>>14304616The problem lies much deeper than that. Say, for instance, that Europeans have genes which predispose their carrier towards homosexuality while also making their carrier more intelligent. Suppose Africans underwent some evolution, and they carry homosexuality genes which also make you tall.
Then you get F1 African x European individuals, and they carry both sets of genes, and thus have 2x the rate of homosexuality, despite not needing the height genes. Homosexuals have fewer kids, thus it'll cause negative selection on both sets of genes.
When two populations intermingle it causes a depletion of rare gene variants, some of those variants aren't rare because they're deleterious, but are rare because they're evolutionarily new. This "cultural diffusion" thing is even used to explain why humans seemingly have such low levels of gene diversity compared to other animals. Ashkenazi Jews, for example, represent an extreme genetic isolate, and due to this certain extremely rare genes have been allowed to reach large frequencies, on the order of 10-20%, you add admixture, those genes will undergo negative selection for about 10 or so generations regardless of whatever advantage they give in reality.
