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Possible Human Evolution

I am working on a series set in Alpha Centauri where (in the universe) there are 4 main habitable worlds and a couple that have protected surface dwellings. As well, there are hundreds, if not thousands, of artificial habitats floating around both stars.

Background on the world:

In the mid 2100s, a colony fleet left for a 180 year journey from Earth to aCen with 800,000 people. The basic ethnic makeup was similar to the average makeup of Earth. The main story takes place in mid 2700. Throughout that time, millions of people have come on thousands of other colony ships, especially after it became faster and cheaper to do so.

Now, at the system, the main habitats are the 4 Earth-like planets with gravitational strengths that range from 0.9g to 1.2g. The orbital colonies keep it at 1g because they can. The orbital colonies vary between inner and outer so they receive varying amount of stellar light and radiation.

The question:

Between the current trend of human evolution and then the trip across interstellar space, followed by living on several types of habitats; what are the possible future "ethnicity types"? Meaning, would everyone look the same like in the movie Cloud Atlas, would they look the same as now? A long answer could breakdown how a people might evolve on each of the habitat types; however other good answers could provide information on how certain features (star-type, gravity strength, atmospheric pressure, atmospheric composition [while being breathable] could affect the development of humans over the course of a few hundred years.

Assumptions made:

  • Human ethnic and racial barriers have been more or less broken and marriages are random.
  • Humans originally selected were genetically screened and only the best candidates were selected.
  • The system population is around 30,000,000,000 people.
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  • $\begingroup$ Ethinicity is about culture -- what people eat, how they speak, how they behave. Phenotypical attributes such as hair texture, eye color, avergae height and skin pigmentation have very very little correlation with ethnicity. There are blonde French people and brunette French people, blue-eyed Afghans and dark-eyed Afghans, very light skinned Russians and quite dark skinned Russians and so on. And in 500 years from now people will look just as they look today; look for example at the large collection of paintings by Titian on Wikimedia. $\endgroup$ – AlexP Jun 4 '20 at 21:23
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Firstly there would be virtually no true genetic evolutionary effects after a few hundred years. Evolutionary effects take many thousands of even millions of years in higher organisms. However a great deal of selection from the existing gene pool would occur. So for example on a higher gravity world you might expect stronger members of society to become more prevalent and those with Tibetan or Andean heritage to be more successful in lower pressure environments. But unless the conditions were extreme the effects might take many hundreds of years to show.

It is similar to horse breeding; in a few centuries horses have been breed for racing and have achieved a good pace at running, but only using the genes available in the native horse gene pool. There are very few if any improvements in horse speed records today because we have probably got the best of the genetic bunch more or less. If we were to continue for a few hundred thousand years we might expect some beneficial mutations to occur and horse speed would increase a little, given millions of years we might end up with horses running much faster more like slow cheetahs.

In terms of genetic diversity it is likely that there would be a slight loss in genetic diversity in those circumstances, but considering the size of the populations being shipped, not much. I would however expect the genes to become widely distributed during the trips, so all skin and hair colours would be expected, even combinations that do not currently occur (or are extremely rare if they do) such as ginger haired Orientals.

As a separate point of interest, a gravitational field strength of much more than 1g might prove impossible to leave with chemical rockets due to the exponential function in the rocket equation (so they're stuck there unless they use nuclear rockets or other fancy hand-waved propulsion).

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  • $\begingroup$ Thanks for the answer.. Do you think it would be feasible for the travellers to alter themselves at the final point in order to adapt better to their new environment? That being said, by my setup, once the original colonists arrive they stay in orbit for about 50 years to continue the terraforming and infrastructure build that was started by drones almost a hundred years earlier. As for the gravity well situation, since this is the future and advanced tech is present, the major planets will have orbital rings or space elevators for getting on and off world $\endgroup$ – Markitect Jun 5 '20 at 2:40
  • $\begingroup$ Yes I would imagine some form or genetic engineering and artifical selection would be available to them $\endgroup$ – Slarty Jun 5 '20 at 7:56
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What is the atmospheric composition of your worlds?

This will determine everything. From what I see your planets are all roughly equivalent gravity; lowest is about Venus gravity and highest is somewhere in the middle of estimates for Proxima b. Given that for at least one of these there have been serious studies on exploring with a manned mission, and that NASA sees no major issues for the astronauts staying in this gravity for months at a time, I find it difficult to believe any major physiological changes would occur.

The same applies to your 1g colonies, and probably even less change would occur there since pressure is regulated. Atmospheric pressure on the planets won't really change too much in the way of evolution either, as you would need to build habitats in 1atm in order to keep the colonists initially comfortable anyway. This brings us to the final long term consideration of atmospheric composition and temperature; based on this you may want and need to develop a higher genetic resistance to extreme conditions. Although that is the only way I could imagine a major evolutionary change being motivated, feel free to correct me.

I hope this helps!

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  • $\begingroup$ I would think the composition would be very similar to earth, if not they would alter what they could before completely inhabitanting the planet. I'm assuming the smaller planets will have a lower atmospheric pressure and also less of the lighter atmosphere components because of their lower gravity. And maybe the bigger planet will have lower oxygen levels and higher nitrogen and CO2 levels because they are heavier (at least at the surface level) probably not much to be noticeable though. I'm no atmospheric specialist though so I am completely swinging in the weeds here. $\endgroup$ – Markitect Jun 5 '20 at 2:47

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