The Archbishop of York is Primate of England. The Archbishop of Armagh is Primate of Ireland. The Archbishop of Warsaw is Primate of Poland. The Pope is Primate of Italy. The Archbishop of Canterbury is Primate of the planet, at least as far as his Anglican communicants are concerned. These ancient titles come from the medieval Latin word primus, which in turn derives from older Latin words meaning “principal” and “first.” The ecclesiastic use was straightforward: A primate of a region was the chief (“first”) of all its bishops. In recent centuries the title has devolved often to little more than an honorific. Other titles have taken precedence. But “Prime Minister” and “President” and “Premier” come from similar linguistic roots, all meaning “first.”

When Linnaeus was drawing up the family tree of life on Earth he was, as we’ve noted, afraid to include humans among the apes. But despite widespread opposition, it was impossible to deny some deep connections of monkeys, apes, and humans.* So all were classified into the order (for him, one taxon higher than genus) that he called primates. Scientists who study non-human primates—of course, they’re all primates themselves—are called primatologists.

This other meaning of “primate” also derives from the Latin for “first.” It’s hard to see by what standard a squirrel monkey, say, could be considered “first” among the lifeforms of Earth. But if a case is made that humans are “first,” then the tarsiers, bushbabies, mandrills, marmosets, sifakas, aye-ayes, mouse lemurs, pottos, lorises, spider monkeys, titis, and all the rest are dragged in along with us. We’re “first.” They’re our close relatives. So they, in some sense, must be “first” also—an undemonstrated and suspect conclusion in a biological world that runs from virus to great whale. Perhaps, instead, the argument goes the other way, and the humble status of most members of the primate tribe casts doubts on the lofty title we have appropriated to ourselves. It would make things so much easier for our self-esteem if those other primates weren’t—anatomically, physiologically, genetically, and in their individual and social behavior—so much like us.

Surely there is at least a hint in the word “primate,” not just of self-congratulation, but of the idea, fully realized in the practices of our own time, that we humans arrogate command and control of all life on Earth into our own hands. Not primus inter pares, first among equals, but just plain primus. We’ve found it convenient, even reassuring, to believe that life on Earth is a vast dominance hierarchy—sometimes called “The Great Chain of Being”—with us as the alphas. Sometimes we claim that it wasn’t our idea, that we were commanded by a Higher Power, the most Alpha of Alphas, to take over. Naturally, we had no choice but to obey.

About two hundred species of primates are known. Conceivably, in the quickly dwindling tropical rainforest another species or two—nocturnal or elegantly camouflaged—may have so far escaped our notice. There are about as many species of primates as there are nations on Earth. And like the nations, they have their different customs and traditions, which we sample in this chapter.

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Take the baboons—“the people who sit on their heels,” as the !Kung San people of the Kalahari Desert respectfully call them. Hamadryas baboons are different from savanna baboons (from whom they diverged perhaps 300,000 years ago), and free baboons behave very differently from baboons crowded together in zoos (the latter “insolently lascivious,” as an eighteenth-century naturalist described them). One telltale trait they all have in common: Sharing meat is virtually unknown among baboon males of either species, although it’s fairly widespread among the chimps.

At sunrise the baboons rouse themselves from their sleeping cliffs and break up into a number of smaller groups. Each group wends its separate way over the savanna, foraging, scampering, playing, intimidating, mating—all in a day’s work. But at the end of the day, all the groups converge on the same distant waterhole, and it may be a different waterhole on different days. How do the groups, out of sight of one another for most of the day, know to wind up at the same waterhole? Have the leaders negotiated the matter as the sun was rising over the sleeping cliffs?

Adult male hamadryas baboons are almost twice as large as the females. They display a leonine mane, enormous, almost fanglike canine teeth, and a ruthless character. These males were deified by the ancient Egyptians. They utter deep and prolonged grunts as they copulate. Their faces are “the color of raw beef steak—as different from the mousey grey-brown females as if they belonged to two different species.”² As females approach sexual maturity, they are chosen by particular males and herded into harems. Squabbling among competing males over ownership of the females may have to be worked out. A high priority of the males is maintaining and improving their status in the dominance hierarchy.

Hamadryas harems characteristically comprise from one to ten females; the males are concerned to keep peace among the females and to make sure that they do not so much as glance at another male. This is a bondage with little hope of escape. A female must follow her male about for the rest of her days. She must be sexually submissive: the least reluctance and she is bitten in the neck. It is not unknown for a hamadryas female to have her skull punctured and crushed in the massive jaws of the male for a minor infraction of the behavioral code he ruthlessly enforces.³ Conflict and tension around her are high when she’s ovulating, and somewhat muted when she’s pregnant or nursing the young. Unlike the chimps, you can see sexual coercion in the very posture of the baboon copulatory style: The male typically grasps the female’s ankles with his prehensile feet while mating, guaranteeing that she cannot run away. Compared to hamadryas behavioral norms, chimps live in an almost feminist society.

In a quarrel among females, one will sometimes threaten her rival with her teeth and forearms and, at the same time, alluringly present her rump to the male; with this postural offer of a deal, she sometimes induces him to attack her adversary. Subordinate male savanna baboons, as well as barbary apes, may use an infant—an unrelated infant, a bystander infant, or maybe an infant he is baby-sitting—as a hostage or shield or placatory object when approaching a high-ranking male. This tends to calm the alpha down if he’s in a grumpy mood.

The hamadryas male’s larger size and ferocious temperament doubtless are useful when the troop is imperilled by predators, or in conflict with other groups. But, as in the rest of the animal kingdom, when there are conspicuous differences in stature between the sexes (usually, it’s the males who are bigger), there’s exploitation and abuse of the smaller and weaker (usually the females).* Another distinction of the hamadryas baboons is that, alone among nonhuman primates so far as we know, two groups have been observed to ally themselves in combat against a third.⁴

Among savanna baboons, where the size difference between the sexes is not so striking, there are no harems. They are great walkers; it’s not unknown for a troop to cover twenty miles a day. Unlike chimps and hamadryas baboons, here it’s the male who leaves the natal troop around puberty—again, probably as an evolutionary device to avoid incest, and genetically to connect semi-isolated populations. When he attempts to enter a new troop, objections are likely to be raised by the resident males. Acceptance by the group often requires the time-honored method of submission, bluff, coercion, and alliance-making in the male hierarchy. But in many cases another strategy works well: make friends with a particular female in the troop and her children. He grooms her. He baby-sits and cares for her young. No killing off the young here in order to bring her into ovulation, as with rats and lions. If all goes well, she sponsors his entry into the troop. We can imagine a certain exhilaration as, gingerly, he attempts to enter the new community, his gaffes and old enemies left behind, a clean slate before him, and success dependent almost entirely on his social skills.

The males are more flighty and tempestuous than the females. Social stability is mainly provided on the female side. Indeed, since savanna baboon males are transients, the only hope for coherent group structure lies with the females. In all things, female baboons are comparatively conservative; it is the testosterone-pumped males who take the risks.

The female dominance hierarchy is largely hereditary. Daughters of alpha females are given unusual deference, even as juveniles, and have a good chance of achieving alpha status when they grow up. Every close relative of the dominant female may outrank every other member of the troop—a royal family. Submission and dominance in the female hierarchy of savanna baboons and many other monkey species is conveyed in the time-honored idiom of presenting and mounting, the heterosexual metaphor again adapted to another purpose.

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For reasons not fully understood but worth speculating on, much more attention—at least in public discussion and until recently—has been given to hamadryas baboons than to their savanna cousins. Sometimes the impression has been left that hamadryas behavior is representative of all nonhuman primates, or even all primates. For example, the hamadryas males, in a species in which nothing else is owned, have a clear sense of females as private property. But this is by no means true of all primates. The hamadryas baboons, it turns out, provide perhaps the most extreme example of hierarchy and brutality in the entire order of the primates. This behavior was especially marked under a set of cruel circumstances devised by humans who meant them no harm:

Living with apes or monkeys in the wild did not much appeal to primatologists until recently. More typical was an expedition back to his native South Africa by Solly Zuckerman, anatomist to the Zoological Society of London:

He dutifully noted how much fresh semen there was at various depths within the reproductive tracts of his female victims; “collected,” it turns out, is a euphemism for “killed.” Baboons had been officially declared “vermin” in South Africa, because they’re smart enough to defeat the efforts of farmers to safeguard their crops. A bounty was paid for each dead baboon. So a few baboons “collected” for science hardly mattered, compared with the wholesale slaughter being organized by the farmers. Through such studies Zuckerman “had the luck to discover from post-mortem study that ovulation in mature females occurs in the middle of the monthly sexual cycle.”⁶ The corresponding discovery about the human menstrual cycle was made around the same time.

He had long been interested in the standing of humans among the primates, and was dissecting baboons in South Africa while still a teenager.⁷ But he was not wholly unmoved by the plight of the hunted baboons, and later quoted this early-twentieth-century account:

If you wanted to meet a baboon—and you lived in a country where they didn’t roam about in the wild—you could always go to the local zoo and see the bedraggled and deracinated inmates, lifers pent up in tiny cubicles. After World War I, some European zoos thought it would be better, as well as more “humane,” if a large number of baboons could be gathered together in a partly open enclosure admitting observation by city-bound primatologists. The London Zoo was among them, and Dr. Zuckerman was playing a central role in the organization of one of these multiyear experiments:

In the spring of 1925, about one hundred hamadryas baboons were introduced into moat-bordered Monkey Hill, about 33 by 20 meters in area. So each baboon had, on average, less than 7 square meters, or some 60 square feet, indeed about the size of a small prison cell. It had been intended that this be an all-male group, but through an “accidental inclusion” six of the hundred baboons proved to be female. After a time, the oversight was rectified and the group was augmented by a further thirty females and five males. By late 1931, 64% of the males were dead, and 92% of the females:

Despite this last qualification, the hamadryas colony at the London Zoo reinforced a widespread belief in an unconstrained Darwinian struggle for existence. Even though baboons would quickly have exterminated themselves from the world if the events at Monkey Hill were characteristic of life in the wild, many people felt that they had now glimpsed Nature in the raw, a brutal Nature, red in claw and fang, a Nature from which we humans are insulated and protected by our civilized institutions and sensibilities. And Zuckerman’s vivid descriptions of the unrestrained sex lives of the baboons—he was one of the first to stress that baboon social organization may be determined largely by sexual considerations—increased the contempt that many humans felt toward the other primates.

What had gone wrong on Monkey Hill? First, almost all of the baboons introduced into the “colony” were unknown to one another. There was no long-term mutual habituation, no prior establishment of dominance hierarchies, no common understanding in these harem-obsessed males of who was to have many females and who none at all. No kinship-based female dominance hierarchy had been established. Unlike the situation in the wild, there were many more males than females. Finally, these baboons were crowded together to a degree rarely experienced in their natural state.

Because of their powerful jaws and spectacular canines, baboon males within a troop hardly ever fight among themselves in earnest, although corporal punishment is visited on the females for the slightest infractions. But in the London Zoo, dominance hierarchies had to be established, dedicated attempts were made to steal females, escape from a formidable attacker was cut off by the moat, and the calming influence of many sexually compliant females was almost entirely wanting. The result was carnage. In all six and a half years, only one infant survived. When the males would fight over them, the adult females would listlessly wait, as if “paralysed.” The battered, lacerated, punctured females would be sexually used by a quick succession of males.

But the females were not mere passive instruments:

When females were killed, the males would continue to drag them around, one male after another, to fight over them, and to copulate with their corpses. When the keepers, grimly watching this necrophilial tableau unfold, felt it necessary—for “anthropocentric” reasons—to enter the compound and remove the dead body, the males, in concert, would violently object and resist. Zuckerman, writing back then in the 1920s, used and may have coined the phrase “a sexual object”¹¹ in describing the lot of the female baboon.

We’ve seen in Calhoun’s experiments with rats that—even when there’s plenty of food, even when there are as many males as females—severe crowding induces violent and other modes of behavior that many would describe as aberrant and maladaptive. We’ve also seen in the Arnhem chimp colony how, under similar circumstances, new modes of behavior come to the fore to inhibit violence. From the baboons in the London Zoo we learn that if you take a species given to sexual violence in the best of conditions, provide a small number of sexual prizes to be fought over, arrange to have no pre-existing social order in which the animals know where they fit, and now crowd everybody together with no hope of escape, mayhem is the likely outcome. Monkey Hill reveals a deadly intersection of sex, hierarchy, violence, and crowding that may or may not apply to other primates.*

In Nature, as Zuckerman recognized, hamadryas baboons live much more peaceably. Dominant males are surrounded by a small corona of females, their offspring, and a few affiliated “bachelor” males. These harems wander over the landscape in bands, collecting food. Hundreds of baboons, a kind of gathering of the tribes, camp out each night near one another on sleeping cliffs. Fights to the death for possession of the females (or for any other reason) hardly ever happen. Everyone knows his, and especially her, place. The females are of course routinely abused, bitten on average once a day, but not so deeply as to draw blood. They are certainly not all killed off because they might be interested in other males, as happened in the London Zoo.

Hamadryas baboons in very small groups behave very differently: A bachelor baboon male watches a couple—on their first date—in an adjacent cage. Days go by, and he is forced to observe their deepening sexual relationship while he sits alone. When he’s then introduced into their cage, he makes no effort to attack the male or to lure the female away. He respects their relationship. He looks away when they have sex. He is a model of rectitude and circumspection, even if he’s of larger stature than either.¹²

Unsurprisingly, there are ways of arranging a primate society so its structure collapses and almost everybody dies. Shall we think of primates who find themselves in such circumstances as criminals? Are they accountable for their actions? Do they have free will? Or shall we attribute the bulk of the responsibility for what happens to those through whose miscalculation the social environment was established? For a society to be successful, it must be consonant with the nature and character of the individuals who must live in it. If those contriving social structures overlook who these individuals are, or sentimentalize their nature, or are incompetent social engineers, disaster can result.

Zuckerman has consistently argued that almost nothing about human nature or evolution can be learned by studying monkeys and apes—quite the opposite of many students of animal behavior who believe that understanding primates might provide a direct route to understanding humans: “[M]y unbending critical attitude to attempts to explain human behavior by analogies from the animal world must have been acquired at a very early age.”¹³ He describes Konrad Lorenz, Desmond Morris, and Robert Ardrey—who popularized, with at least some excesses, the idea that we have something to learn about ourselves from studying other animals—as “three writers who are equally adept at devising superficial analogies.”¹⁴

As “Prosector” of the London Zoo—the officer in charge of animal autopsies—Zuckerman later submitted the manuscript of a book, entitled The Social Life of Monkeys and Apes, for approval to his superior in the zoo’s dominance hierarchy. It was promptly rejected on grounds of displaying an undecorous explicitness on matters sexual (for example, “The overlord’s attention is caught by the perineal region of one of his females, usually when her sexual skin is swollen. He bends his head forward, his hand reaches out, his lips and tongue move and, having thus stimulated the sexual response in the female, he mounts and copulates”¹⁵). Zuckerman offered the book for publication anyway. In his autobiography, From Apes to Warlords, published forty-six years later—amidst much vivid detail of those years—he makes only the most tangential reference to the events at Monkey Hill.

At the start of World War II Zuckerman studied the consequences of aerial bombardment on civilian populations—his anatomical knowledge could there be put to good use. He soon moved on to analyzing the effectiveness of aerial bombing in the accomplishment of strategic goals, where his skeptical proclivities came in handy: The RAF’s Bomber Command (and the U.S. Army Air Corps), he found, had consistently exaggerated the potential of massive aerial bombardment to lessen the enemy’s will to fight and to shorten the war.

After the war Zuckerman headed the London Zoo, and through a few turns in his career wound up to be the principal scientific adviser to the British Ministry of Defence, where his expertise in understanding dominance hierarchies may have been germane. Created a Life Peer, Lord Zuckerman worked for many years to slow the nuclear arms race.

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Baboons as a whole represent only one small corner in the vast arena of primate behavior. We could just as easily have focused

Consider the gibbon. Its preternaturally long arms permit it to make great balletic leaps through the canopy of the forest—sometimes ten meters or more from branch to branch—that put champion human gymnasts to shame. Gibbons are, apparently without exception, monogamous. They marry for life. They produce haunting songs heard a kilometer or more away. Adult males often sing long solos in the darkness just before sunrise. Bachelors sing longer than old married males, and at a different time of day. Wives prefer duets with their husbands. Widows bear their grief in silence and sing no more.

Gibbons are also territorial and their matins serve to keep intruders away. A nuclear family, typically parents and two children, tends to control a small turf. Defense of the home territory is accomplished not so much by throwing stones or raining blows as by singing anthems. Perhaps there are cadences, timbres, frequencies, and amplitudes that other gibbons, contemplating a little poaching, find especially impressive and daunting. At least sometimes, an aging father will confer responsibility for territorial defense on his adolescent son, passing the patriotic torch on to the younger generation. In other equally poignant instances, adolescents are banished from the home territory by the parents, perhaps to avoid the temptations of incest. Adult males and females behave pretty much alike, and have nearly equal social status. Primatologists describe the females as “codominant,” and the partners in a marriage as “relaxed” and “tolerant.”¹⁷

Gibbon life seems downright operatic. It’s easy to conjure up feverish love solos, duets sung in praise of marital felicity, and ritual intimidation chants cast into the forest night: “We’re here, we’re tough, we sing good songs. Better leave our turf alone.” Perhaps there are gibbon Verdis singing power-transfer arias, rich with pathos, soulful lamentations on the passing of glory and of time.

Or consider the bonobo. This is a reclusive species or subspecies of chimpanzee that lives in a single group in Central Africa, south of the Zaire River.¹⁸ Bonobos have certain traits that render them conventionally ineligible for the local zoo, which may be one reason that they’re not nearly so well known as the common chimp we’ve described in the preceding chapters. Bonobos, given the Linnaean name Pan paniscus, are also called pygmy chimpanzees; they’re smaller and more slender and their faces protrude less than the usual variety, Pan troglodytes, which we’ll here and there continue to describe simply as chimpanzees.* Bonobos often stand up and walk on two legs. (They have a kind of webbing of skin between their second and third toes.) They stride with their shoulders squared and do not slouch as much as chimps do. “When bonobos stand upright,” writes de Waal, “they look as if they had walked straight out of an artist’s impression of prehistoric man.”¹⁹

Unlike chimp females, among whom estrus is advertised and is a time of pronounced sexual receptivity, bonobo females display genital swellings about half the time; and they’re nearly always attractive to the adult males. We recall that common chimps, Pan troglodytes, like almost all animals, have sex with the male entering the female’s vagina from behind, his front against her back. But in bonobos, about a quarter of the time, the matings are face-to-face. This is the position the females seem to prefer, probably because their clitorises are large and positioned far forward compared to chimps. Bonobos indicate their mutual attraction by prolonged gazing into one another’s eyes, a practice which precedes almost all their matings, and which is unknown among common chimps. The initiation of sexual activity among the bonobos is mutual, unlike the chimps, where it is peremptory and nearly always by the males. While in general, especially in larger social contexts, male bonobos dominate females, this is not always the case, especially when they’re alone together. At night, in the forest canopy, a male and a female will sometimes snuggle up together in the same nest of leaves. Adult chimps never do.

The sexual activity of common chimps, which by human standards seems obsessive to the point of mania, is almost puritanical by bonobo standards. The average number of penile thrusts in an average copulation—a measure of sexual intensity that primatologists are drawn to, in part because it can be quantified—is around forty-five for bonobos, compared to less than ten for chimps. The number of copulations per hour is 2½ times greater for bonobos than for chimps—although these observations are for bonobos in captivity, where they may have more time on their hands or more need for mutual comfort than when they are free. Less than a year after giving birth, bonobo females are ready to resume their lives of sexual abandon; it takes three to six years for chimp females.²⁰

Bonobos use sexual stimulation in everyday life for many purposes besides mere satisfaction of the erotic impulse—for quieting infants (a practice said once to have flourished also among Chinese grandmothers), as a means of resolving conflict among adults of the same sex, as barter for food, and as a generic, all-purpose approach to social bonding and community organization. Less than a third of the sexual contacts among bonobos involve adults of opposite sexes. Males will rub rumps together or engage in oral sex in ways unheard of among the more prudish chimps; females will rub their genitalia together, and sometimes prefer it to heterosexual contacts. Females characteristically engage in genital rubbing just before they’re about to compete for food or for attractive males; it seems to be a way of reducing tension. In times of stress, a bonobo male will spread his legs and present his penis to his adversary in a friendly gesture.

Despite these differences in nuance, bonobos are still chimpanzees. There’s a male dominance hierarchy, although not nearly as pronounced as among common chimps; dominant males have preferential access to females, although males do not always dominate females; there are submissive gestures and greetings; the size of groups is about the same as with chimps, a few dozen; adolescent females wander over to adjacent groups; the males preferentially hunt animal prey, although apparently not in hunting parties; males are proportionately larger than the females by about the same ratio as among chimps; and encounters between groups sometimes become violent—although groups may also on encountering one another, behave very peaceably and laid-back. Infanticide and all other killing of bonobo by bonobo are, so far, unknown. Their standard initial response on meeting unfamiliar humans, as we ourselves experienced, is a very chimp-like, and adequately intimidating, charging display.

Grooming is most frequent between males and females and least common between males and males, the reverse of chimp practice. The grin serves not mainly as a gesture of submission, but performs a range of functions similar to those of the human smile. Male bonding is much weaker than in chimp society, and the social position of females much stronger. Certain mothers and sons associate closely until the son becomes an adult; among chimps the relationship tends more often to be broken off when the young male reaches adolescence. Social skills for resolving conflicts are much more highly developed among the bonobos than among the chimps, and dominant individuals are much more generous in making peace with their adversaries.

If we feel a certain revulsion at having hamadryas baboons as relatives, we may take some comfort from our connection with the gibbons and the bonobos. Indeed, we’re far more closely related to the apes than to the monkeys. Chimps and bonobos are certainly members of the same genus and, according to some taxonomic classifications, even the same species. Given that, it’s startling how different they are from one another. Perhaps many of the distinctions between the two—ranging from the frequency, increased variety, and social utility of sex to the relatively higher status of females—are due to the evolution in the bonobos of a new step: abandoning the monthly badge of ovulation, graduating from estrus. Perhaps when ovulation is not evident at a glance or a sniff, females can be viewed as more than sexual property.

The primates are so rich in potential that even a small change in anatomy or physiology may provide an aperture to a universe never dreamt of in the rude sleeping pallets made each night in the low branches of the once-vast tropical forests.