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In 10,000 yrs, barring human interference, what kinds of evolution might we expect in familiar animals? Leaving aside the causes of the adaptation, for example, is it possible that the grey squirrel could evolve into a jet-black squirrel? Is it possible that a raven or a vulture could increase in size to be twice as big as before?

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    $\begingroup$ Gray squirrel to black squirrel: quite possible. Assuming that by "gray squirrel" you mean Sciurus carolinensis, then Wikipedia says that "particularly in urban situations where the risk of predation is reduced, both white and black-colored individuals are quite often found": black gray squirrels already exist, all that's needed is a reason for them to become dominant. As for ravens, assuming you mean Corvus corax, there already is a large difference in size between different subspecies. $\endgroup$ – AlexP Oct 24 '18 at 21:32
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    $\begingroup$ The California Condor might already be as large as it is possible for a vulture to be. $\endgroup$ – Jasper Oct 25 '18 at 1:19
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    $\begingroup$ Any answer will depend on the natural selection pressures in the environment of any organism. If there is no change in the environment, there will be no impetus for the organism to evolve and change any of its characteristics. If the environment changes radically, natural selection will select the offspring most suited to survive & reproduce. It wil, therefore, evolve. So ti's either not at all or lots -- depending on environmental changes. $\endgroup$ – a4android Oct 25 '18 at 1:26
  • $\begingroup$ A disease outbreak, major geographic change, or climate change can cause a species to go extinct. If the species goes almost extinct, or if small population(s) are cut off from the rest of the species, then rapid genetic drift is possible in small populations. For an example of how much a small population can evolve, consider the cheetah. $\endgroup$ – Jasper Oct 25 '18 at 1:33
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    $\begingroup$ I'm voting to close this question as too broad. Not only do you ask multiple questions, but the evolution of animals in 10,000 is more than enough to fill a library of the possible variations and reasons why it occurs. If you have an idea for the sake of a story or game, I would simply say Yes, the change can happen. $\endgroup$ – Shadowzee Oct 25 '18 at 2:59
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The example to look to is dogs.

dogs https://www.laboratoryequipment.com/news/2017/05/research-evolution-dog-breeds-may-lead-new-therapies-human-diseases

Humans did interfere, but not via genetic manipulation. They simply selected for the dogs which fit the criteria they wanted. 10,000 years has produced the range of sizes and shapes dogs have today. But there have not been flying dogs, or photosynthetic dogs. Your example of color differences and size difference falls well within the range of what has happened with dogs.

Arguably environmental circumstances would produce evolution more slowly than artificial selection but not necessarily so. If twice as many black squirrels make it to reproductive age as any other color squirrel, it will be all black squirrels very quickly.

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    $\begingroup$ In soot-filled nineteenth-century English cities, peppered moths went from 100 % camouflaged-white to 98% camouflaged-black in 50 years. $\endgroup$ – Jasper Oct 25 '18 at 1:15
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    $\begingroup$ Hint: It's not only survival which determines genetic propagation, but also sexual selection. Usually males propose and females select with whom they reproduce based on some hierarchical rivalry and/or competition among the males. What also occurs is that specimen which succeed to be more healthy and fed turn out to be among the "better" ones, thus often being more likely successful, and be of higher chance to be chosen as a mating partner. So survival is a criteria especially until the specimen in question succeeds to reproduce (or while it can do it). $\endgroup$ – Battle Oct 25 '18 at 14:12
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Without environmental changes, one would expect no evolutionary changes at all. Indeed, throughout biological history most species have stayed relatively stable, with tiny, slow changes, for hundreds of thousands of years. Hundreds of millions, in the case of species like sharks.

On the other hand, if you are supposing some kind of major environmental change -- the sudden absence of humans, for example -- then minor changes (like coloration) can happen in a dozen generations, and major changes can happen in a few hundred. Given that 10,000 years is 10,000 squirrel generations, for example, says that you would expect at least minor changes in coat and coloration among squirrels, and substantial changes in appearance with any environmental change.

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