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I was exploring the trope of a non-evolutionary species, and then I realised that what makes species evolve are differences in their local environment. So I thought if there was a way for a planet to have one biome, then it must be a tidally-locked planet around a red dwarf star.

The side of that planet facing the star would be baking hot, and the side facing away from the star would be freezing cold, but halfway around the planet would be a band of liveable temperature, like the Equator.

If the biome around the Equator was the same, then the organisms would find no need to adapt, and they would be locked in one state forever.

Is my presumption correct, or are there any flaws in my reasoning?

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    $\begingroup$ Living fossils like sturgeon experience stabilizing selection, allowing them to look mostly unchanged over a hundred million years. Is this the kind of thing you're looking for or are you looking for something that does not mutate at all? $\endgroup$
    – jb6330
    Sep 12 at 14:34
  • $\begingroup$ Yes, I think that sounds something like it. $\endgroup$ Sep 13 at 14:51

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Your reasoning is flawed for several reasons:

  • @L.Dutch is correct concerning variation within a single biome, but to expand on it a bit, a single biome can have hot summers and cold winters, times of proverbial feast and proverbial famine, random events like forest fires and earthquakes. Even a single biome is not static. But to expand on @L.Dutch's answer: even the narrow band you're talking about is highly unlikely to be just a single biome. I'm assuming your life needs water, and the biome in a lake is different from the biome on the shore of the lake is different from the biome twenty miles away from the lake. In short, you're oversimplifying.

  • Next, you're not correct that environmental conditions are what drive evolution. Evironment is just one of a great many conditions that drive evolution. Competition for food, competition for reproduction, adaptation to localized conditions (such as the various depths of a lake/ocean), the need to solve problems (how to climb that tree? The fruit looks tasty!) all lead to evolutionary change. In fact, pure, random chance can (and will) lead to evolution.

  • You're not correct in assuming the plausibility of a "non-evolutionary species." Such a species would require creation by God — otherwise you have the embarrassing necessity of explaining how your species came to be without the privilege of evolution. I'm not even convinced it's possible to postulate the cessation of evolution — that would require the possibility of change and/or mutation stopping completely. If you can do that, congratulations, you've stumbled onto the secret of eternal youth.

I'm afraid you're doomed by the requirements of the Science-Based tag. That tag forces us to realize that variation naturally occurs in a species. Using Humans as an example, some are taller, some shorter. Some have light skin, some dark. Some eyes are green, others blue. Some hair is light, others dark. These are nearly superficial examples of the problem. The second one of those variations becomes useful for the survival of the species (your plant life is predominantly dark colored, so dark skin and dark hair provides better protection) the process of natural selection (i.e., light skinned and/or light haired humans get eaten more often) causes an adaptive change.

In other words, the idea of a non-evolutionary species fails the Science-Based tag.

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    $\begingroup$ +1. But..."Such a species would require creation by God"...or creation by another species. I think the Bandersnatchi of Larry Niven's Known Space are the closest thing I can think of to a non-evolving species in sci-fi. $\endgroup$
    – Qami
    Sep 12 at 18:09
  • $\begingroup$ @Qami While a species could create another species without prior evolutionary dependencies, I have my doubts that they could thereafter keep the species from evolving unless the only method of procreation is laboratory-based - but at that point it's not a "species," which is defined by its ability to self-procreate. $\endgroup$
    – JBH
    Sep 13 at 1:19
  • $\begingroup$ Maybe I'm nitpicking but most of the examples your gave in human (skin eye and hair color) and results of environmental pressure, mainly in temperature and amount of sunlight. One could easily argue humans would have much less diversity if there was a single biome with constant temperature, sunlight, humidity, altitude etc. A species that only lives in, say, hot sand deserts doesn't have as much diversity. $\endgroup$ Sep 13 at 13:41
  • $\begingroup$ "I'm not even convinced it's possible to postulate the cessation of evolution" this could be achieved via genetic engineering and a very absolutist/weird ideology $\endgroup$
    – Hobbamok
    Sep 13 at 14:57
  • $\begingroup$ @TeleportingGoat There's no such thing as a single biome with constant temperature, sunlight... etc. You're correct, though that there would be less diversity - but there would be diversity. A "non-evolutionary species" is defined as having no diversity. $\endgroup$
    – JBH
    Sep 13 at 15:20
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You reasoning is flawed in that even in a single biome there are differences:

  • temperature at different depth in the water will change, for example, and what thrives at 10 meter deep will be different than what thrives at 500 meter deep.
  • availability of nutrients can be different
  • etc.

Any of the above can be the trigger for speciation. However, I doubt that you can scientifically have life without evolution, because evolution is what has driven the early biotes or biote-like aggregates of molecules to what has become life.

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TL:DR; Mutation will ensure that no species is stable and will constantly evolve

Evolution is driven by differing survivability of individuals in response to environmental pressures (Natural Selection), rather than variability of the environment itself. All zebras (to pick a completely random example) evolved in, essentially, the same environment. The differences that drove their evolution was between the zebras. Those zebras that possessed better responses to that environment had more surviving descendants and, through the responses of those individuals, zebras as a species became better adapted to that environment over time.

The differences between individual zebras are encoded in their genomes, which is also how they pass those traits on to their descendants.

Now, one might suppose that in an unchanging environment eventually zebras would be perfectly adapted, and from then on never change.

But this is not the case because there is another factor in evolution. The genome is not unchanging. It is constantly subject to subtle naturally occurring mutations. Most are neutral, many are harmful, but a few are beneficial. A zebra with such a mutation will eventually have more descendants than zebras lacking it, and zebras will evolve, even in the absence of environmental change.

Finally consider that zebras do not exist in isolation and what is true for them is also true for the grass they eat and the lions that eat them, so their environment (even if climate and geology could somehow be stable for millions of years) constantly changes, and changes in environment mean that the great great grandchildren of todays perfect zebras will have to adapt to meet the new challenges and evolution will continue.

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