Scientists have been searching for genetic markers of sexual orientation for decades. To date, a so-called “gay gene” has been elusive, but a new study out last week in the journal Scientific Reports is a potential game-changer: For the first time, researchers have honed in on two specific genes that could potentially play a role in the development of sexual orientation.
A research team, led by Alan Sanders at NorthShore University, compared DNA samples from 1,077 homosexual and 1,231 heterosexual men of European descent. Men were classified into groups on the basis of both their sexual identities and Kinsey Scale scores.
Scientists scanned the entire genome for each person and found two genes that appeared to differ based on sexual orientation: one on chromosome 13, and the other on chromosome 14. The gene finding on the 13th chromosome is particularly noteworthy because that gene is expressed in a part of the brain known as the diencephalon—a region scientists previously found to differ in size between men of different sexual orientations.
The gene on the 14th chromosome is one that is mainly expressed in the thyroid. Some research has found that gay men have an elevated rate of thyroid disorders (namely, Grave’s disease, which involves an overproduction of thyroid hormones), so the fact that this gene linkage showed up is also intriguing.
While these findings are fascinating, according to the study’s authors, “these potential connections are best characterized as speculative.” This study had a number of limitations, not the least of which is that only men of European descent were studied. Also, the sample size—though it might sound large—is considered modest for a complex genetic analysis. As such, we need to replicate these findings with larger and more diverse samples before we can draw firm conclusions. If the current “replication crisis” in science has taught us anything, it’s that we shouldn’t focus too much on single studies because false positives can and do emerge from time to time.
This study also doesn’t tell us anything about women. The reality is that women’s sexuality hasn’t received nearly as much scientific study as men’s. This is probably due, in part, to the fact that women exhibit more sexual fluidity. This finding has led to the frequent—and problematic—characterization of female sexuality as inherently “complex.” Research does suggest that women’s sexual orientation has a genetic basis, too, though.
Exploring the origins of sexual orientation is controversial. Look no further than the response that greeted a recent study that used deep neural networks to determine people’s sexual orientation from facial images. The backlash was swift and one of the authors received death threats.
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This controversy stems, in part, from the fact that some do not think this kind of research is even necessary—and, in fact, some view the search for a cause of homosexuality as inherently pathologizing and “othering.” Sex scientists, however, feel quite differently. According to Qazi Rahman, a researcher who studies sexual orientation at King’s College London, “gaining insight into this is useful to biological science.”
Rahman says that such research is important because it could potentially help us to understand the evolution of sexual orientation: “Are these gene hits related to other traits that benefit reproduction in some way, and so carry on the genes for same-sex attraction in some manner?”
Some studies have found that gay men’s female relatives on their mother’s side of the family tend to have more children than do straight men’s maternal female relatives. This suggests the possibility that male homosexuality might be a byproduct of female fertility. In other words, whatever genetic traits code for male homosexuality might have reproductive benefits for the women who carry them.
Insights like this can not only help us to better appreciate and understand sexual diversity—they may also have important political implications: If sexual orientation isn’t something that we choose, it therefore can’t be modified by so-called “conversion therapy.” Just nine US states currently have bans in place on conversion therapy for minors. More evidence of a genetic basis for sexual orientation might be just what we need to kick-start a nationwide effort to outlaw this harmful practice.
Though research in this area may have benefits both scientifically and politically, some question whether those benefits are overshadowed by the potential risks. Most notably, some worry that by pinpointing the genes linked to homosexuality, it will eventually lead to efforts to modify those genes in an attempt to eradicate homosexuality. According to Rahman, though, we don’t have anything to be worried about here—at least not any time in the foreseeable future. “The genetic science of sexuality is way off [from] generating anything that could be used in a damaging way, mostly because genes for sexuality are likely to be many and complex.”
Researchers increasingly believe that there may be multiple “types” of homosexuality and that each type may have a distinct biological pathway. This means there could potentially be a lot of different genes involved here.
And just because research shows a link between a gene and a given sexual orientation, it doesn’t necessarily mean that the gene is the cause of that orientation. More importantly, even if we were to discover a gene that plays a causal role, the reality is that two people could carry the same gene, but that gene could express itself in different ways in each person.
Epigenetic research reveals that there’s an important interaction between our genes and the environment: Environmental factors have the potential to effectively turn certain genes off and on. What this means is that not everyone who carries “gay genes” will necessarily be gay. In other words, we probably won’t be able to predict someone’s sexual orientation from their genetic profile.
Further complicating matters, Rahman says that because traits for sexuality and reproduction “might well be tied to other, really important biological traits necessary for survival,” tinkering with them “might not be such a great idea.” Translation: There could be serious unintended consequences if anyone were to try and modify these genes.
In short, our understanding of human genetics is far too nascent for the research in this area to pose a clear and present danger. And even if it were to do so in the future, Rahman says it’s ultimately society that “determines the limits of technologies arising from basic science.”
So, while the scientific and political benefits of this research would seem to outweigh the potential risks right now, it might not be a bad idea for us as a society to begin a conversation about the limits we might want to impose on future applications of genetic research on human sexuality.
Justin Lehmiller is the director of the social psychology program at Ball State University, a faculty affiliate of The Kinsey Institute, and author of the blog Sex and Psychology. Follow him on Twitter @JustinLehmiller.
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