Robert Sapolsky is one of my favorite writers

and he's got an amazing essay called "A Natural History of Peace" up at Foreign Affairs. (A publication that has just been barraging me at home and at work with invitations to subscribe--I laughed and threw them in the trash, those are the articles I always skip in the New York Review of Books because I am ridiculously frivolous--perhaps I must reconsider if they publish things like this often.)

To some 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.

The first two studies to show that primates were somewhat independent from their 'natures' involved a classic technique in behavioral genetics called cross-fostering. Suppose some animal has engaged in a particular behavior for generations -- call it behavior A. We want to know if that behavior is due to shared genes or to a multigenerationally shared environment. Researchers try to answer the question by cross-fostering the animal, that is, switching the animal's mother at birth so that she is raised by one with behavior B, and then watching to see which behavior the animal displays when she grows up. One problem with this approach is that an animal's environment does not begin at birth -- a fetus shares a very intimate environment with its mother, namely the body's circulation, chock-full of hormones and nutrients that can cause lifelong changes in brain function and behavior. Therefore, the approach can be applied only asymmetrically: if a behavior persists in a new environment, one cannot conclude that genes are the cause, but if a behavior changes in a new environment, then one can conclude that genes are not the cause. This is where the two studies come in.

In the early 1970s, a highly respected primatologist named Hans Kummer was working in Ethiopia, in a region 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, multilevel society. Because they live in a much harsher, drier region, hamadryas have a distinctive ecological problem. Some resources are singular and scarce -- like a rare watering hole or a good cliff face to sleep on at night in order to evade predators -- and large numbers of animals are likely to want to share them. Other resources, such as the vegetation they eat, are sparse and widely dispersed, requiring animals to function in small, separate groups. As a result, hamadryas have evolved a "harem" structure -- a single adult male surrounded by a handful of adult females and their children -- with large numbers of discrete harems converging, peacefully, for short periods at the occasional desirable watering hole or cliff face.

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. Among hamadryas, if a male threatens a female, it is almost certainly this brute who dominates the harem, and the only way for the female to avoid injury is to approach him -- i.e., return to the fold. But among savanna baboons, if a male threatens a female, the way for her to avoid injury is to run away. In Kummer's experiment, 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 assimilated 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 de Waal 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. Male stump tail macaques, in contrast, which share almost all of their genes with their rhesus macaque cousins, display much less aggression, more affiliative behaviors, looser hierarchies, and more egalitarianism.

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. When the newly warm-and-fuzzy rhesus macaques were returned to a larger, all-rhesus group, finally, their new behavioral style persisted.

Thanks to Lynn for the link.