Let the Mystery Be?

Researchers may soon isolate the genetic roots of homosexuality. As a scientist, that excites me. But as a gay man, I worry about what might happen next.

Two men with faces close to each other, an engraving of a family tree, and a 3D Illustration of a method of colored DNA sequencing.
Photo illustration by Lisa Larson-Walker. Photos by Library of Congress, Glow/Getty Images Plus, ktsimage/iStock/Getty Images.

This piece is part of the Legacies issue, a special Pride Month series from Outward, Slate’s home for coverage of LGBTQ life, thought, and culture. Read an introduction to the issue here.

Queer people have a complicated relationship with our genes. On the one hand, “born this way” is recognized as the argument that won same-sex relationships equal treatment under the law. On the other hand, actually thinking about what it means for same-sex orientation to have a genetic basis can get awkward, fast.

Long before I came out as gay and completed a Ph.D. in evolutionary biology, I was a closeted teenager with just enough understanding of natural selection to be a danger to myself. Homosexuality couldn’t be genetic, I reasoned (in the confines of my own head, and in cafeteria conversations after biology class, and once in a kitchen-counter exchange with my mother that is still seared into my memory), because gene variants that make people uninterested in the kind of sex that makes babies should be eliminated from the population in a generation. If homosexuality wasn’t genetic, whatever it was that I felt about other boys was only in my head, and therefore fully under my control.

I eventually learned better, in so many ways. Notably, that a trait being genetic (or not) isn’t remotely the same as it being a fundamental part of a person’s being (or not). But also that there is good evidence for a genetic basis to same-sex attraction, and that this is far from anathema to natural selection.

Biologists have proposed a number of hypotheses for how “gay gene” variants might evolve and persist. They might reappear through mutation as quickly as selection eliminates them. They might boost reproductive output in small “doses”—if there are, say, 10 genes that affect orientation, maybe someone carrying gay variants at five will still be straight but raise more children than someone carrying no gay variants. Or maybe variants that make men more likely to be gay boost the fertility of straight women who carry them. Or it’s even possible that gay men and women contribute to the next generation indirectly by helping close relatives raise more children. I haven’t contributed directly to this line of scholarship, but I keep abreast of it for obvious reasons, and it’s tended to make me optimistic about the value of research into the genetics underlying my queer identity.

That optimism hasn’t been universally shared by other queer biologists, though. One of the most prominent is Douglas Futuyma, who wrote the very textbook from which I teach evolutionary biology and who was out as a gay man in the field since the 1980s. Futuyma’s research focuses on interactions between plants and insects, as does mine, so I’ve long seen him as something of a role model. (I was terrified to learn he was in the audience for my first-ever presentation at a scientific conference and grateful that he didn’t grill me too badly in the Q&A afterward.)

Thirty-five years ago, in the Journal of Homosexuality, Futuyma and his colleague Stephen Risch expressed strong skepticism in research seeking a genetic basis to same-sex attraction—both the prospects that it would succeed and its potential impacts on the queer community. “Most of the psychological and medical literature on homosexual behavior concerns ways to prevent or to ‘cure’ it,” Futuyma and Risch noted, and finding a genetic basis for orientation is the prerequisite for that “cure.” Even studies aiming to promote acceptance of queer identities were, they argued, fundamentally flawed.

Research continued all the same, and studies comparing the sexual orientation of identical twins (who share 100 percent of their genes) to fraternal twins (who share half their genes, like non-twinned siblings) established that genetics contribute to orientation, even though specific causal genes were elusive. Futuyma remained leery, though. In 2005, writing in the journal Evolution, he reiterated the unease that underlay his original objections: “There is only a short distance between understanding the genetic or environmental origins of sexual variation and the possibility of intervention—in medical terms, ‘cure.’ ”

When I read that article as a graduate student, this thought seemed pessimistic, verging on paranoid. The methods of evolutionary genetics that I was learning seemed only to open up exciting promises, if we only knew the gene variants responsible for sexual orientation. We could use patterns in the frequency of such variants across human populations, and in the DNA sequences near them, to reconstruct the history of natural selection acting on them. This approach has revealed how humans evolved traits with known genetic bases, like the ability to digest milk as adults and tolerance of high-altitude conditions. A list of genes contributing to same-sex orientation could reveal how queer folks have lived over millennia of human history.

It could also revise queer folks’ relationship to our ancestry. Like most gay men, I was born to straight parents, and (barring the sort of revelation that would upend a family reunion) my grandparents were just as straight. I can’t trace my queerness back along my family tree in the same way I can trace my blue eyes, my small but sturdy stature, or my ancestors’ immigration from the Low Countries to the colony of Pennsylvania to freely practice a fringe take on Protestantism. But the genes that help make me gay form another kind of family tree, intertwined with and beyond the one recorded in the family Bible. The branches of that tree are a biological link from me to my queer chosen family, and to queer historical figures who have shaped the world we live in today, from Harvey Milk to Sappho.

We may be closer than ever to tracing that tree. Last year, a team working with very large datasets from the U.K. Biobank and the “personal genomics” company 23andMe reported, at two different conferences, that they’ve identified about 40 genes at which different variants are associated with differences in orientation. Adding up the effects of many more genes into “polygenic scores” accounted for up to 20 percent of variation in sexual orientation—not the full genetic effect seen in twin studies, but not nothing. The collaborators haven’t published a formal peer-reviewed article yet, but it looks likely that the final, fully reported project will be solid work.

So why, on the threshold of that revelation, do I find myself occupied with Futuyma’s worries about the search for gay genes?

Maybe it’s because I’ve seen how humanity is applying the advances in genetics we’ve acquired just since I began my scientific career. Genome-scale descriptions of human diversity have been accompanied by a resurgence of “scientific” definitions of race, and law enforcement started mining genealogy databases to pinpoint suspects from their relatives’ DNA before anyone seems to have thought through the privacy implications. The former is a misunderstanding of genetic data while the latter is a misuse—but both are harmful in ways that geneticists had not fully anticipated before publishing. Last year saw the birth of children whose genomes had been edited—most geneticists agree this was beyond the pale, but that consensus didn’t have much preventative power, it turns out.

Closer to the issue at hand, polygenic scores like the one calculated for same-sex orientation in that soon-to-be-released study are already being used to screen embryos fertilized in vitro for risks of disease and mental disability, even though the effectiveness of such screening hasn’t been evaluated. (It may be quite low.) The co-founder of Genomic Prediction, the company offering that testing, has said he expects to eventually select embryos for higher intelligence and envisions offering that service in a country where such “soft eugenics” isn’t regulated. Genomic Prediction might balk at screening embryos for prospective sexual orientation, but none of the component parts of the procedure are out of reach for people with fewer qualms.

Such a technology would probably not, realistically, put homosexuality at risk of extinction. But a world in which even a genetic screen for queerness exists—whether it’s rarely used or ineffective—seems to me to be a world that’s less safe for queer people. For one thing: Imagine growing up gay, knowing that your parents could have paid to ensure you were straight before you were even in utero. Then, too, anti-gay governments from midcentury Canada to modern Tunisia have shown far too much interest in “objective” tests for homosexuality, regardless of how accurate those tests actually are. And all this is apart from the subtler issues arising from reducing sexual orientation to something you can diagnose with a genetic test.

I have no doubt the authors of the pending study of genes underlying sexual orientation are working with the best of intentions. From what I’ve seen, they’ve followed the ethical and methodological standards of our field to the letter, and then some. I expect they’re motivated by the discoveries the project may ultimately provide, just as I used to see research into the biology of sexuality as an unalloyed good. But given the world into which those discoveries will be released, I’ve come to think that uncovering queer folks’ shared genetic legacy comes with real risks for our future. Genetic studies can reveal the queer family tree reaching back through time—but making that tree visible also makes it vulnerable to those who would happily uproot it.

Read more of Outward’s Legacies issue.

This piece has been updated to clarify scientists’ hypotheses for how “gay gene” variants might evolve.