A report in Nature on 10,000-year-old skeletons unearthed in West Turkana, Kenya, is being touted as evidence for the assertion that war has deep evolutionary roots. According to this claim, the tendency for lethal group fighting dates back millions of years to the common ancestor of humans and chimpanzees, who have been observed engaging in deadly raids.
A leading proponent of this view, Harvard anthropologist Richard Wrangham, once said: "Chimpanzee-like violence preceded and paved the way for human war, making modern humans the dazed survivors of a continuous, five-million-year habit of lethal aggression."
The Nature report does not bolster the case for what I call the deep-roots theory of war. Far from it. But it does reveal how eager some scientists and journalists are to accept the theory in spite of a lack of evidence.
The report describes a site containing the remains of 27 individuals--including a pregnant woman and six children—who were apparently massacred near a lagoon. Ten of the skeletons show clear-cut signs of violence, including crushed skulls and broken limbs and embedded obsidian spear points.
An author of the Nature paper, Robert Foley of the University of Cambridge, told Bret Stetka of Scientific American that “if one looks at chimpanzees we see similar levels of intergroup conflict, and that might be an indication that it has a deeper ancestry in our evolutionary past.” Anthropologist Luke Glowacki, a colleague of deep-rooter Wrangham, concurs that the West Turkana massacre “suggests a continuum between chimpanzee raiding and full-blown human warfare.”
Other publications suggesting that the massacre reveals war’s deep evolutionary roots include The Atlantic (“warfare was alive and well even among hunter-gatherer communities”), The Telegraph (“demonstrates the terrifying aggression of early man”), International Business Times (“aggression in our bones”), and The Guardian (“attacks were normal part of hunter-gatherer relations”).
James Gorman of The New York Times treats this claim more skeptically, with good reason. Here are problems posed by the deep-roots theory:
*The theory holds that lethal group conflict evolved not ten thousand or tens of thousands or hundreds of thousands but millions of years ago. Critics of the theory have long accepted that some humans, including hunter-gatherers, engaged in group violence 10,000 years ago and even earlier. As I note in a 2010 blog post, the oldest clear-cut relic of group violence is a 13,000-year-old grave in the Jebel Sahaba region of Sudan. The grave contains 59 skeletons, 24 of which bear marks of violence, such as embedded projectile points.
*Other than the Jebel Sahaba site, evidence of war or even homicide dating back more than 10,000 years is extremely rare. As I reported in 2013, anthropologists Jonathan Haas and Matthew Piscitelli have carried out an exhaustive review of hominid remains over 10,000 years old, including more than 2,900 skeletons from over 400 different sites. Excluding the Jebel Sahaba skeletons, Haas and Piscitelli found only four skeletons bearing signs of violence.
*The West Turkana massacre victims might not have been nomadic hunter-gatherers, as our ancestors were throughout most of the Paleolithic era (which began just over two millions years ago and lasted until the dawn of agriculture). Instead, the victims might have been making the transition to a more settled mode of existence, as were other societies in northern Africa, Mesopotamia and elsewhere. According to the Nature authors, 10,000 years ago West Turkana was “a fertile lakeshore landscape sustaining a substantial population of hunter-gatherers; the presence of pottery may be indicative of some storage and so reduced mobility.”
*Research by anthropologist Brian Ferguson shows that even after humans began settling down, war emerged slowly and sporadically. As I wrote in a post on Ferguson’s work, hunter-gatherers started settling in the Southern Levant 15,000 years ago, and populations surged after the emergence of agriculture there 11,000 years ago. But there is no significant evidence of warfare in the Southern Levant until about 5,500 years ago, when the region increasingly came under the influence of the emerging military empire of Egypt.
*A study by anthropologists Douglas Fry and Patrik Soderberg found scant evidence of warfare among 21 modern-era hunter-gatherer societies on five continents. As I reported in 2013, three of the societies had no observed killings of any kind, and 10 had no killings carried out by more than one perpetrator. In only six societies did ethnographers record killings that involved two or more perpetrators and two or more victims. A single society, the Tiwi of Australia, accounted for almost all of these group killings. Their findings, Fry and Soderberg concluded, "contradict recent assertions that [mobile foragers] regularly engage in coalitionary war against other groups.”
*Finally, there is little evidence that inter-group violence among chimpanzees is innate. As I reported in 2014, researchers tracking 18 chimp communities for an average total of 23 years per community have observed only 15 inter-group killings of adults and adolescents. That comes to one inter-group killing every 28 years in a typical community. Even Wrangham has acknowledged that such killings are “certainly rare.” Moreover, researchers have not observed a single deadly attack by the chimp species Pan paniscus, or bonobos, who are as closely related to humans as the more common species, Pan troglodytes.
The debate over the deep-roots theory matters. As a New York Times editorial on the Kenyan dig points out, President Barack Obama seems to favor the notion that war has “deep biological roots.” During his 2009 Nobel Prize speech, Obama stated that war “appeared with the first man” and that “we will not eradicate violent conflict in our lifetimes.” This sort of fatalism could undermine efforts to achieve permanent peace.
The evidence is overwhelming that war, far from being an innate behavior that evolved millions of years ago, was a cultural innovation—an “invention,” as Margaret Mead put it--that emerged relatively recently in our prehistory, toward the end of the Paleolithic era. We should take responsibility for our wars instead of blaming them on our genes.