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 few years many strands of
knowledge have come together concerning 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
anatomist, 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
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. satyrus--
which refers to the myth of apes as lustful satyrs--would
have been perfect 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 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 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 separation between
sex and reproduction.
A Near Relative
This finding commands attention because the bonobo shares
more than 98 percent of our genetic profile, making it as
close to a human as, say, a fox is to a dog. 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 chimpanzee's need to adapt to relatively
open, dry habitats [see "East Side Story: The Origin of
Humankind," by Yves Coppens; SCIENTIFIC AMERICAN, May 1994].
In contrast, bonobos probably never left the protection of
the trees. Their present range lies in humid forests south
of the Zaire River, where perhaps fewer than 10,000 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 1930s 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,
since its anatomy is less specialized than is the
chimpanzee's. 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 artist's impression of early
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
1970s, 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:
male superiority remained the natural state of affairs. 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.
Enter the bonobo. 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.
In physique, a bonobo is as different from a chimpanzee as a
Concorde is from a Boeing 747. 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 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 females 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 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 Hellabrun, Germany, the bonobos in a nearby
zoo all died of fright from the noise; the chimpanzees were
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 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: throwing rocks, breaking branches and uprooting
small trees in the process. 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.
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. 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
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 each other, 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 1983, I chose the San Diego
Zoo. At the time, it housed the world's largest captive
bonobo 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 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 1954 that the
chimpanzees at Hellabrun 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 bonobo's humanlike sexuality
needed to be rediscovered in the 1970s 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
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 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
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, 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.)
Male bonobos, too, may engage in pseudocopulation but
generally perform 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 penises together.
The diversity of erotic contacts in bonobos includes
sporadic oral sex, massage of another individual's genitals
and intense tongue-kissing. Lest this leave the impression
of a pathologically oversexed species, I must add, based on
hundreds of hours of watching 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 engage in sex only occasionally, not continuously.
Furthermore, with the average copulation lasting 13 seconds,
sexual contact in bonobos is rather quick by human
That sex is connected to feeding, and even appears to make
food sharing possible, 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
Zaire's Lomako Forest engage in sex after they had entered
trees loaded with ripe figs or when one among them had
captured a prey animal, 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 activity at feeding time
could be that excitement over food translates into sexual
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 sexual
contact. If two bonobos approach a cardboard box thrown into
their enclosure, they will briefly mount each other before
playing with the box. Such situations lead to squabbles in
most other species. But bonobos are quite tolerant, perhaps
because they use sex to divert attention and to diffuse
Second, bonobo sex often occurs in aggressive contexts
totally unrelated to food. A jealous male might chase
another 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 immediately 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 uttered a sharp peep and stayed put. Then
Leslie rubbed her vulva against his shoulder. 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 behavior is
indistinguishable from social behavior. Given its
peacemaking and appeasement functions, it is not surprising
that sex among bonobos occurs in so many different partner
combinations, including between juveniles and adults. The
need for peaceful coexistence is obviously not restricted to
adult heterosexual pairs.
Apart from maintaining harmony, sex is also involved in
creating the singular 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-1970s,
more than a decade after the most important studies on wild
chimpanzees had been initiated. In terms of continuity and
invested (wo)manpower, the chimpanzee projects of Jane
Goodall and Toshisada Nishida, both in Tanzania, are
unparalleled. But bonobo research by Takayoshi Kano and
others of Kyoto University is now two decades under way at
Wamba in Zaire and is beginning to show the same payoffs.
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 composition 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
Initially this flexibility baffled investigators, making
them wonder if these apes formed any social groups with
stable membership. After years of documenting the travels of
chimpanzees in the Mahale Mountains, Nishida first reported
that they form large communities: all members of one
community mix freely in ever changing parties, but members
of different communities never gather. Later, Goodall added
territoriality to this picture. That is, not only do
communities not mix, but males of different chimpanzee
communities engage in lethal battles.
In both bonobos and chimpanzees, males stay in their natal
group, whereas females tend to migrate during adolescence.
As a result, the senior males of a chimpanzee or bonobo
group have known all junior males since birth, and all
junior males have grown up together. 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 single out one or two senior resident females for
special attention, using frequent GG rubbing and grooming to
establish a relation. If the residents reciprocate, close
associations are set up, and the younger female gradually
becomes accepted into the group. After producing her first
offspring, the young female's position becomes more stable
and central. Eventually the cycle repeats 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 dependent
on them for protection in aggressive 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 battles, often relying on the support of other
males. Furthermore, adult male chimpanzees travel together
in same-sex parties, grooming each other frequently. Males
form a distinct social hierarchy with high levels of both
competition and association. Given the need to stick
together against males of neighboring communities, their
bonding 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 considerably fewer males than
Serious conflict between bonobo groups has been witnessed in
the field, but it seems quite rare. On the contrary, reports
exist of peaceable mingling, including mutual sex and
grooming, between what appear to be different communities.
If intergroup combat is indeed unusual, it may explain the
lower rate of all-male associations. Rather than being male-
bonded, bonobo society gives the impression of being female-
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 monkeys, such as macaques and
baboons, where males are the migratory sex.
Bonobos are unique in that the migratory sex, females,
strongly bond with same-sex strangers later in life. In
setting up an artificial sisterhood, bonobos can be said to
be secondarily bonded. (Kinship bonds are said to be
primary.) Although we now know HOW this happens--through the
use of sexual contact and grooming--we do not yet know WHY
bonobos and chimpanzees differ in this respect. The answer
may lie in the different ecological environments of bonobos
and chimpanzees--such as the abundance and quality of food
in the forest. But it is uncertain if such explanations will
Bonobo society is, however, not only female-centered but
also appears to be female-dominated. Bonobo specialists,
while long suspecting such a reality, have been reluctant to
make the controversial claim. But in 1992, at the 14th
Congress of the International Primatological Society in
Strasbourg, investigators of both captive and wild bonobos
presented data that left little doubt about the issue.
Amy R. Parish of the University of California at Davis
reported on food competition in identical groups (one adult
male and two adult females) of chimpanzees and bonobos at
the Stuttgart Zoo. Honey was provided in a "termite hill"
from which it could be extracted by dipping sticks into a
small hole. As soon as honey was made available, the male
chimpanzee would make a charging display through the
enclosure and claim everything for himself. Only when his
appetite was satisfied would he let the females fish for
In the bonobo group, it was the females that approached the
honey first. After having engaged in some GG rubbing, they
would feed together, taking turns with virtually no
competition between 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, reported
similar findings. If a male bonobo tried to harass a female,
all females would band together to chase him off. Because
females appeared more successful 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 zoologist Takeshi Furuichi's summary of the
relation between the sexes at Wamba, 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.
Occasionally, the role of sex in relation 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 reproduction in our species because it serves
to cement mutually profitable relationships between men and
women. The human female's capacity to mate throughout her
cycle and her strong sex drive allow her to exchange sex for
male commitment and paternal care, thus giving rise to the
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 elements 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 attractive state, she would not hesitate to
approach 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 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 families.
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 ancestors started out with a sex life
similar to that of bonobos, the evolution of the family
would have required dramatic 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 society lacks any such guarantee, but
humans protect the integrity of their family units through
all kinds of moral restrictions and taboos. Thus, although
our species is characterized by an extraordinary 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 behavioral peculiarities may
help us understand the role of sex and may have serious
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 societies, 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 chimpanzees or even on bonobos but on a
three-way comparison of chimpanzees, bonobos and humans.
Social Organization among Various Primates
- Bonobo communities are peace-loving and generally
egalitarian. The strongest social bonds are those among
females, although females also bond with males. The status
of a male depends on the position of his mother, to whom he
remains closely bonded for her entire life.
- 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 or to any one male.
- Gibbons establish monogamous, egalitarian relations, and one
couple will maintain a territory to the exclusion of other
- Human society is the most diverse among the primates. Males
unite for cooperative ventures, whereas females also bond
with those of their own sex. Monogamy, polygamy and
polyandry are all in evidence.
- The social organization of gorillas provides a clear example
of polygamy. 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.
- Orangutans live solitary lives with little bonding in
evidence. Male orangutans are intolerant of one another. In
his prime, a single male establishes a large territory,
within which live several females. Each female has her own,
separate home range.
FRANS B. M. de WAAL was trained as an ethologist in the
European tradition, receiving his Ph.D. from the University
of Utrecht in 1977. After a six-year study of the chimpanzee
colony at the Arnhem Zoo, he moved to the U.S. in 1981 to
work on other primate species, including bonobos. He is now
a research professor at the Yerkes Regional Primate Research
Center in Atlanta and professor of psychology at Emory
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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
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University Press, 1989.
- 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. R. Wrangham, W. C. McGrew, F.B.M. de
Waal and P. Heltne. Harvard University Press, 1994.