On a sweltering day in June 1997, a gay pride parade passed down Market Street, San Francisco. Among the thousands marching was Joan -- then Jonathan -- Roughgarden, a theoretical ecologist and marine biologist of some repute. A few months later, at 52, she underwent a sex change to become a transgendered woman. But that day was a turning point of a different sort.
"I was looking at all these people and realizing that my discipline said they weren't possible," she recalls. "Homosexuality is not supposed to exist, according to biology."
She did not know what the future held for her, but she resolved that if she managed to keep her job as a biology professor at Stanford University she would explore how widespread variation in gender and sexuality was in animals. She was forced to give up some administrative responsibilities and started to catalogue homosexuality in other species.
What she found astounded her. Studies document same-sex courtship rituals and mating in more than 300 species. Still more species have multiple genders, or exhibit gender reversal and hermaphroditism. Yet no one had collated them, no one had sought to explain this phenomenon.
"Biologists know there is a problem there, they know there is a lot of same-sex sexuality, and it is in the back of everyone's mind that we are going to have to deal with it at some point," she says.
The problem is that dealing with it means challenging the master text in biology: Darwin's theory of evolution. Or more precisely, the part on the selection of sexual characteristics. In her book Evolution's Rainbow, due out next March, Roughgarden asserts that Darwin's theory is "false and inadequate" and that there is no patching it up.
Her main point of contention is over Darwin's notion that females select males for show, because their showy secondary sexual characteristics -- the peacock's tail, for instance -- reflect good genes. Because eggs are supposed to be costly to produce and sperm cheap, this in turn has led to the stereotypical -- and, she believes, erroneous -- depiction of males as promiscuous and females as coy and discerning. That false message has been picked up by evolutionary biologists, says Roughgarden, but you only have to look at animal societies to see that it is not true.
Take Japanese macaques, whose females are promiscuously gay. During the breeding season, they form lesbian consortships as well as heterosexual pairings. Among bonobos -- the only primates apart from us to mate face-to-face -- most females indulge in lesbian behavior, rubbing their vulvas together, because, says Roughgarden, "If you did not do it, then you would not have any sisters. You would not have any buddies. It is absolutely necessary."
Bonobos perfectly illustrate the theory she offers up to replace Darwin's: social selection. According to this, much of the sexual behavior observed in animals is not designed to propagate genes, at least not directly, but to make the protagonist socially acceptable to a powerful clique, thus ensuring him or her access to potential mates and a safe environment.
The penis of the female spotted hyena is very similar to the male's, although it contains the urethra and birth canal. This she erects and flashes about to other females, says Roughgarden, to advertise her eligibility to join their gang.