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Are there any problems with a single species, in which all fertile members are able to bear fertile offspring with all other fertile members, having extreme amounts of diversity? For example, having members with different types of limbs, different methods of locomotion, different diets, etc.

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    $\begingroup$ You mean more so than domestic dogs? $\endgroup$
    – Zeiss Ikon
    Aug 12, 2021 at 18:32
  • $\begingroup$ @ZeissIkon Yes I do $\endgroup$ Aug 12, 2021 at 18:32
  • $\begingroup$ There are undoubtedly any number of potential genetic mechanisms that might allow for extremely diverse body plans. This happens with humans (occasionally) with digits, some have fewer, some more. Likely though, while you might have varied shape in a limb, or a variable number of them (6 rather than 4, etc), you'd still be limited somewhat... say by bilateral symmetry. For alien biology, I don't think it's far-fetched to go all out though. Variability plus translational symmetry could give rise to all sorts of strange body plans. $\endgroup$
    – John O
    Aug 12, 2021 at 19:12
  • $\begingroup$ "For example, having members with different types of limbs, different methods of locomotion, different diets, etc." Do that and the entire point of categorizing animals into species goes "poof". You'd need to either think up your own category system that doesn't take the anatomy and biology into account, or just have a completely homogenous biosphere with no species at all. $\endgroup$ Aug 13, 2021 at 15:09

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I suspect this is not what you’re after, but the closest we have is holometabolous insects, i.e. those whose body plan is dramatically remodelled between the larval and adult stage, like butterflies and moths. Having “different types of limbs, different methods of locomotion, different diets” is precisely the point of holometabolism, so that the growth phase and the mating phase can each specialise in their single purpose.

With this in mind, you could imagine a species that, instead of going through the phases in strict sequential order, responds to environmental cues to develop into one of several genetically available body plans/life strategies. You could have the “summer body” with a short, fiery lifespan sustained by abundant available food, and the “drought body” with rugged anti-evaporation scales and so on.

Current holometabolous insects are not fertile across stages, but that’s because they have specialised to optimise to eating vs sex. Your species may have specialised instead to optimise to different environments, but potentially reproduce at any stage. As long as their mate attractant (say, a pheromone) is the same for all variants and their mating organs are compatible, there would be no problem in keeping them cross-fertile. In fact, I imagine that seeking a mate from a different variant would be advantageous, because each parent has been selected against a different developmental scheme, so the genes that the kids inherit contain two different body plans that have successfully passed evolutionary selection.

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The Diversity Isn't Genetic, It's Developmental:

One simple way to have this work is if the diversity of body plans is caused by developmental differences, not genetic ones. In cold climates, small, thick stubby fingers develop. Moms eating fish during pregnancy have kids with webbed feet and toes. The presence of tropical trees causes extra arms and flexible joints for tree climbing.

So you can have different tribes of people who look completely different, yet have kids adapted to their local environment. While having such designs is complex, for a species that moves a lot and migrates from biome to biome, this could be a definite survival adaptation. On a world where frequent environmental change happens (forcing people to move to new environments), they can intermarry with the locals or not, and still get kids adapted to the new conditions.

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  • $\begingroup$ The underlying mechanism for such behavior would likely be epigenetics, which refers to phenotype changes that don't alter the DNA. $\endgroup$
    – jb6330
    Aug 15, 2021 at 3:53
  • $\begingroup$ @jb6330 Epigenetics is somewhat different than developmental biology, in that epigenetics is inherited non-DNA-code information, whereas developmental biology is more about gene regulation during development, which can vary depending on environmental factors. It is a pretty subtle difference, and epigenetics could certainly play a significant role. To some extent, it is more semantics than real difference. $\endgroup$
    – DWKraus
    Aug 15, 2021 at 4:49
  • $\begingroup$ I actually like this answer better than my own. if genetics and evolution have made your species Very F-ing Adaptable Indeed then the attraction mechanism that brings individuals together to breed will be tailored to something that remains constant about an individual no matter how they have adapted to their Niche. Now .. is the adaptation operating as a chameleon-like ability OR as as part of foetus or early childhood development? Meaning individuals continuously adapt as they change location or just once to fit the birth location and then have to stay there? $\endgroup$
    – vulcan_
    Aug 16, 2021 at 10:29
  • $\begingroup$ @vulcan_ Developmental changes are almost exclusively in the womb, and since this is the time when the body lays down the signals for body pattern, life-long changes can be made (like fetal alcohol poisoning and thalidomide exposure). Smaller changes are possible later in life, but they aren't developmental at that point. Biology is harsh, and the old generation is sacrificed while the new generation adapts. For more, they would need to metamorphose or regenerate (both much less likely for big, complex organisms). $\endgroup$
    – DWKraus
    Aug 16, 2021 at 12:56
  • $\begingroup$ indeed DW, that is how are species does it. But the author seems to want strong differentiation between breeding adults that will still be attracted to one another despite being quite different. The premise is that this species has a genetics quite different from ours and in the case of this answer, the key is an ability to modify the bodies of individuals to adapt to location or whatever else is driving differentiation. $\endgroup$
    – vulcan_
    Aug 19, 2021 at 12:43
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Sure, just have them spread to different locations with something like an ocean to prevent mixing the gene pools .. think Galapagos and turtles. Okay, they are actually tortoises and the differences in species from the different islands are not that large. But they do show a level of diversity greater than Darwin could observe in England.

But .. as you specify different number of limbs, and eat different foods .. now you are talking genetic level differences that would probably not allow for attraction to potential mates, let alone for fertility. Sorry, but do not see any mammal looking at an insect with a view on procreation, as just one example.

Genetics and evolution operate to fill every niche in the energy budget of a given area. They call them niches because they are small and tight, so creatures that exploit them have to fit rather precisely. But that is the situation here on our earth.

If your story needs wildly different individuals to reproduce then you need to have an ecological mechanism (problem/danger) that requires a far out evolutional advantage that has to be overcome to ensure survival of the species.

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    $\begingroup$ Generally, that's how you get speciation (division into multiple species, like the Darwin finches) rather than maintaining interfertility. Interfertility comes from frequent (enough) crossbreeding, not from long term isolation. $\endgroup$
    – Zeiss Ikon
    Aug 12, 2021 at 18:39
  • $\begingroup$ Ikon, I quite agree. The questioner is hoping to have a strongly diverse species that I think is not possible to achieve without some bizarre variation on biochemistry and environment that enables it in the evolutionary sense. $\endgroup$
    – vulcan_
    Aug 12, 2021 at 18:43
  • $\begingroup$ Interesting point about attraction - most animals use visual cues to estimate a potential mate's fitness, but that gets way more difficult with highly diverse body plans, since few will have much ability to know what a "healthy" individual should look like. It could still work if attraction is based on non-visual cues like pheromones, however. $\endgroup$ Aug 12, 2021 at 19:21
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There are legless lizards that look a lot like a snake, but aren't snakes. I read recently that the "crab" body plan has evolved no less than four times in the last half billion years. None of that, however, happens within a species.

For diverse animals to remain interfertile, they need to interbreed at least occasionally (this is why humans are still, well, human, despite some populations being isolated for tens of thousands of years: they weren't totally isolated).

You can get domestic cats with very short legs, folded ears, crimped hair, bobbed tails, extra toes -- but you won't find any that diverge much more than that. Domestic dogs, with the largest genetic diversity of any known single species, have a body mass range of about 50 to 1 between the smallest variety of Chihuahua and the biggest mastiffs; some have long tails and some just a stub (if any), coats ranging from nearly none to angora-like, boar bristle like, eyes that don't match or are startling white, black/blue patches inside their mouths, a huge range of genetic defects that have been bred as desirable traits for some breed or other -- but they all walk more or less the same way, eat the same kind of food, and behave (at their core) like dogs. And they're all interfertile with wolves and coyotes because they've never completely stopped interbreeding in the past hundred thousand years.

To have a single species with more diversity than dogs might be possible -- one could, for instance, seek mutations that lead to complete deletion of one or both pairs of legs (extreme forms of the achrondroplasia that makes basset hounds so squat, perhaps), produce non-functioning (or even deleted) eyes, and so forth -- but the resulting animals probably wouldn't be viable, likely couldn't even breed without assistance. Steeper divergence, like a dog with hooves or horns like a goat, likely isn't possible because if dogs had those genes in their background, they wouldn't be dogs.

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No

Locomotion method and diet are major facets of an organism, their entire anatomy will be shaped by these things. You will not get much variation in them in the same life stage for an organism, and basically no variation in the same sex.

there is a way to get a drastic difference but you still are left with only 2 modes not a spectrum. Males and females in some species have different diets and locomotion. this is mostly seen in insects but there are some vertebrates that do it. in angle fish adult males lack feeding mechanisms and eventually lose the ability to swim, this is because they attach themselves as parasites to the female. This will not work with hermaphrodites which seems to be what you want. Sex specialization and hemaphrodites don't mesh.

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