Some conservatives argue that homosexuality is a personal choice or the result of environmental influences. Some gay rights activists insist that homosexuality is genetic, hoping that proof from that domain will lead to greater acceptance. Still others, backing the same cause, discourage any investigation into the biological origins of sexual orientation, fearful that positive results will lead to attempts to rid the world of potential homosexuals. A handful of scientists, though, are just curious. For them, the discovery of how an individual becomes gay is likely to shed light on how sexuality-related genes build brains, how people of any persuasion are attracted to each other, and perhaps even how homosexuality evolved.
“Who cares about gay men or lesbian women?” asks geneticist Sven Bocklandt of the David Geffen School of Medicine at UCLA. “Sexual selection defines evolution and creation—such a major player in determining society—and we have no idea how it works. This is much larger than the gay gene; it’s about all sexual reproduction.”
Sven Bocklandt of UCLA's medical school studies
the DNA of gay and straight male twins.
Image courtesy of Sven Bocklandt
Bocklandt was once a mere science journalist. It was while producing a documentary for Belgian TV that he first met geneticist Dean Hamer. Hamer had just published a study that claimed not only to have finally proved that male homosexuality was at least partially genetic but also to have pinpointed the stretch of chromosome where one of the genes involved resided. Hamer and his colleagues conducted extensive interviews with 76 pairs of gay brothers and their family members and found that homosexuality seemed to be inherited through the maternal line. This led him to compare the X chromosomes—which can be inherited only from the mother—in those same brothers. There he discovered a shared genetic marker, a patch of DNA called Xq28. Interviews with the subjects also revealed them to be either gay or straight. (In this respect, men are entirely different from women. Studies have shown that women respond to all types of sexual depictions—not only heterosexual and homosexual images but even those of chimpanzees having sex.)
The interview with Hamer fascinated Bocklandt. Not long after, he quit his job and moved to Washington, D.C., to work with Hamer. There he did research on the X chromosome, with hopes of someday finding the gay gene or genes themselves.
Fourteen years later, neither Bocklandt nor any other researcher has pinpointed the precise base pairs that might turn a man gay. Part of this is due to the politics of funding for sex research. For a long period NIH grant proposals that included words like “gay,” “condom,” or even “sexuality” were turned down, much to the ire of researchers like Hamer. Shortly after he published his gay brothers study, Hamer completed a similarly designed family study looking into a genetic cause for a certain kind of anxiety. Since then there have been more than 400 independent studies looking into those genes. There have been no such studies for the gay gene.
It is not clear if Hamer and his team found the locus of the genetic code that causes men to memorize lines from A Star Is Born. Although a follow-up study by the team replicated their findings, a study by George Rice, a neuroscientist at the University of Western Ontario, refuted Hamer’s findings completely. In addition, two other researchers told me they don’t consider Hamer’s study valid. Yet Hamer contends that his results suggest there is a link to Xq28 and that the Rice study was biased because one of the coauthors told Hamer that he didn’t believe a gay gene could exist. Hamer also says that, if read correctly, the two other studies confirm his findings. “They didn’t even look at the entire X chromosome,” says Hamer. “They gave up immediately.” For laymen, science journalists, and researchers alike, the question remains unresolved.
Whether or not a gay gene, a set of gay genes, or some other biological mechanism is ever found, one thing is clear: The environment a child grows up in has nothing to do with what makes most gay men gay. Two of the most convincing studies have proved conclusively that sexual orientation in men has a genetic cause.
William Reiner, a psychiatrist at the University of Oklahoma Health Sciences Center, explored the question of environmental influences on sexuality with a group that had been surgically shifted from boys to girls. These boys had been born with certain genital deformities; because it is easier to fashion a vagina than a penis, the boys were surgically made into girls at birth. In many cases they were raised as girls, kept in the dark about the surgery, and thought themselves female long into adulthood. Invariably, Reiner found that the faux females ended up being attracted to women. If societal nudging was what made men gay, at least one of these boys should have grown up to be attracted to men. There is no documented case of that happening.
The second study was an examination of twins by psychologist Michael Bailey of Northwestern University. Among identical twins, he found that if one was gay, the other had a 50 percent chance of also being gay. Among fraternal twins, who do not share the same DNA, there was only a 20 percent chance.
At first glance, those results seem to suggest that at least some homosexuality must not be genetic. Identical twins have the same genes, right? How could one turn out gay and the other not gay as often as 50 percent of the time? There are many other traits that are not always the same in identical twins, however, like eye color and fingerprints. The interesting question is, how do any of these major differences arise between two products of the same code?
The solution to that question is exactly what Bocklandt is trying to find. By looking not at DNA but at where DNA is switched off, he hopes to find the true genetic seat of homosexuality. Hamer looked at broad regions of chromosomes using genetic markers, a low-resolution result that tells little more than “something’s going on somewhere around here.” Bocklandt is hoping to look with a much stronger magnifying glass at the areas Hamer’s research highlighted. If he succeeds, it will be a triumph not only for the genetics of homosexuality but also for genetic research in general.
Bocklandt has collected DNA from two groups of 15 pairs of identical twins. In one group, both twins are gay. In the second, one twin is gay, and the other is straight. Identical twins have the same DNA, but the activity of their genes isn’t necessarily the same. The reason is something called methylation.
Methylation turns off certain sections of genetic code. So even though we inherit two copies of every gene—one from our mother, one from our father—whether the gene is methylated often determines which of the two genes will be turned on. Methylation is inherited, just as DNA is. But unlike DNA, which has an enzyme that proofreads both the original and the copy to minimize errors, methylation has no built-in checks. It can change from one generation to the next and may be influenced by diet or environment. It’s in this mutability that Bocklandt hopes to find the secret, by seeing which flipped genetic switches correlate with homosexuality.
“For each pair we expect to see a whole lot of things that are random—sometimes someone smoked, or medication was used for long periods of time,” Bocklandt says. “But basically we compare the gay results with the straight ones and see if any region shows up multiple times for these subjects.”
