The Behavioral Ecology of Chimpanzee War and Liberal Peace

I have argued that if political science ever becomes a science, it will be a biopolitical science of political animals.  An important part of such a biopolitical science would be the behavioral ecology of war and peace among human beings, chimpanzees, and other political animals.

Behavioral ecology is the study of animal behavior as shaped by evolution for adaptive responses to ecological conditions so as to increase the probability that animals will survive and reproduce.  If those ecological conditions are fixed and predictable, then evolution will favor rigid behavioral responses to those conditions that are adaptive.  But if those ecological conditions are changeable and unpredictable, then evolution will favor flexible behavioral responses based on gathering and assessing information about the costs and benefits of alternative strategies of behavior.  For social and political animals, the most important features of their ecology are other members of their species, whose behavior is changeable and unpredictable.  Consequently, their brains and nervous systems are adapted for making social judgments about the contingencies of their social environment.

Thus, in competing with other animals for access to scarce resources (like mates, food, or territory), they will decide to fight only when the likely benefits outweigh the likely costs.  A species will have an evolved propensity to warfare, therefore, only if in its ancient environment of evolutionary adaptation, lethal attacks by one group on another could under some conditions enhance the inclusive fitness of the attacking group.  But even if a species has such an evolved propensity to warfare, war is not inevitable, because the behavioral flexibility of these animals can be such that they will not engage in lethal fighting in conditions where the likely costs of such fighting outweigh the likely benefits.

So we should be able to decide the debate over whether warfare is a natural adaptation for human beings, chimpanzees, and other political animals by seeing if there is evidence of warfare in their ancient evolutionary history.  The problem, however, is that the most prominent scientists in this debate seem to interpret the evidence in opposing ways as conforming to one of two opposing intellectual frameworks--the Hobbesian view or the Rousseauean view.

As suggested by Thomas Sowell's A Conflict of Visions, much of the social thought of the past three centuries shows a contrast between a "constrained vision" and an "unconstrained vision" of social life, which I call the "realist vision" and the "utopian vision."  Those with the realist vision of life believe that since the moral and intellectual limits of human beings are rooted in an unchanging human nature, a good social order must make the best of these natural limitations rather than trying to change them.  But those with the utopian vision of life believe that since the moral and intellectual limits of human beings are rooted in social customs and institutions that are changeable, the best social order would arise from rationally planned reforms in these customs and institutions that would perfect human nature.  On the side of the realist vision, Sowell places thinkers like Thomas Hobbes, Edmund Burke, Adam Smith, and Friedrich Hayek.  On the side of the utopian vision, he places thinkers such as Jean Jacques Rousseau, William Godwin, Thomas Paine, and John Rawls. 

This conflict of visions is manifest in the debate over the evolution of war among chimpanzees.  Those scientists who insist that warfare is not a natural adaptation for chimpanzees are criticized by their opponents as Rousseaueans, who naively ignore the harsh reality of chimpanzee warfare.  And those scientists who insist that warfare is a natural adaptation for chimpanzees are criticized by their opponents as Hobbesians, who cynically defend the image of the "killer ape" against the evidence of chimp peacemaking.

Prior to 1960, when Jane Goodall began the first long-term study of chimpanzees in the wild, there was not enough evidence to resolve this debate, because of the lack of precise observation of chimpanzee politics.  Now, however, we have had many decades of studying wild chimpanzees at many different sites in Africa.  We have also had many studies of chimpanzees in captivity by people like Frans de Waal and Michael Tomasello, which are studies that more easily lend themselves to experimental research than is typically the case for studies in the wild.

One serious limitation in studies of captive chimpanzees is that the observer has no chance to see warfare, since the closed environment of captivity does not give the chimps enough room to divide up into groups that might engage in warfare.  Even in the wild, however, it's hard to see chimp warfare. 

Throughout the 1960s, Goodall reported on how peaceful the chimps were in what is now Gombe National Park in Tanzania, and thus she confirmed the common view that human beings were the only animals that deliberately killed members of their own species in war.  Beginning with her first article in National Geographic in August of 1963--"My Life Among Wild Chimpanzees"--Goodall became one of the world's most famous naturalists, a heroic young woman whose adventures with wild chimpanzees took on mythic proportions.  But then, in the early 1970s, she shocked the world with her reports of brutal chimp warfare.

 

  

By the beginning of 1973, Goodall recognized that her community of chimpanzees had split into two separate communities--the northern or Kasakela community and the southern or Kahama community.  By early 1974, she saw the first of a series of violent attacks against members of the Kahama community by Kasakela males moving southward into the Kahama community range.  By the end of 1977, the Kahama community had been annihilated, and the Kahama territory was annexed into the Kasekela territory.

Adult males of the Kasakela community seemed to be raiding the territory of Kahama.  When these Kasakela males found isolated Kahama individuals, they used their numerical superiority to brutally kill these individuals without any injury to the attackers.  The killing was similar to what chimpanzees do in hunting other animals, so it was as though the chimpanzee victims had been "dechimpized" by the chimpanzee killers.

In The Chimpanzees of Gombe (1986), Goodall suggested that chimpanzee warfare showed the primate precursors of human warfare:  "The chimpanzee, as a result of a unique combination of strong affiliative bonds between adult males on the one hand and an unusually hostile and violently aggressive attitude toward nongroup individuals on the other, has clearly reached a stage where he stands at the very threshold of human achievement in destruction, cruelty, and planned intergroup conflict" (534).

Goodall and others in her research team worried, however, that their artificial feeding of the chimpanzees had disrupted their behavior in ways that might cast doubt on whether the behavior they were observing was typical for chimpanzees in the wild.  Goodall had discovered during her early years that the animals were so wary of her that the only way she could observe them and photograph them was to feed them bananas.  Only in later years did the animals become so habituated to human presence that they could be observed without artificial feeding.

I remember in 1986 attending a conference on chimpanzee and bonobo studies in Chicago sponsored by the Chicago Academy of Sciences.  Most of the leading researchers were there, including Goodall.  I noticed that in many of the films shown by the speakers, the animals were being fed bananas or sugar cane by the human observers.  In one of the question-and-answer sessions, I asked one of the speakers about whether this artificial feeding might distort the behavior of the animals.  Some of the speakers became visibly agitated by my question, and some of them claimed that they had stopped the artificial feeding at their sites.

In 1991, Margaret Power's book The Egalitarians--Human and Chimpanzee argued that both humans and chimpanzees were peaceful egalitarians by nature in their original condition as hunter-gatherers.  She insisted that the apparently aggressive, warlike, and hierarchical behavior of the chimps observed by Goodall and others was produced by the human disruption of artificial feeding.  When chimps crowd around the food, they have to fight and form dominance hierarchies in ways that would not occur without the artificial feeding.  By contrast with provisioned chimps, she argued, wild chimps are like human hunter-gatherers in being "Rousseauean foragers" who live in a "mutual dependence system" in which all individuals cooperate peacefully and generously as equals acting for the common good of all, and thus they conform to Rousseau's theory of the best social order, in contrast to the common assumption in Western culture that inequality and war are natural.

When William McGrew wrote an review of Power's book for Nature (November 28, 1991), it was entitled "Apes Cast Out of Eden?"  He accused her of forcing chimpanzees into a utopian Rousseauean model.  He admitted that artificial provisioning was a dubious technique.  But he argued that research at sites in Africa where chimps were not artificially provisioned had confirmed Goodall's observations.  And thus it was unlikely that artificial feeding had brought about "the Fall that cast out the apes from their equatorial Garden of Eden."  He concluded that "we must face up to the fact that chimpanzees are probably very like us, warts and all."

In 1996, Richard Wrangham and Dale Peterson in Demonic Males: Apes and the Origins of Human Violence elaborated Goodall's suggestion that human violence and war were rooted in an evolutionary history shared with chimpanzees.  They argued that humans and chimpanzees share in a unique combination of social traits, in having male-bonded communities in which coalitions of males engaged in lethal raiding against outside groups.  They developed an "imbalance of power theory" for the evolution of warfare:  adult males will engage in coalitionary attacks against other groups when they can surprise isolated members of the other group, so that the attackers can injure or kill their victims to gain valuable resources (access to food, mates, and territory) without the attackers risking any injury to themselves.  Thus, for the attackers, the benefits of fighting outweigh the costs, with costs and benefits measured in terms of survival and reproductive fitness.

In their first chapter--entitled "Paradise Lost"--Wrangham and Peterson described the blissful image of wild chimpanzees conveyed by Gooodall during the first decade of her observations: "Wild chimpanzees in the dappled forest teaching and learning, playing, communicating with invented signals, doctoring themselves, using tools to enrich their food supply.  These scenes conjure classic visions of a peace in nature, an Eden of prehistory. . . . Like a rich fantasy of Jean Jacques Rousseau . . . . The apes seemed to wander without boundaries, with no fear of strangers.  Sex was public, promiscuous, and unprovocative.  There was little fighting over food" (11). 

But then, shortly after Wrangham first arrived at Gombe in 1970 as a zoology graduate student, the rift in the chimpanzee group and the eventual annihilation of the Kahama community exposed the dark side of chimpanzee life, which also exposed the dark evolutionary origins of the human natural propensity to violence and war as rooted in the aggressive temperament of "demonic males."  When many anthropologists refuse to believe that such aggression among chimpanzees and humans has deep evolutionary roots, Wrangham observes, they show their deep yearning for Rousseau's noble savage and their Rousseauean commitment to the thought that human evil is culturally acquired and thus not a natural adaptation.

Charged with showing a stubborn Rousseauean bias that distorts their view of the evidence, the proponents of peaceful egalitarianism as natural for both humans and chimps respond by charging their opponents with showing a Hobbesian bias.  As I have indicated in an earlier post, that's the response of those like Marshall Sahlins and Douglas Fry.  So here again we see Sowell's conflict of visions.

We might hope that with more study of chimpanzee behavior, we might eventually have enough evidence to resolve this conflict over the evolution of war and peace among chimpanzees.  The best recent survey of that evidence that I have seen is a chapter in War, Peace, and Human Nature edited by Douglas Fry--Michael Wilson's "Chimpanzees, Warfare, and the Invention of Peace."  Wilson opens his chapter by framing the debate as a dispute between the intellectual traditions associated with Hobbes and Rousseau--Hobbesians asserting that warfare is a natural adaptation and Rousseaueans asserting that it is a cultural invention.  Wilson is an evolutionary anthropologist at the University of Minnesota who specializes in the study of chimpanzee conflict.  Having worked with Wrangham, Wilson is clearly on the Hobbesian side of the debate in arguing that war is a natural adaptation, and peace is a cultural invention.

Most of the contributors to Fry's book are on the Rousseauean side, and so comparing what they say with Wilson's chapter allows one to judge the strength of Wilson's case.  If one does that, I think one has to conclude that the evidence supports Wilson's position.  But one also has to conclude that the Hobbesians and Rousseaueans are more in agreement than they realize.

The first point of agreement is that violent aggression among humans and chimps is a flexible natural propensity that tends to be stronger in males than in females, and the expression of that propensity depends on the social circumstances that determine the relative costs and benefits of violent fighting.  So, for example, Fry, David Barash, Robert Sussman, and Wilson all seem to agree on this (35-37, 104, 108, 451, 455-56, 467).  As Fry says in Beyond War, violent aggression is a "flexible, or facultative, adaptation" of males rather than a "fixed, or obligate, adaptation," and thus its expression depends on environmental conditions (173-74).  Wilson stresses that viewing adaptive violence through behavioral ecology highlights the fact that the expression of violence depends on the social circumstances (362-64, 381).  Thus, he agrees with Azar Gat that war is "innate but optional."

The second point of agreement is that the social life of humans and chimps is mostly peaceful, because they have evolved capacities for cooperating peacefully and reconciling conflicts.  It took Goodall over ten years before she observed lethal violence among her chimps.  Similarly, most human beings live out their lives without directly observing homicidal violence.  We can all agree with Fry that "in societies around the world, most disputes are resolved without any violence at all" (545).  This is also true for chimps, because, as Wrangham and Peterson observed, "chimpanzees lead very peaceful lives" (11).

The third point of agreement is that we can use our evolutionary understanding of war and peace among chimps and humans to promote the cultural conditions for peace.  We can see that the formation of states that enforce legal codes can pacify conflict by establishing the governmental punishment of aggressors.  We can also see how global institutions and global networks of trade can raise the costs of war and the benefits of peace so that warfare is unattractive.  Wilson observes that human beings differ from chimps in that "chimpanzees have nothing to trade with their neighbors," while human beings can use trade to turn intergroup interactions into a nonzero-sum game rather than a zero-sum game, which contributes to what is now called the liberal or democratic peace (381-82).  This confirms Adam Smith's claim about the human uniqueness of the "propensity to truck, barter, and exchange," and how this allows human beings to expand the gains from trade.

So where's the disagreement over Wilson's view of chimpanzee warfare?  Some of the Rousseaueans repeat Power's argument that chimpanzees as "Rousseauean foragers" have been transformed into Hobbesian animals by artificial feeding.  But as Wilson indicates, this cannot be true, because extensive study of chimpanzees at many sites in Africa where there has been no artificial feeding confirm Goodall's earlier observations (376-78).

Sussman argues that it is not just food provisioning that is disruptive but stress caused by all kinds of human impact--"habitat loss, snare poaching and hunting, epidemics, demographic disruption, impacts of research and tourism, and so on" (104).  Wilson's responds to this by claiming that if one compares chimpanzee study sites across Africa, estimates of human disturbance do not explain much of the variation in rates of lethal violence (378).  Here he cites a recent conference paper that he coauthored with others, which I have not yet read.

Sussman also argues that killing among chimpanzees is too infrequent for it to be an evolved adaptation.  He calculates that the reports from the long-term research sites show a rate of only one chimpanzee killing every 7.5 years (104).  Wilson's response to this is to argue that the frequency of killing is not a measure of its evolutionary importance.  Moreover, Wilson indicates, the rate of chimpanzee intraspecific killing is higher than the homicide rate in the United States, when one calculates this as the number of violent deaths per 100,000 individuals per year (370).

And yet, even if the Rousseaueans are forced to agree with Wilson's conclusions about chimpanzee warfare, they can point to bonobos as the true "Rousseauean foragers," whose evolutionary lineage is as close to human beings as is that of the chimpanzees.  The dedication of Fry's book is "To Bonoboess," because Fry thinks female bonobos offer us the best Rousseauean path to peaceful egalitarianism.  Bonobos seem to be peaceful, because they have never been observed engaging in lethal fighting.  Bonobos seem to be egalitarian, because while they have both male and female dominance hierarchies, the females seem to bond with one another to resist male dominance over the females.  Most famously, bonobos use sexual activity, including homosexual activity, to release social tension and promote social bonds.

Immediately after Wilson's chapter in Fry's book, Frances White, Michel Waller, and Klaree Boose have a chapter on "Evolution of Primate Peace" that compares chimpanzees and bonobos.  Frances White is one of the most experienced observers of bonobos.  Like Wilson, White employs a behavioral ecology approach to show how chimpanzees and bonobos differ in their behavioral strategies because they are adapted to differing ecological conditions depending on the importance of monopolizable resources.

Wild bonobos are found only south of the Congo River in the Democratic Republic of the Congo.  White argues that in this area the large size of the food patches lowers the level of feeding competition, which allows a female-bonded social structure.  Greater female-bonded groups constitute a monopolizable resource, and individual males compete for access to these groups.  But there is no advantage for males to cooperate in male coalitions to defend and expand territories containing females.

White suggests that while studying chimpanzee warfare will help us to understand human war, studying bonobos might help us to understand the conditions for peacemaking.  Similarly, Wrangham and Peterson indicate how lessons from the bonobos identify some paths to peace.  We might move from a male-dominated system of power to a sharing of power between men and women, which can be promoted through a feminization of culture and democratic institutions.  We might also promote a world system of moral sanctions favoring peace.  In considering these possibilities, we see that "male demonism is not inevitable" (Demonic Males, 251). 

Here we see the anticipation of Steven Pinker's argument for how a liberal culture promotes a liberal peace by appealing to the "better angels of our nature."  But still this remains within the Hobbesian tradition, because it's a "constrained vision" in which the "better angels" are constrained by the "inner demons" that can be tamed but not abolished.

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