If Bonobos Are Aggressive, Does That Deny the "Self-Domestication Hypothesis"?

                                                Vergil, A Male Bonobo at the Cincinnati Zoo

For many years, I taught a course at Northern Illinois University on "Chimpanzee Politics," which included some comparative study of chimpanzees and bonobos, the two primate species most closely related to human beings, because all three species evolved from a common ancestor about 7 million years ago.  

Every time I taught the course, I took the students on a field trip to the Milwaukee County Zoo, which has the largest captive group of bonobos in the world (over 20 individuals).  I have also been to the Cincinnati Zoo, which has about 12 bonobos.  Of course, it would be better to study the social behavior of bonobos in the wild.  But that is hard to do because they are only found in one place in the world--in dense rainforest areas south of the Congo River in the Democratic Republic of the Congo.  Even those biologists who go there to study them find it hard to observe them as they move through the dense canopy of the rainforest.

Chimpanzees seem to be far more aggressive and violent than are bonobos.  Male chimps attack females and other males.  Sometimes these attacks are lethal.  Male chimps also form coalitions with other males to assert a male dominance hierarchy over females and other males.  These male coalitions also patrol the borders of their community, and they can launch attacks against other communities--even to the point of annihilating the whole community in war.

By contrast, bonobos have never been observed to engage in lethal attacks on other bonobos.  Female bonobos seem to be dominant over males.  And the females form coalitions with one another to attack males and mediate their conflicts.  In contrast to chimps, bonobo communities have never been observed to go to war with one another.  Bonobos from different communities can interact with one another peacefully.  All of this peacemaking depends on mutually pleasurable bisexual lovemaking--rubbing their genitals together--females with other females and with males.  This is why the bonobos have been dubbed the "hippie apes" who "make love not war."

Comparing human beings with these two ape species in working out the evolutionary links between the three species has provoked a debate among evolutionary biologists and social scientists.  The Hobbesian scientists argue that human beings are closer to chimps, which shows that the human state of nature was a state of war.  The Rousseauean scientists argue that human beings are closer to bonobos, which shows that the human state of nature was a state of peace.

In my posts on bonobos and the human state of nature, I have argued that Locke's account of the state of nature is closer to the truth than either Hobbes' or Rousseau's, and that evolved human nature combines the natural propensities of both chimps and bonobos.  As Steven Pinker would say, our human nature has both Inner Demons and Better Angels.  Lockean liberalism constructs a cultural niche of social institutions, mental attitudes, and moral traditions that tame the Inner Demons while eliciting the Better Angels to motivate voluntary cooperation and nonviolent relationships.

But in contrasting bonobos and chimpanzees, we should not assume that bonobos are utterly peaceful.  That bonobos are often aggressive in their attacks on one another is made clear in new research by Maud Mouginot and her colleagues that was just published online on Friday (Mouginot et al. 2024).

The message from this study as reported in the press--as in Carl Zimmer's report for the New York Times--is that "male bonobos commit acts of aggression nearly three times as often as male chimpanzees do."  That would seem to deny the common view that chimps are far more aggressive than bonobos.  But if you read the article carefully, you will see that the story is much more complicated than that.

Mouginot and her colleagues employed what scientists studying animal behavior call the "focal-animal sampling" method (Altman 1974).  All occurrences of specified actions of an individual, or specified group of individuals, are recorded for a pre-determined period of time.  

For their study, they had all-day focal follow data for 14 chimpanzee adult males from two communities in the Gombe National Park in Tanzania and 12 bonobo adult males from three communities in the Kokolopori Bonobo Reserve in the Democratic Republic of the Congo.  They had recorded hundreds of aggressive dyadic interactions, including contact aggression (physical contact such as hit, pull, bite, kick, or jump-on) and non-contact aggression (such as charge and chase).  They had also recorded whether the focal-male was the aggressor or the victim and whether he was interacting with another male or with a female. 

They wanted to use this data to test the "self-domestication hypothesis" of Brian Hare and Richard Wrangham.  They suggested that bonobos evolved to be less aggressive than chimpanzees just as dogs evolved to be less aggressive than wolves.  Humans selected less aggressive (or friendlier) wolves to become their companions, and over time, wolves evolved into dogs through domestication by human selection.  Similarly, if female bonobos formed coalitions to punish aggressive males, and if females preferred to mate with less aggressive males, which would tend to produce less aggressive offspring, bonobos could have been self-domesticated for being less aggressive or friendlier to one another (Hare, Wobber, and Wrangham 2012).

Moreover, Hare and Wrangham have also suggested that humans could have undergone a similar process of evolution by self-domestication to be less aggressive or friendlier towards individuals within their community (Hare 2017; Hare and Woods 2020; Wrangham 2019).  I have extended this idea of human self-domestication to explain the evolution of Lockean liberalism and the bourgeois virtues as symbolic niche-construction.

What Mouginot and her colleagues have found does not deny the self-domestication hypothesis of Hare and Wrangham, although it might require some refinement in the theory.  They found that there was a higher rate of male-male contact aggression among bonobos than chimpanzees.  And in both species, the more aggressive males had higher mating success.  But they found no evidence to contradict the observation that bonobos never kill other bonobos, while chimpanzees do kill other chimpanzees in fighting both within and between communities.

One possible explanation for why bonobo males engage in more non-lethal aggression with other males than do chimpanzee males is that since bonobo females prevent males from forming coalitions, bonobo males can attack other males without suffering reprisals from male coalitions.

As Hare told Carl Zimmer, the one dramatic difference in aggressiveness between the two species remains:  "Chimpanzees murder, and bonobos don't."

REFERENCES

Altman, Jeanne. 1974. "Observational Study of Behavior: Sampling Methods." Behaviour 48: 227-65.

Hare, Brian. 2017. "Survival of the Friendliest: Homo sapiens Evolved via Selection for Prosociality." Annual Review of Psychology 68: 155-86.

Hare, Brian, and Vanessa Woods.  2020.  Survival of the Friendliest: Understanding Our Origins and Rediscovering Our Common Humanity. New York: Random House.

Hare, Brian, V. Wobber, and Richard Wrangham.  2012.  "The Self-Domestication Hypothesis: Evolution of Bonobo Psychology Is Due to Selection Against Aggression."  Animal Behaviour 83: 573-85.

Wrangham, Richard.  2019.  The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution.  New York: Pantheon Books.

Zimmer, Carl.  2024.  "No 'Hippie Ape':  Bonobos Are Often Aggressive, Study Finds." The New York Times, April 12.

Bonobo Politics

In a previous post, I commented briefly on Ian Parker's article on bonobo research in The New Yorker. The article was slanted against Frans de Waal, arguing that de Waal has been responsible for a naive view of bonobos as "hippie primates" based on his limited observations of bonobos in the San Diego zoo, but without having ever seen a bonobo in the wild. Now, de Waal has written a response, which I find persuasive.

Here's how I would summarize the points of agreement and disagreement in this debate. The fundamental problem is that the observational study of bonobos is not as extensive as that for chimpanzees. In the wild, bonobos are found only south of the Congo River in the Democratic Republic of Congo. It's very hard to study them there because of the density and inaccessibility of their jungle habitat, and because of the political violence in the DRC. Most of the behavioral research has been done in zoos. In 2006, there were only a total of 84 bonobos in North America and 76 in Europe. The largest captive group is in the Milwaukee County Zoo, which has 21 individuals. By contrast, there are far more chimps in zoos around the world. Moreover, chimps have been studied in the wild for many decades at multiple sites.

Chimps have both male and female dominance hiearchies, but the alpha male dominates overall. Chimps are both competitive and cooperative. Their competition can be violent, even to the point of lethal violence. Until the 1970s, Jane Goodall was reporting that chimps were remarkably peaceful. But then she observed the chimps at Gombe dividing into two territorial groups that went to war, with the northern group (led by aggressive males) decimating the southern group. There have also been observations of lethal violence within chimp groups in the competition for alpha male status.

Bonobos also have both male and female dominance hierarchies, but it seems that the females dominate over the males. Although the adult bonobo males are bigger and stronger than the females, the females seem to be able to intimidate the males through a sexual bonding of females, who engage in elaborate bisexual acrobatics. The situation here is unclear because some primatologists speak of bonobos as showing "co-dominance," in which the alpha male and alpha female share dominance. Richard Wrangham, Takayoshi Kano, and Chris Boehm take this position. But de Waal and Amy Parish tend to stress female dominance.

This ambiguity in the dominance structure of bonobos is evident in the group at the Milwaukee Zoo, where I have often taken the students from my "Chimpazee Politics" class. Until recently, the top of the dominance hierarchy has been held by a male-female mated pair. (A good survey of this Milwaukee group can be found in a new book--Jo Sandin's Bonobos: Encounters in Empathy.) Careful observation by keepers at the zoo, supported with meticulous daily records of behavior, suggests that the female Maringa is the "matriarch" over the whole group, although her longtime mate Lody is the alpha male. At times, Lody seemed to be just enforcing the female dominance of "the power chicks." At other times, he seemed to be acting as equal to Maringa, as if they were the "royal couple."

Bonobos seem to use sexual pleasure--homosexual as well as heterosexual--as a way of pacifying conflict and releasing tension. Thus, sexuality is not just for reproduction but also for nonreproductive bonding. This pacifying effect of sexual coupling also seems to be used when bonobo groups meet in the wild. While chimps have been observed using lethal violence in group competition, bonobos have never been seen to do this. This might be because we haven't yet observed bonobos long enough. After all, Goodall had to wait for almost 15 years before she saw warfare among her chimps. But at least as of now, the evidence suggests that bonobos are better at pacifying conflict than are chimps.

Still, this does not mean that bonobos are totally peaceful. As de Waal says, the very fact that bonobos have to work hard at reconciliation shows that there is competition and conflict that needs to be controlled.

And if bonobos seem in some ways to be more egalitarian than chimps, this does not mean that hierarchy is completely absent among bonobos. There is a dominance structure among both females and males, and it's ultimately a matter either of female dominance over the males or co-dominance of alpha female and alpha male.

If human ancestry is traceable back to a common ancestor with bonobos and chimps, then one would expect that human beings show a political nature that is ambivalent in combining competition and cooperation, a propensity to dominance and a propensity to resist dominance. In his newest book Our Inner Ape, de Waal concludes that human beings are the "bipolar ape," combining chimp and bonobo traits, "being both more systematically brutal than chimps and more empathic than bonobos."

In any case, I see nothing here to support the Marxist notion that social engineering in a socialist society could make human beings so selflessly cooperative that they would have no interest in private property or social hierarchy. The failure of the Marxist regimes in the 20th century confirms the conclusion of primatologists like de Waal that Marxism is contrary to human nature.

We are neither selfless cooperators nor rational egoists. We are neither purely egalitarian animals nor purely despotic. We are a complex mixture of natural propensities that balance self-interest against cooperation and dominance against equality.

This goes against the utopian belief of the radical left in human perfectibility as supporting a revolutionary transformation of the human condition through social re-education. Rather, it supports the realistic belief of libertarian conservatism in human imperfectiblity as showing the need for regimes based on traditional morality, family life, private property, and limited government.

Other posts on bonobos can be found here and here.

Bonobos--The Politically Correct Primate

Although bonobos resemble chimpanzees, bonobos are now considered a separate species. They have passed into popular culture as the "hippie chimps." They are sexual swingers who shift easily from heterosexual to homosexual activity. They resolve conflict through sexual pleasure rather than aggressive violence--make love not war! Although bonobo males are bigger and stronger than bonobo females, the females seem to be dominant over the males, which seemed to be enforced by females bound together by lesbian sex attacking any male who becomes too assertive. And while chimps have shown what looks like warfare between distinct territorial groups, bonobo groups seem to mix easily without warfare. So while bonobos would appear to be political animals in the sense that they must manueuver their way through a complex social community, bonobo politics would seem to be more peaceful, egalitarian, and matriarchal than is chimp politics.

But all of this is based on remarkably skimpy observational evidence. Wild chimpanzees are found only in the dense tropical jungle south of the Congo River in the Democratic Republic of Congo. The few primatologists who have tried to study them in the wild have found them so hard to track that some observers have seen them for only a few hours after years of seeking them out. Most of the popular picture of bonobo behavior comes from Frans de Waal, who has seen bonobos in zoos, but who has never seen a bonobo in the wild.

I have regularly taught a course at Northern Illinois University on "Chimpanzee Politics," which includes some reading on bonobos. Each time I teach this course, I take my students on a field trip to the Milwaukee County Zoo, which has the largest group of bonobos in captivity (18-20 individuals). Each time that we go, I am struck by how we don't see the behavior that we have read about in de Waal's books (particularly, the 1997 book Bonobo: The Forgotten Ape). For example, we go there with the voyeur's expectation of seeing lots of sexy encounters, but we're usually disappointed. This experience as well as my reading of the primatology research comparing chimps and bonobos has made me skeptical of de Waal's story of bonobo life and the popular acceptance of this story as showing the potential for confirming Rousseau's image of the noble savage.

In the July 30th issue of The New Yorker, Ian Parker has an article on bonobo research. He surveys the debate among primatologists over de Waal's claim that bonobos are radically different from chimps. One can see here the moral and political implications of these debates. Feminists, gay activists, and those on the political Left would like to see bonobos as the closest living evolutionary relative of human beings, and they like de Waal's account of bonobo life as suggesting that human beings could potentially adopt the "bonobo way" of sexual equality and peaceful hedonism. Darwinian conservatives are suspicious of this as motivated by utopian longings.

As Parker indicates, the direct observations of bonobos in the wild are leading some primatologists to question de Waal's account. Bonobos are probably more violent than de Waal is willing to admit. They are not more bipedal than chimps. They are not more sexually active than chimps. And whether bonobos show female dominance--in contrast to the male dominance of chimps--is open to doubt. Even in de Waal's Bonobo book, there are some occasional suggestions that bonobo males are "slightly dominant" or maybe "co-dominant" with females (60, 74-81).

The Cincinnati Bonobos' Answer to the Creation Museum: In the Image of God or Created from Animals?

 

                            Vergil, A Male Bonobo in the Cincinnati Zoo, Born January 24, 1994

                      Vim, a Male Bonobo in the Cincinnati Zoo, Born September 5, 1995

                            Zanga, a Female Bonobo in the Cincinnati Zoo, Born January 9, 1999

After touring the Creation Museum and the Ark Encounter in northern Kentucky for two days, my wife and I spent a day at the Cincinnati Zoo.  I was particularly interested in seeing the bonobos.  The Cincinnati Zoo is one of the few zoos in the United States with bonobos.  They have about 12 individuals.  When I taught my course at Northern Illinois University on "Chimpanzee Politics," I used to take my students on a bus trip to the Milwaukee County Zoo, which has the largest group of bonobos in the U.S.--about 21 individuals.

I have written a series of posts on bonobos and how bonobos and chimpanzees are the primates most closely related to human beings, which suggests that the last common ancestor of these primates and human beings probably combined the traits that we see in bonobos and chimpanzees.  Certainly, at the Cincinnati Zoo, the signs posted around the bonobos clearly suggest that human beings evolved from some bonobo-like primate.  

Here, then, the Zoo is challenging the claim of the Creation Museum and the Ark Encounter that there is no evolutionary connection between humans, bonobos, and chimpanzees.  As part of the "Starting Points" exhibits at the Creation Museum, bonobos are grouped with gorillas, orangutans, and chimpanzees as "great apes" (CMS, 35-36).  But while evolutionary scientists place the great apes in the same family with human beings--Hominidae--the Creation Museum insists that the great apes should be placed in their own family--Pongidae--so that there is a separation between the "Ape Kind" and "Human Kind."  This is required for their claim that God originally created these two "kinds" as separate, and endowed only the human kind with the moral dignity of being created in God's image.  To teach that the great apes and human beings belong to the same evolutionary lineage, they argue, would destroy the foundations of human morality by denying the moral uniqueness of human beings as the only animals aware of and subject to God's moral law.

But it's not clear that this teaching is grounded in the Bible.  First of all, the Bible never identifies human beings as belonging to the "human kind."  The word "kind" (Hebrew min) appears in Genesis, Leviticus, Deuteronomy, and Ezekial 30 times, but it is never applied to humans.  So, the Bible does not clearly separate the "Ape Kind" from the "Human Kind," as claimed by the Creation Museum.  Moreover, the Bible refers to "apes" only twice (1 Kings 10:22 and 2 Chr. 9:21), and the Bible does not identify the various species of apes.  Everything that the Creation Museum says about the great apes being in their own family has no Biblical basis.  This confirms my point that the Bible is not a science text about natural history.

But surely, Ham and the Creation Museum would say, the Bible does clearly teach that human beings are the only animals created in God's image, with a humanly unique moral awareness, and surely this must mean that God did not allow the human species to evolve from primates, which denies the Darwinian account of human evolution from animals.

But if we compare behaviors in bonobos and chimpanzees, we can see that they are more similar to humans than to each other (Brian Hare and Shinya Yamamoto, "Minding the Bonobo Mind," in Hare and Yamamoto, eds., Bonobos: Unique in Mind, Brain, and Behavior [Oxford: Oxford University Press, 2017], 1-13).  Chimpanzees share at least five traits with humans not manifest in bonobos:  extractive foraging, lethal aggression between groups, infanticide/male coercion of females, cooperative hunting, and male-male alliances.  Bonobos share at least five traits with humans not manifest in chimpanzees:  non-conceptive sexual behavior, mother's importance to adult offspring, high levels of adult play, sharing between strangers, and female gregariousness.

And yet we can also see that human beings are unique animals in at least three respects.  In The Descent of Man, Darwin noted that self-consciousness is uniquely human: "It may be freely admitted that no animal is self-conscious, if by this term it is implied, that he reflects on such points, as whence he comes or whither he will go, or what is life and death, and so forth" (105).  Morality is also uniquely human: "A moral being is one who is capable of comparing his past and future actions or motives, and of approving or disapproving of them.  We have no reason to suppose that any of the lower animals have this capacity. . . . man . . . alone can with certainty be ranked as a moral being" (135).  And language is uniquely human: "The habitual use of articulate language is . . . peculiar to man" (107).  Is the Bible pointing to these three uniquely human traits in saying that humans were created in God's image?

As I have argued previously, we can explain human evolution from primate ancestors through a growing expansion of the number of neurons in the cerebral cortex of the primate brain.  Humans are unique intellectually and morally because of the 16 billion neurons in the human cerebral cortex.  That gives them mental capacities for self-conscious reflection, language, moral reasoning, and symbolic thinking generally, which includes the symbolic capacity for imagining supernatural realities and believing the Bible to be a supernatural revelation of God's creative history and His promise of human immortality with divine judgment in the afterlife.  The Creation Museum and the Ark Encounter are manifestations of that evolved symbolic capacity of the human mind.

The Aristotelian Prudence of Bonobos

In the Department of Political Science at Northern Illinois University, we have "Politics and the Life Sciences" as a field of study at both the undergraduate and graduate levels. Many of our Ph.D. students have combined "biopolitics" with political theory and other traditional areas of research in political science. Andrea Bonnicksen, Rebecca Hannagan, and I are the three faculty members who teach in this area. One of the things we do is compare human politics with the political behavior of other primates--particularly, chimpanzees and bonobos.

The Milwaukee County Zoo has the largest group of bonobos in captivity. And so I have taken some of my students to visit the Milwaukee Zoo to see the bonobos. This semester Bonnicksen will be taking some of her students there.

Many people find it weird, if not ridiculous, that political scientists would be looking for political behavior among apes. But for me, this is an extension of Aristotle's biological science of political animals.

Last year, Jo Sandin published a book--Bonobos: Encounters in Empathy--on the Milwaukee bonobos. Dr. Harry Prosen is a psychiatrist who has worked with the bonobos there for some years. Sandin reports that Prosen's colleagues in the psychiatric community have been impressed by his accounts of the practical judgment shown by some of the bonobos. In particular, Lody--until recently, the alpha male--is said by Dr. Prosen to show "evidence of wisdom, in the Aristotelian sense: the ability to see life in all its aspects and to act in a way that benefits others." According to Prosen, "Lody's empathetic behaviors and ability to use good judgment in parenting skills, discipline and, in many instances, the demonstration of altruistic behaviors have had a powerful impact on the development of the juvenile males in the bonobo group" (Sandin, pp. 51-52).

Many people would dismiss as silly the idea that apes might exercise prudence or practical judgment, which Aristotle regarded as the primary intellectual capacity for moral and political life. But Aristotle's biological writings would suggest that he himself would take this seriously. After all, he often attributes prudence (phronesis) to nonhuman animals--and particularly, to those he identifies as political animals. Although he does not speak of apes as political, he does recognize their remarkable similarities to human beings and suggests that they are the animals most closely related to human beings.

As I have suggested in previous posts, the importance of prudence--judging what is best in the particular circumstances of particular individuals--across many animal species shows the complexity and contingency of animal behavior, so that we cannot predict animal behavior with precision. The failure to achieve predictive power in the scientific study of human politics shows a pattern that holds across all animal behavior. A biological science of political animals would be a historical science of particular individuals and groups with complex cultural traditions.

Two previous posts on bonobos can be found here and here. Some of my posts on animal prudence can be found here, here, and here.

The Evolution of War and Lethal Violence

Over the years, I have written a long series of posts on whether evolutionary science can adjudicate the debate between Thomas Hobbes and Jean-Jacques Rousseau over whether our earliest human ancestors were naturally violent (as Hobbes argued) or naturally peaceful (as Rousseau argued).  Many social scientists have been vehement in taking one side or the other in this debate.  But I have argued that John Locke took a third position that is closest to the truth--that our foraging ancestors lived in a state of peace that tended to become a state of war.  Hobbes is partly right. Rousseau is mostly wrong. And Locke is mostly right.

Now a new study published in Nature has stirred up this debate again.  This research shows how human lethal violence against members of our own species is part of our evolutionary history as mammals. 

Jose Maria Gomez and his colleagues have compiled and analyzed the sources of mortality from a comprehensive sample of more than 4 million deaths from 1,024 mammalian species drawn from 137 mammalian families, which is 80% of the total number of mammalian families.  The data for humans was from over 600 studies, ranging from Paleolithic samples (50,000 to 12,000 years ago) to anthropological studies of the last few centuries. (J. M. Gomez, M. Verdu, A. Gonzalez-Megias, & M. Mendez, "The Phylogenetic Roots of Human Lethal Violence," Nature 538 [13 October, 2016]: 233-37). 

They applied comparative statistical techniques to the phylogeny (the family tree) of mammalian violence to reconstruct the rates of lethal violence, defined as killing by members of the same species.  They calculated that the rate of lethal violence at the phylogenetic origin of mammals was about 0.30%, which is approximately 1 in 300 deaths.  Rates of lethal violence increased across the family tree leading to primates--2.3% for the common ancestor of primates and tree shrews, declining slightly to 1.8% for the ancestor of the great apes (gorillas, orangutans, chimpanzees, and bonobos), and then increasing to 2% at the origin of the human species, which is about six times higher than the rate at the origin of mammals.  Increases in lethal violence were correlated with increasing group living and territoriality.  Apparently, lethal violence increases when individuals are living close together and competing for territorial resources.

Gomez and his colleagues compared the phylogenetically inferred levels of human lethal violence with the levels observed in archaeological and anthropological records.  They found that the phylogenetic prediction of about 2% for prehistoric foragers was about the same as what emerged from their calculations from the archaeological records.  But they also found that levels of lethal violence rose far above 2% in historic times when human beings began to live in chiefdoms and states.  Levels of deaths by lethal violence did not begin to decline until about 500 years ago.  Finally, in the last 100 years, these levels fell to below 2% for the first time in human history.

In his commentary in Nature, Mark Pagel claims that this Gomez study supports the Hobbesian position that human beings are innately violent (Pagel, "Lethal Violence Deep in the Human Lineage," Nature 538 [13 October, 2016]: 180-81).  In an article in The Guardian, Steven Pinker is quoted as claiming that this study does support the Hobbesian position and Pinker's argument in The Better Angels of Our Nature about how modern societies have brought a dramatic reduction in violence from the high levels in prehistoric foraging societies.

On the contrary, John Horgan and Brian Ferguson have claimed that the Gomez study actually supports the Rousseauean position that war is not innate for human beings but largely a product of the cultural environments that arose after human beings left the ancient foraging life.

There are a number of points in dispute here.

The first point is that in measuring how often humans and other mammals kill members of their own species, the Gomez study makes no distinction between individual killing and killing in war.  So they include all forms of human-on-human killing, which includes individual homicides and infanticide.  Rousseaueans like Brian Ferguson and Douglas Fry agree that prehistoric foragers often killed one another, but almost all of this homicidal killing arose in personal disputes or feuding, and so, they argue, this was not warfare.  But notice what this means: the Rousseaueans are conceding that our foraging ancestors were not utterly peaceful, as Rousseau claimed, because they did sometimes kill one another, although this was not killing in war between groups.  One can find high rates of individual killing among ancient foragers, but without war.

The second point is that the Gomez study's estimate of 2% of deaths among ancient foragers being due to lethal violence is much lower than the estimates by Pinker and others of 15-25% of deaths due to warfare.  While Pagel claims that the Gomez study shows "hunter-gatherer societies as being engaged in constant battles" (181), the Gomez study actually concludes that the 2% rate "contrasts with some previous observations," such as that of Pinker (235).

The third point is that the Gomez study shows that rates of lethal killing increase (from 2% to 9%) with the move from ancient foraging bands to chiefdoms.  These high rates do not drop below 2% until the last 100 years.  This looks like the pattern suggested by Douglas Fry--like the letter n--low violence in the ancient foraging past, then increasing violence in more complex societies, followed by declining violence in contemporary states.  Pinker might argue that this conforms to the Hobbesian pacification thesis, because the only form of social order that reduces violence is the modern centralized state.  Ferguson and Fry seem to concede this.  This shows that both the Hobbesians and the Rousseaueans can agree that violence is not genetically determined, because the expression of the natural capacity for violence depends on the social environment.  As Azar Gat has said, "war is innate, but optional."

The fourth point is that the rates of lethal violence in prehistoric bands and tribes is much lower than for bands and tribes studied by anthropologists over the past few centuries.  This suggests that foraging societies become more violent after having contact with colonial societies, and that such high levels of violence cannot be found in the archaeological record for ancient prehistoric foragers.

The final point is that the two living ape species most closely related to humans--chimps and bonobos--show conflicting evidence as to whether the primate phylogeny of humans favors an innate propensity to violence.  Chimpanzees show male coalitional raiding leading to killing that looks like primitive warfare similar to what people like Richard Wrangham see among human foragers.  But there is no clear evidence for even a single case of conspecific killing among bonobos.  Pagel writes: "Even the usually peaceful bonobo Pan paniscus can sometimes display violent behavior" (181).  But he does not cite any evidence for bonobo lethal violence.

In the Supplementary Material for their article (found online at the Nature website), Gomez and his colleagues provide the data for mammalian lethal violence.  For chimpanzees, they say there is documentation for 734 deaths and for 4.49% of these being deaths from conspecific killing.  For bonobos, it's 145 deaths and 0.68% conspecific deaths.  For the bonobo data, they cite five articles.  Apparently, they are relying on one "suspected" case of conspecific killing for bonobos.  But when I contacted Frances White, the leading observer of bonobos in the wild, and asked her about this, she said that this one case is very dubious, and that there is no clear case of conspecific killing among bonobos.  She said that there were at least three cases of bonobo cannibalism, but there was no evidence that these were cases of killing rather than eating already dead carcasses.

It's easy to understand why the Rousseaueans love the bonobos--there're the hippie apes who make love not war.

On the other hand, it's also easy to understand why the Hobbesians love the chimps and not the bonobos, because the chimps are closer to Hobbesian expectations for a evolutionarily close human relative.  Frances White once observed:

"As we have found out more about how bonobos behave in the wild, they have declined in favor as a model for our ancestor . . . This makes me wonder how much our use of models is influenced by how we would like our ancestor to have behaved--clearly the bonobo has fallen from grace because it shows what, for many, is behavior that is socially unacceptable for a close relative of ours."

Some of my other posts on the evolution of war and violence are here, here, here, here, here, here, here, here, here, here, here, here, here, here, here, and here.

Classical Liberalism as Evolutionary Niche Construction for Declining Violence: Bonobos and Humans

At the Liberty Fund conference on "Liberty and Violence," one of the participants was a primatologist who studies bonobos in Africa.  At one point in our discussion of Steven Pinker's Better Angels of Our Nature, she complained about how Pinker unfairly dismisses the evidence for peaceful cooperation among bonobos, in contrast to the violence of chimpanzees.  She noted that Pinker relies on primatologists who study chimps or who have only studied bonobos in zoos, and who want to make bonobos look like chimps in their tendency to violence.

She explained that in the wild bonobo females serve a policing function, in that they intervene in fights to moderate conflicts through impartial mediation, because they benefit from living in a stable social order that is not disrupted by violence.

She also observed that bonobos--like all primates--show a range of personality types, so that some individuals have more violent temperaments than others, and consequently the occurrence of violence can depend on the contingency of whether there are such violent individuals in the group.  She said that many of the deaths of the males comes from "testosterone poisoning"--young males vigorously displaying their virility in the forest canopy can kill themselves by slamming into a tree.

She also said that if dominant males are grouped together in zoos without females who can moderate their male conflicts, then nasty fighting is likely to break out.  She explained then that what the females are doing in the wild groups in pacifying conflicts is "niche construction"--behavior that creates a social environment in which stable and peaceful cooperation is adaptive.

Here she was appealing to an idea developed by F. John Odling-Smee, Kevin Laland, and Marcus Feldman in Niche Construction: The Neglected Process in Evolution (Princeton University Press, 2003).  In most of evolutionary theory, we think of organisms as carrying genes, and the inheritance of these genes by the next generation depends on organisms surviving and reproducing according to chance and natural selection in their environments.  But there is another process of evolution that arises from organisms changing their environments, which modifies the natural selection pressures in their environments.  This is evolutionary niche construction.  Among many animals, evolutionary niche construction includes the transmission of culturally learned traditions.  And among human beings, it includes the transmission of culturally learned symbolic systems such as art, science, religion, and philosophy.

In response to this discussant's comment about social niche construction among bonobos, I suggested that the history of classical liberalism is evolutionary niche construction, and that this is a big part of Pinker's argument: the history of classical liberal philosophy has created a cultural moral environment of liberalism in which peaceful cooperation and declining violence are adaptive.  (This is what Deirdre McCloskey would identify as the work of rhetorical entrepreneurs in the marketplace of ideas who have used moral persuasion to create a liberal culture that honors the bourgeois virtues.)

As Pinker argues, human nature is a mixture of Inner Demons and Better Angels.  Human beings are innately predisposed to violence by their Inner Demons, but the expression of those predispositions is not "hydraulic"--that is, a drive that must necessarily be satisfied--but "strategic"--that is, a propensity that is responsive to environmental triggers.  Classical liberalism constructs a cultural niche of social institutions, mental attitudes, and moral traditions that tend to elicit the Better Angels to motivate voluntary cooperation and nonviolent relationships.

In this way, human nature constrains but does not determine human culture and individual judgment.  Within the constraints of human nature as a mixture of Inner Demons and Better Angels, classical liberalism can foster those cultural traditions and individual judgments that limit the Inner Demons and channel the Better Angels towards a system of liberty and voluntarism.

A few of the people at this Liberty Fund conference were such fervent critics of the Pinker argument that they resolutely rejected this claim that there has been a historical trend towards declining violence as fostered by classical liberal culture.  But by the end of our discussions, I had a strong impression that many--and maybe most--of the people there found the Pinker argument persuasive, even if one could dispute some of Pinker's evidence and argumentation.

Nevertheless, even those of us who were persuaded by Pinker were left with the unsettling conclusion that while the general historical trend of declining violence and increasing liberty was encouraging, the contingencies of history make it impossible to predict that this trend will continue unbroken into the future.

There was a lot of discussion of whether Pinker's science is a falsifiable and predictive science.  I argued that Pinker's science is a historical science, as opposed to nonhistorical sciences like physics and chemistry.  In a historical science, one can make retrospective  predictions about the past and make only broad pattern predictions about the future.  One cannot precisely predict the future.  And, indeed, Pinker stresses that he is only claiming that we can see declining violence in past history, and that we cannot be sure that this will continue into the future.  His entire book, as he indicates in the first paragraph (xxi), is looking backward, so that he does not, because he cannot, make precise predictions about the future.

Pinker suggests that there are four possible historical trends in war--escalation, cyclical, random, and declining sawtooth (191-92).  He is arguing for seeing the trend as a declining sawtooth.  The way he draws this pattern through the Second World War as one data point shows that in a declining sawtooth pattern, there can be generally decline in violence, while still allowing for a sudden jump in violence towards the greatest single atrocity in human history--55 million violent deaths in the Second World War--which indicates the radical contingency in Pinker's historical science.

This contingency is made evident in Pinker's book by his noting how three individuals acting under the influence of illiberal ideologies were responsible for the greatest atrocities of the 20th century.  The Second World War would not have occurred without Hitler.  The Great Purge in the Soviet Union would not have occurred without Stalin.  The Great Famine and the Cultural Revolution in China would not have occurred without Mao.  So "tens of millions of deaths ultimately depended on the decisions of just three individuals" (343).

It will always be possible for such individuals to appear in circumstances that allow them to rise to positions of power that enable them to perpetrate mass atrocities of violence.  But this can be made unlikely insofar as classical liberalism as evolutionary niche construction continues to spread, making us more like bonobos and less like chimpanzees.

Some of these points are elaborated in my series of posts on Pinker (in October to December of 2011) and in my post on "The Behavioral Ecology of Chimpanzee War and Liberal Peace."

A New Study of Chimpanzee Warfare: Hobbes Versus Rousseau

 A chimpanzee war party of males on patrol typically moves in a single-file pattern.

I have written a series of posts on the debate over chimpanzee warfare, which can be found here and here. 

As I have indicated, this is ultimately a debate in political philosophy between Hobbesians who argue that war is rooted in human nature and Rousseaueans who argue that war is a purely cultural trait and that the original state of nature was peaceful.  Since chimpanzees and bonobos are the living primates most closely related to human beings, the dispute over whether chimps and bonobos are naturally warlike or peaceful becomes part of the dispute over the evolutionary roots of human warfare.

A new article favoring the Hobbesian position has just been published in Nature:  Michael L. Wilson, et al., "Lethal Aggression in Pan Is Better Explained by Adaptive Strategies than Human Impacts," Nature 513 (18 September 2014): 414-417.  Here's the abstract:

"Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing.  Two kinds of hypotheses have been proposed.  Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates.  Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning.  To discriminate between these hypotheses, we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades.  Our data include 152 killings (n = 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos.  We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio).  Variation in killing rates was unrelated to measures of human impacts.  Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported."

This is impressive evidence for the Hobbesian argument.  But as indicated by a news story in The New York Times and a  blog post by Marc Bekoff, the Rousseaueans are not ready to surrender.  Four points need to be made here.

First of all, notice that after 50 years of studying 22 communities, there have been only 58 directly observed killings and 41 inferred.  Even if one concedes that intraspecific killing occurs, one can see that it is remarkably rare, and generally these animals are peaceful and cooperative.  The Hobbesians have to admit this.

The second point here for the Rousseaueans is that the bonobos still look even more peaceful than the chimps.  And that's why the hippie bonobos are so loved by the Rousseaueans.

The third point is that Rousseaueans like Brian Ferguson will argue that this study does not go deeply enough into the long history of human disturbance of chimpanzee habitats to see its effects.  Ferguson is writing a book--Chimpanzees and War--that will elaborate his case for the Rousseauean position.  Meanwhile, Ferguson has written a good response to the Nature article.

The final point is that even if lethal coalitional raiding is a natural adaptation for chimpanzees and human hunter-gatherers, complex human warfare as it arose first with bureaucratic states is a largely cultural invention that can be changed through cultural evolution.  Richard Wrangham, one of the senior authors of the Nature article, has stressed this.  And, indeed, if Steven Pinker is correct, the cultural history of recent centuries has shown declining violence.

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.

Sex, War, and Malthusian Doom

In 1971, East Pakistan became Bangladesh after winning a 9-month war of independence from West Pakistan. Shortly after the end of the war, Malcolm Potts led an international team of doctors into Bangladesh to help the women who had been raped and made pregnant. They offered abortions to the women. In a conservative Muslim society, women who have been raped are shunned as unclean by their families and society generally. To have an abortion only adds to their humiliation. Over 100,000women were raped during the conflict, which made it perhaps the largest systematic rape of women in the history of the world.

The horror of this experience--and of similar experiences with warfare--led Potts to want to explain the cruelty of organized aggression in human history. The final product of his thinking is his book (co-authored with Thomas Hayden) entitled Sex and War: How Biology Explains Warfare and Terrorism and Offers a Path to a Safer World (BenBella Books, 2008).

Reading this book in my course on "Biopolitics and Human Nature" has stirred a lively discussion among the students.

THREE THESES

Potts offers an evolutionary explanation for the causes of war and terrorism and for how such violence can be reduced. His argument turns on three claims.

His first claim is that young men have an evolved predisposition to "team aggression," which he identifies as the intentional coordination of young males in launching lethal attacks against members of their own species. He believes that there are only two species of social mammals showing this behavior--human beings and chimpanzees--and he explains this as showing an evolutionary history in which humans and chimps shared a common ancestral species in which young males practiced team aggression.

The primary insight for this claim came a few years after the war in Bangladesh, when Jane Goodall observed the chimps in the Gombe Stream National Park in Tanzania waging a war between two chimp communities, in which young males organized themselves into raiding parties to attack individuals in the opposing community. Through a series of ferocious attacks, the Kasakela troop eventually conquered the territory of the rival Kahama troop.

Potts offers various kinds of arguments and evidence to support his claim that such team aggression among young males has shaped human evolution. There is fossil evidence that many hominid ancestors died from warfare. There is archaeological evidence that warfare is pervasive in human history. And there is anthropological evidence that foraging bands (like the Yanomamo, for example) have engaged in such team aggression. Moreover, there is also evidence for the "warfare hypothesis" in explaining human evolution as shaped by group-against-group violence that drove the evolution of human intelligence, religion, and state-formation.

Potts' second claim is that women do not have this evolved predisposition to team aggression. Of course, women are capable of aggressive violence. But they do not generally organize themselves into raiding parties for lethal violence against their enemies.

This leads to his third claim, which is that the best way to promote peace is to empower women so that their peacemaking tendencies can counter the warmaking tendencies of men. To achieve that, women need to have equal access to political power, and they need to have control over their lives.

Most importantly, women need to have freedom in controlling their reproduction through family planning, which requires access to contraception and abortion. If women are free to choose how many children they will have, Potts believes, they will generally choose to have small families. This will increase their social and political influence, because this will lessen the burdens of child care. This will also slow population growth, which will have the advantage of reducing the number of young males in proportion to older males, which reduces the likelihood of young male violence.

Potts is a life-long proponent of family planning. In 1968, he became the first doctor employed on the staff of the International Planned Parenthood Federation. This has led him to travel around the world promoting family planning.

He argues that family planning is the key to reducing population growth, which is the key to reducing war and terrorism. In over-populated societies, there are too many young males who lack economic resources and who cannot find sexual mates, which creates conditions favoring young male team aggression. Potts thinks this is evident in the societies that foster terrorism. Terrorists tend to be young, unmarried males with few opportunities for success in life, who become vengeful towards dominant outgroups, and who band together to attack their enemies.

I have identified courage in war as one of the 20 natural desires that shape human nature in all societies throughout history. That's the one desire on my list that has provoked the most criticism from people who don't like the idea that war is natural for human beings and a stage for the moral virtue of courage. While I have never written enough to support my evolutionary view of war, Potts' book provides a good survey of the reasoning and evidence for war as a natural desire--particularly, among young men--that manifests both the best and the worst in human beings.

But despite my general agreement with Potts, I do see at least eleven problems with Potts' position.

ELEVEN PROBLEMS

(1) THE NATURAL MALE INHIBITION AGAINST KILLING.
Most men will never kill anyone. In most men, there probably is a natural inhibition against killing. Even soldiers in war are often reluctant to kill the enemy, which is why special training is required to break down this inhibition. This point is elaborated in Dave Grossman's book--On Killing--which surveys the psychology of killing in war.

But if there is such a natural inhibition against killing, then how can Potts argue that young men are predisposed by their evolved nature to team aggression? Potts' answer is that evolution has given us an "empathy switch," so that "we seem to have an innate mental ability to treat our fellow humans with either great compassion or cold disregard, depending on whether we've assigned them to ingroup, or out" (70). The difference between men and women is that for young men, on average, it's easier to turn off the empathy switch when they think they're confronting an outgroup.

(2) VIOLENT WOMEN.
Potts notes the many historical examples of female violence in war. There are female suicide bombers and "warrior Amazons." Women have fought in military units. And in the American military, women are taking ever larger roles that take them into combat. Although this might seem to deny Potts' claim about sex differences in team aggression, he can answer by arguing that women engaging in team aggression are exceptional cases. We might see the behavioral profiles of men and women as two overlapping bell-shaped curves, so that despite the overlapping, we can still see the difference in their central tendencies.

(3) THE BONOBO PROBLEM.
Of the four extant great ape species--gorillas, orangutans, chimpanzees, and bonobos, chimps are the only species that shows male coalitional violence like that of human beings. The contrast is especially evident with bonobos, who have never been observed engaging in lethal violence, and who seem to show a "make-love-not-war" policy enforced by the females banding together to dominate over the males. That's why some feminists and pacifists suggest that if bonobos are closely related to humans, this should deny the claim that human violence is an evolved trait.

It's not clear to me that Potts has an adequate answer to this. He asserts that "team aggression died out in bonobos, while persisting in Pan troglodytes and Homo sapiens" (129). But this remains mere speculation. The problem here is that there is too little known about bonobos to reach clear conclusions on this issue.

(4) CULTURAL CIRCUMSTANCES.
The most common criticism of Potts is likely to be that his biological explanation of war and terrorism does not recognize the importance of cultural circumstances in shaping violent behavior. But, actually, Potts emphasizes that while the behavioral predisposition to team aggression is an evolved trait of men, the expression of that predisposition is determined by economic and social circumstances. So, for example, when there is a high proportion of young males in a society who lack resources and lack access to sexual partners and feel resentment towards a dominant outgroup, this is a social breeding ground for terrorism or street gangs. Consequently, we can control the predispositions to some degree by controlling the circumstances.

(5) THE NOVELTY OF MODERN WAR.
Modern military organizations don't look much like the raiding parties of chimps or human foragers. It was not until the emergence of the state as based on an agricultural economy about 5,000 years ago that mass armies were made possible, and this is too recent in human history to be a biological adaptation.

Potts' answer to this objection is that even modern armies are based on small units--squads (9-15 men) and platoons (45-70 men)--because the the psychology of team aggression still requires that young men see themselves as a "band of brothers" with a sense of camaraderie that can only arise in small units comparable in size to a chimp raiding party. This is true even though modern bureaucracy allows these small units to be organize hierarchically into massively large military organizations.

(6) SANGER AND EUGENICS.
As a proponent of family planning, Potts sees himself in the tradition of Margaret Sanger, who was the founder of the modern family planning movement. But in his praise of Sanger, he is silent about her dark side: she was a proponent of eugenics and sterilization for the "unfit." Although this might seem like a minor point, it's important as an indication of Potts' failure to be candid about the historical connections between family planning and eugenics.

(7) THE BREEDING OF FUNDAMENTALISTS.
Potts is disdainful of religious belief, and particularly, fundamentalist religious belief, because he see religious fundamentalism as opposed to modern science, which is, for him, the voice of reason in the world. But there's a problem here that he doesn't acknowledge. He likes to think that modern scientific rationalism will prevail in its battle with religious fundamentalism. And yet, he notes that religious believers tend to have much higher birth rates than secular people. If that's the case, doesn't that mean that eventually fundamentalist religious believers will prevail, just by virtue of their greater growth in population? Potts never confronts this problem for his argument.

(8) THE JULIAN SIMON PROBLEM.
Potts' argument for family planning to reduce population is based on the reasoning of Thomas Malthus that population growth must lead to a social collapse from the exhaustion of scarce resources. Malthusian doom pervades Potts' book, because he sees all of life as governed by competition over scarce resources. In taking this position, Potts never confronts the serious criticisms of the Malthusian view of the world. In particular, Potts never explicitly responds to the arguments of those like Julian Simon who insist that, on the whole, population growth is more a boon to humanity than a burden, because human beings add to resources through their productivity and their ingenuity. In his book The Ultimate Resource, Simon showed how the data of history refute the gloomy predictions of the Malthusians.

As far as I can see, there is only one paragraph on this point in Potts' book. He writes:

Free-market economists make up yet another important force from the right, arguing that population growth is good because growing markets create prosperity. They tend to believe that as young people reach working age they will contribute to the economy, even though the empirical evidence, as we have seen, is that in countries with rapid population growth young people merely join the lines of the unemployed. Many economists also claim that natural resource scarcities can be compensated for by technologies and price adjustments, and they too have been influential in reducing U.S. political interest in international family planning assistance. (327)

This is all he has to say. He is silent about the extensive evidence provided by Simon (and by others like Bjorn Lomborg and Matt Ridley) supporting the claim that when markets are free, population growth is generally beneficial.

Potts should at least say something about Simon's famous bet with Paul Ehrlich. In 1980, Simon bet Ehrlich $10,000 that the prices of a list of scarce metals would be lower by 1990, while Ehrlich predicted that the growing scarcity of these metals would produce much higher prices. Simon won the bet.

(9) STONE AGE EMOTIONS.
Potts shows how "Stone Age emotions" govern politics. For example, he argues, the "war on terror" as a response to the 9/11 terrorist attacks was an irrational expression of those "Stone Age emotions." The wars in Afghanistan and Iraq were not in the national security interests of the United States. But they were justified by President Bush who appealed to the natural emotional predisposition to team aggression in response to threats from a dangerous outgroup. Instead of yielding to such emotions, Potts claims, we should act by a "cool, objective analysis of risk" like a "dispassionate super computer" (174).

But how is this possible, if "an unemotional response is impossible" (113)? Although Potts often recommends that pure, dispassionate reason should suppress our "Stone Age emotions," he also says that we need to extend our evolved emotions of empathy from the ingroup to the outgroup (166-67, 238, 258). Moreover, in a few passages, he agrees that "the building blocks of human morality are emotional as well as cognitive" (361). Isn't it more realistic to appeal to the moral emotions of empathy, while extending them to ever wider groups, than to try to totally suppress the emotions under some dispassionate Kantian Reason? Isn't this extension of empathy (or "sympathy" as Hume, Smith, and Darwin called it) the psychological basis for "human rights" and humanitarian concern? This would seem to be more compatible with Darwin's view of the moral sense based on sympathy and with the moral psychology of the emotions developed by Darwinian psychologists today.

(10) THE JUSTICE OF MALE HONOR.
Potts gives some attention to the historical movements for abolishing slavery, for standards of just war, and for humanitarian conceptions of human rights, which have put some limits on the cruelty of war. But he does not comment on the fact that these movements have been led by men as well as women. Doesn't this show that the extension of empathy beyond narrow ingroups can be rooted in male moral psychology? Can't we see the traditional standards of just war as expressions of the manly love of honor and the desire to elevate warrior honor above brutish cruelty? If so, then this shows how the taming of manly aggression might come not just from womanly compassion but also from manly chivalry.

(11) THE MANLY HUMANITARIANISM OF SCIENCE.
Potts appeals to modern science as promoting a cosmopolitan community of rational understanding that can check the parochial predispositions of male team aggression. He writes: "Science, with its intrinsic honesty and its rejection of the supernatural as an answer to real world events, has proved the only medium in history capable of linking women and men of all cultures and all races in a common understanding of the real world" (360). But Potts doesn't ponder the fact that, for most of its history, modern science has been dominated by men. Doesn't this show another way in which the natural dispositions of some men--in this case, the Socratic desire for intellectual understanding--can be turned against male violence?

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