As Georges Claude had experienced more than sixty years before, one person’s waste is another one’s treasure.

Think about these different strands: the atoms of a rare gas, unnoticed until 1898; a scientist and engineer tinkering with the waste product from his “liquid air”; an enterprising sign designer; and a city blooming implausibly in the desert. All these strands somehow converged to make Learning from Las Vegas—a book that architects and urban planners would study and debate for decades—even imaginable as an argument. No other book had as much influence on the postmodern style that would dominate art and architecture over the next two decades.

Learning from Las Vegas gives us a clear case study in how the long-zoom approach reveals elements that are ignored by history’s traditional explanatory frameworks: economic or art history, or the “lone genius” model of innovation. When you ask the question of why postmodernism came about as a movement, on some fundamental level the answer has to include Georges Claude and his hundred liters of neon. Claude’s innovation wasn’t the only cause, by any means, but, in an alternate universe somehow stripped of neon lights, the emergence of postmodern architecture would have in all likelihood followed a different path. The strange interaction between neon gas and electricity, the franchise model of licensing new technology—each served as part of the support structure that made it even possible to conceive of Learning from Las Vegas.

This might seem like yet another game of Six Degrees of Kevin Bacon: follow enough chains of causality and you can link postmodernism back to the building of the Great Wall of China or the extinction of the dinosaurs. But the neon-to-postmodernism connections are direct links: Claude creates neon light; Young brings it to Vegas, where Venturi and Brown decide to take its “revolving and oscillating” glow seriously for the first time. Yes, Venturi and Brown needed electricity, too, but just about everything needed electricity in the 1960s: the moon landing, the Velvet Underground, the “I Have a Dream” speech. By the same token, Venturi and Brown required the noble gases, too; the odds are pretty good that they needed oxygen to write Learning from Las Vegas. But it was the rare gas of neon that made their story unique.

—

IDEAS TRICKLE OUT OF SCIENCE, into the flow of commerce, where they drift into the less predictable eddies of art and philosophy. But sometimes they venture upstream: from aesthetic speculation into hard science. When H. G. Wells published his groundbreaking novel The War of the Worlds in 1898, he helped invent the genre of science fiction that would play such a prominent role in the popular imagination during the century that followed. But that book introduced a more specific item to the fledging sci-fi canon: the “heat ray,” used by the invading Martians to destroy entire towns. “In some way,” Wells wrote of his technologically savvy aliens, “they are able to generate an intense heat in a chamber of practically absolute non-conductivity. This intense heat they project in a parallel beam against any object they choose, by means of a polished parabolic mirror of unknown composition, much as the parabolic mirror of a lighthouse projects a beam of light.”

The heat ray was one of those imagined concoctions that somehow get locked into the popular psyche. From Flash Gordon to Star Trek to Star Wars, weapons using concentrated beams of light became almost de rigueur in any sufficiently advanced future civilization. And yet, actual laser beams did not exist until the late 1950s, and didn’t become part of everyday life for another two decades after that. Not for the last time, the science-fiction authors were a step or two ahead of the scientists.

But the sci-fi crowd got one thing wrong, at least in the short term. There are no death rays, and the closest thing we have to Flash Gordon’s arsenal is laser tag. When lasers did finally enter our lives, they turned out to be lousy for weapons, but brilliant for something the sci-fi authors never imagined: figuring out the cost of a stick of chewing gum.

Like the lightbulb, the laser was not a single invention; instead, as the technology historian Jon Gertner puts it, “it was the result of a storm of inventions during the 1960s.” Its roots lie in research at Bell Labs and Hughes Aircraft and, most entertainingly, in the independent tinkering of physicist Gordon Gould, who memorably notarized his original design for the laser in a Manhattan candy store, and who went on to have a thirty-year legal battle over the laser patent (a battle he eventually won). A laser is a prodigiously concentrated beam, light’s normal chaos reduced down to a single, ordered frequency. “The laser is to ordinary light,” Bell Lab’s John Pierce once remarked, “as a broadcast signal is to static.”

Unlike the lightbulb, however, the early interest in the laser was not motivated by a clear vision of a consumer product. Researchers knew that the concentrated signal of the laser could be used to embed information more efficiently than could existing electrical wiring, but exactly how that bandwidth would be put to use was less evident. “When something as closely related to signaling and communication as this comes along,” Pierce explained at the time, “and something is new and little understood, and you have the people who can do something about it, you’d just better do it, and worry later just about the details of why you went into it.” Eventually, as we have already seen, laser technology would prove crucial to digital communications, thanks to its role in fiber optics. But the laser’s first critical application would appear at the checkout counter, with the emergence of bar-code scanners in the mid-1970s.

The idea of creating some kind of machine-readable code to identify products and prices had been floating around for nearly half a century. Inspired by the dashes and dots of Morse code, an inventor named Norman Joseph Woodland designed a visual code that resembled a bull’s-eye in the 1950s, but it required a five-hundred-watt bulb—almost ten times brighter than your average lightbulb—to read the code, and even then it wasn’t very accurate. Scanning a series of black-and-white symbols turned out to be the kind of job that lasers immediately excelled at, even in their infancy. By the early 1970s, just a few years after the first working lasers debuted, the modern system of bar codes—known as the Universal Product Code—emerged as the dominant standard. On June 26, 1974, a stick of chewing gum in a supermarket in Ohio became the first product in history to have its bar code scanned by a laser. The technology spread slowly: only one percent of stores had bar-code scanners as late as 1978. But today, almost everything you can buy has a bar code on it.

In 2012, an economics professor named Emek Basker published a paper that assessed the impact of bar-code scanning on the economy, documenting the spread of the technology through both mom-and-pop stores and big chains. Basker’s data confirmed the classic trade-offs of early adoption: most stores that integrated bar-code scanners in the early years didn’t see much benefit from them, since employees had to be trained to use the new technology, and many products didn’t have bar codes yet. Over time, however, the productivity gains became substantial, as bar codes became ubiquitous. But the most striking discovery in Basker’s research was this: The productivity gains from bar-code scanners were not evenly distributed. Big stores did much better than small stores.

There have always been inherent advantages to maintaining a large inventory of items in a store: the customer has more options to choose from, and items can be purchased in bulk from wholesalers for less money. But in the days before bar codes and other forms of computerized inventory-management tools, the benefits of housing a vast inventory were largely offset by the costs of keeping track of everything. If you kept a thousand items in stock instead of a hundred, you needed more people and time to figure out which sought-after items needed restocking and which were just sitting on the shelves taking up space. But bar codes and scanners greatly reduced the costs of maintaining a large inventory. The decades after the introduction of the bar-code scanner in the United States witnessed an explosion in the size of retail stores; with automated inventory management, chains were free to balloon into the epic big-box stores that now dominate retail shopping. Without bar-code scanning, the modern shopping landscape of Target and Best Buy and supermarkets the size of airport terminals would have had a much harder time coming into being. If there was a death ray in the history of the laser, it was the metaphoric one directed at the mom-and-pop, indie stores demolished by the big-box revolution.

—

WHILE THE EARLY SCI-FI FANS of War of the Worlds and Flash Gordon would be disappointed to see the mighty laser scanning packets of chewing gum—its brilliantly concentrated light harnessed for inventory management—their spirits would likely improve contemplating the National Ignition Facility, at the Lawrence Livermore Labs in Northern California, where scientists have built the world’s largest and highest-energy laser system. Artificial light began as simple illumination, helping us read and entertain ourselves after dark; before long it had been transformed into advertising and art and information. But at NIF, they are taking light full circle, using lasers to create a new source of energy based on nuclear fusion, re-creating the process that occurs naturally in the dense core of the sun, our original source of natural light.

Deep inside the NIF, near the “target chamber,” where the fusion takes place, a long hallway is decorated with what appears, at first glance, to be a series of identical Rothko paintings, each displaying eight large red squares the size of a dinner plate. There are 192 of them in total, each representing one of the lasers that simultaneously fire on a tiny bead of hydrogen in the ignition chamber. We are used to seeing lasers as a pinpoint of concentrated light, but at NIF, the lasers are more like cannonballs, almost two hundred of them summed together to create a beam of energy that would have made H. G. Wells proud.

The multibillion-dollar complex has all been engineered to execute discrete, microsecond-long events: firing the lasers at the hydrogen fuel while hundreds of sensors and high-speed cameras observe the activity. Inside the NIF, they refer to these events as “shots.” Each shot requires the meticulous orchestration of more than six hundred thousand controls. Each laser beam travels 1.5 kilometers guided by a series of lenses and mirrors, and combined they build in power until they reach 1.8 million joules of energy and five-hundred-trillion watts, all converging on a fuel source the size of a peppercorn. The lasers have to be positioned with a breathtaking accuracy, the equivalent of standing on the pitcher’s mound at AT&T Park in San Francisco and throwing a strike at Dodger Stadium in Los Angeles, some 350 miles away. Each microsecond pulse of light has, for its brief existence, a thousand times the amount of energy in America’s entire national grid.

When all of NIF’s energy slams into its millimeter-sized targets, unprecedented conditions are generated in the target materials—temperatures of more than a hundred million degrees, densities up to a hundred times the density of lead, and pressures more than a hundred billion times Earth’s atmospheric pressure. These conditions are similar to those inside stars, the cores of giant planets, and nuclear weapons—allowing NIF to create, in essence, a miniature star on Earth, fusing hydrogen atoms together and releasing a staggering amount of energy. For that fleeting moment, as the lasers compress the hydrogen, that fuel pellet is the hottest place in the solar system—hotter, even, than the core of the sun.

The goal of the NIF is not to create a death ray—or the ultimate bar-code scanner. The goal is to create a sustainable source of clean energy. In 2013, NIF announced that the device had for the first time generated net positive energy during several of its shots; by a slender margin, the fusion process required less energy than it created. It is still not enough to reproduce efficiently on a mass scale, but NIF scientists believe that with enough experimentation, they will eventually be able to use their lasers to compress the fuel pellet with almost perfect symmetry. At that point, we would have a potentially limitless source of energy to power all the lightbulbs and neon signs and bar-code scanners—not to mention computers and air-conditioners and electric cars—that modern life depends on.

Vaughn Draggoo inspects a huge target chamber at the National Ignition Facility in California, a future test site for light-induced nuclear fusion. Beams from 192 lasers will be aimed at a pellet of fusion fuel to produce a controlled thermonuclear blast (2001).

Those 192 lasers converging on the hydrogen pellet are a telling reminder of how far we have come in a remarkably short amount of time. Just two hundred years ago, the most advanced form of artificial light involved cutting up a whale on the deck of a boat in the middle of the ocean. Today we can use light to create an artificial sun on Earth, if only for a split-second. No one knows if the NIF scientists will reach their goal of a clean, sustainable fusion-based energy source. Some might even see it as a fool’s errand, a glorified laser show that will never return more energy than it takes in. But setting off for a three-year voyage into the middle of the Pacific Ocean in search of eighty-foot sea mammals was every bit as crazy, and somehow that quest fueled our appetite for light for a century. Perhaps the visionaries at NIF—or another team of muckers somewhere in the world—will eventually do the same. One way or another, we are still chasing new light.

Conclusion

The Time Travelers

n July 8, 1835, an English baron by the name of William King was married in a small ceremony in the western suburbs of London, at an estate called Fordhook that had once belonged to the novelist Henry Fielding. By all accounts it was a pleasant wedding, though it was a much smaller affair than one might have expected given King’s title and family wealth. The intimacy of the wedding was due to the general public’s fascination with his nineteen-year-old bride, the beautiful and brilliant Augusta Byron, now commonly known by her middle name of Ada, daughter of the notorious Romantic poet Lord Byron. Byron had been dead for a decade, and had not seen his daughter since she was an infant, but his reputation for creative brilliance and moral dissolution continued to reverberate through European culture. There were no paparazzi to hound Baron King and his bride in 1835, but Ada’s fame meant that a certain measure of discretion was required at her wedding.

After a short honeymoon, Ada and her new husband began dividing their time between his family estate in Ockham, another estate in Somerset, and a London home, beginning what promised to be a life of domestic leisure, albeit challenged by the enviable difficulties of maintaining three residences. By 1840, the couple had produced three children, and King had been elevated to earldom with Queen Victoria’s coronation list.

By the conventional standards of Victorian society, Ada’s life would have seemed any woman’s dream: nobility, a loving husband, and three children, including the all-important male heir. But as she settled into the duties of motherhood and of running a landed estate, she found herself fraying at the edges, drawn to paths that were effectively unheard-of for Victorian women. In the 1840s, it was not outside the bounds of possibility for a woman to be engaged in the creative arts in some fashion, and even to dabble in writing her own fiction or essays. But Ada’s mind was drawn in another direction. She had a passion for numbers.

When Ada was a teenager, her mother, Annabella Byron, had encouraged her study of mathematics, hiring a series of tutors to instruct her in algebra and trigonometry, a radical course of study in an age when women were excluded from important scientific institutions such as the Royal Society, and were assumed to be incapable of rigorous scientific thinking. But Annabella had an ulterior motive in encouraging her daughter’s math skills, hoping that the methodical and practical nature of her studies would override the dangerous influence of her dead father. A world of numbers, Annabella hoped, would save her daughter from the debauchery of art.

Augusta Ada, Countess Lovelace, circa 1840

For a time, it appeared that Annabella’s plan had worked. Ada’s husband had been made Earl of Lovelace, and as a family they seemed on a path to avoid the chaos and unconventionality that had destroyed Lord Byron fifteen years before. But as her third child grew out of infancy, Ada found herself drawn back to the world of math, feeling unfulfilled by the domestic responsibilities of Victorian motherhood. Her letters from the period display a strange mix of Romantic ambition—the sense of a soul larger than the ordinary reality it has found itself trapped in—combined with an intense belief in the power of mathematical reason. Ada wrote about differential calculus with the same passion and exuberance (and self-confidence) that her father wrote about forbidden love:

Owing to some peculiarity in my nervous system, I have perceptions of some things, which no one else has . . . an intuitive perception of hidden things;—that is of things hidden away from eyes, ears, and the ordinary senses. This alone would advantage me little, in the discovery line, but there is, secondly, my immense reasoning faculties, and my concentrative faculty.

In the late months of 1841, Ada’s conflicted feelings about her domestic life and her mathematical ambitions came to a crisis point, when she learned from Annabella that, in the years before his death, Lord Byron had conceived a daughter with his half sister. Ada’s father was not only the most notorious author of his time; he was also guilty of incest, and the offspring of this scandalous union was a girl Ada had known for many years. Annabella had volunteered the news to her daughter as definitive proof that Byron was a wretch, and that such a rebellious, unconventional lifestyle could only end in ruin.

And so, at the still young age of twenty-five, Ada Lovelace found herself at a crossroads, confronting two very different ways of being an adult in the world. She could resign herself to the settled path of a baroness and live within the boundaries of conventional decorum. Or she could embrace those “peculiarities of [her] nervous system” and seek out some original path for herself and her distinctive gifts.

It was a choice that was deeply situated in the culture of Ada’s time: the assumptions that framed and delimited the roles women could adopt, the inherited wealth that gave her the option of choosing in the first place, and the leisure time to mull over the decision. But the paths in front of her were also carved out by her genes, by the talents and dispositions—even the mania—Ada had inherited from her parents. In choosing between domestic stability and some unknown break from convention, she was, in a sense, choosing between her mother and her father. To stay settled at Ockham Park was the easier path; all the forces of society propelled her toward it. And yet, like it or not, she was still Byron’s daughter. A conventional life seemed increasingly unthinkable.

But Ada Lovelace found a way around the impasse she had confronted in her mid-twenties. In collaboration with another brilliant Victorian who was equally ahead of his time, Ada charted a path that allowed her to push the barriers of Victorian society without succumbing to the creative chaos that had enveloped her father. She became a software programmer.

—

WRITING CODE IN THE MIDDLE of the nineteenth century may seem like a vocation that would be possible only with time travel, but as chance would have it, Ada had met the one Victorian who was capable of giving her such a project: Charles Babbage, the brilliant and eclectic inventor who was in the middle of drafting plans for his visionary Analytical Engine. Babbage had spent the previous two decades concocting state-of-the-art calculators, but since the mid-1830s, he had commenced work on a project that would last the rest of his life: designing a truly programmable computer, capable of executing complex sequences of calculations that went far beyond the capabilities of any contemporary machines. Babbage’s Analytical Engine was doomed to a certain practical failure—he was trying to build a digital-age computer with industrial-age mechanical parts—but conceptually it was a brilliant leap forward. Babbage’s design anticipated all the major components of modern computers: the notion of a central processing unit (which Babbage dubbed “the mill”), of random-access memory, and of software that would control the machine, etched on the very same punch cards that would be used to program computers more than a century later.

Ada had met Babbage at the age of seventeen, in one of his celebrated London salons, and the two had kept up a friendly and intellectually lively correspondence over the years. And so when she hit her crossroads in the early 1840s, she wrote a letter to Babbage that suggested he might prove to be a potential escape route from the limitations of life at Ockham Park:

I am very anxious to talk to you. I will give you a hint on what. It strikes me that at some future time, my head may be made by you subservient to some of your purposes & plans. If so, if ever I could be worth or capable of being used by you, my head will be yours.

Babbage, as it turned out, did have a use for Ada’s remarkable head, and their collaboration would lead to one of the founding documents in the history of computing. An Italian engineer had written an essay on Babbage’s machine, and at the recommendation of a friend, Ada translated the text into English. When she told Babbage of her work, he asked why she hadn’t written her own essay on the subject. Despite all her ambition, the thought of composing her own analysis had apparently never occurred to Ada, and so at Babbage’s encouragement, she concocted her own aphoristic commentary, stitched together out of a series of extended footnotes attached to the Italian paper.

Charles Babbage

Those footnotes would ultimately prove to be far more valuable and influential than the original text they annotated. They contained a series of elemental instruction sets that could be used to direct the calculations of the Analytical Engine. These are now considered to be the first examples of working software ever published, though the machinery that could actually run the code wouldn’t be built for another century.

Babbage’s Analytical Engine

There is some dispute over whether Ada was the sole author of these programs, or whether she was refining routines that Babbage himself had worked out previously. But Ada’s greatest contribution lay not in writing out instruction sets, but rather in envisioning a range of utility for the machine that Babbage himself had not considered. “Many persons,” she wrote, “imagine that because the business of the engine is to give its results in numerical notation the nature of its processes must consequently be arithmetical and numerical, rather than algebraical and analytical. This is an error. The engine can arrange and combine its numerical quantities exactly as if they were letters or any other general symbols.” Ada recognized that Babbage’s machine was not a mere number cruncher. Its potential uses went far beyond rote calculation. It might even someday be capable of the higher arts:

Supposing, for instance, that the fundamental relations of pitched sounds in the science of harmony and musical composition were susceptible of such expressions and adaptations, the Engine might compose elaborate and scientific pieces of music of any degree of complexity or extent.

To have this imaginative leap in the middle of the nineteenth century is almost beyond comprehension. It was hard enough to wrap one’s mind around the idea of programmable computers—almost all of Babbage’s contemporaries failed to grasp what he had invented—but somehow, Ada was able to take the concept one step further, to the idea that this machine might also conjure up language and art. That one footnote opened up a conceptual space that would eventually be occupied by so much of early twenty-first-century culture: Google queries, electronic music, iTunes, hypertext. The computer would not just be an unusually flexible calculator; it would be an expressive, representational, even aesthetic machine.

Of course, Babbage’s idea and Lovelace’s footnote proved to be so far ahead of their time that, for a long while, they were lost to history. Most of Babbage’s core insights had to be independently rediscovered a hundred years later, when the first working computers were built in the 1940s, running on electricity and vacuum tubes instead of steam power. The notion of computers as aesthetic tools, capable of producing culture as well as calculation, didn’t become widespread—even in high-tech hubs such as Boston or Silicon Valley—until the 1970s.

Most important innovations—in modern times at least—arrive in clusters of simultaneous discovery. The conceptual and technological pieces come together to make a certain idea imaginable—artificial refrigeration, say, or the lightbulb—and all around the world, you suddenly see people working on the problem, and usually approaching it with the same fundamental assumptions about how that problem is ultimately going to be solved. Edison and his peers may have disagreed about the importance of the vacuum or the carbon filament in inventing the electric lightbulb, but none of them were working on an LED. The predominance of simultaneous, multiple invention in the historical record has interesting implications for the philosophy of history and science: To what extent is the sequence of invention set in stone by the basic laws of physics or information or the biological and chemical constraints of the earth’s environment? We take it for granted that microwaves have to be invented after the mastery of fire, but how inevitable is it that, say, telescopes and microscopes quickly followed the invention of spectacles? (Could one imagine, for instance, spectacles being widely adopted, but then a pause of five hundred years before someone thinks of rejiggering them into a telescope? It seems unlikely, but I suppose it’s not impossible.) The fact that these simultaneous-invention clusters are so pronounced in the fossil record of technology tells us, at the very least, that some confluence of historical events has made a new technology imaginable in a way that it wasn’t before.

What those events happen to be is a murkier but fascinating question. I have tried to sketch a few answers here. Lenses, for instance, emerged out of several distinct developments: glassmaking expertise, particularly as cultivated on Murano; the adoption of glass “orbs” that helped monks read their scrolls later in life; the invention of the printing press, which created a surge in demand for spectacles. (And, of course, the basic physical properties of silicon dioxide itself.) We can’t know for certain the full extent of these influences, and no doubt some influences are too subtle for us to detect after so many years, like starlight from remote suns. But the question is nonetheless worth exploring, even if we are resigned to somewhat speculative answers, the same way we are when we try to wrestle with the causes behind the American Civil War or the droughts of the Dust Bowl era. They’re worth exploring because we are living through comparable revolutions today, set by the boundaries and opportunities of our own adjacent possible. Learning from the patterns of innovation that shaped society in the past can only help us navigate the future more successfully, even if our explanations of that past are not falsifiable in quite the same way that a scientific theory is.

—

BUT IF SIMULTANEOUS INVENTION is the rule, what about the exceptions? What about Babbage and Lovelace, who were effectively a century ahead of just about every other human being on the planet? Most innovation happens in the present tense of the adjacent possible, working with the tools and concepts that are available in that time. But every now and then, some individual or group makes a leap that seems almost like time traveling. How do they do it? What allows them to see past the boundaries of the adjacent possible when their contemporaries fail to do so? That may be the greatest mystery of all.

The conventional explanation is the all-purpose but somewhat circular category of “genius.” Da Vinci could imagine (and draw) helicopters in the fifteenth century because he was a genius; Babbage and Lovelace could imagine programmable computers in the nineteenth century because they were geniuses. No doubt all three were blessed with great intellectual gifts, but history is replete with high-IQ individuals who don’t manage to come up with inventions that are decades or centuries ahead of their time. Some of that time-traveling genius no doubt came from their raw intellectual skills, but I suspect just as much came out of the environment their ideas evolved in, the network of interests and influence that shaped their thinking.

If there is a common thread to the time travelers, beyond the nonexplanation of genius, it is this: they worked at the margins of their official fields, or at the intersection point between very different disciplines. Think of Édouard-Léon Scott de Martinville inventing his sound-recording device a generation before Edison began working on the phonograph. Scott was able to imagine the idea of “writing” sound waves because he had borrowed metaphors from stenography and printing and anatomical studies of the human ear. Ada Lovelace could see the aesthetic possibilities of Babbage’s Analytical Engine because her life had been lived at a unique collision point between advanced math and Romantic poetry. The “peculiarities” of her “nervous system”—that Romantic instinct to see beyond the surface appearances of things—allowed her to imagine a machine capable of manipulating symbols or composing music, in a way that even Babbage himself had failed to do.

To a certain extent, the time travelers remind us that working within an established field is both empowering and restricting at the same time. Stay within the boundaries of your discipline, and you will have an easier time making incremental improvements, opening the doors of the adjacent possible that are directly available to you given the specifics of the historical moment. (There’s nothing wrong with that, of course. Progress depends on incremental improvements.) But those disciplinary boundaries can also serve as blinders, keeping you from the bigger idea that becomes visible only when you cross those borders. Sometimes those borders are literal, geographic ones: Frederic Tudor traveling to the Caribbean and dreaming of ice in the tropics; Clarence Birdseye ice fishing with the Inuits in Labrador. Sometimes the boundaries are conceptual: Scott borrowing the metaphors of stenography to invent the phonautograph. The time travelers tend, as a group, to have a lot of hobbies: think of Darwin and his orchids. When Darwin published his book on pollination four years after Origin of Species, he gave it the wonderfully Victorian title, On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing. We now understand the “good effects of intercrossing” thanks to the modern science of genetics, but the principle applies to intellectual history as well. The time travelers are unusually adept at “intercrossing” different fields of expertise. That’s the beauty of the hobbyist: it’s generally easier to mix different intellectual fields when you have a whole array of them littering your study or your garage.

One of the reasons garages have become such an emblem of the innovator’s workspace is precisely because they exist outside the traditional spaces of work or research. They are not office cubicles or university labs; they’re places away from work and school, places where our peripheral interests have the room to grow and evolve. Experts head off to their corner offices and lecture halls. The garage is the space for the hacker, the tinkerer, the maker. The garage is not defined by a single field or industry; instead, it is defined by the eclectic interests of its inhabitants. It is a space where intellectual networks converge.

In his famous Stanford commencement speech, Steve Jobs—the great garage innovator of our time—told several stories about the creative power of stumbling into new experiences: dropping out of college and sitting in on a calligraphy class that would ultimately shape the graphic interface of the Macintosh; being forced out of Apple at the age of thirty, which enabled him to launch Pixar into animated movies and create the NeXT computer. “The heaviness of being successful,” Jobs explained, “was replaced by the lightness of being a beginner again, less sure about everything. It freed me to enter one of the most creative periods of my life.”

Yet there is a strange irony at the end of Jobs’s speech. After documenting the ways that unlikely collisions and explorations can liberate the mind, he ended with a more sentimental appeal to be “true to yourself”:

Don’t be trapped by dogma—which is living with the results of other people’s thinking. Don’t let the noise of others’ opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition.

If there’s anything we know from the history of innovation—and particularly from the history of the time travelers—it is that being true to yourself is not enough. Certainly, you don’t want to be trapped by orthodoxy and conventional wisdom. Certainly, the innovators profiled in this book had the tenacity to stick with their hunches for long periods of time. But there is comparable risk in being true to your own sense of identity, your own roots. Better to challenge those intuitions, explore uncharted terrain, both literal and figurative. Better to make new connections than remain comfortably situated in the same routine. If you want to improve the world slightly, you need focus and determination; you need to stay within the confines of a field and open the new doors in the adjacent possible one at a time. But if you want to be like Ada, if you want to have an “intuitive perception of hidden things”—well, in that case, you need to get a little lost.

Acknowledgments

here is a predictable social rhythm to writing books, in my experience at least: they begin very close to solitude, the writer alone with his or her ideas, and they stay in that intimate space for months, sometimes years, interrupted only by the occasional interview or conversation with an editor. And then, as publication nears, the circle widens: suddenly a dozen people are reading and helping usher a rough, unformed manuscript into life as a polished final product. And then the book hits the shelves, and all that work becomes almost terrifyingly public, with thousands of bookstore employees, reviewers, radio interviewers, and readers interacting with words that began their life in such a private embrace. And then the whole cycle starts all over again.

But this book followed a completely different pattern. It was a social, collaborative process from the very beginning, thanks to the simultaneous development of our PBS/BBC television series. The stories and observations—not to mention the overarching structure of the book—evolved out of hundreds of conversations: in California and London and New York and Washington, via e-mail and Skype, with dozens of people. Making the series and book was the hardest work I have ever done in my life—and not just when they forced me to descend into the sewers of San Francisco. But it was also the most rewarding work I’ve ever done, in large part because my collaborators were such inventive and entertaining people. This book has benefited from their intelligence and support in a thousand different ways.

My gratitude begins with the irrepressible Jane Root, who persuaded me to try my hand at television, and remained a tireless champion of this project throughout its life. (Thanks to Michael Jackson for introducing us so many years ago.) As producers, Peter Lovering, Phil Craig, and Diene Petterle shaped the ideas and narratives in this book with great skill and creativity, as did the directors Julian Jones, Paul Olding, and Nic Stacey. A project this complex, with so many potential narrative threads, would have been almost impossible to complete without the help of our researchers and story producers, Jemila Twinch, Simon Willgoss, Rowan Greenaway, Robert MacAndrew, Gemma Hagen, Jack Chapman, Jez Bradshaw, and Miriam Reeves. I’d also like to thank Helena Tait, Kirsty Urquhart-Davies, Jenny Wolf, and the rest of the team at Nutopia. (Not to mention the brilliant illustrators at Peepshow Collective.) At PBS I’m indebted to the extraordinary vote of confidence from Beth Hoppe and Bill Gardner, as well as from Jennifer Lawson at CPB, Dave Davis from OPB, and Martin Davidson at the BBC.

A book that covers so many different fields can only succeed by drawing on the expertise of others. I’m grateful to the many talented people we interviewed for this project, some of whom were kind enough to read portions of the manuscript in draft: Terri Adams, Katherine Ashenburg, Rosa Barovier, Stewart Brand, Jason Brown, Dr. Ray Briggs, Stan Bunger, Kevin Connor, Gene Chruszcs, John DeGenova, Jason Deichler, Jacques Desbois, Dr. Mike Dunne, Caterina Fake, Kevin Fitzpatrick, Gai Gherardi, David Giovannoni, Peggi Godwin, Thomas Goetz, Alvin Hall, Grant Hill, Sharon Hudgens, Kevin Kelly, Craig Koslofsky, Alan MacFarlane, David Marshall, Demetrios Matsakis, Alexis McCrossen, Holley Muraco, Lyndon Murray, Bernard Nagengast, Max Nova, Mark Osterman, Blair Perkins, Lawrence Pettinelli, Dr. Rachel Rampy, Iegor Reznikoff, Eamon Ryan, Jennifer Ryan, Michael D. Ryan, Steven Ruzin, Davide Salvatore, Tom Scheffer, Eric B. Schultz, Emily Thompson, Jerri Thrasher, Bill Wasik, Jeff Young, Ed Yong, and Carl Zimmer.

At Riverhead, my editor and publisher Geoffrey Kloske’s usual astute sense of what the book needed editorially was accompanied by an artful vision of the book’s design that shaped the project from the very beginning. Thanks also to Casey Blue James, Hal Fessenden, and Kate Stark at Riverhead, and my UK publishers, Stefan McGrath and Josephine Greywoode. As always, thanks to my agent, Lydia Wills, for keeping faith in this project for almost half a decade.

Finally, my love and gratitude to my wife, Alexa, and my sons, Clay, Rowan, and Dean. Writing books for a living has generally meant that I spend more time with them, procrastinating by puttering around the house and chatting with Alexa, picking the kids up from school. But this project took me away from home more than it kept me there. So thanks to all four of you for tolerating my absences. Hopefully they made the heart grow fonder. I know they did mine.

Notes

Introduction

“We could imagine” . . . “system of cogs and wheels”: De Landa, p. 3.

“I have a friend who’s an artist”: From The Pleasure of Finding Things Out, a 1981 documentary.

Chapter 1. Glass

A small community of glassmakers from Turkey: Willach, p. 30.

In 1291, in an effort: Toso, p. 34.

After years of trial and error . . . Angelo Barovier: Verità, p. 63.

For several generations, these ingenious new devices: Dreyfus, pp. 93–106.

Within a hundred years of Gutenberg’s invention: http://faao.org/what/heritage/exhibits/online/spectacles/.

Legend has it that one of them: Pendergrast, p. 86.

“one of the worst teachers”: Quoted in Hecht, p. 30.

“If I had been promised”: Quoted ibid., p. 31.

Some of the most revered works of art: Woods-Marsden, p. 31.

Back in Murano, the glassmakers had figured out: Pendergrast, pp. 119–120.

“When you wish to see”: Quoted ibid., p. 138.

“It is as if all humans”: Macfarlane and Martin, p. 69.

“The most powerful prince in the world”: Mumford, p. 129.

“How from these ashes”: Quoted ibid., p. 131.

Chapter 2. Cold

“Ice is an interesting subject”: Thoreau, p. 192.

“Plan etc for transporting Ice to Tropical Climates”: Quoted in Weightman, loc. 274–276.

“In a country where at some seasons”: Quoted ibid., loc. 289–290.

“fortunes larger than we shall know what to do with”: Quoted ibid., loc. 330.

“No joke. A vessel”: Quoted ibid., loc. 462–463.

“On Monday the 9th instant”: Quoted ibid., loc. 684–688.

“This day I sailed from Boston”: Quoted ibid., loc. 1911–1913.

“Thus it appears that the sweltering inhabitants”: Thoreau, p. 193.

“In workshops, composing rooms, counting houses”: Quoted in Weightman, loc. 2620–2621.

“cooling rooms packed with natural ice”: Miller, p. 205.

“It was this application of elementary physics”: Ibid., p. 208.

“a city-country [food] system that was the most powerful”: Ibid.

“the greatest aggregation of labor”: Sinclair.

“a direct sloping path”: Dreiser, p. 620.

A string of shipwrecks delayed ice shipments: Wright, p. 12.

“might better serve mankind”: Quoted in Gladstone, p. 34.

By 1870, the southern states: Shachtman, p. 75.

Any meat or produce that had been frozen: Kurlansky, pp. 39–40.

“The inefficiency and lack of sanitation”: Quoted ibid., p. 129.

His first great test came: http://www.filmjournal.com/filmjournal/content_display/news-and-features/features/technology/e3iad1c03f082a43aa277a9bb65d3d561b5.

“It takes time to pull down”: Ingels, p. 67.

Swelling populations in Florida, Texas: Polsby, pp. 80–88.

Millions of human beings around the world: http://www.theguardian.com/society/2013/jul/12/story-ivf-five-million-babies.

Chapter 3. Sound

Reznikoff’s theory is that Neanderthal communities: http://www.musicandmeaning.net/issues/showArticle.php?artID=3.2.

In the annals of invention . . . Phonautograph: Klooster, p. 263.

Just a few years ago, a team of sound historians: http://www.firstsounds.org.

His name was Alexander Graham Bell: Mercer, pp. 31–32.

“It may sound ridiculous to say”: Quoted in Gleick 2012, loc. 3251–3257.

Eventually, the antitrust lawyers: Gertner, pp. 270–271.

Effectively, they were taking snapshots: http://www.nsa.gov/about/cryptologic_heritage/center_crypt_history/publications/sigsaly_start_digital.shtml.

“We are assembled today”: Quoted ibid.

Working out of his home lab: Hijiya, p. 58.

As a transmission device for the spoken word: Thompson, p. 92.

“I look forward to the day”: Quoted in Fang, p. 93.

“The ether wave passing over the tallest towers”: Quoted in Adams, p. 106.

But somehow, lurking behind all of De Forest’s accumulation: Hilja, p. 77.

Almost overnight, radio made jazz: Carney, pp. 36–37.

“It is no wonder that so much of the search for”: Quoted in Brown, p. 176.

“Sympathetic to the society’s mission”: Thompson, pp. 148–158.

“No one could figure out the sound”: Quoted in Diekman, p. 75.

Just a few days before the sinking: Frost, p. 466.

The German U-boats roaming the North Atlantic: Ibid., p. 476–477.

“I pleaded with them”: Quoted ibid., p. 478.

China was almost 110 boys: Yi, p. 294.

Chapter 4. Clean

In December 1856, a middle-aged Chicago engineer: Cain, p. 355.

During the Pleistocene era, vast ice fields: Miller, p. 68.

“You have been guilty”: Quoted ibid., p. 70.

“green and black slime”: Miller, p. 75.

That rate of growth . . . a lot of excrement: Chesbrough, 1871.

“The gutters are running”: Quoted in Miller, p. 123.

“The river is positively red”: Quoted ibid., p. 123.

Many of them subscribed . . . “death fogs”: Miller, p. 123.

“the most competent engineer”: Cain, p. 356.

Building by building, Chicago was lifted: Ibid., p. 357.

“The people were in [the hotel]”: Cohn, p. 16.

“Never a day passed”: Macrae, p. 191.

Within three decades, more than twenty cities: Burian, Nix, Pitt, and Durrans.

“came out cooked”: http://www.pbs.org/wgbh/amex/chicago/peopleevents/e_canal.html.

“The grease and chemicals”: Sinclair, p. 110.

Working in Vienna’s General Hospital: Goetz, loc. 612–615.

“Bathing fills the head”: Quoted in Ashenburg, p. 100.

As a child, Louis XIII: Ashenburg, p. 105.

Harriet Beecher Stowe and her sister: Ibid., p. 221.

“By the last decades”: Ibid., p. 201.

“A large part of my success”: http://www.zeiss.com/microscopy/en_us/about-us/nobel-prize-winners.html.

Koch established a unit of measure: McGuire, p. 50.

It was an interest born: Ibid., pp. 112–113.

“Leal did not have time”: Ibid., p. 200.

“I do there find and report”: Quoted in ibid., p. 248.

“And if the experiment turned out”: Quoted ibid., p. 228.

About a decade ago, two Harvard professors: Cutler and Miller, pp. 1–22.

“In total, a woman’s thighs”: Wiltse, p. 112.

Annie Murray had created America’s first commercial bleach: The Clorox Company: 100 Years, 1,000 Reasons (The Clorox Company, 2013), pp. 18–22.

In 2011, the Bill and Melinda Gates Foundation: http://www.gatesfoundation.org/What-We-Do/Global-Development/Reinvent-the-Toilet-Challenge.

Chapter 5. Time

In October 1967, a group of scientists from around the world . . . But the General Conference on Weights and Measures: Blair, p. 246.

To confirm his observations: Kreitzman, p. 33.

“The marvelous property of the pendulum”: Drake, loc. 1639.

His astronomical observations had suggested: http://galileo.rice.edu/sci/instruments/pendulum.html.

The watchmakers were the advance guard: Mumford, p. 134.

“On a rainy day”: Thompson, pp. 71–72.

“the employer must use the time of his labour”: Ibid., p. 61.

“deadly statistical clock”: Dickens, p. 130.

Dennison had a vision of machines: Priestley, p. 5.

Dennison’s “Wm. Ellery” watch . . . cost just $3.50: Ibid., p. 21.

“It is simply preposterous”: http://srnteach.us/HIST1700/assets/projects/unit3/docs/railroads.pdf.

The United States remained temporally challenged . . . William F. Allen: McCrossen, p. 92.

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