WASHINGTON — A study published by Science on Thursday has found that people who have had same-sex partners are likely to have one or more certain genetic markers.
However, the report said, the markers wouldn’t predict if someone was LGBTQ. It’s more that many different genes can influence sexual behavior. Also, the study called any one who had had even a single same-sex encounter in their lives as non-hetero.
Science said the study builds on results presented by the same team at a 2018 meeting.
The report did say that the study is being called the most solid evidence to date linking specific genetic markers to same-sex sexual behavior. “For the first time we can say without a reasonable doubt that some genes do influence the propensity to have same-sex partners,” says psychologist Michael Bailey of Northwestern University in Evanston, who was not involved in the study.
Neale’s team examined DNA markers and data from surveys of sexual behavior filled out by nearly 409,000 UK Biobank participants and about 69,000 customers of 23andMe, the consumer testing service; all were of European ancestry. The UK Biobank survey asked: “Have you ever had sexual intercourse with someone of the same sex?”; the 23andMe survey featured a similar question. The team found five genetic markers significantly associated with answering yes to those queries. Two markers were shared by men and women, two were specific to men, and one was found only in women.
One of the genetic variants was near genes associated with male baldness, suggesting a tie to sex hormones such as testosterone, and another was in an area rich in smell genes, which have been linked to sexual attraction. When the researchers combined all the variants they measured across the entire genome, they estimate that genetics can explain between 8% and 25% of nonheterosexual behavior. The rest, they say, is explained by environmental influences, which could range from hormone exposure in the womb to social influences later in life.
But the five DNA markers they found explained less than 1% of this behavior, as did another analysis that included more markers with smaller effects. As with other behavioral traits such as personality, there is no single “gay gene,” says Broad team member Andrea Ganna. Instead, same-sex sexual behavior appears to be influenced by perhaps hundreds or thousands of genes, each with tiny effects.
As the researchers had reported last year, they also found people with these markers were more open to new experiences, more likely to use marijuana, and at higher risk for mental illnesses such as depression. LGBTQ people might be more susceptible to mental illness because of societal pressures, the researchers note.