In what ways do men and women differ? Do we find the same differences in our fellow primates? Do apes learn sex roles or is gender uniquely human? World-renowned primatologist Frans de Waal offers key insights into gender, drawing on his extensive experience observing chimpanzees and bonobos. While some insights appear confirmed in his observations, de Waal unearths several startling discoveries about gender in his work. This surprising look at the nature of primates has a lot to say about what it means to be human.

In this excerpt from his book, Different: Gender Through the Eyes of a Primatologist, de Waal examines his relationship with a chimpanzee named Luit to uncover what truth of gender lay in the animal kingdom.

Frans de Waal delivered a keynote address on this subject at Bioneers 2022. Listen to a podcast episode featuring his talk here.

Below are the first few pages of my book on gender in humans and other primates. The book itself is of course much more detailed and treats topics ranging from dominance and power, the toys young primates like to play with, to sexual orientation and gender diversity. It offers basically a triangular comparison between humans, chimpanzees, and bonobos, each with their own balance and tension between the sexes. Enjoy!

The saddest day of my career began with a phone call telling me that my favorite male chimpanzee had been butchered by two rivals. Having hurried on my bike to Royal Burgers’ Zoo, in the Netherlands, I found  Luit sitting in a puddle of blood, leaning his head dejectedly against the bars of his night cage. Normally aloof, he heaved the deepest sigh when  I stroked his head. It was too late, though. He died the same day on the operating table. 

Rivalry among male chimps can grow so intense that they kill each other, and not only at the zoo. There are now a dozen reports of high ranking males slain in the wild during the same sort of power struggles. While jockeying for the top spot, males opportunistically make and break alliances, betray each other, and plot attacks. Yes, plot, because it was no accident that the assault on Luit took place in the night quarters where three adult males were kept apart from the rest of the colony. Things might have unfolded differently out on the large forested island of the world’s best-known chimpanzee colony. Female chimps don’t hesitate to interrupt clashes among male contenders. While Mama, the alpha female, couldn’t keep the males from politicking, she did draw the line at bloodshed. Had she been present on the scene, she’d no doubt have rallied her allies to step in. 

Luit’s untimely death affected me deeply. He had been such a friendly character, who as leader had brought peace and harmony. But on top of that, I was deeply disappointed. Until then, the battles I had witnessed had always ended in reconciliation. Rivals would kiss and embrace after each skirmish and were perfectly capable of handling their disagreements. Or so I thought. Adult male chimps act like friends most of the time, grooming each other, and roughhousing in fun. The disastrous fight taught me that things can also spiral out of control and that the same males are capable of intentionally killing each other. Fieldworkers have described assaults in the forest in similar tones. They seem deliberate enough to speak of “murder.” 

The high-intensity aggression of male chimps has a female equivalent. The circumstances that trigger female anger are quite different,  though. Even the biggest male knows that every mother will turn into a raging hurricane if he lifts a finger against her progeny. She will become so undaunted and fierce that nothing will stop her. The ferocity with which a mother ape defends her young exceeds that with which she defends herself. Maternal protectiveness is such a universal mammalian trait that we joke about it, such as when U.S. vice-presidential candidate  Sarah Palin called herself a Mama Grizzly. Mindful of this reputation, Gary Larson drew a cartoon in which a businessman carrying a briefcase enters an elevator with a large and a small bear standing in the back.  The caption reads: “Tragedy struck when Conroy, his mind preoccupied  with work, stepped into the elevator—directly between a female grizzly and her cub.” 

The greatest fear of fandis in the jungles of Thailand—hunters who in the old days captured wild elephants for timber labor—was not that they’d snare a tusker. A large bull in the ropes posed less acute danger than a small calf captured while its mother was within hearing range. Quite a few fandis have lost their lives to enraged elephant cows. In our species, a mother’s defense of her children is so predictable that, according to the Hebrew Bible, King Solomon counted on it. Faced with two women who both claimed to be the mother of a baby, the king asked for a sword. He proposed to split the baby so that each woman could have half of it. While one woman accepted the verdict, the other protested and pleaded that the baby be given to the other. This is how the king knew who the real mother was. As the British detective writer Agatha Christie put it, “A mother’s love for her child is like nothing else in the world. It knows no law, no pity, it dares all things and crushes  down remorselessly all that stands in its path.”

While we admire mothers who take their children’s side, we hold a dim view of human male combativeness. Boys and men often instigate confrontations, act tough, hide vulnerabilities, and seek danger. Not everyone likes men for this, and some experts disapprove. When they say that “traditional masculinity ideology” fuels men’s behavior, they hardly mean it as a compliment. In a 2018 document, the  American Psychological Association defined this ideology as revolving around “anti-femininity, achievement, eschewal of the appearance  of weakness, and adventure, risk, and violence.” The APA’s attempt to save men from this ideology revived debate about “toxic masculinity”  but also triggered backlash over its blanket denunciation of typical male behavior. 

It’s easy to see why male and female patterns of aggression are valued so differently: only the first creates trouble in society. Horrified by the death of Luit, I don’t want to depict male rivalry as an innocuous pastime. But who says it’s a product of ideology? A huge assumption is being made here, which is that we are the masters and designers of our own behavior. If this were true, shouldn’t it stand apart from that of other species? But it hardly does. In most mammals, males strive for status or territory whereas females vigorously defend their young. Whether we approve or disapprove of such behavior, it’s not hard to see how it evolved. For both sexes, it has always been the ticket to a genetic legacy. 

Ideology has little to do with it. 

Sex difference in animal and human behavior raise questions that lie at the heart of almost any debate about human gender. Does the behavior of men and women differ naturally or artificially? How different are they really? And are there only two genders, or are there more? 

But before I dive into this topic, let me make clear why I am interested in it and where I stand. I am not here to justify existing human gender relations by describing our primate heritage; nor do I think that everything is fine as it is. I recognize that the genders are not now and have never been equal for as long as we can remember. Women get the short end of the stick in our society and in almost every other one. They have had to fight for every improvement, from the right to education to voting rights, and from legalized abortion to equal pay. These aren’t little improvements. Some rights have been secured only recently, some are still being resisted, and some were achieved but have come under fresh attack. I see all this as highly unfair and consider myself a feminist. 

Disdain for the innate abilities of women has a long tradition in the West going back at least two millennia. It’s the way gender inequality has always been justified. Thus the nineteenth-century German philosopher  Arthur Schopenhauer thought that all their lives women remain children,  who live in the present, whereas men have the ability to think ahead.  Another German philosopher, Georg Wilhelm Friedrich Hegel, thought that “men correspond to animals, while women correspond to plants.” Don’t ask me what Hegel meant, but as noted by the British moral philosopher Mary Midgley, when it comes to women, the heavyweights of  Western thought have produced extraordinarily silly reflections. Their usual divergence of opinion is nowhere to be found: “There cannot be many matters on which Freud, Nietzsche, Rousseau and Schopenhauer agree cordially both with each other and with Aristotle, St. Paul and St. Thomas Aquinas, but their views on women are extremely close.”    

Even my beloved Charles Darwin didn’t escape the trend. In a letter to Caroline Kennard, an American women’s rights advocate, Darwin opined about women, “There seems to me to be a great difficulty from  the laws of inheritance in their becoming the intellectual equals of man.” 

All this in an era when disparities in education could easily account for the proposed intellectual contrasts. As for Darwin’s “laws of inheritance,” all I can say is that I’ve devoted my entire career to the study of animal intelligence and never noticed a difference between the sexes. We have brilliant individuals and not-so-brilliant ones on both sides,  but hundreds of studies by myself and others have revealed no cognitive gaps. While there is no shortage of behavioral contrasts between primate males and females, their mental capacities must have evolved in tandem.  In our species, too, even the cognitive domains traditionally associated with one gender and not the other, such as mathematical ability, prove indistinguishable by gender if tested on a large enough sample. The whole idea of one gender being mentally superior receives no backing from modern science. 

A second issue that needs to be cleared up is the stereotypical view  of our fellow primates that is sometimes used to defend inequalities in human society. In the popular imagination a male monkey boss “owns”  the females, who spend their lives making babies and following his orders. The chief inspiration for this view was a baboon study of one century ago that, as I will explain, had major flaws and gave rise to a  dubious metaphor. Unfortunately, it hit the public like a barbed arrow that proved impossible to dislodge despite all the contrary information gathered since then. That male supremacy is the natural order was promulgated over and over by a slew of popular writers in the previous century, while a 2002 book, entitled King of the Mountain, by the American psychiatrist Arnold Ludwig still maintains: 

Most humans have been socially, psychologically, and biologically programmed with the need for a single dominant male figure to govern their communal lives. And this programming corresponds closely to how almost all anthropoid primate societies are run.

One of my goals here is to disabuse readers of this notion of the obligatory male overlord. The primate study at its origin concerned a  species that we are not particularly close to. We belong to a small family of apes (large tailless primates), not of monkeys like baboons. By studying our next of kin, the great apes, a more nuanced picture emerges, one in which males exert less control than imagined. 

While it is undeniable that male primates can be bullies, it’s also good to realize that they didn’t gain their aggressiveness and size advantage in order to dominate females. This is not what their life is about. Given the ecological demands, females evolved to be the perfect size. Their bodies are optimal given the foods they gather, the amount of traveling they do,  the number of offspring they raise, and the predators they elude. Evolution has pushed males to deviate from this ideal so as to better fight each other. The more intense the competition among them, the more impressive their physical features. In some species, such as the gorilla,  the male is twice the female’s size. Since the whole point of male fighting is to get close to females with whom to reproduce, harming them or taking away their food is never the males’ goal. In fact, most female primates enjoy a great deal of autonomy, foraging all day for themselves and socializing with each other, while the males are peripheral to their existence. The typical primate society is at heart a female kinship network run by older matriarchs. 

We heard the same reflection when The Lion King was newly released. In the movie, the male lion is depicted as the boss—because most people cannot conceive of a kingdom any other way. The mother of Simba, the cub destined to become the next king, hardly plays any role at all. However, while it is true that lions are bigger and stronger than lionesses, they hold no central position in the pride. The pride is essentially a sisterhood,  which does the bulk of hunting and offspring care. Male lions stay for a couple of years before they are kicked out by incoming rivals. As Craig Packer, one of the world’s leading lion experts, puts it, “Females are the core. The heart and soul of the pride. The males come and go.”

While comparing ourselves with other species, the popular media feature a surface reality. The deeper reality, however, can be quite different. It may reflect substantial sex differences but not necessarily the ones we expect. Moreover, many primates have what I call potentials, which are capacities that are rarely expressed or hard to see. A good example is female leadership, such as I described in my last book, Mama’s Last Hug, for the longtime alpha female at Burgers’ Zoo. Mama was absolutely central to social life, even though, measured by the outcome of fights, she ranked below the top males. The oldest male, too, ranked below them but was equally central. Understanding how these two aging apes together ran a large chimpanzee colony requires looking beyond physical dominance and recognizing who makes the critical social decisions.  We need to distinguish political power from dominance. In our societies, no one confuses power with muscularity, and the same holds true for those of other primates. 

Another potential is the caretaking capacity of male primates. We sometimes get a glimpse of it after a mother’s death, when all of a sudden an orphan whimpers for attention. Adult male chimpanzees in the wild have been known to adopt a little one and lovingly care for it, sometimes for years. The male will slow down his travel for the adopted youngster, search for him if he’s lost, and be as protective as any mother. Since scientists tend to stress typical behavior, we don’t always dwell on these potentials. Still, they bear on human gender roles given that we live in a changing society, which tests the limits of what our species is capable of. There is every reason, therefore, to see what we can learn about ourselves from comparisons with other primates.

Even those who doubt evolutionary explanations, and think that the same rules don’t apply to us, will have to admit to one basic truth about natural selection. No person currently walking the earth could have gotten here if it weren’t for ancestors who survived and reproduced. All our ancestors conceived children and raised them successfully or helped others raise theirs. There are no exceptions to this rule because those who failed to do so are ancestors to no one.