...we would be a very peculiar animal species if we did not have sex differences in behavior as well as anatomy. In virtually every mammal and nearly all birds, males are more aggressive, females more nurturing. It is a distinction that goes right back to active sperm competing for stationary eggs in the primeval ocean. It was only reinforced when the invention of the placenta and the mammary gland gave male mammals a gigantic prize to compete for: nine months and several years of somebody else's bodily efforts. Wombs are worth fighting over—and granting to favored applicants only.
So it's no zoological accident that in all societies, however peaceful or violent, men are about 50 times more likely to kill other men than women are to kill women, and they do so most in young adulthood, when most actively competing for mates. Likewise, it is no neurophysiological accident that women coo over newborn babies more enthusiastically than men do. Women who showed interest in babies left more genes behind than those who were indifferent; men who turned violent left more genes.More.