Genetic analysis of different kinds of aggressive behavior.

Various kinds of aggressive behavior such as spontaneous intermale aggression, predatory aggression (locust-killing behavior), and irritable (shock-induced) aggression were investigated in inbred strains of mice. Genotype was shown to affect significantly the phenotypic variety of these kinds of aggression. There were, however, no interstrain correlations either between intermale aggression and predatory behavior or between intensity of intermale, shock-induced aggression and locust-killing behavior. Moreover, the intermale aggression level (percentage of fighting mice in each strain) did not correlate with the intensity of fighting. It has been shown by Mendelian analysis on C57BL/6J and BALB/c strains that these indices of intermale aggression are under different genetic control. The selection of Norway rats over 20 generations for reduced fear-induced aggressiveness toward man resulted in a decrease in irritable aggression and loss of an aggressive response to man. No changes in intermale and predatory aggression, however, were found. Hence, different kinds of aggressive behavior--intermale, predatory, and fear-induced aggression--seem to be controlled by different genetic mechanisms.