Shadows of Forgotten Ancestors

Or consider the bonobo. This is a reclusive species or subspecies of chimpanzee that lives in a single group in Central Africa, south of the Zaire River.¹⁸ Bonobos have certain traits that render them conventionally ineligible for the local zoo, which may be one reason that they’re not nearly so well known as the common chimp we’ve described in the preceding chapters. Bonobos, given the Linnaean name

Pan paniscus, are also called pygmy chimpanzees; they’re smaller and more slender and their faces protrude less than the usual variety, Pan troglodytes

, which we’ll here and there continue to describe simply as chimpanzees.* Bonobos often stand up and walk on two legs. (They have a kind of webbing of skin between their second and third toes.) They stride with their shoulders squared and do not slouch as much as chimps do. “When bonobos stand upright,” writes de Waal, “they look as if they had walked straight out of an artist’s impression of prehistoric man.”¹⁹

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

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

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

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