A Chimpanzee Civil War: The Inner Demons and Better Angels of Primate Nature

               Ngogo Chimpanzees from the Western Group Attacking the Central Group

As I have indicated in previous posts, evolutionary anthropologists studying the evolution of war and peace have been divided into Hobbesians who believe that our hunter-gatherer ancestors were naturally violent and warlike and Rousseauans who believe that hunter-gatherers were naturally peaceful.  But in setting up this debate as Hobbes versus Rousseau, they have overlooked the position of Locke.  This is a serious mistake, because the weight of the evidence and argumentation on this issue today is on the side of Locke's account of the state of nature as a state of peace that tended to become a state of war.  It seems now that while Hobbes was partly right and partly wrong about the state of nature, Rousseau was mostly wrong, and Locke was mostly right.

THE GOMBE CHIMPANZEES

I have also indicated, how this debate extends to chimpanzees.  The Hobbesians see chimpanzees as showing an evolved propensity to war, and the clearest evidence for this is the chimpanzee civil war that Jane Goodall observed in Gombe in the 1970s.  At the beginning of 1973, she and her colleagues noticed that the chimps had formed two separate communities--the northern or Kasakela community, based on the valleys of the Kakombe and Kasakela rivers, and the southern or Kahama community, based on the valley of the Kahama river.  By early 1974, they saw the first of a series of attacks by the Kasakela community on the Kahama community, which led over four years to the complete annihilation of the Kahama community, which allowed the Kasakela chimps to expand their territory over the area once claimed by the Kahama chimps.  Since human beings are closely related to chimps phylogenetically--chimps and humans evolved from a shared common ancestor some 5-6 million years ago--chimpanzee war could show the evolutionary roots of the human propensity to war.

But the Rousseauans insist that in normal circumstances, chimpanzees are naturally peaceful, and they explain the Four-Year War in Gombe as provoked by the abnormal circumstances created by human impacts on the chimps--particularly, their being fed bananas at Goodall's camp.  During her first two years at Gombe, Goodall was frustrated by her failure to closely observe the chimps because if she attempted to follow them, they ran away from her.  She spent a lot of her time sitting on a hill trying to see the chimps through binoculars.  But then in the summer of 1962, she discovered that if she set out bananas every day, the chimps would crowd into her camp.  Soon they were eating 30, 40, or even 60 bananas per day.

Fighting over the bananas caused increased aggression among the chimps.  They even threw rocks at humans who got too close.  Goodall was shocked by the violence that came from competition for bananas.  Eventually, she tried to lower the violence by restricting the supply of bananas.  This did reduce the violence.  But it also drastically reduced the nutritional benefits that the chimps had gained from the bananas.  Some of Goodall's Rousseauan critics--particularly, R. Brian Ferguson (2023)--have argued that the restriction of the banana feeding created the frustration that prompted the violence of the Four Year War.  When Kasakela males sought food in the southern areas of their range, Kahama males chased them away.  But when Kahama chimps came into Goodall's camp, they were always fed bananas.  So it's not surprising that the Kasakela chimps developed a deep animosity toward the Kahama chimps, although they had once belonged to the same community.

THE NGOGO CHIMPANZEES

Now we have a new report--in the journal Science--of a long-running chimpanzee civil war that has divided the Ngogo chimpanzees in the Kibale National Park in Uganda (Sandel et al. 2026).  The scientists who have studied this group since 1995 have never fed them bananas or any other food.  So artificial provisioning cannot be a factor in explaining their violence.

The Ngogo group is the largest group of chimpanzees ever studied by scientists.  The size has increased from 118 individuals in 1998 to 201 in 2016.  The number of mature males (over 12 years old) has fluctuated around 40 individuals.

The Ngogo chimpanzees range over a large territory, which they have expanded through war with their neighbors.  From 1999 to 2008, they ranged over a territory of about 29 square kilometers (18 square miles).  During this time, they engaged in intensive border patrols, particularly along their northeastern border.  In 2009, they engaged in numerous lethal attacks on their neighbors to the northeast, which allowed them to expand their territory, adding about 6 square kilometers (3.7 square miles) to their territory.  This seemed to confirm the "resource acquisition hypothesis" for explaining chimpanzee warfare as adaptive for territorial expansion (Mitani, Watts, and Amsler 2010).

Prior to 2015, the Ngogo chimpanzees belonged to a single group, although there was a social substructure of two to four "clusters" that could be identified each year.  They were generally divided into a Western cluster and a Central cluster, but this cluster membership was fluid, because individuals could move freely between these clusters.  But then on June 24, 2015, when members of the Western and Central clusters approached each other near the center of their territory, the Western chimpanzees ran away, and the Central chimpanzees chased them.  For at least six weeks, the two groups avoided one another, which had never previously been observed.

In 2016, the Western males started territorial patrols directed toward the Central chimpanzees.  In 2017, what was once the center of a shared territory became a border.  In 2018, the Western group initiated lethal attacks on the Central group.  These aggressive attacks by the Western group have continued up to the present.  Remarkably, the Western group is smaller than the Central group.  In 2018, the Western group had a population of 83 (including 10 adult males and 22 adult females), while the Central group had a population of 107 (including 30 adult males and 39 adult females).  The death toll from the war drove the population of the Central group down to 80 in 2024.

This Ngogo civil war differs from the Gombe civil war in one striking way.  At Gombe, the larger group (the Kasakela chimps) attacked and defeated the smaller group (the Kahama chimps).  This led some primatologists like Richard Wrangham to develop the "imbalance-of-power hypothesis"--that larger groups (particularly, in the number of adult males) will attack smaller groups.  The Ngogo civil war is evidence against that hypothesis.

Actually, the scientists who have studied the Ngogo civil war have not been able to agree on any alternative hypothesis for explaining the war.  Some of them have wondered, however, whether shifting social bonds could explain the rupture that led to the war.  In 2014, five adult males died, perhaps because of disease.  Dr. Aaron Sandel, one of the leaders of the Ngogo Chimpanzee Project, has suggested that these five individuals might have been social bridges that held the Ngogo groups together into one community.  So that the contingency of their deaths in one year created the conditions for the polarization of the community that then led to the war.

Similarly, if Abraham Lincoln had died before or shortly after the beginning of the American Civil War, the history of that war would probably have been radically altered.  Or if Thomas Crooks had assassinated Donald Trump on July 13, 2024, American politics might be very different from what it is today.  America might be less polarized.  And perhaps there would have been no war with Iran.  Such unpredictable contingencies often determine the history of war and politics.

INNER DEMONS, BETTER ANGELS, AND LOCKEAN LIBERAL NICHE CONSTRUCTION

So what, if anything, does the history of chimpanzee wars teach us about the evolutionary history of human war and peace?  How we answer that question may depend a lot on whether we think humans are more closely related to chimpanzees or to bonobos.

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 (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, who have 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."

Frances White, one of the leading scientists studying bonobos in the wild, has 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 has 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 has 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 has 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.

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 (Odling-Smee, Laland, and Feldman 2003).  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.

I have 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 and enables 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.

REFERENCES

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

Ferguson, R. Brian. 2023. Chimpanzees, War, and History: Are Men Born to Kill? Oxford, Oxford University Press.

Goodall, Jane. 1986. The Chimpanzees of Gombe. Cambridge: Harvard University Press.

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.

Mitani, John C., David P. Watts, and Sylvia J. Amsler. 2010. "Lethal Intergroup Aggression Leads to Territorial Expansion in Wild Chimpanzees." Current Biology 20:R507-R508.

Odling-Smee, F., Kevin Laland, and Marcus Feldman. 2003. Niche Construction: The Neglected Process in Evolution. Princeton University Press.

Pinker, Steven. 2011. The Better Angels of Our Nature: Why Violence Has Declined. New York: Penguin Books.

Sandel, Aaron A. et al. 2026. "Lethal Conflict After Group Fission in Wild Chimpanzees." Science 392(9 April):216-220.

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.

A Rebuttal of Jonathan Leaf's Rebuttal: Combining Phylogenetic and Convergent Evolution Explains Human Nature

Jonathan Leaf loves straw man arguments.  In my review of his book The Primate Myth for Law & Liberty, I criticized him for making a straw man argument.  Now he has written a reply to my criticism by . . . making a straw man argument.

In my review, I pointed out that evolutionary biologists and anthropologists generally agree that to explain the evolution of human nature--or of any animal nature--they need to consider both phylogenetic evolution and convergent evolution.  Phylogenetic evolution explains why human beings are similar to other primates with whom they share common genetic descent.  Convergent evolution explains why human beings are different from other primates and similar to non-primate animals that have evolved adaptations for environments of evolutionary adaptation similar to the human environments of evolutionary adaptation.

Convergent evolution explains why a dolphin looks like a fish: it has evolved to have the fish-like anatomy that allows it to swim smoothly through its aquatic habitat. But phylogenetic evolution explains why a dolphin is not a fish but a mammal: it has all the mammalian traits that it inherited from its mammalian ancestors that were originally adapted for a terrestrial habitat.

Similarly, we need to consider both phylogeny and convergence in explaining the evolution of the human mind.  Leaf correctly argues that the convergent evolution of the earliest human ancestors, as adapted for collaborative hunting, set them apart from other primates, who show very little collaborative hunting.  But we also need to understand the phylogenetic evolution of the human brain.

Leaf criticizes what he calls the Primate Myth--the idea that humans are most like primates and unlike all non-primate animals--because this denies the convergent evolution that makes humans more like herd and pack animals than primates.  But this Primate Myth is a straw man because most evolutionary scientists recognize both the phylogenetic similarities of humans to other primates and the convergent similarities of humans to herd and pack animals.

So, for example, Frans de Waal could see how similar humans are to chimps and bonobos because they share a common phylogenetic ancestry.  But he also could see how similar humans are to some non-primates because of convergent evolution.  For instance, de Waal recognized that while chimps and bonobos were sexually promiscuous, with no enduring pair-bonding of sexual mates, convergent evolution had made humans more like the pair-bonding animals.  He observed: "The intimate male-female relationship, which zoologists have dubbed a 'pair bond,' is bred into our bones.  I believe this is what sets us apart from the apes more than anything else."

Therefore, in attacking the Primate Myth that phylogenetic evolution counts for everything, and convergent evolution counts for nothing, in explaining human nature, Leaf is attacking a straw man.

In his rebuttal, Leaf criticizes me for "asserting that leading primatologists have not said that their study of apes is a means by which we might infer aspects of human nature."  "Actually," he says, "they have been saying this for decades."  Then he quotes from the first page of Chimpanzee Politics de Waal's remark that "apes hold up a mirror to us."

So here we go again with another straw man.  I have not asserted that leading primatologists have never said that the study of apes can illuminate some "aspects of human nature."  What I have asserted is that leading primatologists like de Waal have said that we need to study both phylogenetic evolution and convergent evolution to see how humans can be similar to apes in some ways but similar to non-primate animals in other ways.  

It's the same for explaining the evolved nature of other animals.  Emergent evolution explains why dolphins look similar to fish.  Phylogenetic evolution explains why they are actually mammals and not fish.

Would Leaf have to say that since dolphins are so similar to fish that must mean that they really are fish and not mammals?  Should his next book be all about dolphins with the title The Mammal Myth?

Or are we constructing a straw man here?

Monogamy, Polyamory, and the Primate Myth

That we can understand human nature by comparing ourselves with our closest living primate relatives--chimps and bonobos--has been a recurring theme in my blog posts over the years.  So it might seem that Jonathan Leaf's new book--The Primate Myth--is a powerful critique of my position, because Leaf argues that we cannot learn who we are by studying chimps and bonobos, assuming that the underlying patterns of their behavior are the same as ours, which is what Leaf calls the Primate Myth.  Even if we share some common genetic ancestry with primates--particularly, the great apes--we are radically different from apes, Leaf insists, in our genetic profile, in the configuration of our brains, in our anatomy, and in our social behavior.  To explain those differences, we need to see how our evolutionary adaptations for hunting and language made our earliest human ancestors less like apes and more like dolphins, dogs, rats, and elephants.  

Leaf stresses that human beings are unique in their extreme sociality--their social awareness and their capacity for social collaboration.  While primates are social animals, they are not as highly social as the animals that live in packs or herds.  Humans are more a herd or pack animal than a primate, because our earliest evolutionary ancestors depended on collaborative hunting in packs and herding together to repel predators.

Because of the Primate Myth, humans have been classified as belonging to the Order of Primates and the Family of Hominidae (humans and the other great apes--chimpanzees, bonobos, gorillas, and orangutans).  But if we recognized how radically different human beings are from primates, Leaf argues, we would classify humans as belonging to their own order (Homo), or at least in their own family, separated from the great apes (245).

Leaf is certainly right in saying that to understand human evolution, it is not sufficient to look for human similarities to those other primates with whom we share common descent, because we must also see how humans differ radically from those primates.  By convergent evolution our human ancestors evolved adaptations for filling an evolutionary niche--collaborative hunting--that made them more like the herd or pack animals than like the other primates with whom they shared genetic ancestry.

But Leaf is wrong in saying that most evolutionary scientists today deny this because they are so committed to the Primate Myth that humans are most like primates--particularly, chimps and bonobos--in their behavioral and psychological propensities and unlike all non-primate animals.  The Primate Myth is a straw man, because in attacking the Primate Myth, Leaf distorts what most evolutionary scientists say about human evolution to make it easier to refute.

In a few places in his book, Leaf comes close to admitting this.  One example is a passage about Frans de Waal, who is the primary villain in Leaf's book (38-40). Leaf says that many readers of de Waal's first book--Chimpanzee Politics--mistakenly assumed that he was saying "that humans were almost exactly the same as chimps." In fact, Leaf observes, de Waal in that book points to "a number of critical differences" between humans and chimps. And in his later writings, de Waal "emphasized the kinship that humans bear to an array of non-primate animals." "In other words, what de Waal was thought to be arguing in his first and most influential book and what he was actually proposing aren't the same."  But then Leaf devotes most of his book to attacking what he here recognizes to be a mistaken interpretation of de Waal--the belief that humans are almost the same as chimps and other primates.

I can imagine, however, that Leaf could respond by saying no, this is not a straw man, because I point to good examples of people assuming the Primate Myth in explaining human evolution.  The best example might be the argument of Christopher Ryan and Cacilda Jetha in their popular bestseller Sex at Dawn: How We Mate, Why We Stray, and What It Means for Modern Relationships (2010).  Under the influence of the Primate Myth--"the idea that human behavior is very much like ape behavior"--they say that since chimps and bonobos are sexually promiscuous, with no enduring pair-bonding of sexual mates, that must mean that our earliest human ancestors were just as promiscuous, and therefore monogamous pair-bonding is contrary to our evolved human nature.  Human beings would be happier, Ryan and Jetha insist, if married couples were "polyamorous"--if they felt free to have extramarital sexual affairs without feeling shame or fearing that this must break up their marriage: couples can happily live together and rear their children together but sleep around without harming themselves or their children, because primate promiscuity is natural for human beings.  

Leaf devotes over eight pages of his book to explaining and refuting their argument (168-177).  He has also taken excerpts from this part of his book for an article on "The Polyamory Delusion" for National Review that will be the cover story for the February 2026 issue.  His preoccupation with Sex at Dawn makes me think that his reading of this book some fifteen years ago was what originally motivated him to write The Primate Myth to counter the harmful consequences of teaching people that imitating the behavior of chimps and bonobos would make them happy.

Leaf is correct in criticizing Ryan and Jetha for their refusing to see that ape sexuality is different from human sexuality, because in contrast to ape promiscuity, the evolutionary function of human sexuality is to strengthen monogamous pair-bonds and the biparental care of children.  He is mistaken, however, in his claim that evolutionary biologists agree with Ryan and Jetha in their primate model of human sexuality as naturally inclined to polyamorous promiscuity.  The Primate Myth embraced by Ryan and Jetha is a fringe position that is outside the mainstream thinking of most evolutionary scientists, and that's why I say the Primate Myth is a straw man.

Previously, I have written about how the evolution of monogamous pair-bonding among our prehistoric foraging ancestors gave birth to the unique structure of human society that sets it apart from the social life of chimps and bonobos as based on sexual promiscuity in mating and reproduction.  Even in cultures that allow polygamy, most people are in monogamous marriages.  And there is plenty of evidence that polygamous marriages tend to be full of conflict: the cowives fight amongst themselves, men fight with one another over access to women, and children often suffer from parental neglect.

It is true, of course, that even in societies where monogamy is the norm, there is sexual promiscuity that can create some uncertainty about paternity.  But remarkably, recent research shows that the rate of "extra pair paternity"--where a woman bears offspring from a man other than her spouse--is usually below 3 percent (Larmuseau et al. 2013, 2019; Zimmer 2016).  By contrast, extra-pair fertilization in socially monogamous bird species can range as high as 20 percent (Brouwer and Griffith 2019; Griffith et al. 2002).

Leaf cites this kind of evidence as showing that while promiscuity is a problem for human beings, it is not as pervasive as it is for primates because human beings have an evolved natural desire for monogamous pair-bonding.  Leaf rightly concludes that this refutes Ryan and Jetha's primate model of human sexuality as naturally inclined to polyamorous promiscuity rather than sexual monogamy.

But Leaf is wrong when he says that evolutionary biologists agree with Ryan and Jetha (Leaf 2025, 171, 173).  In fact, Ryan and Jetha repeatedly insist that they are attacking the "standard narrative of human sexual evolution" that upholds monogamous pair-bonding as crucial for human evolution (Ryan and Jetha 2010, 7-8, 11, 25, 34-35, 38-39, 46-60, 99, 137, 142, 149, 223, 266, 300).  Leaf is silent about this.

For example, Ryan and Jetha criticize Frans de Waal for embracing the "standard narrative."  They quote various remarks by de Waal as illustrating the "standard narrative" of human sexual monogamy that they reject.  De Waal argued that the nuclear family is "intrinsically human," and the pair-bond is "the key to the incredible level of cooperation that marks our species," because "our success as a species is intimately tied to the abandonment of the bonobo lifestyle and to a tighter control over sexual expressions." He observed: "The intimate male-female relationship . . . which zoologists have dubbed a 'pair bond,' is bred into our bones.  I believe this is what sets us apart from the apes more than anything else."   He also said: "Both chimps and bonobos are far more promiscuous than we are. Our testicles reflect this: they are mere peanuts compared to our ape relatives' coconuts" (de Waal 2005, 108, 113, 124-25; Ryan and Jetha 2010, 76, 115, 225).

Leaf does not allow his readers to see this.  Because if his readers saw that the Primate Myth as embraced by Ryan and Jetha is rejected by de Waal and most other evolutionary scientists, they would see that when Leaf attacks the Primate Myth, he is attacking a straw man.

REFERENCES

Brouwer, Lyanne, and Simon Griffith. 2019. "Extra-Pair Paternity in Birds." Molecular Ecology. 28: 4864-4882.

de Waal, Frans. 2005. Our Inner Ape: A Leading Primatologist Explains Why We Are Who We Are. New York: Riverhead Books.

Griffith, Simon, Ian Owens, and Katherine Thuman. 2002. "Extra Pair Paternity in Birds: A Review of Interspecific Variation and Adaptive Function. Molecular Ecology 11: 2195-2212.

Larmuseau, M. H. D., et al. 2013. "Low Historical Rates of Cuckoldry in a Western European Human Population Traced by Y-chromosome and Genealogical Data." Proceedings of the Royal Society B. 280:20132400.

Leaf, Jonathan. 2025. The Primate Myth: Why the Latest Science Leads Us to a New Theory of Human Nature. New York: Bombardier Books.

Ryan, Christopher, and Cacilda Jetha. 2010. Sex at Dawn: How We Mate, Why We Stray, and What It Means for Modern Relationships. New York: Harper.

Zimmer, Carl. 2013. "Monogamy and Human Evolution." New York Times, August 2.

Zimmer, Carl. 2016. "Fathered by the Mailman? It's Mostly an Urban Legend." New York Times, April 8.

If Humans and Chimps Are 15 Percent Genetically Different, What Difference Does That Make?

Think about how often you've heard it said that the genetic difference between human beings and chimpanzees is only slightly more than 1 percent, and therefore humans are 99 percent similar to chimps.  It is also said that this proves that chimps--and also bonobos--are our closest living evolutionary relatives.  This seems to be confirmed by the fact that chimpanzees and bonobos are more genetically similar to humans than to gorillas.  This 1 percent difference between humans and chimps fits the evolutionary timeline of five to eight million years since humans and chimps diverged from their last common ancestor.

But now an article published last May in Nature (Yoo et al., 2025) reports that a complete sequencing of ape genomes shows that the genetic difference between humans and chimps is a lot greater than 1 percent--more like 15 percent!  And yet perhaps I shouldn't say this article "reports" this because if you read the main article, you won't see this claim of a 15 percent difference.  You have to go to the Nature website and print out the "Supplementary Data" for the article, and even then, you have to work through the technical jargon to find the 15 percent difference.  Casey Luskin has posted a helpful article at the Discovery Institute website that digs deep into the "Supplementary Data" to uncover this remarkable finding.  You would think that such a surprising discovery would be prominently announced in Nature and in press releases: "The Chimp-Human Genetic Difference Is Not 1% But 15%!"  I think Luskin is right to suggest that the editors at Nature must have worked hard to hide this finding because it refutes the popular claim about "only a 1% difference" separating humans and chimps.  

Luskin says this refutes one of the "icons of evolution," as Jonathan Wells called them--that is, widely believed assertions about evolution that the proponents of "intelligent design theory" and "young-Earth creationism" deny.  It's not surprising, therefore, that creationists like Ken Ham have cited Luskin's article as proving that the creationists are right to deny that there is any common evolutionary ancestry linking humans and apes.  Ham explains that Bible teaches us that God created the "ape kind" and the "humankind" separately and created humans as a unique kind made in the image of God.

And yet I don't see that this newly discovered "15% difference" provides any support for the intelligent design theorists or the creationists in their denial of evolutionary science.

But first we need to understand how this new research allows us to calculate genetic difference and similarity.  The title of the article in Nature is "Complete Sequency of Ape Genomes."  The emphasis is on "complete," because the first human and ape genome sequences were incomplete.  They excluded extremely repetitive sequences and large-scale structural differences such as inversions and duplications of genomic sequences.  So the first reports of only 1% differences between human and chimp genomes were based on incomplete drafts of the genomes.  But now the complete sequency in this article allows for a fuller comparison of similarities and differences in the sequences.

The authors found two kinds of differences--"gap divergence" and "single nucleotide variation" (SNV).

Luskin prepared this figure to illustrate the difference between "SNVs" and "Gaps" between two genomes.  Gaps represent nucleotides or segments of nucleotides that don't exist in one of the genomes.  SNVs represent places where the nucleotides are different for the two genomes.  In this illustration, we have 30 nucleotides of the target genome with 3 SNVs and 9 gaps relative to the query genome.  So SNV divergence is 10%, and gap divergence is 30%, which means a total divergence of 40%.

If you go to the Supplemental Data for the Yoo et al. article, you will see that Figure III.12 shows the SNVs in comparing the genomes for humans, chimpanzees, bonobos, and orangutans--the four "great ape" species who belong to the Hominidae family.  When the human genome is the "target" genome, the "gap divergence" for the gorilla genome is 27.3 percent, for the Sumatran orangutan it's 16.5 percent, for the bonobo it's 14.4 percent, and for the chimpanzee it's 13.3 percent. 

Figure III.11 shows the SNV divergences, which are 2 percent for the gorilla, 3.6 percent for the Sumatran orangutan, 1.6 percent for the bonobo, and 1.6 percent for the chimpanzee.

If we add the gap divergences to the SNV differences, we get these total degrees of difference between human and ape genomes: 29.3 percent for the gorilla, 20.1 percent for the Sumatran orangutan, 16 percent for the bonobo, and 14.9 percent for the chimpanzee.  That's how we get the estimate of almost 15 percent difference between the chimp and human genomes, which is a lot higher than the purported 1 percent difference.  

It should be noted that these comparisons are for the 44 non-sex chromosomes in the human genome--that is, excluding the X and Y chromosomes.  As compared with chimps, the human X chromosome has a 4.4 percent gap divergence and 1.1 percent SNV divergence, while the human Y chromosome has an amazing 56.6 percent gap divergence and 3.9 percent SNV divergence.

Although this new research shows that the genetic differences between humans and apes are greater than had been previously reported, this does not deny the evolutionary story of the common evolutionary ancestry of humans and apes.  The genetic similarity between humans and apes is still very great--85 percent!  And humans are more genetically similar to chimps and bonobos than they are to orangutans and gorillas, which supports the claim that chimps and bonobos really are our closest living evolutionary relatives.

ALL IN THE GENES?  OR FOUR DIMENSIONS OF EVOLUTION?

There is an obvious problem here, however.  All of us have seen chimpanzees in zoos.  And many of us have seen bonobos if we have gone to zoos in San Diego, Milwaukee, or Cincinnati that have bonobos.  Those zoos often have displays that say something about the 1 percent difference between humans and chimpanzees.  Now those displays might have to be changed to read 15 percent.  But even so, when we look at those apes and compare them with humans, it's very hard to believe that the difference is only 1 to 15 percent.  It's simply not true that humans and apes are 85 percent the same.  The gap between the mental achievements of human beings and those of the apes is staggering.

Most human beings don't believe that evolutionary genetics can fully explain that gap, and that's why so many people reject the science of evolution, and why so many believe that the superiority of the human mind over the ape mind can only be explained by the supernatural work of an Intelligent Designer or Divine Creator.

They are right to believe that evolutionary genetics cannot fully explain the achievements of the human mind.  But that's because genetics is only a small part of evolutionary science.  As I have indicated in some previous posts, there are four levels of evolutionary inheritance--genetics, epigenetics, culture, and symbolism (Jablonka and Lamb, 2005).

The genetic inheritance system is the foundation for the Neo-Darwinian theory of evolution. But genetic reductionism and determinism fail to see how gene action depends on the complexity of interacting causes within the genome, within cells, within organisms, within groups of organisms, and within ecological circumstances. Except for a few single-gene genetic disorders, "genetic astrology"--the idea that genes directly control specific traits--must be dismissed as foolish.

The epigenetic inheritance system is evident in the differences between specialized cells. Brain cells, liver cells, and skin cells are very different, although the nucleus of each cell has the same genome. Their differences are epigenetic, rather than genetic, because they have arisen through their developmental history in which there were different patterns of gene activation and interaction within the cell. This developmental information is passed on as these cells divide to produce more cells of the same kind. It is possible for evolution to occur through heritable epigenetic variation even without genetic variation. Just as a musical recording transmits interpretations in musical performances of a musical score, so does an epigenetic inheritance system transmit interpretations of the information in DNA, so that there is a Lamarkian inheritance of phenotypes instead of genotypes. One version of such inheritance that is now under active study is DNA methylation: strands of DNA are chemically modified during development, and these modifications can be transmitted through reproduction.  The chemical modification in epimutation is not in the DNA itself but in the chromatin marking. Methylated DNA has a small methyl group attached to some of its bases. The pattern of methylation influences which regions of DNA are expressed. The different kinds of cells in the human body have the same DNA, but the different patterns of methylation regulate the expression of DNA.

The behavioral inheritance system is the transmission of information among animals through social learning. For example, among some animals (including human beings) mothers transmit food preferences to their offspring, because information about what mother is eating is transmitted either in the womb or through suckling, so that the offspring inherits a preference for that food. More complex forms of social learning come through animal culture. For example, some chimpanzees can discover how to open nuts with a stone and then pass on this practice within their group so that it becomes a social tradition. Different communities of chimps in Africa have different cultures based on distinctive profiles of traditional practices transmitted by social learning. As opposed to genetic evolution, cultural evolution is not blind but targeted to functional change.

The symbolic inheritance system is uniquely human because it shows the qualitative leap that defines our humanity as based on our capacity for symbolic thought and communication. Other animals can communicate through signs. But only human beings can communicate through symbols. The evolution of human language was probably crucial for the evolution of symbolism. Symbolic systems allow us to think about abstractions that have little to do with concrete, immediate experiences. Symbolic systems allow human beings to construct a shared imagined reality. These symbolic constructions are often fictional and future-oriented. Art, religion, science, and philosophy are all manifestations of human symbolic evolution. 

To explain why humans are somewhat similar to the great apes and yet radically different from them, we have understand how all four levels of human evolution have shaped human beings to be the unique animals that they are.

COMMON DESCENT OR INTELLIGENT DESIGN?  OR BOTH?

Although Casey Luskin is an advocate of intelligent design theory as the best alternative to evolutionary science, he stresses that he is not pointing to the new estimate of 15 percent difference between humans and chimps as evidence that refutes evolution.  As long as the five to eight million years since humans and chimps diverged from their last common ancestor is enough time for this 15 percent difference to evolve, then the evolutionary story of common ancestry is still defensible.  

But still, Luskin suggests, intelligent design theory has a better explanation for this genetic similarity--85 percent--between chimps and humans:  "Functional genetic similarities between humans and chimps could be explained by common ancestry or by common design.  Common ancestry is not the only way to explain genetic similarities.  Intelligent agents can re-use functional code in different designs.  Common design can explain shared functional genetic similarities just as well as common descent can."

There are two mistakes in Luskin's reasoning, however.  First, he mistakenly assumes a dichotomy between common descent and common design, as if they were mutually exclusive.  As I have noted previously, one of the leading advocates of intelligent design theory--Michael Behe--argues (in The Edge of Evolution) that the genetic similarity between humans and chimps is evidence that human beings evolved from primate ancestors shared with chimpanzees.  He explains that intelligent design is required to explain the emergence of the higher taxonomic levels of life (kingdoms, phyla, classes) but not the lower levels (orders, families, genera, species).  This means that the evolution of species could be fully Darwinian.

Behe is an intelligent-design evolutionist, because he insists: "The possibility of intelligent design is quite compatible with common descent, which some religious people disdain.  What's more, although some religious thinkers envision active, continuing intervention in nature, intelligent design is quite compatible with the view that the universe operates by unbroken natural law, with the design of life perhaps packed into its initial set-up" (166).  Luskin refuses to recognize Behe's position.

Luskin is also mistaken, however, in assuming the plausibility of the arguments for intelligent design.  He thus ignores my objection that the arguments for intelligent design are fallacious in two respects.  First, intelligent design reasoning depends completely on the fallacy of negative argumentation from ignorance, in which intelligent design proponents argue that if evolutionary scientists cannot fully explain the step-by-step evolutionary process by which complex living forms arise, then this proves that these complex forms of life must be caused by the intelligent designer.  This is purely negative reasoning because the proponents of intelligent design can offer no positive explanation of their own as to exactly when, where, and how the intelligent designer caused these forms of life.  

The second fallacy is the subtle use of the fallacy of equivocation--in the equivocation between human intelligent design and supernatural intelligent design.  We have all had the experience of seeing how human intelligent agents create artificial products by intelligent design.  But it does not follow logically from this that we have all had the experience of seeing how supernatural intelligent agents create artificial products by intelligent design.

CREATED BY GOD IN HIS IMAGE?  OR EVOLVED IN THE IMAGE OF PRIMATES?  OR BOTH?

Ken Ham (2025) argues, on the contrary, that even if we have not seen with our own eyes God creating everything out of nothing, this has been revealed to us through the Bible; and part of that revelation is that God created all the "kinds" of plants and animals separately, and He created the "chimp kind" to be utterly different from the "humankind," which was created in His image.

But as I have said in my previous posts on Ham and his two museums in Kentucky--the Creation Museum and the Ark Encounter--he mistakenly assumes that he is conveying the clear meaning of the Bible and that the Bible's clear teaching is incompatible with Darwinian evolution.

The Bible says nothing about God creating apes and humans as separate "kinds."  The Book of Genesis never mentions apes.  Actually, in the whole Bible, the Hebrew word for "ape" appears only twice (I Kings 10:22, 2 Chronicles 9:21), and never in the context of creation.  And while Genesis speaks of God creating plants and animals "after their kind," it never identifies human beings as a "kind."  Consider Genesis 1:26--"And God said, Let us make man in our image, after our likeness."  The phrase "after our likeness" takes the place of "after their kind," suggesting that in being created in the likeness of God, man is not bound by a "kind."  So there is no Biblical basis for Ham to speak of "humankind."

Moreover, the Hebrew word min that is translated as kind in the King James Bible is ambiguous.  In the Latin translation of the Bible, min is translated as the Latin word species.  Consequently, for almost two thousand years, Biblical believers assumed that God's creating "kinds" meant that God created each "species" separately, and that each species was eternally fixed.  But then after Darwin published his Origin of Species in 1859, in which he argued against the "theory of special creation" that God had created each species separating, some Christians began to believe that the created "kinds" in the Bible referred not to "species" but to some higher level of taxonomy.  Then, in 1941, the Christian biologist Frank Marsh coined the word baramin (combining the Hebrew words for "created" and "kind") as the best term for "created kind."  He argued that a "created kind" was not at the taxonomic level of "species" but at or near the level of "family."  This allowed Biblical believers to accept Darwin's theory of the origin of "species" by natural selection while also believing that God had created the "families" of plants and animals to be fixed and separate.  So, for example, we could say that God originally created the "family" of the finches, but within the limits of that "family," the separate species of finches endemic to the Galapagos Islands evolved by natural selection to be adaptive to those islands.

Notice what this means for the taxonomic classification of human beings.  If the "kind" of human beings refers to their taxonomic "family," then in modern taxonomy, human beings belong to the "family" of Hominidae, which includes chimps, bonobos, gorillas, and orangutan.  Even the young-earth creationist Todd Wood (2010) accepts this Hominidae classification of humans with the great apes, although he identifies the "human holobaramin" as the genus Homo.

This idea of "created kinds" was crucial for Ham in solving an old problem with Noah's Ark.  If the Ark carried all the "kinds" of land-based plants and animals, how could the Ark be big enough to hold all of the land-based species--which could be numbered in the millions?

Ham's creationist researchers have solved this problem by calculating that among these land-dependent vertebrate species, there are fewer than 1,400 known living and extinct kinds (that is, families).  This allows them to estimate that Noah had to have fewer than 6,744 individual animals on the Ark.  Once these animals left the Ark, speciation by natural selection within kinds could create all the living and extinct species that we know today.  The Ham's Ark Encounter is designed to show how as many as 6,744 animals and 8 human beings (Noah and his extended family) could survive on the Ark for almost a year.  But notice that this is a speculative reading of the Bible that never defines "kind" in this way.  This is not the clear meaning of the Bible, as Ham claims.  Indeed, if you go to the Ark Encounter in Kentucky, you might notice one display that speaks of the need for "Arktistic license" in making up details in the story of the Ark that have no basis in the Bible.

Since the Bible is so obscure in its creation story, and since so much of that story sounds like a figurative folk tale that was not meant to be a literal account of natural history, many Christians (like C. S. Lewis, Francis Collins, and Deborah Haarsma) have decided that the Bible could be read as allowing for theistic evolution or evolutionary creation.  According to this conception, God created the universal laws of nature at the beginning of the Universe, but then He allowed all the forms of life to emerge by natural evolution.  God is the "primary cause" of everything.  But the evolutionary process unfolds through the "secondary causes" of nature.  Even Darwin himself accepted this metaphysical conception of "dual causality" that reconciles belief in God as First Cause with acceptance of evolutionary science.  At various points in the Creation Museum and the Ark Encounter, there are displays that acknowledge that many if not most Christians accept some version of this theistic evolution.

But what about the creation of human beings in the image of God?  If the "image of God" refers to the God-like intellect of man, then we might argue that the extraordinary mental capacities of human beings could have evolved through the evolution of the primate brain.  I have argued that the evolution in the size and complexity of the primate brain passed over a critical threshold so that now there are 86 billion neurons in the human brain, and of that total, 16 billion are in the cerebral cortex, which includes 1.3 billion neurons in the prefrontal cortex.  That emergent evolution of the brain created the uniquely powerful human mind.  We were created in the image of the primate brain.

Even if we are only 15 percent genetically different from chimps, we are different in kind from chimps because we have the mental capacities for language, morality, and symbolic abstraction that they do not have at all.  That's the difference that makes all the difference.

REFERENCES

Behe, Michael. 2007. The Edge of Evolution: The Search for the  Limits of Darwinism. New York: The Free Press.

Ham, Ken. 2025. "Study Finds Chimp DNA Is Not '99% Identical' to Ours." Answers in Genesis. Ken Ham Blog. May 27. Online.

Jablonka, Eva, and Marion J. Lamb. 2014. Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Revised edition. Cambridge: MIT Press.

Luskin, Casey. 2025. "Fact Check: New 'Complete' Chimp Genome Shows 14.9 Percent Difference from Human Genome." Science and Culture Today, May 21, online.

Wood, Todd Charles. 2010. "Baraminological Analysis Places Homo habilis, Homo rudolfensis, and Australopithecus sediba in the Human Holobaramin." Answers Research Journal 3: 71-90.

Yoo, Dong Ahn, et al. 2025. "Complete Sequencing of Ape Genomes." Nature 641: 401-418.

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.

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.