Sex: I had already seen an awful lot of it, and when I spotted that rhythmically swaying clot of torsos and limbs high in the trees, I thought I had stumbled across just one more loving couple. I pulled out the binoculars for a better look. My companion in the forest, Harvard University anthropologist and chimpanzee expert Richard Wrangham, did the same.

Chimpanzee sex is sometimes brutal, typically business-like, and invariably brief. But these weren't chimps Wrangham and I gazed at through our trembling tubes. These were bonobos, a separate though closely-related ape species, and I was excited to be witnessing an act that appeared just somehow different from the mating of chimpanzees. True, the male had positioned himself behind the female, very much in the chimpanzee style. Nevertheless, the whole act still seemed, in some not quite definable way, rather un-chimp-like. . . .

Only after the couple in the trees had finished and separated did I recognize just how un-chimp-like the behavior actually was. Both participants, I saw then, still had erect penises. And so what I had at first imagined to be a male-female event high in the trees, a pleasantly lingering heterosexual dalliance, turned out to be two males having a go at homosexual sex. They were too far away for either of us to observe any of the plumbing, but their position and movements suggested anal intercourse, or something close to it.

Sex between females we saw far more often, and it soon began to seem perfectly ordinary. For paired females, sex often takes place in the missionary position. One lies on the ground on her back, legs apart, inviting the other. Her partner moves on top. Face to face, eyes open, they embrace. With hips moving from side to side, they rub the sensitive tips of their large clitorises together, slowly at first but with an increasing intensity and frequency until, at last, they clutch and squeal and cry out, apparently reaching a pleasure-filled orgasm.

Sexual contact between females often takes the form of such front-to-front embracing and mutual clitoris-rubbing. Primatologist Takayoshi Kano, our host at the research site in D. R. Congo, and his Japanese colleagues describe this style of bonobo sex as genito-genital rubbing, an expression usually shortened to G-G rubbing. That's an excessively clinical way to speak of an obviously passionate activity. Wrangham and I one day asked two of Kano's field assistants, Norbert Batwafe and Ikenge Lokati, what their own people, the Mongandu, call this sexual act between bonobo females. Oh, they said, it's called hoka-hoka.

Sex between males? Sometimes males assume a quadrapedal stance and, oriented back to back, rub their bottoms and scrota together, an act the Japanese call rump-rubbing. Other times they will stroke or rub their penises together, and sometimes (this activity is reported only from Kano's site, so it might be a cultural invention among one population of bonobos) they will hang face-to-face from a tree branch while rubbing penises. It's a dramatic behavior dubbed penis-fencing. Males will also take the position I described above, the dorsal-ventral stance common in heterosexual copulation. Kano describes this as mounting, and he notes that both males may have erections during the event, although anal intercourse has never been confirmed.

Many people believe that sex done for purposes other than reproduction (such as, for recreation, exploration, pleasure, friendship, et cetera) is one more decisive mark of our own species' awesome (or troubling) uniqueness. Bonobos demonstrate the falseness of that belief.

Many people argue that human homosexuality is "immoral" because it's "unnatural." Bonobos suggest the weakness of that argument.

How widespread is homosexuality in the natural world? We can imagine there are rules defining human morality, but are there equivalent sorts of rules defining animal morality? If so, how do these rules happen? These questions can be asked . . . and reasonably answered. Stay tuned.

About the Author

Dale Peterson, Ph.D.

Dale Peterson, Ph.D., has written nearly a dozen books about conservation, natural history, and animal science and scientists.

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