Sex differences in aggression: a rejoinder and reprise.

A meta analysis of observational studies of peer-directed aggression by children aged 6 and younger yields a highly significant sex difference. Out of 32 studies, z values reflected higher male aggression in 24, no difference in 8, higher female aggression in none. Furthermore, boys' aggression is most often displayed in the presence of male partners. Evidence is presented that the sex difference is probably not merely an artifact of higher rates of male activity or social interaction. Existing cross-cultural evidence also shows higher rates of male aggression, as does most of the work on free-living primates. Specifically, the 3 observational studies of chimpanzees show considerably more aggression in males. Evidence for a hormonal contribution to male aggression is clear in animals and inconclusive in human beings, although the existing human findings are consistent with such a contribution. Recent evidence on the differential socialization of boys and girls supports our earlier view: that boys do not receive more reinforcement for aggression than girls, and that rates of punishment are also similar once the differential base rates in aggression are taken into account. The role of self-socialization (including choice of same-sex models) is discussed, and the view is expressed that this probably depends upon the development of certain cognitions about sex identity which normally do not develop until a later age than the age at which a consistent sex difference in aggression first appears.