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Far into the future, humanity is largely split into 2 groups.

  • The first group consists of space-dwelling humans, who live in enormous space stations equipped to sustain human life indefinitely, getting their resources from asteroids and small moons.
  • The second group consists of planet-dwelling humans, who live lives very similar to those we live today.

The planets that these humans inhabit are entirely Earth-like, so I don't expect much evolutionary change for the planet-dwellers. However, I'm curious as to how millennia in space might affect humans from an evolutionary standpoint.

I'll try to give as much detail as possible as to what life is like for these space-dwelling humans.

Most people live on large space stations, and, when I say large, I mean they average Manhattan-sized, with a similar population density (although there will be much larger "Super Stations" and much smaller stations). The living quarters of these stations are equipped with artificial gravity. The personal quarters of individuals is typically the size of a small apartment, although wealthier individuals can, of course, purchase themselves larger compartments.

Although the living quarters are equipped with artificial gravity, working and living in 0g is something that occupants deal with on a daily basis on industrial spacecrafts (such as haulers and mining craft) and in industrial areas of the space station.

Occupants mainly subsist on genetically altered algal oil that is designed to provide all necessary nutrition, however "real" food does still exist as a luxury product that you can buy as a special treat now and again. Water is produced by a combination of ice mining and synthesizing oxygen(produced as a biproduct of algal production) and hydrogen(harvested from nearby stars), and is recycled very efficiently (nearly 97%!).

The technology level of these civilizations is incredibly advanced: cybernetic enhancements are commonplace. Poverty still exists, but in a different form: no one goes hungry because food production is simply a bi-product of oxygen production. Instead, the poor are "poor" because they are denied luxuries such as enjoyable living quarters, cybernetic implants, and "real" food.

Over the course of hundreds of thousands of years, how might these humans evolve in their new environment, far away from the conditions that they had originally evolved in?

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  • $\begingroup$ I'm assuming the space-farring humans have access to medicine and life support systems (doesn't have to be anything futuristic, just what we have nowadays). If so, evolution doesn't exactly work anymore (atleast not in a way you'd expect) as everyone with genetic weaknesses are kept alive regardless. The only thing I can say is that unless something is done, both groups would progressively become dumber (yes like in the film idiocracy) as not knowing how to properly use contraceptives is an excellent way to have many descendants. $\endgroup$
    – AngelPray
    Jan 20, 2017 at 19:23
  • $\begingroup$ hmmm, that is a good point, maybe I should rewrite the question to just be "What evolutionary changes would be advantageous in the described environment", and then write it so that the inhabitants, using genetic modification create "better" humans as test tube babies $\endgroup$
    – Bitsplease
    Jan 20, 2017 at 19:35
  • $\begingroup$ From the show The 100, those in space were exposed to higher radiation from the sun for such a long time that they were fundamentally different than those who had stayed on Earth. $\endgroup$
    – nightsurfer
    Jan 20, 2017 at 21:17
  • $\begingroup$ This video explains what would happen to the people born in space: youtube.com/watch?v=jTL_sJycQAA It shows that with out artificial gravity a colony on space stations aren't really viable. $\endgroup$
    – Garto
    Jan 21, 2017 at 12:24

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Strictly speaking the OP hasn't specified the two populations are isolated. Also, they aren't two populations they're actually two classes of populations living in multiple locations. Interbreeding could still take place, thereby reducing any probability of speciation occurring due to genetic drift.

There will be epigenetic impacts to different environments. The stationers may become more cancer resistant (higher background radiation) but the quality of medicine may neutralize that as a selection factor. Given enough time the main selection factor in both classes of populations will be sexual selection.

There is every suggestion that is extensive space travel in this hypothetical universe. It would be relatively easy for genetic material to be exchanged between planet-based and station-based populations. This would maintain genetic diversity in populations. Coincidently this would obviate the tendencies towards speciation.

Also, humans have a well-developed tendency towards exogamy. Marriage and reproduction outside your own group will enhance diversity and cancel genetic drift.

Generally there doesn't seem to be any major selection pressures to make the two groups of populations evolve. Other than cultural factors which could influence sexual selection.

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  • $\begingroup$ Sexual selection would indeed be the only evolutive pressure as it is the only one that can't be circumvented by medicine... well... except through plastic surgery... +1 $\endgroup$
    – AngelPray
    Jan 21, 2017 at 4:48
  • $\begingroup$ @AngelPray Everybody knows cosmetic surgery isn't real medicine except for the transfusion of money out of the pockets of the gullible into those of the surgeons. $\endgroup$
    – a4android
    Jan 21, 2017 at 5:05
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Since the two populations are isolated, they won’t be interbreeding or part of the genetic bucket chain that keeps everyone related. This is one of the necessary factors to allow speciation. So, you might get some set of random changes to biochemestry that results in incompatibility. Likewise, isolated colonies will have traits that become universal due to the founder effect, and random shifts in population statistics.

You might suppose a higher mutation rate because of radiation, and some specific traits that still affect survivability in a major way even with modern technology (e.g. cliff dwelling people tend not to have inner ear problems).

If the community is isolated enough that help can’t be sent, then you might have survivors of a disease outbreak who have a particular blood difference or whatever that affects the protein used by the pathogen to be infectious.

Look at things like that to promote evolution even in the face of modern technology.

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  • $\begingroup$ This feels more like a good start on an answer, but not a good answer. That second paragraph and last sentence... are there examples you can point to today? $\endgroup$
    – SRM
    Jan 21, 2017 at 2:53

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