Bonobo_Sex_and_Society - 14 SCIENTIFIC AMERICAN...

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Unformatted text preview: 14 SCIENTIFIC AMERICAN “0&3 zodo BECOMING HUMAN FRANS LANTING Minden Pictures The behavior of a close relative challenges assumptions t 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 dis- covery that females play a central, per- haps 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 con- cerning a relatively unknown ape with an unorthodox repertoire of behavior: the bonobo. The bonobo is one of the last large mammals to be found by science. The creature was discovered in 1929 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 juve- nile 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 dis- tinct species within the same genus as the chimpanzee, Pan. The bonobo was officially classified as Pan paniscus, or the diminutive Pan. ButI believe a different label might have been selected had the discoverers known then what we know now. The old taxo- nomic name of the chimpanzee, P. sa- tyrus—which refers to the myth of apes as lustful satyrs—would have been per- fect for the bonobo. 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 BONUBD FEMALE interacts with an infant. Juvenile bonobos depend on their mothers for milk and transport for up to five years. They are extremely well tolerated by adults, who have rarely been seen to attack or threaten them. www.sciam.com about male supremacy in human evolution relations—and not just between males and females. Bonobos engage in sex in virtually every partner combination (al- though such contact among close fam- ily members may be suppressed). And sexual interactions occur more often among bonobos than among other pri- mates. Despite the frequency of sex, the bonobo’s 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 sepa— ration between sex and reproduction. A Near Relative T HIS F I N D I N G commands attention because the bonobo shares more than 98 percent of our genetic profile, mak- ing it as close to a human as, say, a fox is to a dog. The split between the hu- man 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 chimpanzee’s need to adapt to rela— tively open, dry habitats. In contrast, bonobos probably nev- er left the protection of the trees. Their present range lies in humid forests south of the Congo River, where perhaps few- er than 10,000 bonobos survive. (Given the species’ slow rate of reproduction, the rapid destruction of its tropical hab- itat and the political instability of cen- tral Africa, there is reason for much concern about its future.) If this evolutionary scenario of eco- logical continuity is true, the bonobo may have undergone less transforma- tion than either humans or chimpan- zees. It could most closely resemble the common ancestor of all three modern species. Indeed, in the 19303 Harold]. Coolidge—the American anatomist who gave the bonobo its eventual taxo- nomic status—suggested that the ani- mal might be most similar to the pri- mogenitor, because its anatomy is less specialized than is the chimpanzee’s. Bonobo body proportions have been compared with those of the australopith— ecines, a form of prehuman. When the apes stand or walk upright, they look as if they stepped straight out of an art- ist’s impression of early hominids. Not too long ago the savanna ba- boon was regarded as the best living model of the human ancestor. That primate is adapted to the kinds of eco- logical conditions that prehumans may have faced after descending from the trees. But in the late 19705 chimpan— zees, which are much more closely re- lated 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 rec- ognize themselves in a mirror, a sign of self-awareness not yet demonstrat- ed 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: male superiority remained the natural state of affairs. In both baboons and chimpanzees, males are conspicuously dominant over fe- males; they reign supremely and often brutally. It is highly unusual for a fully grown male chimpanzee to be domi- nated by any female. Enter the bonobo. Despite their common name—the pygmy chimpan- zee—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 bono- bos. Although female bonobos are much smaller than the males, they seem to rule. SCIENTIFIC AMERICAN 15 Graceful Apes IN PHYS I QUE , a bonobo is as different from a chimpanzee as a Concorde is from a Boeing 747. I do not wish to of- fend 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 red- dish in a black face, the ears small and the nostrils almost as wide as a gorilla’s. These primates also have a flatter, more open face with a higher forehead than the chimpanzee’s 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 fe— males give birth for the first time at 13 or 14 years of age, becoming full grown by about 15. A bonobo’s longevity is unknown, but judging by the chimpan- zee 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 inver- tebrates and occasionally capture and eat small vertebrates, including mam- mals, their diet seems to contain rela— tively little animal protein. Unlike chimpanzees, they have not been ob- served to hunt monkeys. Whereas chimpanzees use a rich ar— ray of strategies to obtain foods—from cracking nuts with stone tools to fish- ing for ants and termites with sticks— tool use in wild bonobos seems unde- veloped. (Captive bonobos use tools skillfully.) Apparently as intelligent as chimpanzees, bonobos have, however, a far more sensitive temperament. Dur- ing World War II bombing of Hella— brunn, Germany, the bonobos in a near- mate Behavior at Emory University. 16 SCIENTIFIC AMERICAN FRANS B. M. DE WAAL was trained as an ethologist in the European tradition, receiving his Ph.D. from the University of Utrecht in the Netherlands in 197?. After a six-year study ofthe chimpanzee colony atthe Arnhem Zoo, he moved to the US. in 1981 to work on other primate species, including bonobos. He is now director of Living Links at the Yerkes National Primate Research Center in Atlanta and C. H. Candler Professor of Pri- Gorilla Chimp 10 16 22 Millions onears Ago Bonobo Human HUMANS AND APES Baboon Macaque Orangutan OLD WORLD MONKEYS EVOLUTIONARY TREE ofprimates, based on DNA analysis, shows that humans diverged from bonobos and chimpanzees a mere eight million years ago. The three species share more than 98 percent oftheir genetic makeup. by 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 “blindman’s 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 can- not look until I lose my balance.” Oth- er apes and monkeys also indulge in this game, but I have never seen it per- formed with such dedication and con- centration 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 emo— tions—whether it be joy, sorrow, excite- ment or anger—than are the extrovert— ed chimpanzees. Male chimpanzees often engage in spectacular charging displays in which they show off their strength: throwing rocks, breaking branches and uprooting small trees in the process. They keep up these noisy performances for many minutes, dur— ing 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 drag— ging 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 commu- nication of humans. For example, bono- bos will beg by stretching out an open hand (or, sometimes, a foot) to a pos- sessor of food and will pout their lips and make whimpering sounds if the ef— fort is unsuccessful. But bonobos make different sounds than chimpanzees do. The renowned low-pitched, extended “huuu—huuu” pant—booting of the latter contrasts with the rather sharp, high- pitched barking sounds of the bonobo. Love, Not War MY OWN INTEREST in bonobos came not from an inherent fascination with their charms but from research on aggressive behavior in primates. Iwas particularly intrigued with the after— math of conflict. After two chimpan— zees have fought, for instance, they may come together for a hug and mouth-to- mouth kiss. Assuming that such re— unions serve to restore peace and har- BECOMING HUMAN LAURIE GRACE 1N LAURIE GRACE LAURIE GRACE mony, 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 peacemak- ing in these apes, too, I was little pre- pared for the form it would take. For my study, which began in 1983, I chose the San Diego Zoo. At the time, it housed the world’s largest captive bo- nobo colony—10 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: males would invite females, and females would invite males and other females. Sex, it turned out, is the key to the social life of the bonobo. The first sug- gestion that the sexual behavior of bonobos is different had come from ob— servations at European zoos. Wrapping their findings in Latin, primatologists Eduard Tratz and Heinz Heck reported in 1954 that the chimpanzees at Hel— labrunn mated more canum (like dogs) and bonobos more hominum (like peo- ple). In those days, face-to-face copula- tion 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 bonobo’s human- like sexuality needed to be rediscovered in the 19708 before it became accepted as characteristic of the species. Bonobos become sexually aroused remarkably easily, and they express this excitement in a variety of mount- ing positions and genital contacts. Al- SOCIAL ORGANIZATION AMONG VARIOUS PRIMATES BONOBO “‘fl. Bonobo communities are peace-loving and generally egalitarian. The strongest social bonds [blue lines] are those among females {green}, although females also bond with males. The status ofa male [gray] depends on the position ofhis mother. to whom he remains closely bonded for her entire life. CHIMPANZEE M‘M‘ifl In chimpanzee groups the strongest bonds are established between the males in order to hunt and to protect their shared territory. The females live in overlapping home ranges within this territory but are not strongly bonded to other females orto any one male. www.sciam.com GIBBON Gibbons establish monogamous, egalitarian relations, and one couple will maintain a territoryto the exclusion ofother pairs. 1 ,.." 15W. . “.1;er ! m”; mu“; Human society is the most diverse amongthe primates. Males unite for cooperative ventures, whereas females also bond with those oftheir own sex. Monogamy, polygamy and polyandry are all in evidence. GORILLA The social organization of gorillas provides a clear example ofpolygamy. Usually a single male maintains a range for his family unit, which contains several females. The strongest bonds are those between the male and his females. ORANGUTAN Orangutans live solitary lives with little bonding in evidence. Male orangutans are intolerant ofone another. In his prime, 3 single male establishes a large territory, within which live several females, Each female has her own, separate home range. SCIENTIFIC AMERICAN 1? BONOBD DUMINA'NCE BY BONDING is evinced by female bonobos, who engage in genito-genital [GG] rubbing before eating sugarcane [a], while a bigger male displays to no avail.The females then share the food without competition [b]. Only when they leave can the male get to the sugarcane [c]. In male-dominated chimpanzee society the male eats first [d], while the females wait at a safe distance. After he leaves [e], carrying as many bananas as he can, the dominant female gets what is left (f). Small amounts of sugarcane and bananas are provided at some research sites in the Democratic Republic ofthe Congo [formerly Zaire). though chimpanzees virtually never adopt face-to-face positions, bonobos do so in one out of three copulations in the wild. Furthermore, the frontal ori- entation of the bonobo vulva and clito- ris 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 female’s genitals, resulting in a pink swelling that signals willingness to mate, covers a much lon— ger 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 ac- tive [see illustration on page 20]. Perhaps the bonobo’s 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, emit— ting grins and squeals that probably re— flect orgasmic experiences. (Laboratory experiments on stump-tailed macaques have demonstrated that women are not the only female primates capable of physiological orgasm.) Male bonobos, too, may engage in pseudocopulation but generally per- 18 SCIENTIFIC AMERICAN form a variation. Standing back to back, one male briefly rubs his scrotum against the buttocks of another. They also practice so-called penis-fencing, in which two males hang face to face from a branch while rubbing their erect pe— nises together. The diversity of erotic contacts in bonobos includes sporadic oral sex, massage of another individual’s geni- tals and intense tongue—kissing. Lest this leave the impression of a patholog— ically oversexed species, I must add, based on hundreds of hours of watch- ing bonobos, that their sexual activity is rather casual and relaxed. It appears to be a completely natural part of their group life. Like people, bonobos en- gage in sex only occasionally, not con- tinuously. Furthermore, with the aver— age copulation lasting 13 seconds, sex- ual contact in bonobos is rather quick by human standards. That sex is connected to feeding, and even appears to make food sharing pos— sible, has been observed not only in zoos but also in the wild. Nancy Thompson— Handler, then at the State University of New York at Stony Brook, saw bonobos in the Lomako Forest of the Democratic Republic of the Congo (formerly Zaire) engage in sex after they had entered trees loaded with ripe figs or when one among them had captured a prey ani— mal, such as a small forest duiker. The flurry of sexual contacts would last for five to 10 minutes, after which the apes would settle down to consume the food. One explanation for the sexual ac- tivity at feeding time could be that ex— citement over food translates into sexu— al arousal. This idea may be partly true. Yet another motivation is probably the real cause: competition. There are two reasons to believe sexual activity is the bonobo’s answer to avoiding conflict. First, anything, not just food, that arouses the interest of more than one bonobo at a time tends to result in sex— ual contact. If two bonobos approach a cardboard box thrown into their enclo- sure, they will briefly mount each other before playing with the box. Such situ- ations lead to squabbles in most other species. But bonobos are quite tolerant, perhaps because they use sex to divert attention and to diffuse tension. Second, bonobo sex often occurs in aggressive contexts totally unrelated to food. A jealous male might chase an- other away from a female, after which the two males reunite and engage in scrotal rubbing. Or after a female hits a juvenile, the latter’s mother may lunge at the aggressor, an action that is im— mediately followed by genital rubbing between the two adults. I once observed a young male, Kako, inadvertently blocking an older, female juvenile, Leslie, from moving along a branch. First, Leslie pushed him; Kako, who was not very confident in trees, tightened his grip, grinning nervously. Next Leslie gnawed on one of his hands, presumably to loosen his grasp. Kako ut- BECOMINE HUMAN ~n x" \f \‘l 16. IO 16 at 1e :x- l a lo— er 61' 1t, rt SUZANNE BARNES CHIMPANZEE tered a sharp peep and stayed put. Then Leslie rubbed her vulva against his shoul- der. This gesture calmed Kako, and he moved along the branch. It seemed that Leslie had been very close to using force but instead had reassured both herself and Kako with sexual contact. During reconciliations, bonobos use the same sexual repertoire as they do during feeding time. Based on--an analysis of many such incidents, my study yielded the first solid evidence for sexual behavior as a mechanism to overcome aggression. Not that this function is absent in other animals—or in humans, for that matter—but the art of sexual reconciliation may well have reached its evolutionary peak in the bonobo. For these animals, sexual be- havior is indistinguishable from social behavior. Given its peacemaking and appeasement functions, it is not sur- prising that sex among bonobos occurs in so many different partner combina- tions, including between juveniles and adults. The need for peaceful coexis- tence is obviously not restricted to adult heterosexual pairs. Female Alliance A PA RT F R0 M maintaining harmony, sex is also involved in creating the singu- lar social structure of the bonobo. This use of sex becomes clear when studying bonobos in the wild. Field research on bonobos started only in the mid-19703, a decade after the most important stud- ies on wild chimpanzees had been initi— ated. In terms of continuity and invest- ed (wo)manpower, the chimpanzee projects of Jane Goodall and Toshisada www.5ciam.com Nishida, both in Tanzania, are unparal- leled. But bonobo research by Taka- yoshi Kano and others of Kyoto Univer- sity began to show the same payoffs after two decades at Wamba in the Democratic Republic of the Congo. Both bonobos and chimpanzees live in so-called fission-fusion societies. The apes move alone or in small parties of a few individuals at a time, the com- position of which changes constantly. Several bonobos traveling together in the morning might meet another group in the forest, whereupon one individual from the first group wanders off with others from the second group, while those left behind forage together. All associations, except the one between mother and dependent offspring, are of a temporary character. Initially this flexibility baffled in- vestigators, making them wonder if these apes formed any social groups with stable membership. After years of documenting the travels of chimpan- zees in the Mahale Mountains, Nishida first reported that they form large com- munities: all members of one commu- nity mix freely in ever changing parties, but members of different communities never gather. Later, Goodall added ter— ritoriality to this picture. That is, not only do communities not mix, but males of different chimpanzee commu- nities engage in lethal battles. In both bonobos and chimpanzees, males stay in their natal group, whereas females tend to migrate during adoles- cence. As a remit, the senior males of a chimpanzee or bonobo group have known all junior males since birth, and all junior males have grown up togeth- er. Females, on the other hand, transfer to an unfamiliar and often hostile group where they may know no one. A chief difference between chimpanzee and bonobo societies is the way in which young females integrate into their new community. On arrival in another community, young bonobo females at Wamba sin- gle out one or two senior resident fe- males for special attention, using fre- quent GG rubbing and grooming to establish a relation. If the residents re- ciprocate, close associations are set up, and the younger female gradually be- comes accepted into the group. After producing her first offspring, the young female’s position becomes more stable and central. Eventually the cycle re- peats with younger immigrants, in turn, seeking a good relation with the now established female. Sex thus smooths the migrant’s entrance into the community of females, which is much more close-knit in the bonobo than in the chimpanzee. Bonobo males remain attached to their mothers all their lives, following them through the forest and being de- pendent on them for protection in ag- gressive encounters with other males. As a result, the highest-ranking males of a bonobo community tend to be sons of important females. What a contrast with chimpanzees! Male chimpanzees fight their own bat- tles, often relying on the support of other males. Furthermore, adult male chimpanzees travel together in same- sex parties, grooming one another fre- SCIENTlFlC AMERICAN 19 quently. Males form a distinct social hierarchy with high levels of both com- petition and association. Given the need to stick together against males of neighboring communities, their bond- ing is not surprising: failure to form a united front might result in the loss of lives and territory. The danger of being male is reflected in the adult sex ratio of chimpanzee populations, with consid- erably fewer males than females. Serious conflict between bonobo groups has been witnessed in the field, but it seems quite rare. On the contrary, reports exist of peaceable mingling, in- cluding mutual sex and grooming, be— tween what appear to be different com- munities. If intergroup combat is in- deed unusual, it may explain the lower rate of all-male associations. Rather than being male-bonded, bonobo soci— ety gives the impression of being fe— male-bonded, with even adult males relying on their mothers instead of on other males. No wonder Kano calls mothers the “core” of bonobo society. The bonding among female bonobos violates a fairly general rule, outlined by Harvard University anthropologist Richard W. Wrangham, that the sex that stays in the natal group develops the strongest mutual bonds. Bonding among male chimpanzees follows naturally because they remain in the community of their birth. The same is true for female kinship bonding in Old World mon- keys, such as macaques and baboons, O Extent of Swelling 0 16 32 where males are the migratory sex. Bonobos are unique in that the mi- gratory sex, females, strongly bond with same-sex strangers later in life. In setting up an artificial sisterhood, bono— bos can be said to be secondarily bond- ed. (Kinship bonds are said to be pri- mary.) Although we now know how this happens——through the use of sexu- al contact and grooming—we do not yet know why bonobos and chimpan- zees differ in this respect. The answer may lie in the different ecological envi— ronments of bonobos and chimpan- zees—such as the abundance and qual- ity of food in the forest. But it is uncer- tain if such explanations will suffice. Bonobo society is, however, not only female—centered but also appears to be female-dominated. Bonobo spe- cialists, while long suspecting such a reality, had been reluctant to make the controversial claim. But in 1992, at the 14th Congress of the International Pri— matological Society in Strasbourg, in- vestigators of both captive and wild bonobos presented data that left little doubt about the issue. Amy R. Parish of the University of California, Davis, reported on food competition in identical groups (one adult male and two adult females) of chimpanzees and bonobos at the Stutt- gart Zoo. Honey was provided in a “termite hill” from which it could be ex- tracted by dipping sticks into a small hole. As soon as honey was made avail— 48 54 80 96 Days Ii Menstruation FEMALE RECEPTlVlTY for sex, manifested by swollen genitals, occupies a much larger proportion ofthe estrus cycle ofbonobos [top] than ofchimpanzees [bottom]. The receptivity of bonobos continues through lactation. {in chimpanzees, it disappears] This circumstance allows sex to play a large part in the social relations ofbonobos. The graph was provided by Jeremg Dahl of the Yerkes National Primate Research Center. 20 SCIENTIFIC AMERICAN able, the male chimpanzee would make a charging display through the enclo- sure and claim everything for himself. Only when his appetite was satisfied would he let the females fish for honey. In the bonobo group, it was the fe- males that approached the honey first. After having engaged in some GG rub- bing, they would feed together, taking turns with virtually no competition be- tween them. The male might make as many charging displays as he wanted; the females were not intimidated and ignored the commotion. Observers at the Belgian animal park of Planckendael, which currently has the most naturalistic bonobo colony, re- ported similar findings. If a male bono- bo tried to harass a female, all females would band together to chase him off. Because females appeared more success- ful in dominating males when they were together than on their own, their close association and frequent genital rubbing may represent an alliance. Females may bond so as to outcompete members of the individually stronger sex. The fact that they manage to do so not only in captivity is evident from zo- ologist Takeshi Furuichi’s summary of the relation between the sexes at Wam— ba, where bonobos are enticed out of the forest with sugarcane. “Males usually appeared at the feeding site first, but they surrendered preferred positions when the females appeared. It seemed that males appeared first not because they were dominant, but because they had to feed before the arrival of females,” Furuichi reported at Strasbourg. Sex f or Foo d OCCASIONALLY, the role ofsex in re- lation to food is taken one step further, bringing bonobos very close to humans in their behavior. It has been speculated by anthropologists—including C. Owen Lovejoy of Kent State University and Helen Fisher of Rutgers University—that sex is partially separated from repro- duction in our species because it serves to cement mutually profitable relation- ships between men and women. The hu- man female’s capacity to mate through- out her cycle and her strong sex drive BECOMING HUMAN LAURIE GRACE um .v. bar‘— a! :- “stagnant-ma a... —_~=e- .- LAURIE GRACE FRANS LANTING Minden Pictures [top left and lop right; bottom left); MARTIN HARVEY PeterArnald, Inc. [bottom right] BEHAVIOR among bonobos is often reminiscent ofthat among humans. A female and an infant play [top left}; a bonobo walks upright, using his hands to carry food [top right]; twojuveniles practice sex without penetration [bottom left}; and a male and female have sexwhile facing each other [bottom right]. a position once thought to be uniquely human. allow her to exchange sex for male com- mitment and paternal care, thus giving rise to the nuclear family. 'This arrangement is thought to be favored by natural selection because it allows women to raise more offspring than they could if they were on their own. Although bonobos clearly do not establish the exclusive heterosexual bonds characteristic of our species, their behavior does fit important ele- ments of this model. A female bonobo shows extended receptivity and uses sex to obtain a male’s favors when— usually because of youth—she is too low in social status to dominate him. At the San Diego Zoo, I observed that if Loretta was in a sexually attrac- tive state, she would not hesitate to ap- proach the adult male, Vernon, if he had food. Presenting herself to Vernon, she would mate with him and make high— pitched food calls while taking over his entire bundle of branches and leaves. When Loretta had no genital swelling, she would wait until Vernon was ready www.sciam.com to share. Primatologist Suehisa Kuroda reports similar exchanges at Wamba: “A young female approached a male, who was eating sugarcane. They copulated in short order, whereupon she took one of the two canes held by him and left.” Despite such quid pro quo between the sexes, there are no indications that bonobos form humanlike nuclear fam- ilies. The burden of raising offspring appears to rest entirely on the female’s shoulders. In fact, nuclear families are probably incompatible with the diverse use of sex found in bonobos. If our an- cestors started out with a sex life simi- lar to that of bonobos, the evolution of the family would have required dra— matic change. Human family life implies paternal investment, which is unlikely to develop unless males can be reasonably certain that they are caring for their own, not someone else’s, offspring. Bonobo soci- ety lacks any such guarantee, but hu- mans protect the integrity of their fam- ily units through all kinds of moral re— strictions and taboos. Thus, although our species is characterized by an ex- traordinary interest in sex, there are no societies in which people engage in it at the drop of a hat (or a cardboard box, as the case may be). A sense of shame and a desire for domestic privacy are typical human concepts related to the evolution and cultural bolstering of the family. Yet no degree of moralizing can make sex disappear from every realm of human life that does not relate to the nuclear family. The bonobo’s behav- ioral peculiarities may help us under- stand the role of sex and may have seri- ous implications for models of human society. Just imagine that we had never heard of chimpanzees or baboons and had known bonobos first. We would at present most likely believe that early hominids lived in female-centered soci- eties, in which sex served important social functions and in which warfare was rare or absent. In the end, perhaps the most successful reconstruction of our past will be based not on chimpan- zees or even on bonobos but on a three- way comparison of chimpanzees, bo- nobos and humans. The Pygmy Chimpanzee: Evolutionary Biology and Behavior. Edited by Randall L. Susman. Plenum Press, 1984. The Communicative Repertoire of Captive Bonobos [Pan paniscus] Compared to That of Chimpanzees. F.B.M. de Waal in Behaviour, Vol. 106, Nos. 3—4. pages 183-251; September 1988. Understanding Chimpanzees. Edited by Paul Heltne and Linda A. Marquardt. Harvard University Press, 1989. The Last Ape: Pygmy Chimpanzee Behavior and Ecology. Takayoshi Kano.Stanford University Press, 1992. Chimpanzee Cultures. Richard Wrangham,W. C. McGrew, Frans B. M. de Waal and Paul Heltne. Harvard University Press, 1994. Bonobo: The Forgotten Ape. Frans B. M. de Waal, with photographs by Frans Lanting. University of California Press, 1996. SCIENTIFIC AMERICAN ...
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