Sexual selection, Machiavellian intelligence, and the origins of psychosis.

According to Darwin's theory of sexual selection some features that differentiate the two sexes evolve by a process of "male competition" and "female choice". The sex difference in age of onset of psychotic illness in man may relate to a sexual dimorphism in cerebral organisation (the male brain being more lateralised or asymmetrical than the female brain), a difference consistent with a role for sexual selection in the evolution of the human brain. Differing criteria (reflected in a cross-culturally stable difference in mean age at marriage) in males and females for selecting personality characteristics in a mate may generate diversity in the balance of growth between the hemispheres, and this could maintain the high and relatively constant rates of psychosis in human populations.