(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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Which probably forces inbreeding... but probably in some places, it's so bad that local customs prohibit it for just that reason!
Just guessing, however, I've read nothing relevant that I can remember!
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