Study Finds No Evidence of Homosexuality in DNA
Six years ago, researchers uncovered a genetic sequence linked to homosexuality. But a new study casts doubt on that finding. (ABCNEWS.com)
By Claudine Chamberlain
April 22 It's a seemingly endless debate: Why are some people attracted to the opposite sex, while others are drawn to their own gender? Thanks to new research published today, that question just got even harder to answer.
A team of researchers at the University of Western Ontario in Canada has found no evidence of the so-called "gay gene," directly contradicting studies from 1993 and '95 that pinpointed a specific genetic marker on the X chromosome linked to homosexuality in men.
Whether genes play a part in sexual orientation has long been a hot button topic for people who support or oppose gay rights. If gays and lesbians are biologically predisposed to homosexuality--through their genes or some other way--that makes for a stronger case against discrimination.
That's why the gay community welcomed the 1993 study by biologist Dean Hamer of the National Cancer Institute. Hamer found that in 40 pairs of gay brothers, 33 had the same set of DNA sequences in a region of the chromosome called Xq28.
Attempting to replicate those findings, Ontario neurologist George Rice examined the DNA of 52 pairs of gay brothers, and found that their Xq28 sequences were no more similar than what might be expected from sheer chance.
Rice's results appear in today's edition of the journal Science.
"What we have here is a scientific controversy," says Michael Bailey, a Northwestern University psychologist who has studied homosexuality in twins. The latest research effort "is a good study and it certainly raises questions about whether Hamer was right, but I don't think it proves him wrong either."
That's because both studies were relatively small, and because specific genes are difficult to find. "A definitive study," says Bailey, "would entail substantially larger numbers of people."
Maybe the Gene Is Elsewhere
Rice himself doesn't discount the idea of a genetic link to homosexuality. He just doesn't think Xq28 is the spot. "The search for genetic factors in homosexuality should continue," he says, adding that he's currently searching for other genes that could be linked to sexuality.
But Hamer stands by his earlier findings, especially since two subsequent studies (one of which has not yet been published), found the same thing. "All this proves is that not every case of homosexuality is because of Xq28," he asserts. "I expect we'll find that many genes are involved. One of them will be on Xq28."
Twin studies, like those done by Bailey, have fueled the search for such genes. In 1991, he studied the twin brothers of gay men and found that 52 percent of identical twins were also gay, while only 22 percent of fraternal twins were. Among women, 48 percent of identical twins were also lesbian, while the rate dropped to 16 percent for fraternal twins.
As with all twin studies, a greater similarity among identical twins usually indicates a genetic link. But because the connection wasn't 100 percent, researchers know that genes aren't the whole picture. Environment (family, friends, society) could also be an important influence.
Does It Really Matter?
Gene or no gene, gay rights groups maintain that what "causes" homosexuality isn't really important. "The vast majority of gay people will tell you that same-sex orientation is an innate part of who you are and is not changeable," says David Smith, a spokesperson for Human Rights Campaign. "But in the final analysis, is really shouldn't matter. Public policy should treat all people equally and fairly."
Conservative groups, on the other hand, say Rice's study proves that homosexuality is a learned, chosen behavior that doesn't deserve legal protection.
"Dean Hamer's study has been used by gay activists for years," says Yvette Cantu, policy analyst for the Family Research Council. "We're saying you can't grant someone special minority status for something that's just a sexual behavior, a choice."
For now, though, the scientific debate is far from over. Sex, says Hamer, "is one of the most interesting things we do. And biologically, it's the most important thing we do." That's why we'll always wonder why some people do it differently than others.
Biological Links to Homosexuality
1991: Northwestern University's Michael Bailey and others find greater homosexual correlation among identical twins than fraternal.
1991: Salk Institute's Simon LeVay discovers that a tiny section of the hypothalamus in the brain is smaller in gay men than in straight men.
1992: Laura Allen and Richard Gorski of the University of California at Los Angeles discover that a section of the fibers connecting the right and left hemispheres of the brain is one-third larger in gay men than straight men.
1993: National Cancer Institute?s Dean Hamer study finds possible location of "gay gene" on the X chromosome, inherited from mothers.
1995: Geneticists Shang-Ding Zhang and Ward Odenwald of the National Institutes of Health discover that a single transplanted gene can cause fruit flies to display homosexual behavior.
1995: Hamer repeats his 1993 findings with a follow-up study.
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