haven't looked into the jewish inbreeding too much, but what i read that they suffered several population bottlenecks and sometimes married within small communities. this led to a "genetic bottleneck" were some specific diseases are more likely. i'm also confident this is mostly specific to ashkenazis, who also experienced specific selective pressures which led to their famous higher iq. the muslims on the other hand habitually marry their cousins over generations and have done so for 1400 years, leading such an absurdly low average iq (~80) and high disorders, amongst other problems.
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