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On the other hand, many gays are wary of the genetic hypothesis. It could, they fear, help promote the notion that gayness is a "defect" in need of "fixing." "Any finding will be used and twisted for homophobic purposes," says Martin Duberman, head of the Center for Lesbian and Gay Studies at the City University of New York. "If it does turn out that for some people, there is a genetic or hormonal component, the cry will then arise to take care of that." Indeed, the cry is already rising. The Rev. Louis P. Sheldon, president of the Traditional Values Coalition in Anaheim, California, says that if a biological cause of homosexuality is found, then "we would have to come up with some reparative therapy to correct that genetic defect."
No matter how people feel about the issue, it is increasingly hard to argue that genes play no role in homosexuality. The evidence began to pile up in 1991, when studies showed that identical twins were more likely to have the same sexual orientation than other pairs of siblings. That same year, a California scientist reported slight brain differences between gay and straight men, although the conclusion is disputed. And in 1993, an NIH researcher found a stretch of DNA on the X chromosome that seemed to harbor one or more genes affecting sexual orientation. But no one has proved that a particular gene promotes gayness or has offered any convincing theory of how genes could influence a person's choice of sleeping partners.
Odenwald and Zhang do not pretend to have any easy answers. In fact the type of gene they've been studying in fruit flies could not begin to account for the complex variations in human homosexual behavior. For one thing, the gene does not cause flies to renounce heterosexuality altogether. If a "gay" fly is surrounded by females instead of males, he'll fertilize the lady flies. So strictly speaking, the NIH flies are not homosexual but bisexual. And the gene produces no unusual behavior when transplanted into females: the scientists have produced no lesbian fruit flies.
Yet the way the gene works is intriguing, and may offer some clues to the biochemical roots of gayness. Surprisingly, the swatch of DNA in question was discovered long ago, and is one of the most thoroughly studied of all fruit-fly genes. It is called the "white" gene because, among many effects, it influences eye color, and a particular mutation in the gene causes a fly's normally red eyes to be white. The gene's specific job is to produce a protein that enables cells to utilize an essential amino acid called tryptophan. If fruit flies are unable to process tryptophan properly, then they cannot manufacture red eye pigment.