Brain-Stem Part Different In Gay Men -- Study Suggests Biological Basis For Homosexuality

In a finding that hints at a biological basis for homosexuality, a researcher has found a difference in the brains of gay and straight men.

A microscopically small part of the brain stem that regulates sexual drive was found to be different in heterosexual men compared with the same part in homosexual men or heterosexual women, the researcher reports in today's edition of the journal Science.

While the researcher said he could not conclude whether the difference was the origin or the result of homosexuality, he suggested that it probably "is established early in life and later influences sexual behavior."

The study, based on brain tissue from autopsies of 41 men and women, more than half of whom died of AIDS and the rest from causes not related to AIDS, is considered preliminary because of its size and because it needs to be repeated by other researchers.

The neuroscientist who did the research, Simon LeVay of the Salk Institute for Biological Studies in San Diego, acknowledged in his study that there were several limits. Because most of the brain tissue was donated by people who died of AIDS, there is a chance that the disease skewed the results. The determination of the sexual orientation of the men and women was based on either death certificate information or inferred from circumstantial evidence, and no brain tissue was available from lesbians.

Today's study identifies one cell nucleus containing genetic proteins in the brain's hypothalamus that is half the size in homosexual men as in heterosexual men but about the same size as in heterosexual women.

The similarity of the size of the nucleus in homosexual men and heterosexual women ties into the growing belief among researchers that during development, brains are "female" to begin with, until male hormones lead to the development of "masculine" characteristics. Not enough or too much male hormone during the brain's development could thus affect sexual orientation or any other aspect of sexual differentiation.

But the research may provide some understanding of the origins of human sexuality and raises new questions of whether environment or biology or both are the determining factor in homosexuality.

"It's a very controversial thing, but it's very important," said Roger Gorski, chairman of UCLA's department of anatomy and cell biology.

Identifying differences between homosexual and heterosexual brains could be the start of a better understanding of how the brain differentiates sexually, Gorski and other researchers said.

While representatives of gay and lesbian groups welcomed the notion of a biological basis for homosexuality, they cautioned against using the study results as an excuse for discrimination and said some gays and lesbians opposed research into the biology of homosexuality out of concern that the information would be misused.

Rochelle Diamond of the National Organization of Gay and Lesbian Scientists and Technical Professionals, said: "Unfortunately some people may use this as ammunition to say, `These people are defective.'

"We're all different in our make-up. We all don't have the same nose. We all don't have the same hair. We all don't have the same sexuality."