Writing as someone outside the field of political science, but very much involved in studies of behavior-physiology interactions, James Davies' article seems to me to be compelling in its argument for a reorientation of much of political science to include biology. As Davies points out, there is clear and convincing evidence that different physiological states are associated with different probabilities of aggression. Moreover, he cited only a part of the available evidence. At this time, data strongly support two of his points: multiple factors (e.g., genetic, developmental) contribute to the long-run probability of aggression; and different levels of neurotransmitters and hormones contribute to the short-run probability of aggression. All higher animal forms (and lower forms insofar as is known) are capable of aggression, however, within-animal frequency and type of aggression differ. Thus, what factors alter the probability of aggression under different circumstances becomes a question of great interest. It is this issue that Davies addresses. Yet, he may not have gone far enough in his effort to alert readers about the importance of understanding physiological processes as an essential requisite for understanding aggression in particular and behavior in general.