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I know that strictly speaking the term "involution" referring to the evolution theory doesn't hold any meaning. Organisms keep on evolving and changing with time, that's all.

But the following situation could perfectly happen:

Some event causes some organisms to evolve certain characteristics that allow for a better survival, but with time that event stops and what was previously and advantage for these organisms, now it's a disadvantange, and to adapt to the new situation what they do is to exactly remove these characteristics and they end up being exactly the same as they were previously to the change. It could be considered that they have "involutioned".

Are there checked examples of this? (Not just as theory, examples of organisms where this "involution" has been observed). I'm specially interested in "complex" organisms, I think this is not that far fetched to happen to organisms like bacteria, virus or the like. But for more "complex" organisms I guess it's too much of a coincidence.

Edit: I'm putting an example to clarify:

Let's imagine we have a huge amount of plants of the same species which can grow extremely fast (in the way they could simulate 100000 years in evolution in one hour) and we have an atmosphere for them that is the same as current one. (Not realistic, but let's make the thought experiment). We also put some put of these plants apart.

Little by little we go changing all the carbon dioxide in that atmosphere with something, like, for example, nitrogen, it's to expect, that, with time, some plants will appear to better use the nitrogen, at least up to the point where they can survive, as carbon dioxide is every time lower and lower and plants not adapted to this end up dying.

When we finally have only nitrogen processing plants we start the opposite, we start filling little by little with carbon dioxide, it's to expect that the contrary would happen.

Now, if a biologist were to observe the plants that were set apart at the beginning and the new created plants he wouldn't be able to tell where each plant is from, unless he was aware they were separated to do the experiment.

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  • $\begingroup$ Are you asking about an example of varying selection pressure (with associated adaptation) over time? Something like "temperature decreases, creature evolve to be more hairy. Temperature increase back, creature evolve to be less hairy"? $\endgroup$
    – Remi.b
    Jun 2, 2019 at 14:22
  • $\begingroup$ @Remi.b, it's more than that, it would be creature evolves to be more hairy, creature goes back to be the same. $\endgroup$
    – mylket
    Jun 2, 2019 at 14:23
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    $\begingroup$ Isn't it exactly what I suggested? I had never heard of the concept of "involution". According to wikipedia it refers to the physiological change in organ size. It has nothing to do with evolution. You might want to just get rid of this term alltogether and just ask for an evidence of varying selection pressure (with associated adaptation) over time? Eventually, add a specific example (such as my hairy/hairless example) with it for clarification. $\endgroup$
    – Remi.b
    Jun 2, 2019 at 14:46
  • $\begingroup$ "Involution" is basically a made up word that doesn't hold any meaning in this context, although it's translation is used in my native language for describing behaviors that people make that are not supposed to happen nowadays, as if it were to mean that they are some previous organism. But well, we can forget about the word and I'll put an example that clearly explains it. $\endgroup$
    – mylket
    Jun 2, 2019 at 15:14
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    $\begingroup$ Yes there are several examples of retrograde evolution (traits present in ancestors but lost in a species). It can be subtle as loss of some non-central metabolic pathway (Vit-C synthesis) or drastically visible as loss of body parts (for e.g. limbs of snakes). I just saw an entire book on this topic. But there can be drastic trait losses in micro-organisms too (for e.g. loss of mitochondria). Is this what you are looking for? $\endgroup$
    – WYSIWYG
    Jun 2, 2019 at 16:09

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"Exactly the same" probably doesn't fly, just because there is so much possible variation, but for a fairly obvious example, consider birds. Their ancestors evolved flight: some modern-day birds (ostriches, emus, kiwis, &c) have lost that ability, though their vestigal wings haven't re-evolved into legs. But consider the evolutionary link between birds and theropod dinosaurs, and how many of those (e.g. T. rex) had vestigal forelimbs.

Another example would be dolphins and ichthyosaurs, which both independently "involved" from land-dwelling creatures back to a form that's similar to the ancestral fish.

But of course neither of these are really "involution" in the sense of reversing an evolutionary path. They are cases of organisms exploring new evolutionary paths, where the environmental pressures (such as need for streamlining to move efficiently in water) cause them to resemble some ancestral form.

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