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.
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