Heterosexual women have noisy ears.

Faint, echolike noises generated by the inner ear are louder in heterosexual women than in homosexual or bisexual women, report researchers from the University of Texas at Austin. This finding suggests that some regions of homosexual and bisexual women's brains are different from those of heterosexual women, says neuroscientist Dennis McFadden.

McFadden postulates that differences may also exist in parts of the brain responsible for sexual orientation. The idea that structures in the brain determine sexual destiny is controversial, however (SN: 8/10/96, p. 88).

"This field has a long history of findings that were initially welcomed into the canon but subsequently discredited by their inability to be replicated," says William Byne of Mount Sinai School of Medicine in New York. "Until one of these studies, including McFadden's, is successfully replicated by an independent lab, I will remain skeptical."

McFadden and Edward G. Pasanen analyzed noises, known as click-evoked otoacoustic emissions, that people's ears make in response to brief sounds. The emissions, present from birth, are generally stronger in women and, barring damage to the ear, retain a characteristic strength throughout life, McFadden says. To measure the noises, he and Pasanen insert a small microphone into each person's outer ear, send a series of clicks into the ear, and record the ear's reply They present their findings in the March 3 Proceedings of the National Academy of Sciences.

The researchers tested the otoacoustic emissions of 237 college-age men and women. The scientists found no differences between heterosexual and homosexual or bisexual men. In contrast, the 57 heterosexual women's ears made significantly louder sounds, on average, than those of the 61 homosexual or bisexual women. McFadden cautions that the groups overlap, so "it would not be possible to predict the sexual orientation of someone by simply measuring otoacoustic emissions."

In earlier studies, McFadden and his colleagues found that women with twin brothers have quieter otoacoustic emissions. He proposes that exposure to male hormones, called androgens, during pregnancy changes the hearing systems of female fetuses that share the womb with a male. However, he adds, there is no evidence that such women are more often lesbian. Studies of other mammals have shown leakage of sex hormones from one fetus to another.

McFadden suggests that the lesbian and bisexual women in the current study were also exposed to androgens before birth. "The auditory systems of homosexual and bisexual females were being masculinized at the same time that other brain [regions] were being masculinized," McFadden says.

Bruce Parsons of the New York State Psychiatric Institute in New York doesn't buy McFadden's argument. "There's no evidence to indicate that homosexuality in our species depends on prenatal androgen levels," he says. "So far, we don't have any really good data that suggest that brain structures are responsible for sexual orientation.... We need data--and this [study] isn't it."

McFadden's work is part of a growing body of evidence that biological factors play a role in sexual orientation, says Simon LeVay, a researcher-turned-writer in West Hollywood, Calif. LeVay has detected differences in brain anatomy between heterosexual and homosexual men. "Biology is part of destiny--it's a part of why we are the way we are." But, he adds, "I don't think it's the whole matter--don't be ridiculous."