A far-right twitter account posted that interracial marriage would be more dangerous is caesarian sections weren't widely used because of skull shape/pelvis mismatches (africans have longer skulls, amerinds have wider skulls, whites and asians are somewhere in between and each race has pelvis that match that shape). A little research suggests this is actually true (I even found a NYT article that suggested OBs should be trained differently for delivering black babies) but it's something you couldn't ever ever ever talk about in polite society.