Apes That Swing Many Ways

In a forest clearing near Wamba in equatorial Zaire, a group of bonobos, or pygmy chimpanzees, approaches a juicy stash of sugarcane laid out by Japanese researchers. As the animals draw near the sweets, they begin an astonishing series of sexual interactions. Some females embrace, rubbing their genitals against each other; males rub rumps, and sometimes briefly enter into what looks like mating. There is plenty of heterosexual sex too, as well as adult- infant encounters and enough mixing and matching to offend every puritanical sensibility. Scientists have observed similar orgies when bonobos converge on fig trees ripe with the sticky fruit.

This is not typical ape behavior. In similar situations, the bonobo’s cousin, the common chimpanzee, might engage in greetings and dominance interactions with far less libido in evidence. Why then do the bonobos launch into extended orgies of polymorphous perversity?

One feature of the bonobo’s forest environment offers a possible clue: fruit trees that produce an unusual abundance of food in a small area. This brings large numbers of bonobos into closer social contact than is typical for common chimpanzees. The presence of food can stimulate competition among the apes, and the larger the group the greater the danger of conflict. Frances White of Duke University argues that at these crucial times, sexual encounters reinforce bonds, particularly among females, helping individual apes to maintain access to food. Frans de Waal, the author of Chimpanzee Politics: Power and Sex Among Apes, believes the varied sex reduces tensions and fosters conciliation among these intensely social animals.

Bisexual behavior may serve a similar function for another highly intelligent mammal: the dolphin. “Sometimes male dolphins use homosexual sex to assert dominance over other males, and other times they use it in a friendly way, but always they are negotiating relationships,” says Richard Connor, a biologist at Woods Hole Oceanographic Institution.

With both dolphins and bonobos, however, bisexual behavior appears to be more ritualistic than erotic (quite often, male-male encounters do not lead to ejaculation). Thus such behavior may have little to do with sexual orientation. Instead it may be viewed as a counterpart of the ceremonial sex ; seen in some human cultures.