Many Genes Influence Same-Sex Sexuality, Not a Single ‘Gay Gene’

A new study has found that genetics are “responsible for perhaps a third of the influence” over whether a person is sexually attracted to members of the same sex.

The study out of the Broad Institute at Harvard and M.I.T. was funded by the National Institutes of Health along with other agencies and studied genetic data from 408,000 men and women in a British database called Biobank along with a further 70,000 samples from 23andme of mostly American people who were 51 years old on average and had answered questions about sexuality. All were of white European descent and none were trans. Of the 23andme samples, 19 percent had reported a homosexual experience, while just 3 percent of the Biobank samples had reported the same. Of their admittedly limited sample, scientists found that genetics do play a role in predicting a person’s sexual interest in the same sex, according to the New York Times:

“There might be thousands of genes influencing same-sex sexual behavior, each playing a small role, scientists believe. The new study found that all genetic effects likely account for about 32 percent of whether someone will have same-sex sex.

Using a big-data technique called genome-wide association, the researchers estimated that common genetic variants — single-letter differences in DNA sequences — account for between 8 percent and 25 percent of same-sex sexual behavior. The rest of the 32 percent might involve genetic effects they could not measure, they said.”​

Back in 1993, a study linked homosexuality in men to a region of the human genome called xq28, giving rise to the idea of a “gay gene,” and though the results of that study were never replicated, some scientists involved hoped they could use the new study, published this week to help support the idea that being gay is perfectly natural:

“‘I hope that the science can be used to educate people a little bit more about how natural and normal same-sex behavior is,’” said Benjamin Neale, a geneticist at the Broad Institute of M.I.T. and Harvard and one of the lead researchers on the international team. “‘It’s written into our genes and it’s part of our environment. This is part of our species and it’s part of who we are.’”​

But others, even some researchers within the Broad Institute, worry that the study will fuel even more anti-gay rhetoric by suggesting environment may have some influence over sexuality, an idea that might be twisted by those who believe homosexuality is a “choice” or cause the anti-gay crowd to begin clamoring for gene editing, which is both impossible and dumb:

“‘I deeply disagree about publishing this,’” said Steven Reilly, a geneticist and postdoctoral researcher who is on the steering committee of the institute’s L.G.B.T.Q. affinity group, Out@Broad. “‘It seems like something that could easily be misconstrued,’” he said, adding, “‘In a world without any discrimination, understanding human behavior is a noble goal, but we don’t live in that world.’”​

While even researchers acknowledge the limitations of such a study, it was a broader look at men and women across a spectrum of sexual experiences than previous studies, which mostly focused on gay men who were twins or otherwise related. And of that broader sample, two out of the five genetic variants researchers found only seemed to affect men, including one linked to sense of smell, and one was discovered only in women.

Scientists were also unable to use their findings to predict how respondents in unrelated data sets would respond to questions about sex.