Print Advertisement At a juncture in history during which women are seeking equality with men, science arrives with a belated gift to the feminist movement.
Male-biased evolutionary scenarios--Man the Hunter, Man the Toolmaker and so on--are being challenged by the discovery that females play a central, perhaps even dominant, role in the social life of one of our nearest relatives. In the past two decades many strands of knowledge have come together concerning a relatively unknown ape with an unorthodox repertoire of behavior: The bonobo is one of the last large mammals to be found by science.
The creature was discovered in in a Belgian colonial museum, far from its lush African habitat. A German anato-mist, Ernst Schwarz, was scrutinizing a skull that had been ascribed to a juvenile chimpanzee because of its small size, when he realized that it belonged to an adult. Schwarz declared that he had stumbled on a new subspecies of chimpanzee. But soon the animal was assigned the status of an entirely distinct species within the same genus as the chimpanzee, Pan.
The bonobo was officially classified as Pan paniscus, or the diminutive Pan. But I believe a different label might have been selected had the discoverers known then what we know now. The old taxonomic name of the chimpanzee, P. The species is best characterized as female-centered and egalitarian and as one that substitutes sex for aggression.
Whereas in most other species sexual behavior is a fairly distinct category, in the bonobo it is part and parcel of social relations--and not just between males and females. Bonobos engage in sex in virtually every partner combination although such contact among close family members may be suppressed.
And sexual interactions occur more often among bonobos than among other primates. Despite the frequency of sex, the bonobos rate of reproduction in the wild is about the same as that of the chimpanzee. A female gives birth to a single infant at intervals of between five and six years. So bonobos share at least one very important characteristic with our own species, namely, a partial separation between sex and reproduction.
The split between the human line of ancestry and the line of the chimpanzee and the bonobo is believed to have occurred a mere eight million years ago. The subsequent divergence of the chimpanzee and the bonobo lines came much later, perhaps prompted by the chimpanzees need to adapt to relatively open, dry habitats. In contrast, bonobos probably never left the protection of the trees. Their present range lies in humid forests south of the Congo River, where perhaps fewer than 10, bonobos survive.
Given the species slow rate of reproduction, the rapid destruction of its tropical habitat and the political instability of central Africa, there is reason for much concern about its future.
If this evolutionary scenario of ecological continuity is true, the bonobo may have undergone less transformation than either humans or chimpanzees. It could most closely resemble the common ancestor of all three modern species.
Indeed, in the s Harold J. Coolidge--the American anatomist who gave the bonobo its eventual taxonomic status--suggested that the animal might be most similar to the primogenitor, because its anatomy is less specialized than is the chimpanzees.
Bonobo body proportions have been compared with those of the australopithecines, a form of prehuman. When the apes stand or walk upright, they look as if they stepped straight out of an artists impression of early hominids.
Not too long ago the savanna baboon was regarded as the best living model of the human ancestor. That primate is adapted to the kinds of ecological conditions that prehumans may have faced after descending from the trees. But in the late s chimpanzees, which are much more closely related to humans, became the model of choice.
Traits that are observed in chimpanzees--including cooperative hunting, food sharing, tool use, power politics and primitive warfare--were absent or not as developed in baboons. In the laboratory the apes have been able to learn sign language and to recognize themselves in a mirror, a sign of self-awareness not yet demonstrated in monkeys.
Although selecting the chimpanzee as the touchstone of hominid evolution represented a great improvement, at least one aspect of the former model did not need to be revised: In both baboons and chimpanzees, males are conspicuously dominant over females; they reign supremely and often brutally. It is highly unusual for a fully grown male chimpanzee to be dominated by any female.
Despite their common name--the pygmy chimpanzee--bonobos cannot be distinguished from the chimpanzee by size. Adult males of the smallest subspecies of chimpanzee weigh some 43 kilograms 95 pounds and females 33 kilograms 73 pounds , about the same as bonobos. Although female bonobos are much smaller than the males, they seem to rule. I do not wish to offend any chimpanzees, but bonobos have more style.
The bonobo, with its long legs and small head atop narrow shoulders, has a more gracile build than does a chimpanzee. Bonobo lips are reddish in a black face, the ears small and the nostrils almost as wide as a gorillas. These primates also have a flatter, more open face with a higher forehead than the chimpanzees and--to top it all off--an attractive coiffure with long, fine, black hair neatly parted in the middle.
Like chimpanzees, female bonobos nurse and carry around their young for up to five years. By the age of seven the offspring reach adolescence.
Wild females give birth for the first time at 13 or 14 years of age, becoming full grown by about A bonobos longevity is unknown, but judging by the chimpanzee it may be older than 40 in the wild and close to 60 in captivity.
Fruit is central to the diets of both wild bonobos and chimpanzees. The former supplement with more pith from herbaceous plants, and the latter add meat. Although bonobos do eat invertebrates and occasionally capture and eat small vertebrates, including mammals, their diet seems to contain relatively little animal protein. Unlike chimpanzees, they have not been observed to hunt monkeys.
Whereas chimpanzees use a rich array of strategies to obtain foods--from cracking nuts with stone tools to fishing for ants and termites with sticks--tool use in wild bonobos seems undeveloped. Captive bonobos use tools skillfully. Apparently as intelligent as chimpanzees, bonobos have, however, a far more sensitive temperament.
During World War II bombing of Hellabrunn, Germany, the bonobos in a nearby zoo all died of fright from the noise; the chimpanzees were unaffected. Bonobos are also imaginative in play. I have watched captive bonobos engage in blindmans buff. A bonobo covers her eyes with a banana leaf or an arm or by sticking two fingers in her eyes.
Thus handicapped, she stumbles around on a climbing frame, bumping into others or almost falling. She seems to be imposing a rule on herself: I cannot look until I lose my balance. Other apes and monkeys also indulge in this game, but I have never seen it performed with such dedication and concentration as by bonobos.
Juvenile bonobos are incurably playful and like to make funny faces, sometimes in long solitary pantomimes and at other times while tickling one another. Bonobos are, however, more controlled in expressing their emotions--whether it be joy, sorrow, excitement or anger--than are the extroverted chimpanzees.
Male chimpanzees often engage in spectacular charging displays in which they show off their strength: They keep up these noisy performances for many minutes, during which most other members of the group wisely stay out of their way. Male bonobos, on the other hand, usually limit displays to a brief run while dragging a few branches behind them. Both primates signal emotions and intentions through facial expressions and hand gestures, many of which are also present in the nonverbal communication of humans.
For example, bonobos will beg by stretching out an open hand or, sometimes, a foot to a possessor of food and will pout their lips and make whimpering sounds if the effort is unsuccessful.
But bonobos make different sounds than chimpanzees do. The renowned low-pitched, extended huuu-huuu pant-hooting of the latter contrasts with the rather sharp, high-pitched barking sounds of the bonobo.
I was particularly intrigued with the aftermath of conflict. After two chimpanzees have fought, for instance, they may come together for a hug and mouth-to-mouth kiss. Assuming that such reunions serve to restore peace and harmony, I labeled them reconciliations.
Any species that combines close bonds with a potential for conflict needs such conciliatory mechanisms. Thinking how much faster marriages would break up if people had no way of compensating for hurting one another, I set out to investigate such mechanisms in several primates, including bonobos.
Although I expected to see peacemaking in these apes, too, I was little prepared for the form it would take. For my study, which began in , I chose the San Diego Zoo.
At the time, it housed the worlds largest captive bo-nobo colony members divided into three groups. I spent entire days in front of the enclosure with a video camera, which was switched on at feeding time. As soon as a caretaker approached the enclosure with food, the males would develop erections. Even before the food was thrown into the area, the bonobos would be inviting each other for sex: Sex, it turned out, is the key to the social life of the bonobo.
The first suggestion that the sexual behavior of bonobos is different had come from observations at European zoos. Wrapping their findings in Latin, primatologists Eduard Tratz and Heinz Heck reported in that the chimpanzees at Hellabrunn mated more canum like dogs and bonobos more hominum like people. In those days, face-to-face copulation was considered uniquely human, a cultural innovation that needed to be taught to preliterate people hence the term missionary position. These early studies, written in German, were ignored by the international scientific establishment.
The bonobos humanlike sexuality needed to be rediscovered in the s before it became accepted as characteristic of the species. Bonobos become sexually aroused remarkably easily, and they express this excitement in a variety of mounting positions and genital contacts.
Although chimpanzees virtually never adopt face-to-face positions, bonobos do so in one out of three copulations in the wild. Furthermore, the frontal orientation of the bonobo vulva and clitoris strongly suggest that the female genitalia are adapted for this position. Another similarity with humans is increased female sexual receptivity.
The tumescent phase of the females genitals, resulting in a pink swelling that signals willingness to mate, covers a much longer part of estrus in bonobos than in chimpanzees. Instead of a few days out of her cycle, the female bonobo is almost continuously sexually attractive and active [see illustration on page 20].
Perhaps the bonobos most typical sexual pattern, undocumented in any other primate, is genito-genital rubbing or GG rubbing between adult females. One female facing another clings with arms and legs to a partner that, standing on both hands and feet, lifts her off the ground. The two females then rub their genital swellings laterally together, emitting grins and squeals that probably reflect orgasmic experiences. Laboratory experiments on stump-tailed macaques have demonstrated that women are not the only female primates capable of physiological orgasm.