#does it like cross over during meiosis? could it get mutated?

[pinacoladamatata]

How the hell is bhaal orin's daddy if sarevok is orin's daddy?

[f-nodragonart]

Evolution: An Introduction

so I thought this might be a useful post b/c a lot of stuff we’ve described abt evolution has been spread out over several different posts. now I can just link to this instead of trying to quickly describe something as complex as evolutionary theory, lmao. keep in mind I’m not especially versed in molecular bio-- there are prolly nuances I’m missing here b/c they fly over my “big picture” bio head, so don’t take this as like, a professional review of evolution

anyways this is another longform post, so prepare urself. some of this may be familiar b/c I cut it out of other posts, but most of it is fresh new writing~

Table of Contents

PART 1: Definition

- Genetic Variation/Diversity

- Fitness

- Niche

PART 2: Energy

- Give-and-Take

- Survival vs. Reproduction

PART 3: Speciation

- Species Concepts

- Speciation

PART 4: Taxonomy/Classification

- Cladistic Taxonomy

- Parsimony

PART 5: Some Misconceptions

- Change =/= Improvement

- Impractical =/= Impossible

PART 6: Beyond Darwin

- Epigenetics

- Horizontal Gene Transfer

- Universal Biology

PART 1: Definition

First, a ‘brief’ definition of Darwinian evolution:

Random genetic mutations regularly occur during meiosis (the sexual cell division giving rise to gametes/embryos) and increase the genetic diversity in a species’/community’s gene pool. As environmental conditions naturally shift over time, certain conditions will become more or less favorable for the array of random traits that a species’ gene pool exhibits. Thus, some lucky organisms will exhibit traits that increase their fitness compared to others within their population when these environmental shifts occur. These individuals with high fitness will better survive and/or reproduce, so their genes (including those that produce the advantageous trait) survive and are inherited by their offspring, allowing them survival/reproductive advantage as well. Thus, the advantageous trait lives on, while others without the advantageous trait either die out or shift into a new niche to survive in (and potentially evolve into a new species themselves).

The process of more “fit” organisms surviving over others is natural selection: environmental pressures push species to either adapt to the changes within their current situation, die, or move on to other niches. If there are no fluctuating stresses on organisms to survive, then there is no evolution, because no single trait is more beneficial to survival than any other.

~Genetic Variation/Diversity~

Genetic variation describes the tendency of genotypes (the genetic “blueprint” of an organism) to vary between individuals in a population. These variations are due to random genetic mutations in an individual’s DNA, and genetic “shuffling”.

Genetic mutations are actually far more common than most may think, as we usually associate mutations with visible, sometimes grotesque physical traits. Many mutations aren’t so blatant and unfortunate, instead merely lending to slight variations in our genetic code and physical/psychological state (if they even have a direct effect on us at all). Our genetic code is actually VERY good at minimizing errors due to the redundancy of codes in relation to resulting proteins (look into genetic degeneracy for more info).

The “shuffling” refers to processes like crossing over and independent assortment during meiosis. Without getting too deep into these processes, they’re essentially what recombines the genes provided by the parents into unique combinations for the offspring.

Genetic diversity is the total number of genetic characteristics in a species’/population’s overall genetic makeup. This diversity drives evolution, as it gives individuals a greater chance of possessing genotypes better suited to their environment/circumstances. If all individuals of a species are exactly the same in every aspect, then evolution won’t occur because no individual holds greater survival/reproductive advantage over another. This is why small gene pools can be so deadly to species, because a given individual will have little chance of possessing a lucky random survival trait when their environment inevitably shifts into a new state.

Genetic variation is often confused with diversity, though it’s understandable since the two terms are very similar. Think of it like this: variation is the “flexibility” of a given species/population’s DNA. IE—how common is it for the individual genotypes of a population to vary from each other within a given time frame? Diversity is the number of different characteristics the variation caused within a given population.

It may not be super important to know the difference between these terms for creature-creation purposes (tbh I prolly won’t remember the difference once I post this guide asdfg), but it can help when studying evolution.

~Fitness~

“Fitness”-- despite popular belief-- refers to an organism’s reproductive success as defined by their contribution to the next-generation gene pool. These genes are physically expressed in the organism via phenotype, which must curb the stresses of an individual organism’s external environment in order to successfully pass on to the next generation in via genotype.

An organism does NOT have to be physically fit to have high evolutionary fitness. Though fitness certainly CAN be influenced by more popularized ideas like physical strength or health—there are plenty of animals that intimidate others via size/pheromones/etc., which may lead to an outright battle for control of resources. One great example is the capercaillie—a large grouse that is so aggressive to any perceived threat during breeding season, they’ll even go after humans. Males that succeed in the most battles attract the most females.

However, physical strength or aggressiveness are NOT the only paths to success, as there are plenty of examples of small sizes or social cooperation benefiting a species! Vampire bats, for example, are known for sharing food among roostmates who failed to find food on their own. Surviving strictly on blood is a tough life, and just a couple days without food can spell death for a vampire bat. Thus, well-fed bats will often regurgitate part of their meal to feed those that weren’t so lucky that night. While there is contention over the exact factors that play into this reciprocation (such as kinship), there’s strong evidence that long-term association and past investments correlate with a bat’s willingness to share food.

Now an interesting caveat to this is that a trait that may benefit an individual’s evolutionary fitness can sometimes threaten their individual health and survival. As I will discuss in more detail later (see Part 2), fitness balances BOTH individual survival AND overall reproduction. So long as the individual lives long enough to pass on more of their genes compared to others in their community, their fitness is considered a success. This can sometimes mean an organism only lives a few years, but they produce many successful offspring to pass on their genes. Thus, successful fitness.

~Niche~

A “niche” is how an organism responds to the abiotic and biotic aspects of their environment and the resources available. It’s essentially how an organism fits into the life web of their environment/community, and how they make a space for themselves out of the resources available to them. Competition for resources can result in changes to the organism’s morphology (such as paws/claws better suited for scaling trees to reach fruits), physiology (such as developing a tolerance for the bitter taste of a certain abundant fruit), or behavior (such as only foraging for fruits during the dawn/dusk when less competition for fruit is out and about).

PART 2: Energy

~Give-and-Take~

Evolution is a delicate balance of give-and-take. Often, in order for an organism to have a highly-refined trait in one aspect of their life, a different trait of theirs must be reduced. This is due to energy management-- organisms only have so much energy to spare, and evolution must often must ‘decide’ what traits benefit most compared to other traits.

Thus, one of the most important things to remember when applying evolutionary theory is purpose. Every action, emotion, and additional part of the physical body takes up energy to create during development and/or sustain during an organism’s lifetime. If it doesn’t serve a purpose on the organism, then the energy used to sustain it will likely be redirected towards more important purposes over time. This is why useless structures on organism can be such a liability—if they don’t help out at all, they’re using up precious energy that could be put towards more vital processes.

Of course, evolution is a slow and complex process, so useless structures aren’t gonna disappear overnight. This may even give these ‘useless’ structures enough time to be retrofit for a different purpose, thus making them useful again. Vestigial structures, for example, are often small and useless because they’re usually evolving out of the body plan, but that doesn’t always mean they serve no purpose in the current body plan. The human tailbone is an important anchor for hip muscles, for example, despite the fact that we don’t have a use for anything tail-like in our structures anymore.

Another good example of an evolutionary trade-off could potentially be found in bird wings vs. bat wings. Though keep in mind that this particular assertion is more theorizing on the part of some of the mods here (including me), so take this with a grain of salt compared to the cited parts of this post.

As I’ve discussed in much more detail in the Flight section of this post, bats have highly agile flight due to the membranous structure of their wings, with fingers and tendons that can adjust the exact shape and elasticity of the wing to the smallest degree. These complicated structures require quite a bit of energy to develop, which may explain why bat hind limbs are so underdeveloped in comparison. Sure, bat legs can cling and spread out the wing membrane, but they’re essentially useless for walking or much dexterous action (for most bat species at least). Compare their legs to birds, on the other hand, and you get a completely different story. Bird legs can be very dexterous instruments in many cases, and allow birds a much wider range of movement on land (which of course varies by species, but even this level of diversity isn’t available to bats). Yet, bird wings are much less versatile compared to bats; since developmental energy is directed towards the hindlimbs, the wings can’t afford to take up much more energy. Fortunately, feather development after hatching doesn’t take up nearly the same amount of energy as the development of flesh and bone, BUT these wings don’t have the same level of malleability as fingers and membrane. Thus, the trade-off here is highly versatile flight vs. dexterous hind limbs + land mobility.

Gestation is, understandably, a very important part of this energy-partitioning process, as the type of gestation decides the amount of energy and space available for the animal to develop right off the bat. Placental mammals are able to give their young a constant supply of energy through their own consumption, and a more flexible/stretched space for their young to grow and for their bones to ossify. Egg-laying animals, on the other hand, have a restricted amount of energy and space to develop in, as decided by the energy resources and size of the egg they’re laid in. 

This restrictive space/energy is potentially another reason for birds’ feathered wings—since feathers can grow outside the liquid matrix of the egg (unlike bones), only the fleshy “arm” part of the wing needs to develop within the egg. Bats, being placental mammals, have much more room and energy to build up their complex, fully-flesh wings in the womb. Though this is, again, our theorizing on the subject.

Energy actually factors pretty heavily into to the type of early development an organism undergoes. For example, long-lived animals often have few children, while short-lived animals often have many over their lives.

It takes a LOT of energy to gestate/brood and then care for resulting offspring (often at direct risk to the carrying parent, no less). If an organism isn’t going to live long, it’s much more to their reproductive advantage to simply have many children that they throw out to the world on their own. More offspring are likely to survive than if the short-lived animal spent a lot of energy raising just a few offspring before dying. Long-lived animals, on the other hand, have the time to spend on raising a decent amount of offspring, so they can protect their young for a while and give them each a much higher chance of individual survival.

~Survival vs. Reproduction~

There are the two main forces that drive an organism’s evolution: individual survival and reproductive success.

Individual survival makes sense to us, because obviously an animal can’t pass on their genes if they don’t live long enough to breed. Yet, it’s equally important to remember that no matter how well an animal survives individually, their existence means nothing to evolution if they don’t eventually pass on their genes.

In fact, there are many examples of organisms whose short lives are basically a means to the end of mating, or whose individual lives are directly threatened by the prospect of mating. One rare mammalian example is the Antechinus—a mouse-like marsupial who lives for only a year, and mates only one time at the end of their life. Their short breeding season is so intense, that the males literally breed until their bodies fall apart. Obviously the males don’t individually benefit from breeding so hard as to die, but the strategy clearly works to pass on their genes and continue this cycle. Thus, successful fitness to those that breed "hard" enough.

Even if the reproductive strategy isn’t as drastic as this, individual survival is often at odds with reproduction, which can lead to some interesting compromises and loopholes. For example, vibrant feathers and boisterous displays may attract mates, but it will also certainly attract predators to the easily-spotted target. Most avian species’ eyesight can be classified as either violet-sensitive (VS) or ultraviolet-sensitive (UVS), so some birds will utilize a part of the light spectrum that their fellow avian predators can’t see. Thus, the birds in question are dull to at least some of their predators, but eye-catching to potential partners.

Anyways, it helps to break down these two aspects-- survival and reproduction-- when designing, and figure out what features of an organism may help them accomplish certain tasks:

Survival:

-Gas exchange- How does this animal breathe? Do they live on land, in water, or are they semi-aquatic? Do they have lungs, gills, or semi-permeable skin? If they fly, do they have adaptions for high-altitude flight and efficient gas exchange? How does the placement of their nostrils/gills effect the efficiency of their gas exchange in different environments? Can they hold their breathe for any amount of time?

-Hydration- Where/how does this animal get water? From their meals, large water sources, or maybe direct contact with water while swimming? How abundant is water in their environment, and what adaptions does the animal have for this?  Does this animal have morphological traits or behaviors to prevent desiccation?

-Consumption- What is the animal’s diet? How strict is that diet—are they obligate carnivores or opportunistic omnivores? Scavengers or fresh-foliage herbivores? What adaptations do they have to handle potential toxins/diseases in their meals? How do they locate/track and/or capture their meals? What jaw morphology to they have to properly shred/grind/swallow or otherwise ingest their food? How do they digest these meals, and what nutrients are vital to their physiological survival?

-Shelter/Safety- At what times of the day is the animal awake? What sensory adaptations do they have for changes in light and sound throughout the day? Why are they awake at these times—maybe predator avoidance, or an advantageous foraging time? Is this species typically fight or flight when faced with danger? How far do they have to be pushed to resort to either, and what warnings will they exhibit before that point? Can this species handle a wide gradient of weather/temperature, or can they only survive within a narrow gradient?

-General Homeostasis/Physiology- How does this animal regulate their temperature? What kind of immune system does this creature have, and how effective is it under different conditions? How does this animal grow/develop over time, and what role do external factors play in this?

Reproduction:

-Attracting mates- What behaviors does the animal participate in to find and attract mates? Do they have any physical structures, attention-grabbing behaviors, or both? What senses do they most rely on for this—bright plumage to attract sight? Loud/melodic calls to capture the auditory? Seductive scents?

-Reproductive organs- What kind of reproductive organs does this species have? Do they have multiple kinds exclusive to different sections of the population? Do they all have the same kinds of reproductive organs? Do their reproductive organs change over time, and how much energy does it take for that change to occur?

-Gestation- How does this species incubate their developing young; through an in-body placenta, hard-shell egg, soft-shell egg, or maybe in a marsupial fashion? How might this protect or otherwise effect developing young? What restrictions does this place on energy available to the developing young? How much stress does this incubation method put on the parents? How long do the young incubate, and how developed are they once they hatch/birth?

-Child rearing- Do the adults rear the young for any amount of time, or are the young on their own once they hatch/birth? How long are the young reared, and how does this affect their development? What secondary reproductive organs (such as mammary glands) might be used to help rear offspring? Communal rearing, nuclear family, or single parent? What are the average chances of the young surviving into adulthood?

PART 3: Speciation

~Species Concepts~

Typically, we’re taught that a species is defined as a group of organisms that is capable of breeding and producing viable/fertile offspring.

While this definition may seem intuitive, it can be shaky when applied to nature. We humans like to slot natural processes into neat little boxes of classification, as it helps us better define, organize, and communicate to others what we observe in the world. Though we sometimes forget that these definitions don’t actually confine and control these processes; our language is naturally limited when discussing something as fluid as a natural process. For example, the definition of “species” for a single-celled organism won’t count for a complex vertebrate, nor would the species definition for a sexually-reproducing organism count for an asexually-reproducing organism. Some species’ genetics/reproduction can’t even be observed anymore (long-extinct fossils, for example), so species distinctions must be based on pure morphology!

This is known as the “species problem” in biology, and it highlights the true complexity of life. Instead of just one concept for species, we have several for different conditions. According to this page, there are at least 26 currently being used, which I will copy-paste here (though you should check the link for more info on specific authors/papers and synonyms):

Agamospecies: Asexual lineages, uniparental organisms (parthenogens and apomicts), that cluster together in terms of their genome. May be secondarily uniparental from biparental ancestors.

Autapomorphic species: A geographically constrained group of individuals with some unique apomorphous characters, the unit of evolutionary significance; simply the smallest detected samples of self-perpetuating organisms that have unique sets of characters; the smallest aggregation of (sexual) populations or (asexual) lineages diagnosable by a unique combination of character traits.

Biospecies: Inclusive Mendelian population of sexually reproducing organisms, interbreeding natural population isolated from other such groups. Depends upon endogenous reproductive isolating mechanisms (RIMs).

Cladospecies: Set of organisms between speciation events or between speciation event and extinction, a segment of a phylogenetic lineage between nodes. Upon speciation the ancestral species is extinguished and two new species are named.

Cohesion species: Evolutionary lineages bounded by cohesion mechanisms that cause reproductive communities, particularly genetic exchange, and ecological interchangeability.

Compilospecies: A species pair where one species "plunders" the genetic resources of another via introgressive interbreeding.

Composite Species: All organisms belonging to an internodon and its descendents until any subsequent internodon. An internodon is defined as a set of organisms whose parent-child relations are not split (have the INT relation).

Ecospecies: A lineage (or closely related set of lineages) which occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from all lineages outside its range.

Evolutionary species: A lineage (an ancestral-descendent sequence of populations) evolving separately from others and with its own unitary evolutionary role and tendencies.

Evolutionary significant unit: A population (or group of populations) that (1) is substantially reproductively isolated from other conspecific population units, and (2) represents an important component in the evolutionary legacy of the species.

Genealogical concordance species: Population subdivisions concordantly identified by multiple independent genetic traits constitute the population units worthy of recognition as phylogenetic taxa

Genic species: A species formed by the fixation of all isolating genetic traits in the common genome of the entire population.

Genetic species: Group of organisms that may inherit characters from each other, common gene pool, reproductive community that forms a genetic unit

Genotypic cluster: Clusters of monotypic or polytypic biological entities, identified using morphology or genetics, forming groups that have few or no intermediates when in contact.

Hennigian species: A tokogenetic community that arises when a stem species is dissolved into two new species and ends when it goes extinct or speciates.

Internodal species: Organisms are conspecific in virtue of their common membership of a part of a genealogical network between two permanent splitting events or a splitting event and extinction

Least Inclusive Taxonomic Unit (LITUs): A taxonomic group that is diagnosable in terms of its autapomorphies, but has no fixed rank or binomial.

Morphospecies: Species are the smallest groups that are consistently and persistently distinct, and distinguishable by ordinary means. Contrary to the received view, this was never anything more than a diagnostic account of species.

Non-dimensional species: Species delimitation in a non-dimensional system (a system without the dimensions of space and time)

Nothospecies: Species formed from the hybridization of two distinct parental species, often by polyploidy.

Phylogenetic Taxon species: A species is the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent; the least inclusive taxon recognized in a classification, into which organisms are grouped because of evidence of monophyly (usually, but not restricted to, the presence of synapomorphies), that is ranked as a species because it is the smallest 'important' lineage deemed worthy of formal recognition, where 'important' refers to the action of those processes that are dominant in producing and maintaining lineages in a particular case.

Phenospecies: A cluster of characters that statistically covary, a family resemblance concept in which possession of most characters is required for inclusion in a species, but not all. A class of organisms that share most of a set of characters.

Recognition species: A species is that most inclusive population of individual, biparental organisms which share a common fertilization system

Reproductive competition species: The most extensive units in the natural economy such that reproductive competition occurs among their parts.

Successional species: Arbitrary anagenetic stages in morphological forms, mainly in the paleontological record.

Taxonomic species: Specimens considered by a taxonomist to be members of a kind on the evidence or on the assumption they are as alike as their offspring of hereditary relatives within a few generations. Whatever a competent taxonomist chooses to call a species.

(Note that only one concept-- biospecies-- is the typical concept we’re taught applies to all species.)

And even then, these definitions can be contentious when you’re actually out in the field or working with a set of genetic data (believe me, I know). This post is also a very fun, informative dive into this problem, if you want to take a look.

Now I’ll just be using biospecies as the basic definition of “species” for this section, and evolutionary species for most of this post, but keep this natural flexibility in mind when defining the species in your world! If biospecies doesn’t fit some of your species-- or even your whole batch of species-- then test out other concepts and see how they fit! “Species” is really just a word, after all, not a law of nature.

~Speciation~

that in mind, Speciation is defined as the formation of distinct species by the process of evolution. By the biospecies concept, speciation is usually accomplished by some sort of reproductive isolation. This can develop and present itself in different ways, including:

Different mating times, locations, and/or rituals

A lack of compatibility between sexual organs

Production of offspring that are unviable (don’t live to adulthood) and/or sterile (cannot produce offspring)

There are several types of speciation that can produce this reproductive isolation:

Allopatric: A species is split apart by a physical barrier in their environment, such as fragmentation or a weather event that pushes sections of the population apart.

Peripatric: A version of allopatric speciation where the isolated population is very small.

Parapatric: There’s no physical barrier between different parts of the population, but individuals are more likely to mate with others within a certain range of their territory rather than far-off reaches of the population’s territory. This creates a gradient of genetic differences in the population across the territory, which may lead to speciation between the most physically distant individuals.

Sympatric: When a population gradually develops reproductive barriers without any geographic isolation/distance; likely caused by gradual random mutations, though it can be a bit difficult to observe in nature.

PART 4: Taxonomy/Classification

~Cladistic Taxonomy~

Taxonomy is the practice of naming, defining, and organizing organisms into groups based on shared characteristics. I casually use it to refer to cladistics specifically, but it’s technically a broader field encompassing all sorts of approaches to classification.

Cladistic taxonomy organizes life by tracing direct descendance/genetic history to given organisms’ last common ancestor. As these relations are mapped, certain groups (“clades”) will naturally ‘nest’ within other groups, thus building a ‘tree’ of lineages that connects all life to one another.

Also keep in mind that the nesting pattern of cladistic classification will automatically include any organisms under a given clade’s umbrella. Just because a creature evolves “beyond” a certain taxonomic stage, doesn’t mean that creature stops being a member of that group. It’s why birds ARE dinosaurs-- even if birds evolved “from” dinosaurs, they are still a part of that broad clade. Aves is simply the more specific clade nested within dinosaurs.

This is classic monophyletic grouping-- where a group consists of all descendants of a common ancestor, as defined by their synapomorphies (traits derived from a common ancestor, thus are unique to a particular clade).

Cladistic taxonomy is the usual type of classification you’re gonna come across in biology, and it forms the basis of our understanding of evolutionary history. Generally, an eclectic mix of morphological, behavioral, ecological, and genetic characteristics help string together the evolutionary relationships of organisms. Though more recently, genetic data has become the backbone of taxonomic research, often upheaving decades of theories based only on morphology/ecology/behavior. These other characteristics are still important in defining species, but they can sometimes be... misleading.

See, cladistics is based on the assumption of homology-- that similar characteristics are a result of those traits being passed on to different organisms from a common ancestor; the divergent evolution of related species from a common ancestor that passed on that trait.

This isn’t always the case for similar structures, however. Analogy assumes that similar characteristics are a result of the organisms in question facing similar environmental stressors that would require similar traits to survive and thrive; the convergent evolution of unrelated species towards a similar trait.

The avenue of analogy opens up many more approaches to classification (see this post). However, these different types of classification move a bit beyond evolutionary theory/history into different subjects like ecology, and I don’t want to side-track too much here. Homology is the only real way to track direct descendance and genetic history, so analogy isn’t especially important when considering strictly evolutionary classification. 

~Parsimony~

Now, since shared morphological traits aren’t ALWAYS an indicator of direct evolutionary relations, how exactly do we parse out what is and isn’t clade-defining?

Taxonomists generally work under the assumption of parsimony-- that the theoretical genetic tree that requires the fewest evolutionary changes is probably correct. This mindset is derived from the philosophical theory of Occam’s Razor-- that the simplest answer is probably the correct one, given all other factors are equal.

Thus, a phylogenetic tree that assumes more of a clade’s given traits were passed on from common ancestors is going to be a LOT more realistic than a tree that assumes a lot of traits evolved independently via convergent evolution. It takes a lot of energy to evolve whole new structures, so it just makes more sense that more of these traits would be passed on from an ancestor that had already freshly-evolved them. This isn’t ALWAYS the case (see Part 5), but it’s the safest assumption to make when drawing out evolutionary trees.

Though it’s important to have some understanding of anatomy and basic genetics when practicing parsimony-- this is where the caveat of, “given all other factors are equal,” comes into play. Traits like limb number, pelt color, or cartilaginous frills can’t be treated equally, as they don’t evolve in the same ways or at the same rates.

As I discussed more broadly in Part 2, developmental energy is a critical factor in evolution. Embryonic characters are the most stable, as these characteristics are vital to development (whether they require the liquid matrix of the womb, or are systems absolutely crucial to life once the newborn exits the womb), or are otherwise connected to a creature’s most structural/basal genetics. Thus, these embryonic traits display the most broadly-defining synapomorphies, and evolve veryyy gradually over time. 

For example, human embryos have “gill ridges” remnant of our fishy ancestors, but they’ve been retrofit for other purposes (namely jaw/ear development), so they eventually morph into their humanoid purposes as the embryo develops. Limb number is another good example, and is stable for vertebrate development as far back as our first land-faring fishy ancestors. (potential vertebrate hexapod evolution can be complicated, and I go into more detail about it here)

Compare those traits to more adaptive traits that crop up in mature organisms (like color, general body shape, etc.). These traits use up much less developmental energy (or none, if they end up changing/developing post-hatch/birth), and evolve far more quickly for survival purposes. These adaptive traits could easily evolve independently across a taxonomic tree, depending on the circumstances.

Either way, it’s important to sort out what traits are broadly-defining, developmental traits vs. quickly-evolving, adaptive traits. A tree that uses limb number as a derived trait but shows several independently-evolved color patterns is going to be FAR more realistic than a tree that uses different color patterns as derived traits, but shows limb numbers independently changing just a few times times across the tree. 

Though of course, this is all under the assumption of Earth genetics, which doesn’t necessarily have to be the case for your world (see Part 6).

PART 5: Some Misconceptions

~Change =/= Improvement~

I’m well aware that I’ve been using personified language here for ease of describing evolutionary processes, but I must make this clear: natural evolution is NOT consciously-driven. As long as genes viably and consistently pass on, any given trait could potentially live on.

There’s this idea in popular culture that “evolution” refers to “improvement”, but in reality, evolution simply means “change”. Environments are dynamic, shifting systems, and organisms change to survive these shifts. Sure, evolution technically “improves” species by molding behaviors or body plans to better fit an environment, but this is a temporary value judgement at best. The environment will eventually shift again, and a trait that was ideal for a species in the past may be the thing that drives their doom in the future.

There is no actual “goal” to evolution—no “ideal form” that evolution strives for. We’re all just trying to survive, and that’s exactly what drives our diversity—if we were all the same, we couldn’t survive vying for exactly the same resources and life conditions.

If sociality and empathy help a certain species survive, then that’s their approach. If a different species can live on just fine without sociality/empathy, then that’s their approach. Neither approach is “better” than the other. Trying to impress some sense of subjective “morality” or “hierarchy” on evolution is a fool’s errand, and honestly pretty insulting to the survival approaches of basically every other species.

~Impractical =/= Impossible~

Evolution is less a grid-marked blueprint, and more a patchwork piece of sticky notes and crinkled napkins. Every organism is as evolved as well as they can be in a given moment with the materials they have available to work with. Evolution can’t simply magic up the perfect materials necessary to build a wing, for example; a species’ current morphology must be retrofit to complete the task at hand.

Thus, no form is perfect, nor is any species’ approach to survival fool-proof. If evolution were consciously-driven, for example, we might not choke on water all the time because our throats would be more efficiently designed to prevent water from entering our trachea. But evolution worked with what it had, and our current throat shape is what we’ve got.

Additionally, life isn’t always a vicious struggle for survival-- Life situations vary, and not everyone has to carefully balance out their energy usage. Some organisms live a safe enough life that certain random mutations or vestigial structures stick around purely because there is no outside stressor that requires their energy be directed elsewhere. Thus, they can stand to sacrifice some of that energy for mutations that really don’t matter in the long-run.

As for behavior, as All Yesterdays puts it, “Animals do what they do, not necessarily because it is what they are good at, or even because their anatomy is suited to it, but simply because they can.” Behavior, unlike anatomy, is much more flexible and can vary heavily depending on an individual’s circumstances. Most animals are not constantly battling the elements or each other, and have opportunities to do bizarre things that may not practically help them in any way, but perhaps provides some other sort of satisfaction. This quote is preceded by a list of odd animal behaviors as example, “Elephants are excellent at swimming, crocodiles and alligators sometimes eat fruit and leaves, juvenile iguanas sometimes jump up at the moon at night, and goats in some areas often climb trees in order to browse.”

When you’re first starting out creature design, it’s safest to assume that because an animal has a body plan suited best for a given activity, they will stick more readily to that activity. However, keep in mind that anatomy and behavior do not always align, and that an impractical behavior or structure doesn’t always mean it’s an impossible behavior/structure. To be completely honest, I often have to remind myself of this, as I often fall into the “practical survival” trap of design, which ignores the flexibility of nature and evolution.

Just keep in mind what structures would be actively detrimental to keep around compared to others. A whole new set of limbs, for example, would take up a RIDICULOUS amount of energy to produce and sustain, even for an animal that has a fairly easy life. There are a lot of intricate muscle, bone, and nerve structures in those things! Compare that with a change in color, fur length, or cartilaginous frills—much less complex, and they don’t use up nearly as much energy.

PART 6: Beyond Darwin

Now, I’ve been focusing on exclusively Darwinian evolution here (which is admittedly the bulk of evolutionary theory), but there are a few other modes of evolution/inheritance that I want to briefly touch on.

~Epigenetics~

First, keep in mind that Darwinian evolution occurs through GENERATIONS, not individual lifespans. A giraffe’s long neck isn’t caused by their pre-giraffe parents stretching out their necks and passing on their freshly-stretched necks to offspring. It’s caused by a random mutation in neck length that happened to be useful in reaching higher leaves, helping those long-necked offspring survive better than their short-necked brethren.

However, that doesn’t mean that heritable changes within a lifespan never occur-- they’re just not necessarily as ‘Lamarckian’ as they first appear, nor are they necessarily antithesis to Darwinian evolution.

Epigenetics is the study of heritable changes in gene expression/activity, but not changes to the actual DNA sequence. This means that certain phenotypic traits can shift in an individual lifespan due to environmental pressures, and can pass on to offspring. The key here is that these changes occur in gene expression (which is controlled by the shape/structure of a DNA strand), but NOT the DNA sequence.

Some have referred to this phenomenon as a “genetic memory” since it’s like passing on helpful information to your kids just in case they face the same stressors you did. Arabidopsis plants treated with high salt or heat conditions, for example, have been found to produce offspring that are more tolerant of these conditions, compared to those offspring whose parents didn’t experience these conditions.

While plants provide some of the best examples of epigenetics, since they tend to have more flexible genomes that actively respond to their environments, evidence for epigenetic heredity has been found in animals as well. Chickens that undergo unpredictable food access will have offspring that exhibit more conservative feeding strategies, even without parental contact and under more favorable food conditions. Of course, this research is still rather novel, and it’s always good to be cautious about the varying conditions that could affect the outcome. Research into “inherited trauma” in humans, for example, is still in its infancy, and while it’s yielded interesting results, we’re far from reaching a conclusion about exactly what of trauma/stress could be inherited.

~Horizontal Gene Transfer~

Vertical gene transfer from parent to offspring is the main driver of Darwinian evolution, and is what we use to track direct inheritance and construct directional taxonomic trees. However, life is not always confined to such strict evolution.

Horizontal gene transfer (HGT) involves passing genes from one individual to another by means other than reproduction. This can create HIGHLY complex maps of inheritance, with no real traceable direction of lineage so much as a mass of tangled, interchangeable wires. Thankfully, this *mostly* happens among single-celled organisms like bacteria/archaea, so that’s a microbiologist’s problem to figure out lmfao.

Though it makes for a rather interesting tree of life

The beginnings of life were rife with HGT, with these early cells (and even earlier to what was likely a messy soup of free-floating RNA) sharing and recombining their genes with abandon. As cells increased in complexity, however, HGT became much more difficult, and THAT’S when vertical gene transfer (thus, Darwinian evolution) took over.

Now just because HGT mostly occurs in single-celled organisms doesn’t mean it NEVER occurs in more complex organisms. While these transfers are usually initiated by single-celled organisms, plants and fungi are notorious for not giving a shit about proper genetics and giving us poor botanists hell when trying to track family trees >:( . Not to mention several other multi-cellular examples, including animals. HGT doesn’t seem especially common in complex organisms compared to single-celled organisms, but it’s certainly not unheard of!

~Universal Biology~

So this is a pretty novel, pretty abstract area of research. I’m probably not gonna do it justice, so I’d recommend watching this video for a better breakdown, but I’ll still try to describe this topic for a layman audience.

*Broadly speaking*, most physical phenomenon have some sort of abstract theory to predict their existence. Essentially, we know 1) why the phenomenon can occur, and 2) how it can occur under specific circumstances.

We don’t have that for the theory of life.

All our current theories for life are tied intimately to our subjective experience of life on Earth-- our need for water, our carbon-based structures, etc. etc. But these aren’t really theories of life so much as theories of Earth life. We can’t apply these theories when, say, searching for alien life, because there’s no reason to believe that life outside our planet will utilize the same basal resources in the same exact ways our life has.

We need to divorce the materials from the theory, because the materials don’t provide the true message of life. As Nigel Goldenfeld asks in that linked vid, “what is the abstraction that the biology that we see is the representation of?” What we really need to know is how matter in general, “can self-organize hierarchically to create self-replicating, evolvable structures.”

Essentially, how do molecules come to life?

I wish I could tell you what IS the true theory of life-- the why and the how-- but that’s the ongoing question, right now. Goldenfeld believes that evolution is a key component of the universal theory of life, because biological systems are the only systems known to ‘reprogram’ themselves in response to outside stressors. Other physical systems don’t do that-- they’re bound by fixed equations of motion. Some sort of genetic code is obviously key to evolution-- and specifically, HGT leading to a vertically-evolving universal genome-- thus is also considered a universal component of biology. Beyond that we don’t have a whole lot to go on (besides homochirality, which I... honestly can’t rly wrap my head around, so I rly suggest watching that video for more information).

Stuart Bartlett and Michael L Wong have also recently come up with the concept of “lyfe”, where lyfe would more universally apply to organisms outside our conception of biology, while “life” is simply an Earth-centric subset of lyfe. This definition relies on four main criteria: “dissipation (the ability to harness and convert free energy sources); autocatalysis (the ability to grow or expand exponentially); homeostasis (the ability to limit change internally when things change externally); and learning (the ability to record, process and carry out actions based on information).”

Now I only bring this topic up because it really gets at the heart of specevo and creature design-- the absolute core of what we can create. Obviously I don’t expect most of you to go so deep as to reconstruct the basal molecular structures of your creatures-- hell, it’s not something I even plan on doing much, if at all.

But I hope this perhaps... frees your constraints a bit. There are many ways to make a world, and not all of them have to be Earth-centric. Anything from the genetic building blocks of organisms, how they process energy, and what abiotic stressors restrain their growth/development could be different. There’s no rule stating your world (or even any real-life world out in the universe) has to 1:1 match Earth, so your world may have any number of differing factors, such as different sources of direct energy than sunlight, different gravitational restraints, a different kind of life creation event, or even a different element used as the elemental building block of life (IE- not carbon). These would all lead to different approaches to evolution, morphology/physiology, and behavior.

-Mod Spiral

[fellmother-archive]

{The Inheritance of Holy Blood}

{ ooc. I think I should preface this by saying that I am currently studying a bachelor’s degree in molecular genetics and biotechnology which is why this meta is so long, so if there is anything in this that you do not understand/want to know about, feel free to message me! If you wish to dispute something, please come to me with factual/canon reasons why the concepts I’ve put forward are incorrect-- not ‘this conflicts with my hc so it’s wrong and I don’t need to explain why’. Anyway, I’ve tried my best to explain certain concepts and how they work in this, so let’s get this thing rolling- }

     To start this off, it would be easier to address one misconception that seems to be rampant within the community when discussing how holy blood is inherited:

     The inheritance of holy blood is not sex-linked, as none of the family trees display a pattern indicative of it being linked to either the x or y chromosome, and the presence of methylation in imprinting does not work for this either. If this was the case, Arvis and Saias could not have major Fjalar, and Sigurd could not have major Baldr. Assuming this would also mean ignoring what has been said about holy blood inheritance in fe4’s playing guide— ‘it doesn’t matter if the person is the eldest child or if they’re male, there is no rule’.

     Instead, holy blood is inherited through a much more complicated means, regulated by various factors that, in theory, give the results that can be seen in throughout the Jugdral family trees, but also do not have a strict set of rules for them. When looking at the pedigrees, and if someone with minor blood is a carrier, you get results such as these:

Fjalar:

Naga:

Loptyr:

Thrud:

     Looking at the pedigrees in such a manner, however, is incorrect—there is no distinct pattern that can be discerned, nor are there enough generations to firmly put forward a simple method of inheritance. Though it looks to be a recessive gene, there are glaring exceptions which show that it simply cannot be inherited through that way—in the case of the pedigrees shown above, Deirdre and Julia’s case of having major Naga, Saias having major Fjalar, Arvis having major Fjalar, and Ishtar having major Thrud.

     There are also instances where a parent with major holy blood does not pass anything onto their offspring which also means that looking at holy blood in this way is incorrect—how Lewyn’s father possessed major holy blood, however his brothers had nothing.

     Due to this, holy blood cannot be assumed as someone having minor blood only inheriting one recessive gene, or major blood being someone who has inherited two recessive genes. Instead, the listings of what holy blood an individual has, and whether it is major or minor, should be interpreted as the character’s phenotype—what they express—rather than their genotype. Looking at it this way, a proper inheritance pattern can be seen, and it becomes exceedingly clear that all types of holy blood are more likely to be a dominant gene with decreased penetrance, and variable expressivity. So that it makes more sense, each factor will be explained.

     The reason as to why holy blood would be dominant gene is simply because in almost all cases, the blood is passed on in some way or another and is presented in their phenotype. It is the level of expressivity of the blood in the offspring that changes. If it was a recessive gene, then a carrier would not show any sort of expression related to the blood they have inherited, however that is not the case, as in fe4, minor holders of holy blood still express their lineage through the bonuses that are added onto their growths. This leads onto another factor regulating the gene—variable expressivity.

     Variable expressivity is when people with the same genotype display a range of different phenotypes, however the trait will still be expressed. An example of those would be if you had a group of the same species of organism that all have identical genotypes, with a specific gene encoding for dark brown fur, however all the individuals in the group expressed a range of different shades of brown without another gene that contributes to fur colour or inhibited the expression of said trait. Below is a visual representation of this example, with each square having the genotype Bb—where ‘B’ is the dominant allele that encodes for dark brown, and ‘b’ is a recessive allele that has no impact on colour.

     This concept can be applied to holy blood, with major blood being when the trait is fully expressed, and minor being when it is not. This explains why in certain family trees, such as the Fjalar, Thrud, Forseti, and Baldr ones, the offspring manifest minor holy blood, despite one of their parents having the corresponding major holy blood—they inherited the gene, it just is not being fully expressed. Does this mean that an offspring could potentially have two major holy blood groups? Technically yes, however if this is incompatible with life, then one of the holy blood’s expression would be inhibited slightly, resulting in minor blood.     This also explains how Lissa from fe13 can be born from at least one parent who presumably had major Naga, and not possess a brand, but how Owain can have major Naga. By extension, this also explains how the Grimleal’s breeding program could have spanned over a thousand years without a vessel/someone with major fell blood being born, despite starting with someone who has major fell blood.

     NOTE: decreased expressivity does not mean that the trait/blood has ‘diluted’. They have the same genotype as someone with major blood—it is just being expressed at a lesser level. You cannot ‘dilute’ a gene.

     Decreased penetrance is quite similar to expressivity, however it is a different regulating factor in its entirety. While expressivity deals with individuals having the same genotype, but displaying a certain trait to varying levels, decreased penetrance is when a dominant trait is inherited, but the trait does not manifest. If a dominant allele can be inherited, but not all the individuals with that genotype develop the trait, then it fits under this category. Using the same example as before, this would be if you had another group of those organisms with the same genotype, but some of them did not express dark brown fur at all.

     Despite the lack of expressing the trait, however, they can still pass it down to their offspring—they still have the allele that codes for that specific trait. This explains why an offspring will not express any sort of holy blood, despite their parents having either major or minor blood for that type—why some offspring, such as Daccar and Maios, do not have major or minor holy blood, despite their father possessing the former. It can also explain, specifically for fe15, why Alm and Celica have major blood, but why none of the ancestors before them did.

     When you mix these two factors together, using the same example as before, you would get a genotype that can express itself like this in a population:

     If we were to translate this into holy blood, it starts to match up to the trends seen in the family trees—the dark blue being major blood, the white being nothing expressed, and every shade between those two being minor blood. Every square has the genotype N?, with ‘N’ being the dominant allele encoding for major Naga blood, and ‘?’ being an allele that does not impact on the expressivity of the other.

     So then, what about the situation with Julius? If an offspring inherits one allele for a certain type of holy blood from each parent, what was the point of having two people with minor Loptyr produce an offspring? In this case, it was not necessarily the fact that he has two parents with minor Loptyr that resulted in him having major Loptyr, it is instead that he inherited the allele from Deidre, with his Fjalar blood obviously coming from his father and it was expressed fully. The chances of this happening were increased drastically by having two parents with the allele for Loptyr blood, as he could have inherited one from Deirdre, one from Arvis or both instead of just Deirdre or Arvis.

F= Fjalar, N= Naga, L= Loptyr, ?= unknown allele (not coding for Loptyr blood)

     As you can see, the potential offspring go from 50% of them inheriting the Loptyr blood allele to 75%, which is a considerable amount, and enough to almost ensure that the child will inherit at least one allele for that holy blood.

     Does this still work in Saias’ case if it turns out that canon decides to confirm that he inherited minor Loptyr from his father? Yes, actually—it would be a result of error or mutation during meiosis on Arvis’ side of things—whether it be from nondisjunction, an addition or translocation on the chromosome containing the genes, or from something as simple as the section containing the gene encoding for Loptyr blood crossing over to the chromosome that already has the gene encoding for Fjalar blood.