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I've got an idea and would ask for you evolution enthusiasts: what if humanity could be forced to not travel around the earth and be forced to stay by some alien culture in their home habitats (countries or continents) and not hallowed to intermingle with each other. Centuries goes by and after some time the limitations fade due to external cause. Humans are free once more to travel and communcate, but they're very different from each other. What modification would the body of an African human achieve that a Greenlander human would not?

The idea is of a dystopian future where an alien race (or human themselves perhaps) are so interested in preserving ecosystems that they transform each "biome" in a nature reserve and force all creatures inside these boundaries, therefore hallowing evolution to change themselves into different species.

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  • $\begingroup$ welcome to worldbuilding. We prefer to focus on a single question per post (you have many more), with the question being measurably answerable. Please take the tour and visit the help center to understand our standards, then rework your post to make it fit them. Else it might be closed. $\endgroup$ – L.Dutch - Reinstate Monica Oct 3 '19 at 8:06
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    $\begingroup$ Depends on how small the isolated populations are; this is crucial. A small enough population (say, a few thousand individuals) could gain reproductive incompatibility with the rest of the species quite quickly, say a few thousand generations, maybe as quickly as 50,000 years. Large populations will likely take very much longer. (Note the words "may" and "likely"; this is all driven by chance events.) $\endgroup$ – AlexP Oct 3 '19 at 8:44
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    $\begingroup$ Also please note that "how could they change" and "what modifications" can be answered only in a purely speculative fashion, and any such change would take quite a long time. Evolution is driven by bioth genetic drift and natural plus sexual selection, and one cannot disregard any of them. $\endgroup$ – AlexP Oct 3 '19 at 8:58
  • $\begingroup$ So there is no way to predict such drifts? something akin to giantism or dwarfism in the islands. For example: a creature in a relatively dry environment would likely develop some kind of water supply organ like camel or dromedary. (I know it's not a rule, just a generic direction to start excluding some things from my horizon) $\endgroup$ – R3g0lus Oct 3 '19 at 9:30
  • $\begingroup$ Genetic drift is random. However, your camel example is incorrect; camels store fat in their hump, not water. To get the kind of changes you're looking for would require a lot longer than a few centuries. $\endgroup$ – Frostfyre Oct 3 '19 at 12:32
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Unless only evolution (and not genetic modification) is in game - not much.

As a specie we had a major split 70k years ago, when small group of our ancestors left Africa (yes, a serious genetic bottleneck), from them evolved all out-of Africa races that we have today. We already evolved to match our respective environments, and a few centuries would not change that much.

If anything, the main evolutionary pressure that we have right now is mostly civilisation based. Contemporary social norms (welfare state that allows survival of people who would be otherwise doomed, subsidising reproduction of people at the intellectual bottom of society, social norms which encourage high IQ women to pursue carriers at expense of childbearing) are strongly disgenics, and would shape our evolution in incoming years. In long run, we have a nice choice:

  • slow degeneration which would lead to societal collapse, and return to harsh evolutionary conductive conditions

  • eugenics

  • designer babies

Oh, in order not to sound so pessimistic - apparently we're also evolving some resistance against lifestyle diseases.

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