(some) east asian pops which trad didn't permit 1st cousin OR 1st+2nd cousin marriages. from http://d-place.org pic.twitter.com/TyUfPs1O6m
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People in one valley can go for decades with zero contact with the people from the next valley over, ten miles away, cuz mountains
Which probably forces inbreeding... but probably in some places, it's so bad that local customs prohibit it for just that reason!
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