| That’s fair. I have read that also, but I have some skepticism that what we’ve seen in extant hunter gatherers there represents a universal instinctive practice in hunter gatherer humans. As the mating pool grows and includes more genetic variation, the propagation penalty for non-obvious genetic defects decreases because feature breakages are mitigated by reinforcement from the pool. In a small and relatively homogenous mating pool (let’s say a band cluster with some non-zero interband genetic flow velocity), a genetic feature breakage that does not get filtered out by sexual selection or consistent early death will be extremely harmful to the group and could kill it or cause it to be outcompeted by neighbor clusters. However, in a large scale society, a breakage in an individual is likely not also in the mate, so the breakage can persist as a recessive without causing consistent damage. So, if an extant hunter gatherer group has any substantial mixture with or heritage from any group that was ever living in a large scale society with a large mating pool, we would expect them to face a problem of recessive diseases from this source and an appropriate response would be intermarriage. Which isn’t to say there aren’t other potential sources of recessive diseases, but I do believe the observations of extant hunter gatherer groups is likely corrupted by this vis a vis true ancestral human behavior. There are also other reasons why interband mating could be advantageous as a social cooperation strategy within the band network, but I wouldn’t necessarily expect that to be so universal that it would be baked into instinct, and it seems like it isn’t based on how people feel in similar situations today. Beyond this, even if that was universal (which it could be), that would be like half your children moving in with your cousin’s family in the next neighborhood over, in exchange for a similar number of your cousin’s children coming to you. Not really much like what happens today. |