This paper reviews selected studies of aggression in males and females and concludes that physiological, emotional and behavioral differences exist between the sexes. Primate studies, conducted by Harlow, are employed as evidence that sex differences in aggression are primarily biological and not primarily cultural phenomena. It is further concluded that sex differences are essential to the survival of the individual and the family and that the conceptualization of sex differences in terms of socialized sex-roles is fundamentally mistaken. (RH)