In this column and in my book The End of War, I knock what I call the deep roots theory of war. The theory holds that war stems from an instinct—or “adaptation,” to use the term favored by evolutionary biologists–deeply embedded in the genes of our male ancestors.
Proponents of this theory—notably primatologist Richard Wrangham—claim it is supported by observations of inter-community killings by chimpanzees, Pan troglodytes, our closest genetic relatives. Skeptics have pointed out that chimpanzee violence might be not an adaptation but a response to environmental circumstances, such as human encroachment.
This “human impacts” hypothesis is rejected in a massive new report in Nature by a coalition of 30 primatologists, including Wrangham and lead author Michael Wilson. The paper, “Lethal aggression in Pan is better explained by adaptive strategies than human impacts,” looks impressive at first glance, loaded with data, charts, and tables culled from decades of research.
Wilson, et al. analyzed 152 killings in 18 chimpanzee communities and found “little correlation with human impacts.” Many mass media have interpreted the paper as having confirmed that both chimpanzees and humans are “natural born killers,” as The Independent, a British newspaper, put it.
A close examination of the paper, however, reveals that it does not mention lethal human violence or the deep-roots theory of war. This omission is wise, because the Nature report—contrary to the interpretation of many journalists–undermines the deep-roots theory, and establishes that the “human impact” issue is a red herring.
Of the 152 killings analyzed by Wilson et al., 58 were directly observed by researchers and 41 were “inferred” (a dead chimp is found with bite marks or other signs of violence). Another 53 chimps were “suspected” of being killed, usually because they disappeared; the researchers exclude these data from most of their analyses “to be conservative,” so I will too.
I also exclude infanticides and “intracommunity” (within-group) killings, because chimp killings that provide the closest analog to human warfare involve a group of adults from one community killing one or more adults or adolescents (Wilson et al. call them “weaned victims”) from another community.
After studying 18 communities for a total of 426 years (or 23 years per community, on average), Wilson et al. directly observed only 15 intercommunity killings of weaned victims. That comes to one killing every 28 years in a typical community–or one every 15 years if 14 “inferred” killings of weaned chimps are included.
Wrangham himself has conceded that lethal intercommunity killings are “certainly rare.” Why then does he insist that they are adaptive?
Also, Wilson et al. recorded only one “suspected” killing among 4 communities of Pan paniscus, or bonobos, a less common chimp species clustered in the Congo, that scientists have observed for a total of 92 years. Pan paniscus is just as genetically relate to Homo sapiens as Pan troglodytes is. Deep-rooters have never offered compelling reasons why Pan troglodytes are more illustrative of our ancestry than Pan paniscus.
I do not doubt that chimpanzees—and especially males–are genetically predisposed to violent aggression. But Wrangham and other deep-rooters have made a far more dramatic claim, that chimpanzees are innately predisposed to a particular form of group violence, analogous to human warfare, in which members of one community kill members of another community.
Although the deep-roots theory of war lacks compelling evidence, it has become popular not only among scientists—notably Wrangham, Edward O. Wilson and Steven Pinker–but also some U.S. leaders. Barack Obama was alluding to the theory when he said in 2009, while accepting the Nobel Peace Prize, “War, in one form or another, appeared with the first man.”
Former Secretary of Defense Donald Rumsfeld, who oversaw the U.S. invasions of Afghanistan and Iraq, says in the 2013 Errol Morris documentary The Unknown Known, “Human nature being what it is, I’m afraid we’ll have to continue to ask young men and women to come serve our country.”
Ending war will be far easier if we take responsibility for our militaristic actions and stop blaming them on evolution, genes, and “human nature.”
John Horgan directs the Center for Science Writings, which is part of the College of Arts & Letters. This column is adapted from one originally published on Horgan’s ScientificAmerican.com blog, “Cross-check.”
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