Say that a large amount of humans settled in this system and have been living there for a few tens of thousands of years. The system is a binary system with two stars, a sun-like yellow dwarf and a red dwarf. There are two inhabited planets. One is mostly covered in ice, just barely warm enough for habitation and has 10% less gravity than earth, the other is perfect for human comfortability, but has 30% more gravity than earth and has three moons, all of which are heavier than our moon. It's surface is also about 90% covered in ocean. The atmosphere is about 1.2 Atms of pressure on both planets, with very similar composition to earth's. How would the human settlers evolve on these two planets over tens of thousands of years?
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$\begingroup$ How many tens of thousands of years? $\endgroup$– KEY_ABRADECommented Feb 10 at 1:25
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$\begingroup$ @KEY_ABRADE Probably 70-90,000 years. If more is required in order to generate significant changes, then I can go higher than 100,000. $\endgroup$– OprenSteinCommented Feb 10 at 1:27
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4$\begingroup$ I gave +1 to @D'Monlord's answer. Evolution occurs over millions of years, not tens of thousands. You might... maybe... see a small lessening of height and increase in lower body muscle mass... maybe. There are a bazillion variables when it comes to evolution and you've only told us 3-5 per planet. Worse, there's a very wide variety of physiology in humanity, and everything you've told us could fit within existing physiology. $\endgroup$– JBHCommented Feb 10 at 16:42
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2$\begingroup$ Which reminds me, for future reference, please be aware that asking more than one question per post is literally a reason to close the post (click on "close" and read "Needs More Focus.") Asking what happens on two different planets is asking two questions. Asking about "the star system" doesn't make it one question. $\endgroup$– JBHCommented Feb 10 at 16:43
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1$\begingroup$ Your question is too broad. Planets are HUGE and have dozens of different environments. Think about Earth. Natural selection will favour very different traits in the Central Australian Desert than it does in Greenland. You won't evolve malaria resistance if there is no malaria where you live. $\endgroup$– DrBobCommented Apr 20 at 13:48
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3 Answers
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They would not. Not in any significant manner.
Homo Sapiens is mostly unchanged over last 10k years. We almost completely excluded natural selection. The better our technology is the lest natural selection is a factor in survival. It doesn't look like we got significantly more capable or smart - we just learned to use tools and change the world around us.
One of the main evolutionary mechanisms is excluded from our life. People with genetic problems who would be guaranteed to die in childhood 100 years now live to 80 years.
There is one relatively recent mutation, ability to consume milk. Lactose tolerance emerged ~4300 years ago in Europe. It improved kid's chances of survival because humans didn't have advanced agriculture which now mostly exclude malnutrition as a factor for baby survival.
This mutation wouldn't emerge now. We have less and less reasons to adapt to out environment. It is very likely that we start intentionally changing our genome soon. Evolution is mostly non-factor for humans.
Also, it looks like you want someone to write the story.
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$\begingroup$ OP says they're willing to do up to 100,000 years, however. I think that changes the equation. $\endgroup$ Commented Feb 10 at 2:46
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2$\begingroup$ @KEY_ABRADE - how? Anatomically modern humans emerged ~300 000 years ago. And these are colonist, they have technology way beyond anything we can dream of. They are presumably part of greater humanity in space which means evolution of any locally isolated traits is almost impossible. $\endgroup$ Commented Feb 10 at 3:01
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$\begingroup$ @D'Monlord Yep, unless OP is dumping the original colonists there with little to none of even the most basic tech or equipment (and definitely no science or tech manuals) and they then remain isolated it's not happening, you'd have to isolate them and deny them modern tech if you really wanted results. $\endgroup$– PelinoreCommented Feb 15 at 18:23
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$\begingroup$ There is plenty evolution over the last 10,000 years, but it is mostly "invisible" stuff. Such as genes for being able to digest milk after childhood. Those crop up in all the societies which took up raising cattle, goats, etc for milk. Disease resistance is also important - blood group patterns across Europe reflect the aftermath of smallpox and bubonic plague. $\endgroup$– DrBobCommented Apr 20 at 13:54
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Physiological evolution can occur on the scale of 10,000s of years.
To my knowledge there is little to no adaptive evolution of humany anatomy / morphology on the last 50,000 years. The one exception is human skin color variation. However, there has been substantial physiological evolution, including repeated evolution of lactose tolerance (at least 3x), adaptation to high altitudes (3x), high fat diets (inuit) and pathogens (almost everywhere, but especially tropical areas)
One caveat is that some of this evolution appears to have been facilitated by hybridization with our cousins Neanderthals and Denisovans, who had been adapting to regions outside of Africa for a long time.
Comsistent Differences in gravity would likely have impacts on physiology, and perhaps anatomy. Anatomy isn't my thing, but evolutionary impacts on body mass, bone density and muscle mass could occur. As noted in other responses, evolution in humans would be contingent on technology not being used to overcome selection, as it occurs now with eg vaccines and disease
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Child bearing?
There might be some evolutionary pressure on female reproductive organs gestation in general to cope with carrying children to term and then giving birth under 1.3 G conditions. But apart from that and based on what you've described (or left out) I can't see much.
