The pattern of delusions in a cross-cultural hospital population was studied. It was found that there were cultural differences in persecutory, grandiose and religious, and sexual and fantastic delusions, accounted for mainly by the relatively higher frequencies in the African and West Indian cultural groups. These phenomena can be understood in terms of the cultural backgrounds of these groups...

Whether competition among large groups played an important role in human social evolution is dependent on how variation, whether cultural or genetic, is maintained between groups. Comparisons between genetic and cultural differentiation between neighboring groups show how natural selection on large groups is more plausible on cultural rather than genetic variation.