Friday, August 16, 2013

How Hobbesian Baboons Find Their Inner Rousseau

                                                           Olive Baboons

The debate between Thomas Hobbes and Jean-Jacques Rousseau over the evolution of war, violence, and inequality continues today as one of the most intense debates in the natural and social sciences.  In making their arguments, Hobbes and Rousseau appealed to the best evidence available to them concerning the "state of nature" in which the first human ancestors lived.  They both studied reports about hunter-gatherers in the New World and elsewhere, with the assumption that this must resemble the original condition of the first human beings.  Rousseau also studied reports about primates closely related to human beings.  But this knowledge was too meagre to resolve the debate.  For that reason, Rousseau called for systematic studies through international expeditions that would create a new science of human nature.  It might seem that now we have so much more knowledge--in archaeology, anthropology, and primatology--that we can settle this debate.  And yet, remarkably, the debate continues.  This will be the first of a series of posts on how recent scientific research illuminates--even if it does not fully resolve--this debate in political philosophy between Hobbes and Rousseau (and perhaps including Locke, Hume, and Smith).

Is war an ancient natural adaptation, as the Hobbesians seem to say?  Or is war a recent cultural invention, as the Rousseaueans seem to say?  As I think we'll see, these stark dichotomies--nature versus nurture, biology versus culture, instinct versus learning, Hobbes versus Rousseau--are mistaken.

Consider the case of the baboons.  Until recently, they have been depicted as manifesting the violent aggressiveness of primates that is deeply rooted in their biological nature.  But now there is some evidence that their Hobbesian nature can be at least mitigated by a Rousseauean culture.

Robert Sapolsky has been studying baboons in Kenya for over thirty years.  He is best known for showing how the aggression within baboon troops produces high levels of psychological stress that are manifested in physiological markers of chronic stress, which can produce disease.  Much of this stress comes from displacement aggression, in which an individual who is frustrated for some reason attacks a lower-ranking individual who in turn attacks an even lower-ranking individual.  I first learned about Sapolsky's research in 1988, when he lectured to a class I was auditing in the Program in Human Biology at Stanford.

In 1983, Sapolsky observed that some unusual events brought about a change in the social culture of one baboon troop towards lower aggression and higher affiliative behavior, and this new culture has persisted for decades.  He published his study of this cultural change in 2004 as an article in PLOS Biology, which is available online.  An article on this appeared in the New York Times.  Recently, he has published a revised version of this article as a book chapter: "Rousseau with a Tail: Maintaining a Tradition of Peace Among Baboons," in Douglas Fry, ed., War, Peace, and Human Nature: The Convergence of Evolutionary and Cultural Views (New York: Oxford University Press, 2013), 421-438.

"Forest Troop" is a troop of olive baboons that in the early 1980s slept in trees not far from a tourist lodge, which was within the home range of the "Garbage Dump" troop that got its name from regularly foraging from the open garbage pit at the lodge.  About half of the Forest Troop males developed the habit of feeding at the garbage pit every morning.  These were the most aggressive and least affiliative males, because they had to be aggressive enough to fight the Garbage Dump males, and because they missed the early morning female-male grooming in their troop.

In 1983, tuberculosis from infected meat in the dump killed most of the Garbage Dump baboons and all of the Forest Troop males feeding at the dump.  This eliminated almost half of all the males in Forest Troop.  While baboon troops usually have an equal proportion of males and females, Forest Troop now had almost twice as many females as males, and the males were less aggressive than those who had died.

This changed the social culture of Forest Troop.  The male dominance hierarchy continued, but there was less displacement aggression by dominant males, and they were more relaxed in allowing some occasional reversals of dominance.  There was also more time spent by the troop in grooming one another.

Sapolsky ended his observations of this troop in 1986.  When he resumed study of this troop in 1993, he saw that this new social culture had persisted.  This was especially remarkable because no adult males remained from 1986.  Since all male baboons at puberty migrate out of their natal troop, all of the adult males in Forest Troop in 1993 had grown up in some other troop.  Somehow the culture of low aggression and high affiliation that had been founded in 1983 had been transmitted to the new males.

Sapolsky considers various possible mechanisms though which this cultural transmission could have occurred.  He surmises that this cultural change was preserved by a change in the behavior of the females.  When new males arrive in a troop, the resident females are usually slow to treat them in an affiliative way until two or three months have passed.  But in Forest Troop in 1993, the females were grooming new males within a few weeks of their arrival.  Sapolsky concludes that the new males were responding to this more relaxed and affiliative behavior of the females by becoming themselves more relaxed and affiliative.

In his book chapter, he writes:  "It involves a cascade: when females are less stressed by the random aggression of males, they are more likely to be spontaneously affiliative to new males; when new males are treated in this more affiliative manner, they gradually become more affiliative themselves.  This is not cultural transmission where males acquire a new behavioral style; instead, the social atmosphere of the troop, most proximally mediated by the behavior of females, facilitates the emergence of these behaviors from males.  Within the limits of baboon sociality, in the absence of Hobbesian treatment, a young male reverts to his inner Rousseau" (433-34).

Notice the qualification--"within the limits of baboon sociality."  As Sapolsky explains, this case shows the malleability of baboon social life in being open to cultural change.  But still this new culture of Forest Troop did not bring "an unrecognizably different utopia" (436).  There was still a dominance hierarchy.  There was still displacement aggression, although it had been reduced.  And while the rate of reconciliations had increased, the need for reconciliations showed the persistence of conflict.  In his original article, Sapolsky even indicated that the overall rate of aggressive conflict in Forest Troop was similar to other troops.  So despite the cultural malleability shown here, "there are not infinite amounts of social plasticity in a primate social system" (436).

I suggest that we see three levels of social order here--baboon nature, baboon culture, and baboon individuals.  The repertoire of social behavior characteristic of a baboon species sets the natural limits of baboon sociality.  This baboon nature constrains but does not determine baboon culture.  And, finally, nature and culture constrain but do not determine individual behavior.

Individual baboons have distinctive personalities or temperaments.  Although males tend to be more aggressive and less affiliative than females, there is individual variation among the males, and that's why the elimination of the most aggressive males from Forest Troop changed the social culture.

Do these baboons really have a culture that might be different from troop to troop?  If so, is that culture changeable in response to changeable historical circumstances?  Since the late 1990s, the question of whether some nonhuman animals have culture has been a hot topic, particularly among primatologists. 

This is a critical issue for Rousseau, because the uniqueness of human culture seems to be the basis for what he calls "perfectibility."  By tracing human evolution  back to prehuman ancestors, he shows the malleability of human nature.  Throughout human history, "the soul and human passions, altering imperceptibly, change their nature so to speak" (Second Discourse, Masters ed., 178).  What distinguishes human nature from the nature of other animals is not so much its rationality as its "perfectibility," the plasticity or openness to change in response to the environment (114-15).  To understand human nature, therefore, we must understand its history.

This Rousseauean idea was developed by anthropologists as the idea of culture as the uniquely human realm of freedom from nature that sets human beings apart from all other animals.  Cultural anthropologists like Marshall Sahlins can then argue that sociobiologists and evolutionary psychologists are wrong in trying to explain human social behavior biologically, because this fails to see how human culture transcends animal biology in a way that makes human sociality radically changeable.  When biological anthropologists like Richard Wrangham and Michael Wilson explain the evolution of war by comparing the warfare of chimpanzees and human foragers, the cultural anthropologists argue that human war is a cultural invention, not a biological adaptation.

But if Sapolsky and others are right about animal culture, then explaining the evolution of violence and war among nonhuman animals like baboons has to take into account the contingency and malleability of cultural history among these animals.  Even if their nature is Hobbesian, baboon males can develop a social culture that taps into their "inner Rousseau."

In a commentary accompanying Sapolsky's article in PLOS Biology, Frans de Waal observes that Sapolsky's study of the Forest Troop baboons is a work of social history that shows how an accident of history--the deaths of the most aggressive males feeding at the garbage dump--can change the cultural order of a social group.  And so, "like human societies, each animal society has its own ecological and behavioral history, which determines its prevalent social style."

This was one of my main points in my recent article in Perspectives on Politics responding to an article by John Hibbing on the biological study of politics.  I generally agree with Hibbing and his colleagues, who apply biological reasoning to the study of human political behavior.  But I disagree with them when they restrict biology to genetics and neurobiology and imply that the study of political history in all of its contingency is beyond biology.  Surely, biology includes ethology and behavioral ecology, which include the observational and experimental study of animal societies--such as the work of someone like Sapolsky.  And as one can see in Sapolsky's study of Forest Troop, this includes the scientific study of the cultural and political history of particular societies, which turns on contingent events.  Therefore, I argue, the study of human history in all of its contingency can be part of a comprehensive biopolitical science.

Sapolsky points in this direction in the conclusion of his article in PLOS Biology, where he compares the cultural change brought to Forest Troop by the deaths of the most aggressive males to the cultural consequences of the American Civil War.

It is not clear to me, however, that Sapolsky's study of baboon aggression goes very far in illuminating the evolution of human war.  If the evolutionary ancestry of monkeys separated from the ape-human line over 25 million years ago, then there's a great evolutionary distance between baboons and humans.

An even more fundamental problem is that the violence of baboons is not really war.  Baboon aggression is very different from the lethal raiding of chimpanzees and human foragers.  If war is defined as lethal conflict between coalitions from different groups, then--as Wrangham argues--we would see war among mammals in at least three primates (humans, chimps, and capuchins) and three carnivores (wolves, lions, and spotted hyenas).

If war as an evolved primate adaptation is manifest in the lethal raiding of chimps and human foragers, this suggests that Rousseau was partly wrong and partly right about the evolution of war.  He was wrong if he thought that lethal raiding was not part of the life of the earliest human ancestors.  But he was right in seeing that the emergence of complex warfare--mass military organizations under bureaucratic command--was a cultural invention arising after the development of agricultural societies and centralized states.

Some posts on related topics can be found here, and here.

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