Few aspects of human biology are equally circuitous—or politically fraught—every bit sexual orientation. A clear genetic link would propose that gay people are "built-in this style," every bit opposed to having fabricated a lifestyle choice. Withal some fear that such a finding could be misused "cure" homosexuality, and near enquiry teams accept shied abroad from tackling the topic.

Now, a new study claims to dispel the notion that a single gene or handful of genes make a person prone to aforementioned-sex behavior. The analysis, which examined the genomes of virtually half a million men and women, establish that although genetics are certainly involved in who people choose to have sex with, at that place are no specific genetic predictors. Yet some researchers question whether the analysis, which looked at genes associated with sex rather than attraction, can depict whatsoever real conclusions about sexual orientation.

"The bulletin should remain the same that this is a circuitous behavior that genetics definitely plays a part in," said written report co-author Fah Sathirapongsasuti, a computational biologist at genetic testing company 23andMe in Mountain View, Calif., during a printing conference. The handful of genetic studies conducted in the past few decades have looked at only a few hundred individuals at most—and almost exclusively men. Other studies have linked sexual orientation with environmental factors such as hormone exposure before birth and having older brothers.

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 besides questions about sexual fantasies and the caste to which they identified every bit gay or straight.

The researchers found five unmarried points in the genome that seemed to exist common among people who had had at to the lowest degree one same-sex experience. Two of these genetic markers sit shut to genes linked to sexual activity hormones and to smell—both factors that may play a office in sexual allure. But taken together, these five markers explained less than ane percent of the differences in sex activity among people in the study. When the researchers looked at the overall genetic similarity of individuals who had had a aforementioned-sex feel, genetics seemed to account for betwixt eight and 25 percent of the behavior. The rest was presumably a result of environmental or other biological influences. The findings were published Th in Science .

Despite the associations, the authors say that the genetic similarities still cannot show whether a given private is gay. "Information technology's the end of the 'gay cistron,'" says Eric Vilain, a geneticist at Children's National Wellness System in Washington, D.C., who was not involved in the study.

The enquiry has limitations: virtually all of the participants were from the U.S. or Europe, and the individuals too tended to exist older—51 years old on average in the 23andMe sample and at least twoscore in the UK Biobank sample.

Still, researchers welcome the data. "A lot of people want to understand the biology of homosexuality, and scientific discipline has lagged behind that man involvement," says William Rice, an evolutionary geneticist at the Academy of California, Santa Barbara, who likewise was not involved in the piece of work. "It's been a taboo topic, and now that we're getting information I think it'southward going to blossom."

The study will not be the concluding discussion on the vexing question of what causes homosexuality, notwithstanding. In 1993 geneticist Dean Hamer of the U.Southward. National Cancer Institute and his colleagues published a paper suggesting that an area on the X chromosome chosen Xq28 could contain a "gay factor." Simply other studies, including the new newspaper, found no such link, and Sathirapongsasuti says that the new study is the final nail in the bury for Xq28 as a cause of aforementioned-sex allure.

But Hamer, at present retired, disagrees. His study, which analysed the genomes of 40 pairs of gay brothers, looked exclusively at people who identified as homosexual. He sees the new paper as an assay of risky behavior or openness to experience, noting that participants who engaged in at least one same-sex experience were as well more likely to report having smoked marijuana and having more than sexual partners overall. Hamer says that the findings practise not reveal any biological pathways for sexual orientation. "I'm glad they did it and did a big study, but it doesn't point united states where to look."

Rice and Vilain concord that the determination is unclear. A more detailed questionnaire that looks at more aspects of sexuality and environmental influences would permit the researchers to better pinpoint the roots of attraction.

The authors say that they did see links between sexual orientation and sex activity, only concede that the genetic links do non predict orientation. "I think it's true we're capturing part of that risk-taking behavior," Sathirapongsasuti says, but the genetic links nonetheless suggested that same-sex behavior is related to attraction.

Notwithstanding, Hamer and others praise the new contribution to a field that suffers from a dearth of good studies. "I promise information technology volition be the first of many to come."