Human male violence is paradoxical. On the one hand, within social groups there is a strong tendency for avoidance of direct conflicts such that confrontations between angry individuals or groups normally end without serious harm. On the other hand, our species has a consistent history of intense deliberate violence, ranging from planned homicides and low-level and long-lasting warfare among nomadic hunter-gatherers to massive intermittent conflicts among states. Richard Wrangham (Harvard Univ) shows that the combination of aggression styles is better understood as being due to two neurobiologically distinct patterns that have been subject to contrasting selective regimes. He concludes that the combination of these two styles of aggression makes humans well adapted for both war and avoidance of war. Recorded on 05/16/2014. (#28354)