Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

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  The preceding sections examined the effects of living with lots of people, and in close quarters. How about the effects of living with different kinds of people? Diversity. Heterogeneity. Admixture. Mosaicism.

  Two opposite narratives come to mind:

  Mister Rogers’ neighborhood: When people of differing ethnicities, races, or religions live together, they experience the similarities rather than the differences and view one another as individuals, transcending stereotypes. Trade flows, fostering fairness and mutuality. Inevitably, dichotomies dissolve with intermarriage, and soon you’re happily watching your grandkid in the school play on “their” side of town. Just visualize whirled peas.

  Sharks versus the Jets: Differing sorts of people living in close proximity rub, and thus abrade, elbows regularly. One side’s act of proud cultural identification feels like a hostile dig to the other side, public spaces become proving grounds for turf battles, commons become tragedies.

  Surprise: both outcomes occur; the final chapter explores circumstances where intergroup contact leads to one rather than the other. Most interesting at this juncture is the importance of the spatial qualities of the heterogeneity. Consider a region filled with people from Elbonia and Kerplakistan, two hostile groups, each providing half the population. At one extreme, the land is split down the middle, each group occupying one side, producing a single boundary between the two. At the other extreme is a microcheckerboard of alternating ethnicities, where each square on the grid is one person large, producing a vast quantity of boundaries between Elbonians and Kerplakis.

  Intuitively, both scenarios should bias against conflict. In the condition of maximal separation, each group has a critical mass to be locally sovereign, and the total length of border, and thus of the amount of intergroup elbow rubbing, is minimized. In the scenario of maximal mixing, no patch of ethnic homogeneity is big enough to foster a self-identity that can dominate a public space—big deal if someone raises a flag between their feet and declares their square meter to be the Elbonian Empire or a Kerplakistani Republic.

  But in the real world things are always in between the two extremes, and with variation in the average size of each “ethnic patch.” Does patch size, and thus amount of border, influence relations?

  This was explored in a fascinating paper from the aptly named New England Complex Systems Institute, down the block from MIT.49 The authors first constructed an Elbonian/Kerplaki mixture, with individuals randomly distributed as pixels on a grid. Pixels were given a certain degree of mobility plus a tendency to assort with other pixels of the same type. As self-assortment progresses, something emerges—islands and peninsulas of Elbonians amid a sea of Kerplakis, or the reverse, a condition that intuitively seems rife with potential intergroup violence. As self-assortment continues, the number of such isolated islands and peninsulas declines. The intermediate stage that maximizes the number of islands and peninsulas maximizes the number of people living within a surrounded enclave.*

  The authors then considered a balkanized region, namely the Balkans, ex-Yugoslavia, in 1990. This was just before Serbians, Bosnians, Croatians, and Albanians commenced Europe’s worst war since World War II, the war that taught us the names of places like Srebrenica and people like Slobodan Milošević. Using a similar analysis, with ethnic island size varying from roughly twenty to sixty kilometers in diameter, they identified the spots theoretically most rife for violence; remarkably, this predicted the sites of major fighting and massacres in the war.

  In the words of the authors, violence can arise “due to the structure of boundaries between groups rather than as a result of inherent conflicts between the groups themselves.” They then showed that the clarity of borders matters as well. Good, clear-cut fences—e.g., mountain ranges or rivers between groups—make for good neighbors. “Peace does not depend on integrated coexistence, but rather on well defined topographical and political boundaries separating groups, allowing for partial autonomy within a single country,” the authors concluded.

  Thus, not only do size, density, and heterogeneity of populations help explain intergroup violence, but patterns and clarity of fragmentation do as well. These issues will be revisited in the final chapter.

  THE RESIDUES OF CULTURAL CRISES

  In times of crisis—the London Blitz, New York after 9/11, San Francisco after the 1989 Loma Prieta earthquake—people pull together.* That’s cool. But in contrast, chronic, pervasive, corrosive menace doesn’t necessarily do the same to people or cultures.

  The primal menace of hunger has left historical marks. Back to that study of differences between countries’ tightness (where “tight” countries were characterized by autocracy, suppression of dissent, and omnipresence and enforcement of behavior norms).50 What sorts of countries are tighter?* In addition to the high population-density correlates mentioned earlier, there are also more historical food shortages, lower food intake, and lower levels of protein and fat in the diet. In other words, these are cultures chronically menaced by empty stomachs.

  Cultural tightness was also predicted by environmental degradation—less available farmland or clean water, more pollution. Similarly, habitat degradation and depletion of animal populations worsens conflict in cultures dependent on bush meat. And a major theme of Jared Diamond’s magisterial Collapse: How Societies Choose to Fail or Succeed is how environmental degradation explains the violent collapse of many civilizations.

  Then there’s disease. In chapter 15 we’ll touch on “behavioral immunity,” the ability of numerous species to detect cues of illness in other individuals; as we’ll see, implicit cues about infectious disease make people more xenophobic. Similarly, historical prevalence of infectious disease predicts a culture’s openness to outsiders. Moreover, other predictors of cultural tightness include having high historical incidence of pandemics, of high infant and child mortality rates, and of higher cumulative average number of years lost to communicable disease.

  Obviously, weather influences the incidence of organized violence—consider the centuries of European wars taking a hiatus during the worst of winter and the growing season.51 Even broader is the capacity of weather and climate to shape culture. The Kenyan historian Ali Mazrui has suggested that one reason for Europe’s historical success, relative to Africa, has been the weather—Western-style planning ahead arose from the annual reality of winter coming.* Larger-scale changes in weather are known to be consequential. In the tightness study, cultural tightness was also predicted by a history of floods, droughts, and cyclones. Another pertinent aspect of weather concerns the Southern Oscillation, known as El Niño, the multiyear fluctuation of average water temperatures in the equatorial Pacific Ocean. El Niños, occurring about every dozen years, involve warmer, drier weather (with the opposite during La Niña years) and are associated in many developing countries with droughts and food shortages. Over the last fifty years El Niños have roughly doubled the likelihood of civil conflict, mostly by stoking the fires of preexisting conflicts.

  The relationship between drought and violence is tricky. The civil conflict referred to in the previous paragraph concerned deaths caused by battle between governmental and nongovernmental forces (i.e., civil wars or insurgencies). Thus, rather than fighting over a watering hole or a field for grazing, this was fighting for modern perks of power. But in traditional settings drought may mean spending more time foraging or hauling water for your crops. Raiding to steal the other group’s women isn’t a high priority, and why rustle someone else’s cows when you can’t even feed your own? Conflict declines.

  Interestingly, something similar occurs in baboons. Normally, baboons in rich ecosystems like the Serengeti need forage only a few hours a day. Part of what endears baboons to primatologists is that this leaves them about nine hours daily to devote to social machinations—trysting and jousting and backbiting. In 1984 there was a devastating drought in East Africa. Among baboons, while there w
as still sufficient food, it took every waking moment to get enough calories; aggression decreased.52

  So ecological duress can increase or decrease aggression. This raises the key issue of what global warming will do to our best and worst behaviors. There will definitely be some upsides. Some regions will have longer growing seasons, increasing the food supply and reducing tensions. Some people will eschew conflict, being preoccupied with saving their homes from the encroaching ocean or growing pineapples in the Arctic. But amid squabbling about the details in predictive models, the consensus is that global warming won’t do good things to global conflict. For starters, warmer temperatures rile people up—in cities during the summers, for every three degree increase in temperature, there was a 4 percent increase in interpersonal violence and 14 percent in group violence. But global warming’s bad news is more global—desertification, loss of arable land due to rising seas, more droughts. One influential meta-analysis projected 16 percent and 50 percent increases in interpersonal and group violence, respectively, in some regions by 2050.53

  OH, WHY NOT: RELIGION

  Time for a quick hit-and-run about religion before considering it in the final chapter.

  Theories abound as to why humans keep inventing religions. It’s more than a human pull toward the supernatural; as stated in one review, “Mickey Mouse has supernatural powers, but no one worships or would fight—or kill—for him. Our social brains may help explain why children the world over are attracted to talking teacups, but religion is much more than that.” Why does religion arise? Because it makes in-groups more cooperative and viable (stay tuned for more in the next chapter). Because humans need personification and to see agency and causality when facing the unknown. Or maybe inventing deities is an emergent by-product of the architecture of our social brains.54

  Amid these speculations, far more boggling is the variety of the thousands of religions we’ve invented. They vary as to number and gender of deities; whether there’s an afterlife, what it’s like, and what it takes to enter; whether deities judge or interfere with humans; whether we are born sinful or pure and whether sexuality changes those states; whether the myth of a religion’s founder is of sacredness from the start (so much so that, say, wise men visit the infant founder) or of a sybarite who reforms (e.g., Siddhārtha’s transition from palace life to being the Buddha); whether the religion’s goal is attracting new followers (say, with exciting news—e.g., an angel visited me in Manchester, New York, and gave me golden plates) or retaining members (we’ve got a covenant with God, so stick with us). On and on.

  There are some pertinent patterns amid this variation. As noted, desert cultures are prone toward monotheistic religions; rain forest dwellers, polytheistic ones. Nomadic pastoralists’ deities tend to value war and valor in battle as an entrée to a good afterlife. Agriculturalists invent gods who alter the weather. As noted, once cultures get large enough that anonymous acts are possible, they start inventing moralizing gods. Gods and religious orthodoxy dominate more in cultures with frequent threats (war, natural disasters), inequality, and high infant mortality rates.

  Before turfing this subject to the final chapter, three obvious points: (a) a religion reflects the values of the culture that invented or adopted it, and very effectively transmits those values; (b) religion fosters the best and worst of our behaviors; (c) it’s complicated.

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  We’ve now looked at various cultural factors—collectivism versus individualism, egalitarian versus hierarchical distribution of resources, and so on. While there are others to consider, it’s time to shift to the chapter’s final topic. This is one that has generated shit storms of debate as old as the weathered layers of Olduvai Gorge and as fresh as a newborn baby’s tush, a topic that has scientists who study peace at one another’s throats.

  HOBBES OR ROUSSEAU

  Yes, those guys.

  To invoke some estimates, anatomically modern humans emerged about 200,000 years ago, and behaviorally modern ones about 40,000 to 50,000 years ago; animal domestication is 10,000 to 20,000 years old, agriculture around 12,000. After plant domestication, it was roughly 5,000 more years until “history” began with civilizations in Egypt, the Mideast, China, and the New World. When in this arc of history was war invented? Does material culture lessen or worsen tendencies toward war? Do successful warriors leave more copies of their genes? Has the centralization of authority by civilization actually civilized us, providing a veneer of socially contractual restraint? Have humans become more or less decent to one another over the course of history? Yes, it’s short/nasty/brutish versus noble savage.

  In contrast to the centuries of food fights among philosophers, contemporary Hobbes-versus-Rousseau is about actual data. Some of it is archaeological, where researchers have sought to determine the prevalence and antiquity of warfare from the archaeological record.

  Predictably, half of each conference on the subject consists of definitional squabbles. Is “war” solely organized and sustained violence between groups? Does it require weapons? A standing army (even if only seasonally)? An army with hierarchy and chain of command? If fighting is mostly along lines of relatedness, is it a vendetta or clan feud instead of a war?

  Fractured Bones

  For most archaeologists the operational definition has been streamlined to numerous people simultaneously meeting violent deaths. In 1996 the archaeologist Lawrence Keeley of the University of Illinois synthesized the existing literature in his highly influential War Before Civilization: The Myth of the Peaceful Savage, ostensibly showing that the archaeological evidence for war is broad and ancient.55

  A similar conclusion comes in the 2011 book The Better Angels of Our Nature: Why Violence Has Declined, by Harvard’s Steven Pinker.56 Cliché police be damned, you can’t mention this book without calling it “monumental.” In this monumental work Pinker argued that (a) violence and the worst horrors of inhumanity have been declining for the last half millennium, thanks to the constraining forces of civilization; and (b) the warfare and barbarity preceding that transition are as old as the human species.

  Keeley and Pinker document savagery galore in prehistoric tribal societies—mass graves filled with skeletons bearing multiple fractures, caved-in skulls, “parrying” fractures (which arise from raising your arm to fend off a blow), stone projectiles embedded in bone. Some sites suggest the outcome of battle—a preponderance of young adult male skeletons. Others suggest indiscriminate massacre—butchered skeletons of both sexes and all ages. Other sites suggest cannibalism of the vanquished.

  In their separate surveys of the literature, Keeley and Pinker present evidence of prestate tribal violence comes from sites in Ukraine, France, Sweden, Niger, India, and numerous precontact American locations.57 This collection of sites includes the oldest such massacre, the 12,000- to 14,000-year-old Jebel Sahaba site along the Nile in northern Sudan, a cemetery of fifty-nine men, women, and children, nearly half of whom have stone projectiles embedded in their bones. And it includes the largest massacre site, the 700-year-old Crow Creek in South Dakota, a mass grave of more than four hundred skeletons, with 60 percent showing evidence of violent deaths. Across the twenty-one sites surveyed, about 15 percent of skeletons showed evidence of “death in warfare.” One can, of course, be killed in war in a way that doesn’t leave fractures or projectiles embedded in bone, suggesting that the percentage of deaths due to warfare was higher.

  Otzi, in his current state (left), and in an artist’s reconstruction (right). Note: his killer, still at large, probably looked pretty much the same.

  Keeley and Pinker also document how prehistoric settlements frequently protected themselves with defensive palisades and fortifications. And, of course, as the poster child for prehistoric violence, there is Otzi, the 5,300-year-old Tyrolean “iceman” found in a melting glacier in 1991 on the Italian/Austrian border. In his shoulder was a freshly embedded arrowhead.

  Thus, K
eeley and Pinker document mass casualties of warfare long predating civilization. Just as important, both (starting with Keeley’s subtitle) suggest a hidden agenda among archaeologists to ignore that evidence. Why had there been, to use Keeley’s phrase, “pacification of the past”? In chapter 7 we saw how World War II produced a generation of social scientists trying to understand the roots of fascism. In Keeley’s view, the post–World War II generations of archaeologists recoiled from the trauma of the war by recoiling from the evidence that humans had been prepping a long time for World War II. For Pinker, writing from a younger generation’s perspective, the current whitewashing of prehistoric violence has the flavor of today’s archaeological graybeards being nostalgic about getting stoned in high school and listening to John Lennon’s “Imagine.”

  Keeley and Pinker generated a strong backlash among many notable archaeologists, who charged them with “war-ifying the past.” Most vocal has been R. Brian Ferguson of Rutgers University, with publications with titles like “Pinker’s List: Exaggerating Prehistoric War Mortality.” Keeley and Pinker are criticized for numerous reasons:58

  Some of the sites supposedly presenting evidence for warfare actually contain only a single case of violent death, suggesting homicide, not war.

  The criteria for inferring violent death include skeletons in close proximity to arrowheads. However, many such artifacts were actually tools used for other purposes, or simply chips and flakes. For example, Fred Wendorf, who excavated Jebel Sahaba, considered most of the projectiles associated with skeletons to have been mere debris.59