In the new study, a team led by Brendan Zietsch of the University of Queensland, Australia, mined several massive genome data banks, including that of 23andMe and the UK Biobank (23andMe did not fund the research). They asked more than 477,000 participants whether they had ever had sex with someone of the same sex, and also questions about sexual fantasies and the degree to which they identified as gay or straight.
The researchers found five single points in the genome that seemed to be common among people who had had at least one same-sex experience. Two of these genetic markers sit close to genes linked to sex hormones and to smell—both factors that may play a role in sexual attraction. But taken together, these five markers explained less than 1 percent of the differences in sexual activity among people in the study.
When the researchers looked at the overall genetic similarity of individuals who had had a same-sex experience, genetics seemed to account for between 8 and 25 percent of the behavior. The rest was presumably a result of environmental or other biological influences. The findings were published Thursday in Science.
Despite the associations, the authors say that the genetic similarities still cannot show whether a given individual is gay. “It’s the end of the ’gay gene,’” says Eric Vilain, a geneticist at Children’s National Health System in Washington, D.C., who was not involved in the study.