Bonobo: The Forgotten Ape

Photography by FRANS LANTING
University of California Press

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The Last Ape

When the lively, penetrating eyes lock with ours and challenge us to reveal who we are, we know right away that we are not looking at a "mere" animal, but at a creature of considerable intellect with a secure sense of its place in the world. We are meeting a member of the same tailless, flat-chasted, long-armed primate family to which we ourselves and only a handful of other species belong. We feel the age-old connection before we can stop to think, as people are wont to do, how different we are.

Bonobos will not let us indulge in this thought for long: in everything they do, they resemble us. A complaining youngster will pout his lips like an unhappy child or stretch out an open hand to beg for food. In the midst of sexual intercourse, a female may squeal with apparent pleasure. And at play, bonobos utter coarse laughs when their partners tickle their bellies or armpits. There is no escape, we are looking at an animal so akin to ourselves that the dividing line is seriously blurred.

Whereas the bonobo amazes and delights many people, the implications of its behavior for theories of human evolution are sometimes inconvenient. These apes fail to fit traditional scenarios, yet they are as close to us as chimpanzees, the species on which much ancestral human behavior has been modeled. Had bonobos been known earlier, reconstructions of human evolution might have emphasized sexual relations, equality between males and females, and the origin of the family, instead of war, hunting, tool technology, and other masculine fortes. Bonobo society seems ruled by the "Make Love, Not War" slogan of the 1960s rather than the myth of a bloodthirsty killer ape that has dominated textbooks for at least three decades.


In 1925, Raymond Dart announced the discovery of Australopithecus africanus, a crucial missing link in the human fossil record. This bipedal hominid with apelike features brought the human lineage considerably closer to that of the apes than previously held possible. It also provided the first indication that Charles Darwin had been correct in suggesting Africa, rather than Asia or Europe, as the cradle of humanity.

On the basis of evidence encountered at the discovery site, Dart speculated that Australopithecus must have been a carnivore who ate his prey alive, dismembering them limb from limb, slaking his thirst with their warm blood. The killer-ape myth is the science writer Robert Ardrey's dramatization of these and other ideas, including the proposition that war derives from hunting, and that cultural progress is impossible without aggressivity. The renowned ethologist Konrad Lorenz added that whereas "professional" predators, such as lions and wolves, evolved powerful inhibitions keeping them from turning their weaponry against their own kind, humans have unfortunately not had time to evolve in this direction. Descended from vegetarian ancestors, we became meat-eaters almost overnight. As a result, our species lacks the appropriate checks and balances on intraspecific killing.

It has been suggested that the tremendous appeal of this scenario had more to do with the genocide of World War II than with fossil finds. Confidence in human nature was at a low after the war, and the popularizations of Ardrey and Lorenz merely reinforced the misanthropic mood. In A View to a Death in the Morning, Matt Cartmill summarizes the impact of the by now antiquated idea that the lust to kill has made us what we are:

    During the 1960s, the central propositions of the hunting hypothesis--that hunting and its selection pressures had made men and women out of apelike ancestors, instilled a taste for violence in them, estranged them from the animal kingdom, and excluded them from the order of nature--became familiar themes of the national culture, and the picture of Homo sapiens as a mentally unbalanced predator, threatening an otherwise harmonious natural realm became so pervasive that it ceased to provoke comment.... Millions of moviegoers in 1968 absorbed Dart's whole theory in one stunning image from Stanley Kubrick's film 2001, in which an australopithecine who had just used a zebra femur to commit the world's first murder hurls the bone gleefully in the air--and it turns into an orbiting spacecraft.

Ironically, it is now believed that Australopithecus, rather than having been a predator himself, was a favorite food for large carnivores. The damage to fossil skulls, which Dart interpreted as evidence for club-wielding man-apes, turns out to be perfectly consistent with predation by leopards and hyenas. In all likelihood, therefore, the beginnings of our lineage were marked more by fear than ferocity.


Bonobos are not on their way to becoming human any more than we are on our way to becoming like them. Both of us are well-established, highly evolved species. We can learn something about ourselves from watching bonobos, though, because our two species share an ancestor, who is believed to have lived a "mere" six million years or so ago. Possibly, bonobos have retained traits of this ancestor that we find hard to recognize in ourselves, or that we are not used to contemplating in an evolutionary light.

Not too long ago, a much more distant relative, the savanna baboon, was regarded as the best living model of ancestral human behavior. These ground-dwelling primates are adapted to the sort of ecological conditions that protohominids must have faced after they descended from the trees. The baboon model was largely abandoned, however, when it became clear that a number of fundamental human characteristics are absent or only minimally developed in them, yet present in chimpanzees. Cooperative hunting, food-sharing, tool use, power politics, and primitive warfare have been observed in chimpanzees, who are also capable of learning symbolic communication, such as sign language, in the laboratory. Moreover, these apes recognize themselves in mirrors--an index of self-awareness for which there is thus far little or no evidence in monkeys. Like us, of course, chimpanzees belong to the Hominoidea, a branch that split off long ago from the rest of the primate tree. They are thus genetically much closer to us than are baboons.

Whereas selection of the chimpanzee as the touchstone of human evolution represented a great improvement over the baboon, one aspect of the models did not need to be adjusted: male superiority remained the "natural" state of affairs. In both chimpanzees and baboons, males are conspicuously dominant over females. In baboons, males are not only twice the size of females, they are equipped with canine teeth as formidable as a panther's, whereas females lack such weaponry. Sexual dimorphism may be less dramatic in the chimpanzee, but in this species, too, males reign supreme, and often brutally. It is extremely unusual for a fully grown, healthy male chimpanzee to be dominated by a female.

Enter the bonobo, which is best characterized as a female-centered, egalitarian primate species that substitutes sex for aggression. It is impossible to understand the social life of this ape without attention to its sex life: the two are inseparable. Whereas in most other species, sexual behavior is a fairly distinct category, in the bonobo it has become an integral part of social relationships, and not just between males and females. Bonobos engage in sex in virtually every partner combination: male-male, male-female, female-female, male-juvenile, female-juvenile, and so on. The frequency of sexual contact is also higher than among most other primates.

The bonobo's rate of reproduction is low, however. In the wild, it is approximately the same as that of the chimpanzee, with single births to a female at intervals of around five years. This combination of sexual appetite and slow reproduction sounds familiar, of course: nonreproductive sex is a prominent trait of our own species.

If the sole purpose of sex is procreation, as some religious doctrines would have it, why has the average size of families in industrialized nations dropped to fewer than two children, despite the fact that countless human couples in those countries copulate regularly? Perhaps they do so because it feels good, hence tends to become addictive. Yet this automatically raises the question: Why does it have this effect on people? After all, most other animals restrict their mating activity to a particular season or a couple of days in their ovulatory cycles; they do not seem to feel any sexual needs divorced from reproduction.

The bonobo, with its varied, almost imaginative, eroticism, may help us see sexual relations in a broader context. Certain aspects of human sexuality, such as pleasure, love, and bonding, tend to be overlooked by reproduction-oriented ideologies. The possibility that these aspects have characterized our lineage from very early on has serious implications, given how often moralizing relies on claims about the naturalness or unnaturalness of behavior: what is natural is generally equated with what is good and acceptable. The truth is that if bonobo behavior provides any hints, very few human sexual practices can be dismissed as "unnatural."

Because the role of sex in society is such a loaded and controversial issue, scientists have tended to downplay this side of bonobo behavior, whereas the few journalists who have written about the species have naturally hyped it. In this book, I hope to strike a balance: I intend to give the topic the attention it deserves, without reducing bonobos to the lustful satyrs that our closest relations once were considered to be. Sexual encounters of the bonobo kind are strikingly casual, almost more affectionate than erotic. If the apes themselves are so relaxed about it, it seems inappropriate for us to give in to typically human obsessions. In addition, there is a lot more to bonobo natural history than sex. The entire social organization of the species is fascinating, as is its mode of communication, raising of offspring, remarkable intelligence, and status in the wild. The whole creature deserves attention, not just part of it.

In the past few years, many different strands of knowledge have come together concerning this most enigmatic ape. The findings command attention, as the bonobo is just as close to us as its sibling species, the chimpanzee. According to DNA analyses, we share over 98 percent of our genetic material with each of these two apes. And not only are they our nearest relatives; we are theirs! That is, the genetic makeup of a chimpanzee or bonobo matches ours more closely than that of any other animal, including other primates, such as gorillas, traditionally thought of as closer to them than to us.

No wonder Carl Linnaeus, who imposed the taxonomic division between humans and apes, regretted his decision later in life. The distinction is now regarded as wholly artificial. In terms of family resemblance, only two options exist: either we are one of them or they are one of us.


Years ago, when the conservator of mammals at the Amsterdam Zoological Museum happened to dust off the stuffed remains of an ape named "Mafuca," he immediately recognized its bonobo features despite the label, which said it was a chimpanzee. During Mafuca's short life, from 1911 through 1916, bonobos were not yet recognized as a separate species, even though a few keen observers already had an inkling of the difference.

In 1916, a perceptive Dutch naturalist, Anton Portielje, speculated in a guide to the Amsterdam Zoo that the hugely popular Mafuca might represent a new primate species. A few years later, Robert Yerkes, the American pioneer of ape research, contrasted "Prince Chim," an individual now known to have been a bonobo, with a chimpanzee, noting: "Complete descriptions of the physique of the two animals might suggest the query as to whether they were both chimpanzees." For all intents and purposes, therefore, the species distinction between bonobo and chimpanzee ought to be credited to behavioral scientists such as Portielje and Yerkes.

It was only when anatomists reached the same conclusion, however, that the world paid attention. The distinction, first made in 1929, carried tremendous weight: the bonobo became one of the last large mammals to be known to science. Rather than in a lush African setting, the historic discovery took place in a colonial Belgian museum following the inspection of a skull that, because it was undersized, was thought to have belonged to a juvenile chimpanzee. In immature animals, however, the sutures between skull bones ought to be separated, whereas in this specimen they were fused. Concluding that it must have belonged to an adult with an unusually small head, Ernst Schwarz, a German anatomist, declared that he had stumbled upon a new subspecies of chimpanzee. Soon the differences were considered important enough to elevate the bonobo to the status of an entirely new species, officially classified as Pan paniscus.

Even though Schwarz's name became officially associated with the species--the sort of honor biologists are willing to die for--a far more detailed description was provided, in 1933, by Harold Coolidge, an American anatomist. Half a century later, Coolidge challenged Schwarz's priority. At an international conference of primatologists in 1982, he claimed that he himself had been the first to notice the unusual skull at the museum. In his excitement he had shown it to the museum director, who allegedly told his friend Schwarz two weeks later. Schwarz wasted no time making the discovery public in an obscure journal published by the museum. "I had been taxonomically scooped!" exclaimed Coolidge at the symposium. Unfortunately, Schwarz's side to this story remains unknown: the accusation came after his death.

Oddly enough, the bonobo's genus name, Pan, derives from the Greek god of flocks, shepherds, and woods, who had a human torso, but the legs, beard, ears, and horns of a goat. Playfully lecherous, Pan loved to chase the nymphs and played the shepherd's flute, an obvious phallic symbol. The suffix to the species name of the bonobo, paniscus, qualifies it as diminutive. The other member of the same genus, the chimpanzee, carries the species name troglodytes, or cave dweller. So we are dealing with rather peculiar epithets for animals adapted to the trees, with the bonobo being labeled a small herder deity and the chimpanzee a grotto herder deity.

Since the bonobo and chimpanzee are close relatives, and since the latter is more familiar, the two species are sometimes taken together as two kinds of chimpanzee. Thus, the bonobo is also known as the "bonobo chimpanzee" or "pygmy chimpanzee." Unfortunately, this usage has forced the name "common chimpanzee" upon the chimpanzee--a questionable label for an endangered animal. Furthermore, some scientists object to "pygmy chimpanzee" as inaccurate (there is considerable overlap in size between chimpanzees and bonobos), as well as making it sound too much as if the bonobo is merely a smaller version of its congener. Others, in turn, say the name "bonobo" is meaningless and probably derives from a misspelling on a shipping crate of "Bolobo," a town in Zaire.

The label "bonobo" has stuck, though, not least because it respects its bearer as a fully distinct species, rather than as, so to speak, the poor man's miniature chimp. In addition, "bonobo" has a happy ring to it that befits the animal's nature. Primatologists acquainted with its behavior have even jokingly begun to employ the name as a verb, as in "We're gonna bonobo tonight." (The meaning of this expression will be left to the reader's imagination!)

To complete these notes on the discovery of the last ape, it has recently come to light that, ironically, the bonobo may have been known to science longer than any other great ape. The earliest accurate description of an ape was produced, in 1641, by Nicolaas Tulp, a Dutch anatomist of great repute, immortalized in Rembrandt's The Anatomy Lesson. The ape cadaver that Tulp dissected resembled a human body so closely in its structural details, musculature, organs, and so on, that he commented that it would be hard to find one egg more like another. Although Tulp baptized his specimen an Indian satyr, adding that the local people called it an "orang-outang," it had come straight from Africa. Only its name came from the East Indies (in Malay orang hutan means "man of the forest").

Tulp's gravure, faithfully replicated over and over in books of the seventeenth and eighteenth centuries, appears to show a female chimpanzee. At least this was the consensus until a British primatologist, Vernon Reynolds, asserted that Tulp's satyr could very well have been a bonobo. Reynolds's chief argument was that the original drawing shows a cutaneous connection between the second and third digits of the ape's right foot. Such "webbing" between toes is much more common in bonobos than in chimpanzees. Furthermore, Tulp's specimen was known to have originated in Angola. Although no bonobos live there today, Angola is south of the Zaire River. This immense, at times more than one-kilometer-wide water barrier currently fully separates chimpanzees, to the north, east, and west, from bonobos, to the south.


Yerkes greatly admired his bonobo's character and intelligence, writing: "I have never met an animal the equal of Prince Chim in approach to physical perfection, alertness, adaptability, and agreeableness of disposition."

Much has been made of this opinion of one of the greatest authorities on ape psychology. Before accepting Yerkes's enthusiasm for Chim as a blanket statement about the species, however, we should realize that the scientist seriously underestimated his subject's age. The slight build of the bonobo led him to believe that Chim was only three years old, whereas a postmortem inspection by Coolidge indicated an age closer to six. In the same way that a child twice the age of another is mentally far ahead, Chim may have come across as brilliant compared to the chimpanzee, Panzee, with whom he was raised. Moreover, Panzee suffered from tuberculosis, another serious disadvantage compared to the healthy Chim. Yerkes himself fully realized the limitations of his comparison, stating that intelligence, temperament, and character very much depend on physical constitution.

Unfortunately, these reservations are rarely mentioned when Yerkes's high regard for Chim is cited in support of claims that bonobos are extraordinarily intelligent. There is no doubt in my mind that they are, but whether their intelligence exceeds that of other apes remains an open question. Simian IQs are about as contentious an issue as human IQs. For one thing, there is great individual variability: comparing a few bonobos with a few chimpanzees is not going to tell us much. I know some exceptionally bright anthropoids, but certainly not all of them are bonobos. At this point it is not at all clear in which cognitive areas, if any, the bonobo systematically outshines other apes.

The first study of substance comparing bonobos and chimpanzees was carried out in the 1930s at the Hellabrunn Zoo in Munich. It took Eduard Tratz and Heinz Heck until after World War II to publish their findings, based on an inspection of the preserved bodies of three apes and film footage collected during their lives: terrified by the city's bombardment during the war, all three bonobos had died of heart failure. Tratz and Heck's eight-point list of behavioral differences between the two Pan species still stands as the first outline of the areas of greatest contrast: sexual behavior, intensity of aggression, and vocal expression. Here follows their list in slightly compressed form:

    1. Bonobos are sensitive, lively, and nervous, whereas chimpanzees are coarse and hot-tempered.

    2. Bonobos rarely raise their hair; chimpanzees often do so.

    3. Physical violence almost never occurs in bonobos, yet is common in chimpanzees.

    4. Bonobos defend themselves through aimed kicking with their feet, whereas chimpanzees try to pull attackers close to bite them.

    5. The bonobo voice contains a and e vowels, whereas the chimpanzee uses more u and o vowels.

    6. Bonobos are more vocal than chimpanzees.

    7. Bonobos stretch their arms and shake their hands when calling, whereas chimpanzees do not.

    8. Bonobos copulate more hominum and chimpanzees more canum.

Given what we know now, points 1 through 4 are undoubtedly correct. Even though the difference in aggressivity is one of degree only, it cannot be denied that the treatment to which chimpanzees occasionally subject one another, including biting and full-force hitting, is rare among bonobos. Chimpanzees also erect their hair at the slightest provocation, pick up a branch, and challenge and intimidate anyone perceived as weaker than themselves: they are very much into status. By bonobo standards, the chimpanzee is a wild and untamed beast, or as Tratz and Heck put it: "The bonobo is an extraordinarily sensitive, gentle creature, far removed from the demoniacal primitive force [Urkraft] of the adult chimpanzee."

As regards point 5, Blanche Learned's pioneer (albeit unwitting) comparison of vocal repertoires is worth noting. Before the species difference was established, she listened with a musical ear to Yerkes's two apes, Chim and Panzee. According to my calculations from Learned's phonetic transcriptions of hundreds of vocalizations, Chim mostly uttered a (48%), ae (38%), and oo (10%) sounds, whereas Panzee mostly uttered oo (68%), o (12%), and oa (7%) sounds. There is indeed no quicker way to distinguish the two ape species than by their voices. When Heck, who was the director of Hellabrunn Zoo, first heard bonobo calls coming out of a cloth-covered crate, he was convinced that he had received the wrong animals. Their calls are so high-pitched and penetrating that they do not even remind one of the typical drawn-out "huu ... huu" hooting of the chimpanzee. The difference in timbre between the voices of the two species may well be of the same magnitude as that between a small child and a grown man.

It is also true that bonobos tend to gesticulate when calling, and that vocal activity among them is high. Bonobos are excitable creatures who frequently "comment" on minor events around them through high-pitched peeps and barks. Even if most of these vocalizations are noticeable only at close range, one definitely hears more vocal exchange in a group of bonobos than in a group of chimpanzees. Chimpanzees call when seriously alarmed, aroused by food, or in order to intimidate one another. Few animals can produce the din characteristic of chimpanzees, but much of it occurs on well-circumscribed occasions.

The final point concerns sexuality. Because Tratz and Heck wrote before the sexual revolution, they felt the need to wrap their shocking findings in Latin. In those days, face-to-face copulation was regarded as uniquely human; a cultural innovation reflecting the dignity and sensibility separating the human race from "lower" life forms. The two zoologists claimed, however, that whereas chimpanzees mate like dogs (more canum), bonobos follow the human pattern (more hominum). They added the important observation that the genitals of female bonobos seem adapted to this position: the vulva is situated between their legs rather than oriented to the back, as is the case in chimpanzees.

To this day, both academic and popular writers perpetuate ridiculous claims about human mating patterns, penis size, and general sexiness. The primary reason for overlooking the considerable early knowledge about bonobos must have been that most of it was unavailable in English. Who browses through journals such as Saugetierkundliche Mitteilungen? Apart from their role in the naming game (they were the first to propose "bonobo"), Tratz and Heck were ignored and forgotten by the scientific community. Another overlooked work is an admirably detailed investigation at three European zoos by Claudia Jordan, whose 1977 dissertation, "Das Verhalten zoolebender Zwergschimpansen" (The Behavior of Zoo-living Pygmy Chimpanzees), contains virtually all of the basic behavioral information presented as new discoveries in the literature of subsequent years.

A second reason that little attention was paid to some of the early studies was the tendency to dismiss unusual behavior in zoo animals as artifacts of captivity. Could it be that bonobos act so grotesquely because they are bored to death, or under human influence? We know now that, except under extreme conditions, the effects of captivity on behavior are less dramatic than used to be assumed. Whatever the conditions under which other primates are kept, they never act like bonobos. In other words, it must be something in the species, rather than in the environment, that produces the bonobo's characteristic behavior. It was only when fieldwork got off the ground, however, that the behavior-as-artifact explanation could be put to rest. Research in the bonobo's natural habitat validated rather than contradicted the pioneering observations of Yerkes, Tratz and Heck, Learned, Jordan, and others.

In 1974, Alison and Noel Badrian, a young couple of Irish and South African extraction, bravely entered the remote jungles of northern Zaire on their own, without financial backing. They established a study site in Lomako Forest, which is still in use today, although observation has been discontinuous and conducted by a number of different scientists. The other main study site in Zaire, established in the same year, has known much greater continuity and has, as a result, become the dominant source of information about wild bonobos. This site, named Wamba, was founded by Takayoshi Kano of Kyoto University, in Japan, after a five-month survey of the distribution of Zaire's bonobo population. Transportation by other means being virtually impossible in this region, Kano traveled enormous distances on foot and by bicycle.

These and other dedicated fieldworkers have advanced our knowledge of bonobo behavior by giant strides, confirming the significance and richness of these apes' sexual behavior and putting their social organization in the context of the ecological background to which it is adapted: the swampy rain forest covering the flat basin of the Zaire River. Because wild bonobos are extremely shy, it takes a long time to habituate them to human presence. At Wamba, this problem was solved by a technique widely employed with Japanese macaques in the investigators' home country: food provisioning. By planting a few hectares of sugarcane near their range, Kano was able to entice bonobos out of the forest. At Lomako, such techniques have never been employed. The Lomako site has therefore something unique to offer: a look at the ranging and foraging patterns of bonobos undisturbed by human provisioning.

Despite the establishment of Wamba, Lomako, and a handful of other field sites, bonobo research still lags far behind that on chimpanzees in both scope and intensity. Over recent years, however, interest has grown rapidly, not least because bonobos seem to present a mirror-image of the traditional picture of our primate relatives as male-dominated and violent. As a feminist journalist for a nature magazine once put it to me: "Bonobos are our only hope!" An ideological interest in the species may not sound desirable to most scientists, yet so long as it leads to scholarly, honest, and rigorous study, I do not see much wrong with it. As a result of continued research, current impressions and theories will either be confirmed or require revision, and we shall gain a deeper understanding of why bonobos evolved the sort of society that they live in.

In the meantime, captive bonobos have become more attractive for behavioral studies: zoo colonies now include more individuals in more naturalistic enclosures than the single individuals or small groups of the past. In addition, the apes live longer than before. Bonobos are extremely susceptible to respiratory disease: they used to survive only a couple of years in captivity. With greater care and better nutrition, there now are bonobos aged twenty, thirty, or older in zoos and research institutions. The development towards improved survival and larger social groupings began at the San Diego Zoo, where I conducted my own research. This zoo started out very modestly, in the early 1960s, with a single pair of bonobos: Kakowet and Linda. These two were so prolific that they produced the greatest number of children and grandchildren known of any bonobo couple, captive or wild, in the world. Part of the reason was that every newborn was taken away to the zoo nursery; this allowed Linda to skip the long nursing period and deliver at unusually short intervals: ten children in fourteen years.

Not that this is a desirable procedure! Many of Linda's newborns were featured on Johnny Carson's late-night television show, and I feel they would have been better off with a little less fame and a little more motherly love. Nowadays, zoos, including the San Diego Zoo, do everything in their power to keep mother and infant together.

Linda is still alive (estimated to be around forty, she now lives with one of her adult daughters at the Milwaukee County Zoo), but Kakowet died years ago. Stories about the patriarch of zoo bonobos abound. According to one, Ernst Schwarz was overjoyed to hold Kakowet when he was still a small infant (his name derives from the French word for peanut, cacahuete, because he was so incredibly tiny). Having conducted all of his taxonomic work with museum skeletons and skins, Schwarz had never met a live bonobo. Standing with the ape on his arm, the German anatomist was greeted by a woman who said: "So, you're the man who named that funny little monkey." A shocking thing to say to someone so familiar with the distinction between monkeys and apes!

Now that captive bonobos have become more interesting for students of social behavior, and fieldwork is growing in both quality and quantity, we are in a better situation than ever before to summarize this ape's social life. Our knowledge is far from perfect, but we know enough to drag the bonobo out of the obscure corner in which primate specialists have been debating its peculiarities among themselves. Its behavior is bound to overthrow a number of cherished assumptions about the course of human evolution. In addition, the species is fascinating in itself; it fully deserves a place in the public mind alongside our better-known ape relations.

(C) 1997 The Regents of the University of California All rights reserved. ISBN: 0-520-20535-9

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