AGGRESSION IN HUMANS - WHAT IS ITS BIOLOGICAL FOUNDATION

Although human aggression is frequently inferred to parallel aggressio n based on testosterone in nonprimate mammals, there is little concret e support for this position. High- and low-aggression individuals do n ot consistently differ in serum testosterone. Aggression does not chan ge at puberty when testosterone levels increase. Aggression does not i ncrease in hypogonadal males (or females) when exogenous testosterone is administered to support sexual activity. Similarly, there are no re ports that aggression increases in hirsute females even though testost erone levels may rise to 200% above normal. Conversely, castration or antiandrogen administration to human males is not associated with a co nsistent decrease in aggression. Finally, changes in human aggression associated with neuropathology are not consistent with current knowled ge of the neural basis of testosterone-dependent aggression. In contra st, human aggression does have a substantial number of features in com mon with defensive aggression seen in nonprimate mammals. It is presen t at all age levels, is displayed by both males and females, is direct ed at both males and females, and is not dependent on seasonal changes in hormone levels or experiential events such as sexual activity. As would be expected from current knowledge of the neural system controll ing defensive aggression, aggression in humans increases with tumors i n the medial hypothalamus and septal region, and with seizure activity in the amygdala. It decreases with lesions in the amygdala. The infer ence that human aggression has its roots in the defensive aggression o f nonprimate mammals is in general agreement with evidence on the cons istency of human aggressiveness over age, with similarities in male an d female aggressiveness in laboratory studies, and with observations t hat some neurological disturbances contribute to criminal violence. Th is evidence suggests that human aggression has its biological roots in the defensive aggression of nonprimate mammals and not in hormone-dep endent aggression based on testosterone.