Is there a switch that turns you gay? That's the startling question raised again by a recent experiment in which scientists said they were able to turn on and off homosexual behavior in fruit flies.
Researchers at the University of Illinois at Chicago said they discovered what they call a "gender blind gene," or GB, in male fruit flies. A mutation in this GB gene spurred the males flies to start courting other males, as well as females.
When researchers strengthened neural synapses in the brain, the male flies were attracted, rather than repulsed, by the smell of other male flies.
"We put the males together, and they did to each other what they do when they're interested in a female: They approach her, sing her a song, lick her ... and mount her," researcher David Featherstone told ABCNEWS.com.
"They treated other males exactly the way they would treat other females. We put male flies in a chamber with males and females, and they were attracted to both with equal frequency."
In another recent study, researchers showed how they could alter the way female mice smell the the sexual secretions, or pheromones, of other mice, and turn them into "lesbian mice."
Both studies seem certain to bolster the growing scientific consensus that homosexuality is biological rather than learned. And they point to an answer to the lingering question of whether sexual orientation is hard-wired into the brain or whether it can be altered.
But both sides of the debate agree that just because fruit flies and mice can easily switch from straight to gay doesn't mean that it's that easy for humans to make the same transition.
"This shows that latent homosexual tendencies are there in all of us -- it's a matter of suppressing this synapse in the brain," said Axelrod. "Mice, flies it wouldn't surprise me in humans."
But smells are only one stimulus in the complicated dynamics of human sexuality.
"Humans use a variety of things: pornography, phone sex and cologne," said Axelrod. "And smell is not that strong a factor as it for fruit flies. If you took a guy and made him smell like a woman and even gave him a sexy high voice, it's not going to work."
Dr. Jeffrey Satinover, a controversial psychiatrist known for treating homosexuals who want to change their orientation, doubted that these results had implications for human sexuality.
"The truth is that a single gene in an animal as primitive as a fruit fly really says nothing at all about human beings," he said. "But in the current political environment, it gets translated by gay activists as 'voila, there must be the same gene in humans.'"
Satinover said that the genetic influence on homosexuality in human beings is weak. "Human sexuality is incredibly plastic," he said. "Under the right circumstances, people can be turned on by almost anything. You find temporary homosexuals in jail."
John Corvino, professor of philosophy at Wayne State University and the author of "Same Sex: Debating the Ethics, Science, and Culture of Homosexuality," is more interested in the study's moral implications.
"While science can tell us something about why we exhibit certain feelings and behaviors, it can't answer the moral question of what to do with them," Corvino told ABCNEWS.com in an e-mail. "Should we embrace them? Tolerate them? Change them? Because even if we could change people's sexual orientation, it doesn't follow that we should."