of mathematical expression. There are also thousands of ways of being violent, and equally, ways of

of mathematical expression. There are also thousands of ways of being violent, and equally, ways of counteracting such violence. But none of this takes away from the importance of biology, especially its role in constraining the form that these expressions take in different environmental settings. To think otherwise is just wrong. The debate about version 1.5 of lethal aggression gains interest if we restrict the conversation to the similarities and differences between chimpanzee and human killing. Similarities speak to our shared evolutionary history, including the mechanisms we inherited and the pressures that favored this form of violence. Differences speak to both changes in our biology and the environments we confronted and created. Those who argue that the comparison between human and chimpanzee killing lacks any analytical value come from two different camps. On the one hand are anthropologists such as Robert Sussman and Brian Ferguson who suggest that chimpanzee killing is infrequent, has little benefit in terms of resources or competition, and is restricted to populations that are either artificially provisioned by humans or crowded in by us. They also suggest that the archaeological evidence for human warfare doesn’t really begin until about 12,000 years ago. As Ferguson notes “To argue that war is a result of some sort of innate predisposition to wage it requires that war be practiced throughout our prehistoric past.” This date, so Ferguson continues, is too recent to invoke natural selection as a cause, and leaves unexplained why there is no earlier evidence of massive killing if our last common ancestors had this capacity. These criticisms either fly in the face of contradictory evidence or have little to do with the original ideas. Concerning chimpanzee killing, the evidence comes from multiple sites in East and West Africa, including sites with no provisioning and no crowding from humans. Further, analyses by Wrangham and his colleagues show that humans living as hunter-gatherers or subsistence farmers on the continents of Africa and South America, engage in coalitionary killing, using stealthy raids and imbalances of power to minimize the costs and maximize the benefits. Looking at 32 different small scale societies, calculations of the median death rate were between 164-595 per 100,000 per year. Looking at 9 chimpanzee communities spanning 5 populations in Tanzania, Uganda, and Ivory Coast, the rate was 69-287 per 100,000 per year. Chimpanzees fall well within the range of human hunter-gatherers and subsistence farmers. This evidence not only shows parallels between chimpanzees and human societies living under conditions most like our ancestors, but also provides a resounding rejection of the view that chimpanzee killing is infrequent and of trivial importance. If the rates of killing are comparable, then either they are trivial for both species or trivial for neither. Given that both chimpanzees and human hunter-gatherers live in small groups, killing even a few individuals can have a dramatic effect on their capacity to defend resources. Hauser Chapter 1. Nature’s secrets 42 HOUSE_OVERSIGHT_012788