Apr 5, 2008
(Editor’s Note: One of the most original minds we have ever encountered is that of Robert Sapolsky, the Stanford-based neuroscientist, primatologist, author of A Primate’s Memoir, and more. We highly recommend most of his books. Above all, for anyone interested in brain health, this is a must read and very fun: Why Zebras Don’t Get Ulcers: An Updated Guide To Stress, Stress Related Diseases, and Coping. We are honored to bring you a guest article series by Robert Sapolsky, thanks to our collaboration with Greater Good Magazine.)
Peace Among Primates
Anyone who says peace is not part of human nature knows too little about primates, including ourselves.
–By Robert M. Sapolsky
It used to be thought that humans were the only savagely violent primate. “We are the only species that kills its own, narrators intoned portentously in nature films several decades ago. That view fell by the wayside in the 1960s as it became clear that some other primates kill their fellows aplenty. Males kill; females kill. Some use their toolmaking skills to fashion bigger and better cudgels. Other primates even engage in what can only be called warfare, organized, proactive group violence directed at other populations.
Yet as field studies of primates expanded, what became most striking was the variation in social practices across species. Yes, some primate species have lives filled with violence, frequent and varied. But life among others is filled with communitarianism, egalitarianism, and cooperative child rearing.Patterns emerged. In less aggressive species, such as gibbons or marmosets, groups tend to live in lush rain forests where food is plentiful and life is easy. Females and males tend to be the same size, and the males lack secondary sexual markers such as long, sharp canines or garish coloring. Couples mate for life, and males help substantially with child care. In violent species, such as baboons and rhesus monkeys, the opposite conditions prevail.
The most disquieting fact about the violent species was the apparent inevitability of their behavior. Certain species seemed simply to be the way they were, fixed products of the interplay of evolution and ecology, and that was that. And although human males might not be inflexibly polygamous or outfitted with bright red butts and six-inch canines designed for tooth-to-tooth combat, it was clear that our species had at least as much in common with the violent primates as with the gentle ones. “In their nature thus became “in our nature.” This was the humans-as-killer-apes theory popularized by the writer Robert Ardrey, according to which humans have as much chance of becoming intrinsically peaceful as they have of growing prehensile tails.
That view always had little more scientific rigor than a Planet of the Apes movie, but it took a great deal of field research to figure out just what should supplant it. After decades of more work, the picture has become quite interesting. Some primate species, it turns out, are indeed simply violent or peaceful, with their behavior driven by their social structures and ecological settings. More importantly, however, some primate species can make peace despite violent traits that seem built into their natures. The challenge now is to figure out under what conditions that can happen, and whether humans can manage the trick ourselves.
Old primates and new tricks
To an overwhelming extent, the age-old “nature versus nurture” debate is silly. The action of genes is completely intertwined with the environment in which they function; in a sense, it is pointless to even discuss what gene X does, and we should consider instead only what gene X does in environment Y. Nonetheless, if one had to predict the behavior of some organism on the basis of only one fact, one might still want to know whether the most useful fact would be about genetics or about the environment.
Two classic studies have shown that primates are somewhat independent from their “natures.” In the early 1970s, a highly respected primatologist named Hans Kummer was working in a region of Ethiopia containing two species of baboons with markedly different social systems. Savanna baboons live in large troops, with plenty of adult females and males. Hamadryas baboons, in contrast, have a more complex and quite different multilevel society. When confronted with a threatening male, the females of the two species react differently: A hamadryas baboon placates the male by approaching him, whereas a savanna baboon can only run away if she wants to avoid injury.
Kummer conducted a simple experiment, trapping an adult female savanna baboon and releasing her into a hamadryas troop and trapping an adult female hamadryas and releasing her into a savanna troop. The females who were dropped in among a different species initially carried out their species-typical behavior, a major faux pas in the new neighborhood. But gradually, they absorbed the new rules. How long did this learning take? About an hour. In other words, millennia of genetic differences separating the two species, a lifetime of experience with a crucial social rule for each female and a miniscule amount of time to reverse course completely.
The second experiment was set up by Frans de Waal of Emory University and his student Denise Johanowicz in the early 1990s, working with two macaque monkey species. By any human standards, male rhesus macaques are unappealing animals. Their hierarchies are rigid, those at the top seize a disproportionate share of the spoils, they enforce this inequity with ferocious aggression, and they rarely reconcile after fights. In contrast, male stump tail macaques, which share almost all of their genes with their rhesus macaque cousins, display much less aggression, looser hierarchies, more egalitarianism, and more behaviors that promote group cohesion.
Working with captive primates, de Waal and Johanowicz created a mixed-sex social group of juvenile macaques, combining rhesus and stump tails together. Remarkably, instead of the rhesus macaques bullying the stump tails, over the course of a few months the rhesus males adopted the stump tails social style, eventually even matching the stump tails high rates of reconciliatory behavior. It so happens, moreover, that stump tails and rhesus macaques use different gestures when reconciling. The rhesus macaques in the study did not start using the stump tails reconciliatory gestures, but rather increased the incidence of their own species-typical gestures. In other words, they were not merely imitating the stump tails behavior; they were incorporating the concept of frequent reconciliation into their own social practices. Finally, when the newly warm-and-fuzzy rhesus macaques were returned to a larger, all-rhesus group, their new behavioral style persisted.
This is nothing short of extraordinary. But it brings up one further question: When those rhesus macaques were transferred back into the all-rhesus world, did they spread their insights and behaviors to the others? Alas, they did not at least not within the relatively short time they were studied. For that, we need to move on to a final case.
(To be continued, in a second installment on Saturday April 12th).
— Robert M. Sapolsky, Ph.D., is the John A. and Cynthia Fry Gunn Professor of Biological Sciences and a professor of neurology and neurological sciences at Stanford University. He wrote the classic Why Zebras Don’t Get Ulcers: An Updated Guide to Stress, Stress Related Diseases and Coping. His most recent book is Monkeyluv: And Other Essays on Our Lives as Animals. A longer version of this essay appeared in Foreign Affairs. We bring you this post thanks to our collaboration with Greater Good Magazine, a UC-Berkeley-based quarterly magazine that highlights ground breaking scientific research into the roots of compassion and altruism.