Do genes make people gay? If you put this question to Google, you'll find thousands of pages of Internet commentary on it, posted on the websites of fundamentalist Christian ministries, science blogs, and major newspapers. The reason why this question attracts so much attention is no mystery: Despite real progress on LGBT rights in recent decades, large numbers of people, both in the United States and around the world, still see homosexuality as wrong. But if being gay is inborn, rather than a choice, moral arguments against same-sex relationships become more complicated, because it's harder to condemn people for something that is beyond their control. It's therefore not surprising that the science of sexual orientation often winds up in the middle of moral and political arguments over LGBT rights.
In part because of the longstanding controversies over same-sex relationships, the genetics of sexual orientation has been somewhat neglected compared to other human traits. Over the past few decades, classic genetic studies using traditional statistical methods show that identical twins, who have the same DNA, are more likely to share same-sex orientation than fraternal twins or non-twin siblings—a clear sign of a genetic effect, though in this case the effect is modest. That genetics plays some role in same-sex orientation shouldn't be surprising since scientists consistently find that genetics contributes nearly every human trait that's been examined, even if it's often in a minor way. Many human traits other than sexual orientation have been the focus of modern, genome-wide genetic studies that attempt to find specific genes that contribute to those traits. A recently published study is one of the few designed specifically to look at sexual orientation with modern genetic tools.
This study, led by Alan Sanders at Chicago's North Shore University HealthSystem Research Institute, directly compared about 2,000 homosexual and heterosexual men in order to find genetic differences between them. They didn't find much. The researchers picked up some signal near several genes that are expressed in the brain. They also detected some genetic differences near the gene for the thyroid stimulating hormone receptor. This gene plays a role in Graves' disease, a thyroid autoimmune disorder that, according to a recent Danish study, occurs more often in gay men. These and other related findings, write Sanders and his colleagues, "point to a possible connection between thyroid function and sexual orientation in men."
What can we take away from these modest results? The study, as the authors recognize, is fairly small as far as modern genetic studies go, and so its power to find genes linked to same-sex differences is limited. The results are also limited to men—the genetics of sexual orientation in women, or of transgender individuals is likely to be different. There are no definitive findings here, only clues for later research to build on.
Perhaps the most important question raised by this study is, why bother? What value is there in working out the genetics of sexual orientation? One answer is that geneticists are interested in understanding how genes contribute to human traits, and sexual orientation is clearly an important human trait. But the pursuit of knowledge for its own sake has to be considered in light of possible harms—and tracking down "gay genes" could definitely be harmful.
One of the most obvious risks has to do with genetic testing, especially of children. Given the modest contribution of genetics to same-sex orientation, no genetic test is likely to reliably predict whether a child will grow up to be gay. However, in the era of cheap, direct-to consumer genetic tests, an unreliable test can do some damage. A test that tells a couple that their child has a 25 percent chance of being gay could become an excuse to subject the child to harmful and medically baseless conversion therapy. Legitimate research showing genetic links between sexual orientation and specific genes—like the thyroid stimulating hormone receptor—could end up spurring illegitimate efforts to develop risky new therapies, including unregulated nutritional supplements that try to modify the effects of those genes. Even if we set aside what might happen in the least-tolerant communities, the genetics of sexual orientation won't tell parents how best to support a gay child, or help societies ensure equal rights for their LGBT citizens.
However, one of the authors of the recent genetic study, Michael Bailey of Northwestern University, argues that we need to pursue the science because same-sex relationships are still socially controversial. In an article co-authored with a group of U.S. and international colleagues, Bailey argues that the science of sexual orientation is in the public interest because, "such science is frequently—if not always correctly— used to support political, social, and moral conclusions regarding homosexuality." Without good science, we're left with a void of information that will inevitably be filled with bad claims. "The conflation of political motives and scientific findings has been common in debates related to sexual orientation," they write, "and when this conflation is mistaken, it is to the detriment of both politics and science."
Bailey and his colleagues show how good science can bring clarity to our public debates, though it can't resolve them. They note that the question of whether people are born gay is ill-posed. What we call our sexual orientation isn't so simple: It's a mix of sexual attraction, which seems to be largely inborn; sexual identity, which is highly socialized; and sexual behavior, which is something we choose to engage in—and not always in ways consistent with our declared sexual identities. Good research on all of these aspects of sexual orientation can help public discussion by rebutting bad claims.
Science can serve this role in the debate only if scientists are willing to clearly speak out when their work is put to bad uses. Genetic studies of socially important traits like sexual orientation, educational attainment, political beliefs, and personality, carry the risk of stigmatizing people based on their DNA. Given that the acceptance of LGBT people in our society is still fragile, scientists should proceed with caution.