More recently, some researchers studying bonobos (close relatives of the chimpanzee) have come to similar conclusions. Bonobos are highly promiscuous, and about half their sexual activity involves same-sex partners. Female bonobos rub one another’s genitals so often that some scientists have suggested that their genitalia evolved to facilitate this activity. The female bonobo’s clitoris is  “frontally placed, perhaps because selection favored a position maximizing stimulation during the genital-genital rubbing common among females,” wrote behavioral ecologist Marlene Zuk of the University of California, Riverside, in her 2002 book Sexual Selections: What We Can and Can’t Learn about Sex from Animals. Male bonobos have been observed to mount, fondle and even perform oral sex on one another.

Such behavior seems to ease social tensions. In Bonobo: The Forgotten Ape (University of California Press, 1997), Emory University primatologist Frans B. M. de Waal and his co-author photographer Frans Lanting wrote that “when one female has hit a juvenile and the juvenile’s mother has come to its defense, the problem may be resolved by intense GG-rubbing between the two adults.” De Waal has observed hundreds of such incidents, suggesting that these homosexual acts may be a general peacekeeping strategy. “The more homosexuality, the more peaceful the species,” asserts Petter Böckman, an academic adviser at the University of Oslo’s Museum of Natural History in Norway. “Bonobos are peaceful.”

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