How are the small, remote settlements of the world (i.e. upper Greenland, Nunavut, Pitcairn Island, Tristan de Cunha) able to avoid a completely incestuous population?
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Alright, this eill require explaining why inbreeding is bad on a genetic level first
On a really simplified level, the amount of genetics you share with a relative halfs with each degree of separation (or 1/2^n where N is the degrees of separation)
You are 0 generations removed from yourself, so you share 1/1 or 100% of your genetics with yourself.
You and a sibling share an ancestor 1 generation removed so you share 50% of your genetics, but you also share 50% of genetics with your parents
You share 25% of your genetics with your aunts and uncles (You share 50% of the genetics with your parents and they share 50% of their genetics with their siblings)
You share 12.5% of your genetics with your first cousin because they share 50% of their genetics with their parents who you are 25% genetically identical to, and as you pull back the generation of the shated common ancestor and become 2nd, 3rd, 4th etc cousins that number keeps halfling
This fact is how things like 23 and me can tell you how you’re related to someone with enough data on people surrounding you
The closer to 1 that number is, the more like any recessive genetic disorders contained in that shared genetic code become more likely to appear
Second the closer related to someone you are, the more genetically similar your kids will be. If a pathogen develops that exploits a genetic flaw, the more similar a given population is genetically the more capable the disease is of destroying the entire population of (this is actually a very big problem regarding food monocultures)
Now, those are the reasons that incest is bad from a genetics perspective, but here’s some information that helps mitigate that somewhat
DNA is a fixed length, and most humans are going to share a LOT of DNA because all of our bodies work fundamentally the same way. Similar to how even 2 copies of Windows with heavy modifications are going to share a lot of source code.
So, there is a point where you are no more genetically related to a particularly distant cousin than you are any random person
That’s the key to the puzzle right there, long term stable population groups in highly isolated locations started with enough people that they could avoid incest being an inevitability until after that threshold was met
Give it a long enough time and recessive traits will still be expressed more often because people will have those genes at higher than average rates, but genetic diversity will still be strong enough that a plague won’t instantly kill them faster than any random population for genetic reasons
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