In Ngogo, Gombe and elsewhere in Africa, bands of male chimpanzees regularly make organized raids on neighboring troops and batter their enemies to death. These grim, warring chimps have been held up as a compelling argument for the role of violence in humanity’s evolutionary past. The premeditated violence of male chimp society forms the basis of naturalist E.O. Wilson's argument that warfare, just like social grooming and opposable thumbs, is a trait that humans and chimps have inherited from our common ancestor. War, in his view, is an innate and unavoidable aspect of human nature.

Should we dismiss our species as yet another nasty, brutish product of evolution? In a recent post at Discover Magazine, science writer John Horgan aims to debunk Wilson’s assertions, claiming instead that is little proof we are genetically doomed to war. According to Hogan, the much-studied "coalitionary killing" in chimpanzee society is actually a rare event. From 1974 to 2004, Jane Goodall's famous troop in Gombe had, on average, one death from organized raids every seven years. Chimp war, rather than being behaviorally ingrained, maybe be a response to resource scarcity and societal disruption caused by habitat loss and human hunting. Even without these caveats, it remains deeply flawed to use chimpanzee behavior as an absolute proxy for our own. After all, bonobos, which we now know to be as closely related to humans as chimpanzees, are affectionate apes that prefer recreational sex to violence. The better angels of our genetic heritage, bonobos have never once been observed engaging in murder.

The archeological record also holds clues to our warring past, and the lack thereof. Prior to the last 10,000 years, Hogan asserts that there is no evidence that humans were systematically killing off their neighbors. In the era before the agricultural, sedentary lifestyle of the Neolithic, there are no rock paintings of human-human combat, no fortifications, no weapons designed solely for killing rather than hunting, and no human bones with embedded arrowheads.

I take issue with some of Horgan's points. Hunting weapons and weapons designed for early warfare may be indistinguishable. Hominid bones are frail and unlikely to fossilize, so the odds of finding the skeleton of the rare individual killed in an intergroup raid is astronomically low. The fact that little or no evidence for systematic violence exists before 10,000 years ago may merely mean that it was small, localized, or more likely to result in injuries than outright deaths.

Far more convincing is the commonsense explanation that warfare is a learned behavior.  Just as there is no cluster of genes that codes for "chip this rock to make a spearhead", there is no gene that codes for "take this spearhead, gather your allies, and go slaughter the neighboring tribe". Tool use and organized violence are cultural traits that independently arose in chimps and humans merely because they are simple ideas that aid survival. War is a pernicious cultural meme that has the helpful side effect of killing off anyone who doesn't care to pass it along. Once established, it is a hard weed to dig up.

In his essay, Wilson provides a list of ancient tribal societies where violent deaths ranged from 6% of total deaths up to a staggering 46%. Discounting any errors in estimating group mortality for Nubian tribes 10,000 years ago, this commonality does not imply innateness. Nearly every human culture produces dumpling-like foods, for instance, but no one has wasted much effort on debating whether dim sum is an unavoidable aspect of human behavior.

Rather than acquiescing to Wilson's pessimistic view of human nature, we should adopt the cautiously optimistic argument that human nature is not inherently good or evil, but only extraordinarily plastic. The aggressive instincts in male hominins tend to give rise to systematized violence. And, just as frequently, the altruistic instincts in hominins, male and female, tend to give rise to peaceful negotiations, to charity, and to orderly alliances of societies. Peace may be just as culturally "infectious" as warfare.

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