Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

  Many fractured bones were actually healed. Instead of reflecting war, they might indicate the ritualized club fighting seen in many tribal societies.

  Proving that a human bone was gnawed on by a fellow human instead of another carnivore is tough. One tour-de-force paper demonstrated cannibalism in a Pueblo village from around the year 1100—human feces there contained the human version of the muscle-specific protein myoglobin.60 In other words, those humans had been eating human meat. Nonetheless, even when cannibalism is clearly documented, it doesn’t indicate whether there was exo- or endocannibalism (i.e., eating vanquished enemies versus deceased relatives, as is done in some tribal cultures).

  Most important, Keeley and Pinker are accused of cherry-picking their data, discussing only sites of putative war deaths, rather than the entire literature.* When you survey the thousands of prehistoric skeletal remains from hundreds of sites worldwide, rates of violent deaths are far lower than 15 percent. Moreover, there are regions and periods lacking any evidence of warlike violence. The glee in refuting the broadest conclusions of Keeley and Pinker is unmistakable (e.g., Ferguson in the previously cited work: “For 10,000 years in the Southern Levant, there is not one single instance where it can be said with confidence, ‘war was there.’ [his emphasis] Am I wrong? Name the place.”). Thus these critics conclude that wars were rare prior to human civilizations. Supporters of Keeley and Pinker retort that you can’t ignore bloodbaths like Crow Creek or Jebel Sahaba and that the absence of proof (of early war in so many of these sites) is not proof of absence.

  This suggests a second strategy for contemporary Hobbes-versus-Rousseau debates, namely to study contemporary humans in prestate tribal societies. How frequently do they war?

  Prehistorians in the Flesh

  Well, if researchers endlessly argue about who or what gnawed on a ten-thousand-year-old human bone, imagine the disagreements about actual living humans.

  Keeley and Pinker, along with Samuel Bowles of the Santa Fe Institute, conclude that warfare is nearly universal in contemporary nonstate societies. This is the world of headhunters in New Guinea and Borneo, Maasai and Zulu warriors in Africa, Amazonians on raiding parties in the rain forest. Keeley estimates that, in the absence of pacification enforced by outside forces such as a government, 90 to 95 percent of tribal societies engage in warfare, many constantly, and a much higher percentage are at war at any time than is the case for state societies. For Keeley the rare peaceful tribal societies are usually so because they have been defeated and dominated by a neighboring tribe. Keeley charges that there has been systematic underreporting of violence by contemporary anthropologists intent on pacifying living relics of the past.

  Clockwise, top left: New Guinea, Masai, Amazonian, Zulu

  Keeley also tries to debunk the view that tribal violence is mostly ritualistic—an arrow in someone’s thigh, a head or two bashed with a war club, and time to call it a day. Instead violence in nonstate cultures is lethal. Keeley seems to take pride in this, documenting how various cultures use weapons designed for warfare, meant to cause festering damage. He often has an almost testy, offended tone about those pacifying anthropologists who think indigenous groups lack the organization, self-discipline, and Puritan work ethic to inflict bloodbaths. He writes about the superiority of tribal warriors to Westernized armies, e.g., describing how in the Anglo-Zulu War, Zulu spears were more accurate than nineteenth-century British guns, and how the Brits won the war not because they were superior fighters but because their logistical sophistication allowed them to fight prolonged wars.

  Like Keeley, Pinker concludes that warfare is nearly ubiquitous in traditional cultures, reporting 10 to 30 percent of deaths as being war related in New Guinea tribes such as the Gebusi and Mae Enga, and a 35 to 60 percent range for Waorani and Jivaro tribes in the Amazon. Pinker estimates rates of death due to violence. Europe currently is in the range of 1 death per 100,000 people per year. During the crime waves of the 1970s and 1980s, the United States approached 10; Detroit was around 45. Germany and Russia, during their twentieth-century wars, averaged 144 and 135, respectively. In contrast, the twenty-seven nonstate societies surveyed by Pinker average 524 deaths. There are the Grand Valley Dani of New Guinea, the Piegan Blackfoot of the American Great Plains, and the Dinka of Sudan, all of whom in their prime approached 1,000 deaths, roughly equivalent to losing one acquaintance per year. Taking the gold are the Kato, a California tribe that in the 1840s crossed the finish line near 1,500 deaths per 100,000 people per year.

  No tour of violence in indigenous cultures is complete without the Yanomamö, a tribe living in the Brazilian and Venezuelan Amazon. According to dogma, there is almost always raiding between villages; 30 percent of adult male deaths are due to violence; nearly 70 percent of adults have had a close relative killed by violence; 44 percent of men have murdered.61 Fun folks.

  The Yanomamö are renowned because of Napoleon Chagnon, one of the most famous and controversial anthropologists, a tough, pugnacious, no-holds-barred academic brawler who first studied them in the 1960s. He established the Yanomamös’ street cred with his 1967 monograph Yanomamo: The Fierce People, an anthropology classic. Thanks to his publications and his ethnographic films about Yanomamö violence, both their fierceness and his are well-known tropes in anthropology.*

  A central concept in the next chapter is that evolution is about passing copies of your genes into the next generation. In 1988 Chagnon published the remarkable report that Yanomamö men who were killers had more wives and offspring than average—thus passing on more copies of their genes. This suggested that if you excel at waging it, war can do wonders for your genetic legacy.

  Thus, among these nonstate tribal cultures standing in for our prehistoric past, nearly all have histories of lethal warfare, some virtually nonstop, and those who excel at killing are more evolutionarily successful. Pretty grim.

  And numerous anthropologists object strenuously to every aspect of that picture:62

  Again with the cherry-picking. In Pinker’s analysis of violence among hunter-horticulturalists and other tribal groups, all but one of his examples come from the Amazon or the New Guinea highlands. Global surveys yield much lower rates of warfare and violence.

  Pinker had foreseen this criticism by playing the Keeley pacification-of-the-past card, questioning those lower rates. In particular he has leveled this charge against the anthropologists (whom he somewhat pejoratively calls “anthropologists of peace,” somewhat akin to “believers in the Easter Bunny”) who have reported on the remarkably nonviolent Semai people of Malaysia. This produced a testy letter to Science from this group that, in addition to saying that they are “peace anthropologists,” not “anthropologists of peace,”* stated that they are objective scientists who studied the Semai without preconceived notions, rather than a gaggle of hippies (they even felt obliged to declare that most of them are not pacifists). Pinker’s response was “It is encouraging that ‘anthropologists of peace’ now see their discipline as empirical rather than ideological, a welcome change from the days when many anthropologists signed manifestos on which their position on violence was ‘correct,’ and censured, shut down, or spread libelous rumors about colleagues who disagreed.” Whoof, accusing your academic adversaries of signing manifestos is like a sharp knee to the groin.63

  Other anthropologists have studied the Yanomamö, and no one else reports violence like Chagnon has.64 Moreover, his report of increased reproductive success among more murderous Yanomamö has been demolished by the anthropologist Douglas Fry of the University of Alabama at Birmingham, who showed that Chagnon’s finding is an artifact of poor data analysis: Chagnon compared the number of descendants of older men who had killed people in battle with those who had not, finding significantly more kids among the former. However: (a) Chagnon did not control for age differences—the killers happened to be an average of more than a decade older than the nonkillers, meaning more tha
n a decade more time to accumulate descendants. (b) More important, this was the wrong analysis to answer the question posed—the issue isn’t the reproductive success of elderly men who had been killers in their youth. You need to consider the reproductive success of all killers, including the many who were themselves killed as young warriors, distinctly curtailing their reproductive success. Not doing so is like concluding that war is not lethal, based solely on studies of war veterans.

  Moreover, Chagnon’s finding does not generalize—at least three studies of other cultures fail to find a violence/reproductive success link. For example, a study by Luke Glowacki and Richard Wrangham of Harvard examined a nomadic pastoralist tribe, the Nyangatom of southern Ethiopia. Like other pastoralists in their region, the Nyangatom regularly raid one another for cattle.65 The authors found that frequent participation in large, open battle raiding did not predict increased lifelong reproductive success. Instead such success was predicted by frequent participation in “stealth raiding,” where a small group furtively steals cows from the enemy at night. In other words, in this culture being a warrior on ’roids does not predict amply passing on your genes; being a low-down sneaky varmint of a cattle rustler does.

  These indigenous groups are not stand-ins for our prehistoric past. For one thing, many have obtained weapons more lethal than those of prehistory (a damning criticism of Chagnon is that he often traded axes, machetes, and shotguns to Yanomamö for their cooperation in his studies). For another, these groups often live in degraded habitats that increase resource competition, thanks to being increasingly hemmed in by the outside world. And outside contact can be catastrophic. Pinker cites research showing high rates of violence among the Amazonian Aché and Hiwi tribes. However, in examining the original reports, Fry found that all of the Aché and Hiwi deaths were due to killings by frontier ranchers intent on forcing them off their land.66 This tells nothing about our prehistoric past.

  Both sides in these debates see much at stake. Near the end of his book, Keeley airs a pretty weird worry: “The doctrines of the pacified past unequivocally imply that the only answer to the ‘mighty scourge of war’ is a return to tribal conditions and the destruction of all civilization.” In other words, unless this tomfoolery of archaeologists pacifying the past stops, people will throw away their antibiotics and microwaves, do some scarification rituals, and switch to loincloths—and where will that leave us?

  Critics on the other side of these debates have deeper worries. For one thing, the false picture of, say, Amazonian tribes as ceaselessly violent has been used to justify stealing their land. According to Stephen Corry of Survival International, a human-rights organization that advocates for indigenous tribal peoples, “Pinker is promoting a fictitious, colonialist image of a backward ‘Brutal Savage’, which pushes the debate back over a century and is still used to destroy tribes.”67

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  Amid these roiling debates, let’s keep sight of what got us to this point. A behavior has occurred that is good, bad, or ambiguous. How have cultural factors stretching back to the origins of humans contributed to that behavior? And rustling cattle on a moonless night; or setting aside tending your cassava garden to raid your Amazonian neighbors; or building fortifications; or butchering every man, woman, and child in a village is irrelevant to that question. That’s because all these study subjects are pastoralists, agriculturalists, or horticulturalists, lifestyles that emerged only in the last ten thousand to fourteen thousand years, after the domestication of plants and animals. In the context of hominin history stretching back hundreds of thousands of years, being a camel herder or farmer is nearly as newfangled as being a lobbyist advocating for legal rights for robots. For most of history, humans have been hunter-gatherers, a whole different kettle of fish.

  War and Hunter-Gatherers, Past and Present

  Roughly 95 to 99 percent of hominin history has been spent in small, nomadic bands that foraged for edible plants and hunted cooperatively. What is known about hunter-gatherer (for sanity’s sake, henceforth HG) violence?

  Given that prehistoric HGs didn’t have lots of material possessions that have lasted tens of thousands of years, they haven’t left much of an archaeological record. Insight into their minds and lifestyle comes from cave paintings dating back as much as forty thousand years. Though paintings from around the world show humans hunting, hardly any unambiguously depict interhuman violence.

  The paleontological record is even sparser. To date, there has been discovered one site of an HG massacre, dating back ten thousand years in northern Kenya; this will be discussed later.

  What to do with this void of information? One approach is comparative, inferring the nature of our distant ancestors by comparing them with extant nonhuman primates. Early versions of this approach were the writings of Konrad Lorenz and of Robert Ardrey, who argued in his 1966 best seller The Territorial Imperative that human origins are rooted in violent territoriality.68 The most influential modern incarnation comes from Richard Wrangham, particularly in his 1997 book (with Dale Peterson) Demonic Males: Apes and the Origins of Human Violence. For Wrangham chimps provide the clearest guide to the behavior of earliest humans, and the picture is a bloody one. He essentially leapfrogs HGs entirely: “So we come back to the Yanomamo. Do they suggest to us that chimpanzee violence is linked to human war? Clearly they do.” Wrangham summarizes his stance:

  The mysterious history before history, the blank slate of knowledge about ourselves before Jericho, has licensed our collective imagination and authorized the creation of primitive Edens for some, forgotten matriarchies for others. It is good to dream, but a sober, waking rationality suggests that if we start with ancestors like chimpanzees and end up with modern humans building walls and fighting platforms, the 5-million-year-long trail to our modern selves was lined, along its full stretch, by a male aggression that structured our ancestors’ social lives and technology and minds.

  It’s Hobbes all the way down, plus Keeley-esque contempt for pacification-of-the-past dreamers.

  This view has been strongly criticized: (a) We’re neither chimps nor their descendants; they’ve been evolving at nearly the same pace as humans since our ancestral split. (b) Wrangham picks and chooses in his cross-species linkages; for example, he argues that the human evolutionary legacy of violence is rooted not only in our close relationship to chimps but also in our nearly-as-close kinship with gorillas, who practice competitive infanticide. The problem is that, overall, gorillas display minimal aggression, something Wrangham ignores in linking human violence to gorillas. (c) As the most significant species cherry-picking, Wrangham pretty much ignores bonobos, with their far lower levels of violence than chimps, female social dominance, and absence of hostile territoriality. Crucially, humans share as much of their genes with bonobos as with chimps, something unknown when Demonic Males was published (and, notably, Wrangham has since softened his views).

  For most in the field, most insights into the behavior of our HG ancestors come from study of contemporary HGs.

  Once, the world of humans consisted of nothing but HGs; today the remnants of that world are in the few remaining pockets of peoples who live pure HG lives. These include the Hadza of northern Tanzania, Mbuti “Pygmies” in the Congo, Batwa in Rwanda, Gunwinggu of the Australian outback, Andaman Islanders in India, Batak in the Philippines, Semang in Malaysia, and various Inuit cultures in northern Canada.

  To start, it was once assumed that among HGs, women do the gathering while men supply most of the calories by hunting. In actuality, the majority of calories come from foraging; men spend lots of time talking about how awesome they were in the last hunt and how much awesomer they’ll be in the next—among some Hadza, maternal grandmothers supply more calories to families than do the Man the Hunter men.69

  The arc of human history is readily equated with an arc of progress, and key to the latter is the view that agriculture was the best thing humans ever invented;
I’ll rant about that later. A cornerstone of the agriculture lobby is the idea that primordial HGs were half starved. In reality, HGs typically work fewer hours for their daily bread than do traditional farmers and are longer-lived and healthier. In the words of anthropologist Marshall Sahlins, HGs were the original affluent society.

  Clockwise from top: Hadza; Mbuti, Andaman, Semang

  There are some demographic themes shared among contemporary HGs.70 Dogma used to be that HG bands had fairly stable group membership, producing considerable in-group relatedness. More recent work suggests less relatedness than thought, reflecting fluid fusion/fission groupings in nomadic HGs. The Hadza show one consequence of such fluidity, namely that particularly cooperative hunters find one another and work together. More on this in the next chapter.

  What about our best and worst behaviors in contemporary HGs? Up into the 1970s, the clear answer was that HGs are peaceful, cooperative, and egalitarian. Interband fluidity serves as a safety valve preventing individual violence (i.e., when people are at each other’s throats, someone moves to another group), and nomadicism as a safety valve preventing intergroup violence (i.e., rather than warring with the neighboring band, just hunt in a different valley from them).

  The standard-bearers for HG grooviness were the Kalahari !Kung.*71 The title of an early monograph about them—Elizabeth Marshall Thomas’s 1959 The Harmless People—says it all.* !Kung are to the Yanomamö as Joan Baez is to Sid Vicious and the Sex Pistols.

  Naturally, this picture of the !Kung in particular and HGs in general was ripe for revisionism. This occurred when field studies were sufficiently long term to document HGs killing one another, as summarized in an influential 1978 publication by Carol Ember of Yale.72 Basically, if you’re observing a band of thirty people, it will take a long time to see that, on a per-capita basis, they have murder rates approximating Detroit’s (the standard comparison always made). Admitting that HGs were violent was seen as a purging of sixties anthropological romanticism, a bracing slap in the face for anthropologists who had jettisoned objectivity in order to dance with wolves.