Why Apes and Humans Kill


Twentieth Annual Darwin College Lecture Series 2005


Lecture 3   :   4 February

Richard Wrangham





Human warfare is often claimed to be biologically aberrant partly because in his celebrated book 'On Aggression,' Konrad Lorenz reported that animals are inhibited from killing members of their own species. But we now know that Lorenz was wrong. Many species regularly kill their own, including chimpanzees. These facts have re-opened the questions of whether and how human evolutionary biology has affected our propensity for war. In addressing this problem it is useful to separate two styles of animal violence, i.e. "predatory kills" and "lethal battles." Predatory kills are attacks on helpless victims. Their commonest form is infanticide, but in a few species they also include coalitionary attacks among adults. Thus among chimpanzees and nomadic hunter-gatherers, small groups sometimes kill rivals from neighboring communities; current data indicate that death rates from this style of intergroup aggression are approximately equal in the two species. The pervasiveness of this pattern suggests that both species have had an evolutionary history of lethal violence, and are cognitively adapted for successful killing. But by contrast, there is no evidence for humans that lethal battles have been important in evolution. Lethal battles are escalated contests between competitive equals in which the outcome is uncertain and both opponents are likely to suffer high costs or deaths. Coalitionary lethal battles are absent or exceptional among chimpanzees and hunter-gatherers, and are rare in animals generally. They occur most prominently among social insects and in modern (post-agricultural) warfare, associated with despotic hierarchies. Even though lethal battles are evolutionarily novel in the human lineage, however, they incorporate biologically adaptive patterns such as self-deceptive assessments of relative competitive power. In sum, while chimpanzees and humans have evolved to kill when the killing is easy, hierarchically organized armies have created a new logic for conflict.



RICHARD WRANGHAM is a professor of biology and anthropology at Harvard University who studies chimpanzees, and their behavior, in Uganda. His main interest is in the question of human evolution from a behavioral perspective. He is the author, with Dale Peterson, of Demonic Males: Apes, and the Origins Of Human Violence. He has spent three decades studying chimpanzee cultures in the wild and comparing chimp cultures to human ones. In the early 1970s, he was among the first primatologists to note the tendency of chimpanzees to conduct so-called lethal raids against neighboring groups. His books also include Chimpanzee Cultures, which he edited with a group of internationally distinguished primatologists. 

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