New Study Finds That Your Mother Made You Gay

A new study of gay men in the U.S. has found that male sexual orientation is influenced by genes passed on by the mother.

The British newspaper the Guardian reports that in a test of 400 gay men, genes on at least two chromosomes affected whether a man is gay.

"The study shows that there are genes involved in male sexual orientation," said Michael Bailey, a psychologist at Northwestern University in Illinois, who set out the findings at a discussion event held in conjunction with the annual meeting of the American Association for the Advancement of Science in Chicago.

Bailey has not yet published the work, but said it confirmed the findings of a smaller study that sparked widespread controversy in 1993, when Dean Hamer of the U.S. National Cancer found that more than 10 percent of brothers of gay men were gay themselves, compared to around 3 percent of the general population.

The U.K.'s Telegraph reports that no similar genes have been discovered which influence lesbianism.

"Nobody has found something like this in women," said Daryl Bem, a social psychologist at Cornell University.

Researchers have speculated in the past that genes linked to homosexuality in men may have survived evolution because they happened to make women who carried them more fertile. This may be the case for genes in the Xq28 region, as the X chromosome is passed down to men exclusively from their mothers.

Hamer found that 33 out of 40 gay brothers inherited similar genetic markers on the Xq28 region of the X chromosome, suggesting key genes resided there. He faced a firestorm when his study was published, over the question of nature verses nurture, as well as the prospect of a prenatal test for sexual orientation. At that time, Hamer warned that any attempt to develop a test for homosexuality would be "wrong, unethical and a terrible abuse of research."

Similarly, before these latest results were made public, one of Bailey's colleagues, Alan Sanders, said the findings could not and should not be used to develop a test for sexual orientation.

"When people say there's a gay gene, it's an oversimplification," Sanders said. "There's more than one gene, and genetics is not the whole story. Whatever gene contributes to sexual orientation, you can think of it as much as contributing to heterosexuality as much as you can think of it contributing to homosexuality. It contributes to a variation in the trait."

Bailey added that while genes play a role, so do multiple other factors including hormone levels in the womb.

"Sexual orientation has nothing to do with choice," said Bailey. "We found evidence for two sets [of genes] that affect whether a man is gay or straight. But it is not completely determinative; there are certainly other environmental factors involved."