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Other questions have looked into founding successful colonies, meaning healthy populations that thrive indefinitely. However, many stories concern a colony that is discovered some specific (and historically short) time after it is started.

In Star Trek: The Next Generation and Fallout 3 both featured a group of shut ins where in the former (Season 5 episode 13 The Masterpiece Society) was planned from the start and the latter (Vault 101) was an emergency measure to a nuclear holocaust. Both lasted for about 200 years and both were noted to still have a diverse enough gene pool with plans for selective breeding (it being brought up by the Vault 101 Overseer when you have a high enough intelligence skill).

Now assuming that a Vault or Colony had the right equipment/policies to avoid a skills shortage and there were no accidental deaths, how many people minimum (how many males/females, how many would need to be adults/children at the beginning) would be needed to have a diverse enough gene pool to last about 2 centuries?

That is, when visitors arrived 200 years later, they found living descendants of the original small population.

Brythan
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  • Also this one: https://worldbuilding.stackexchange.com/questions/48376/smallest-self-sufficient-colony – SRM Jan 16 '17 at 03:01
  • Two. That is enough. You should define technological level, cruelty of selection, initial selection of population and technological level of initial selection. This may be not entirely clear based on mentions you have made. – MolbOrg Jan 16 '17 at 08:37
  • Well.. Vault 101 had people from the outside join the Vault (e.g. James) – dot_Sp0T Jan 16 '17 at 09:25
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    I wrote an answer which I could not post in time which looks at a population that only lasts 200 years. The linked dups concern colonies that last indefinitely, so my answer doesn’t fit there. I suggest that this makes it not a dup, and it could be edited to emphasize this distinction. – JDługosz Jan 16 '17 at 09:57
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    @JDługosz I voted for this question to be a dupe because it asks about the same thing; the time difference shouldn't largely matter because the same factors that make genetic diversity important apply here as well as there. If the question would ask about perfect isolation then the answer would be 2 people (or 1 person if cloning was available), because with a perfect genome and no radiation or other influences from outside, there is no need to have different genes... – dot_Sp0T Jan 16 '17 at 10:23
  • @dot_Sp0T less important if it booms and busts within 200 years. The rediscovery team could meet septagenarians whose children all died from cistic fibrosis. – JDługosz Jan 16 '17 at 10:26
  • @JDługosz but then the answer would be so blindingly obvious that the question needn't be asked: to 200 years is maybe some 5-6 generations - that is nothing.. – dot_Sp0T Jan 16 '17 at 10:33
  • A lot of questions are blindingly obvious to some. IAC I saved my answer content which does not “fit” the other questions. It discusses new mutations etc. so is pretty interesting to those who don’t know that Queen Victoria was an “X-man”. – JDługosz Jan 16 '17 at 10:37

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Your question, as posed, is far too vague to be answered. It is a myth that incest necessarily results in unhealthy off-spring. It just ain't true, although it might. So, assuming optimum (good) luck, one adam and one eve is sufficient. Assuming maximum bad luck, a trillion wouldn't be enough. If gene editing continues to advance the way it has in the last 20 years, then assuming that that technology is available, it's likely that in a couple of generations A.I. could repopulate the Earth with humans even if we were all extinct. (Why they would want to do that is another question).

Li Zhi
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  • It's not really a myth but rather statistics. Combining the genes of two people that are very similar just has a higher chance of promoting bad recessive traits – dot_Sp0T Jan 16 '17 at 09:26
  • @dot_Sp0T: Higher chance does not mean certain. Lower chance does not mean impossible. – AlexP Jan 16 '17 at 09:27
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    It Is not impossible that all the atoms in your head move upwards at once, and your head then falls off. It is certain, in every meaningful sense, that it won't. – nigel222 Jan 16 '17 at 10:31