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I’m writing for my Safespace series and I’ve hit a snag: I want Homo sapiens to have been abducted from Earth about 10,000 years ago so that when humans expand to the wider galaxy, they find “divergent humans” that have similar biology but have evolved a different culture. However, it seems unlikely that they would be able to have sufficient genetics to survive on alien worlds if they don’t have a sufficient population to prevent inbreeding. So how many humans need to be in a population to prevent inbreeding?

EDIT: I now realize that due to the way organisms work, a full absence of all inbreeding is impossible. What I need is a population large enough to prevent inbreeding to the degree that it won’t alter genetics significantly.

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    $\begingroup$ "It seems unlikely that they would evolve very similarly to humans" - essentially zero evolution is going to occur on a 10,000 year timescale. Neither population will evolve much at all - the "divergent humans" will still be the same as homo sapiens 10,000 years from now, which are the same as the homo sapiens of today, or of 10,000 years ago. $\endgroup$ Commented Sep 20, 2023 at 15:31
  • $\begingroup$ You do not need that many people if you take frozen eggs and sperm. $\endgroup$ Commented Sep 20, 2023 at 18:28
  • $\begingroup$ @RichardKirk The humans, in the story of Safespace, were abducted by Rovak xenobiologists. They probably wouldn’t have brought those too. $\endgroup$
    – Jobah619
    Commented Sep 20, 2023 at 18:30
  • $\begingroup$ @Jobah619 Silly Rovak. Maybe they should have done. They knew enough to take the right number of people. Eggs and sperm are a lot more portable. $\endgroup$ Commented Sep 20, 2023 at 19:00
  • $\begingroup$ What counts as a significant genetic alteration? Speciation would be damned nigh impossible on that timescale, so, hair colour, eye colour? Handedness? Is that what you mean. $\endgroup$ Commented Sep 21, 2023 at 1:25

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All human relations have some degree of inbreeding because we share a common ancestor. You may have two parents, four grandparents, and eight great-grandparents, but the pattern can't continue back forever because eventually it'd exceed the number of people to have ever lived; instead, pedigree collapse ensures that, because people are at some point having children with their first, second, third, or greater-distance cousins, the number of required ancestors shrinks again.

To answer this post's question literally, to avoid any inbreeding whatsoever, you would require an infinitely large (or at least 2^(10,000 years / generation time)) population, such that you could always find two unrelated ancestors for any later ancestor, for at least 10,000 years back.

However, it seems unlikely that they would evolve very similarly to humans if they don’t have a sufficient population to prevent inbreeding.

Your problem may be getting them to diverge enough that you can call them "similar" but not "literally just humans". 10,000 years is less time than the divergence between major human haplogroups today. When the Europeans and Americans encountered each other, that was after a lot more than 10,000 years of genetic separation. Obviously culture changes on much shorter timescales, so that part is locked down nicely.

In this case, a small starting population may actually help you, because randomly selecting a tiny gene pool by abducting related humans will cause a founder effect that can amplify minor fluctuations in allele frequencies. That is, genetic traits that are rare (but present) today may be common in the descendants of small, isolated populations. In this case, you can probably get away with only hundreds or thousands of people to prevent the most dangerous inbreeding disorders (see previous discussions like on this post) while still bottlenecking the population enough to cause this. Considering the limited time, though, I doubt this would be enough to bring about something that wouldn't fundamentally be just like any other genetic group on Earth today.

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  • $\begingroup$ Plus one for underscoring that the separation between native Americans and Europeans occurred much more than 10,000 years ago, and when they met nobody on either side had any doubt that the others were human. You might want to add that most of the superficial differences between Europeans and (northern) native Americans are just the differences between Europeans and the Paleosiberian ancestors of the native Americans. And even today native speakers of paleosiberian languages, such as Chukchi or Nivkh, look very much like (northern) native Americans. $\endgroup$
    – AlexP
    Commented Sep 20, 2023 at 17:39
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There are several studies / articles which indicate that you can get into the mid to low 2000 range without to much of a genetic bottleneck.

Indeed, all Humans these days are genetically speaking almost identical. What is the difference between you and idk Elle Fanning ? Well it turns out, 99.6 of your, mine, hers and Peters DNA is the same. Which does make some sense. After all Organs are usually always the same. And a lot of differences between the genders are less "different" and more "repurposed" in nature. Look up how genitalia develops if you want to be traumatized.

Even then, something like 2000 base pairs in your DNA determine the vast majority of who you are. I dont have a source for that, outside of my Biology prof. So take it with a grain of salt. For instance, the genetic difference for Blond vs Brunet hair, or just hair color in general, is only 13 DNA variations.

So, we are all very much the same.

TLDR; like 2000, make it 10000 if you want to be fancy.

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