A Natural History of Peace

Robert M. Sapolsky

From Foreign Affairs, January/February 2006

Summary:  Humans like to think that they are unique, but the study of other primates has called into question the exceptionalism of our species. So what does primatology have to say about war and peace? Contrary to what was believed just a few decades ago, humans are not "killer apes" destined for violent conflict, but can make their own history.

Robert M. Sapolsky is John A. and Cynthia Fry Gunn Professor of Biological Sciences and Professor of Neurology and Neurological Sciences at Stanford University. His most recent book is "Monkeyluv: And Other Essays on Our Lives as Animals."

But the lack of violence within small groups can come at a heavy price. Small homogenous groups with shared values can be a nightmare of conformity. They can also be dangerous for outsiders. Unconsciously emulating the murderous border patrols of closely related male chimps, militaries throughout history have sought to form small, stable units; inculcate them with rituals of pseudokinship; and thereby produce efficient, cooperative killing machines.

Is it possible to achieve the cooperative advantages of a small group without having the group reflexively view outsiders as the Other? One way is through trade. Voluntary economic exchanges not only produce profits; they can also reduce social friction -- as the macaques demonstrated by being more likely to reconcile with a valued partner in food acquisition.

Another way is through a fission-fusion social structure, in which the boundaries between groups are not absolute and impermeable. The model here is not the multilevel society of the hamadryas baboons, both because their basic social unit of the harem is despotic and because their fusion consists of nothing more than lots of animals occasionally coming together to utilize a resource peacefully. Human hunter-gatherers are a better example to follow, in that their small bands often merge, split, or exchange members for a while, with such fluidity helping to solve not only environmental resource problems but social problems as well. The result is that instead of the all-or-nothing world of male chimps, in which there is only one's own group and the enemy, hunter-gatherers can enjoy gradations of familiarity and cooperation stretching over large areas.

The interactions among hunter-gatherers resemble those of other networks, where there are individual nodes (in this case, small groups) and where the majority of interactions between the nodes are local ones, with the frequency of interactions dropping off as a function of distance. Mathematicians have shown that when the ratios among short-, middle-, and long-distance interactions are optimal, networks are robust: they are dominated by highly cooperative clusters of local interactions, but they also retain the potential for less frequent, long-distance communication and coordination.

Optimizing the fission-fusion interactions of hunter-gatherer networks is easy: cooperate within the band; schedule frequent joint hunts with the next band over; have occasional hunts with bands somewhat farther out; have a legend of a single shared hunt with a mythic band at the end of the earth. Optimizing the fission-fusion interactions in contemporary human networks is vastly harder, but the principles are the same.

In exploring these subjects, one often encounters a pessimism built around the notion that humans, as primates, are hard-wired for xenophobia. Some brain-imaging studies have appeared to support this view in a particularly discouraging way. There is a structure deep inside the brain called the amygdala, which plays a key role in fear and aggression, and experiments have shown that when subjects are presented with a face of someone from a different race, the amygdala gets metabolically active -- aroused, alert, ready for action. This happens even when the face is presented "subliminally," which is to say, so rapidly that the subject does not consciously see it.

More recent studies, however, should mitigate this pessimism. Test a person who has a lot of experience with people of different races, and the amygdala does not activate. Or, as in a wonderful experiment by Susan Fiske, of Princeton University, subtly bias the subject beforehand to think of people as individuals rather than as members of a group, and the amygdala does not budge. Humans may be hard-wired to get edgy around the Other, but our views on who falls into that category are decidedly malleable.

In the early 1960s, a rising star of primatology, Irven DeVore, of Harvard University, published the first general overview of the subject. Discussing his own specialty, savanna baboons, he wrote that they "have acquired an aggressive temperament as a defense against predators, and aggressiveness cannot be turned on and off like a faucet. It is an integral part of the monkeys' personalities, so deeply rooted that it makes them potential aggressors in every situation." Thus the savanna baboon became, literally, a textbook example of life in an aggressive, highly stratified, male-dominated society. Yet within a few years, members of the species demonstrated enough behavioral plasticity to transform a society of theirs into a baboon utopia.

The first half of the twentieth century was drenched in the blood spilled by German and Japanese aggression, yet only a few decades later it is hard to think of two countries more pacific. Sweden spent the seventeenth century rampaging through Europe, yet it is now an icon of nurturing tranquility. Humans have invented the small nomadic band and the continental megastate, and have demonstrated a flexibility whereby uprooted descendants of the former can function effectively in the latter. We lack the type of physiology or anatomy that in other mammals determine their mating system, and have come up with societies based on monogamy, polygyny, and polyandry. And we have fashioned some religions in which violent acts are the entrée to paradise and other religions in which the same acts consign one to hell. Is a world of peacefully coexisting human Forest Troops possible? Anyone who says, "No, it is beyond our nature," knows too little about primates, including ourselves.

[Footnote #1] Considerable sleuthing ultimately revealed that the disease had come from tainted meat in the garbage dump, which had been sold to the tourist lodge thanks to a corrupt meat inspector. The studies were the first of this kind of outbreak in a wild primate population and showed that, in contrast to what happens with humans and captive primates, there was little animal-to-animal transmission of the tuberculosis, and so the disease did not spread in Forest Troop beyond the garbage eaters.