Sexual orientation can not be predicted by a single “gay gene,” new research indicates.

Instead, a host of genetic and environmental factors play a role, according to a study published Thursday in Science.

Several hundred genes appeared to influence sexuality, according to the researchers.

The findings provide insight into the complex genetics underlying human sexuality. But they do not explain it, wrote the international team of researchers who analyzed genetic data gathered from almost half a million people.

The study analyzed the genetic data of 408,000 men and women from a large British database, the U.K. Biobank. They answered extensive health and behavior questions between 2006 and 2010, when they were between the ages of 40 and 69.

The researchers also used data from nearly 70,000 customers of the genetic testing service 23andMe, who were 51 years old on average, mostly American, and had answered survey questions about sexual orientation.

“Across human societies and in both sexes, some 2% to 10% of individuals report engaging in sex with same-sex partners, either exclusively or in addition to sex with opposite-sex partners,” wrote the study authors.

Same-sex attraction appears to run in families, and identical twins are more likely to be aligned in their sexuality than either fraternal twins or other siblings, noted the researchers.

The analysis also showed different genetics in play for women and men. This could reflect the influence of hormones or possibly social differences among gays, lesbians and bisexuals, the study authors speculated.

Associate Professor Greg Neely at the University of Sydney said, “a major weakness of this study is that it is primarily based on data from 40- to 70-year-old people across the UK.” And same-sex attraction might be underrepresented “based on societal pressure from a previous era.”

Despite its limitations, the research was much larger and more varied than previous studies, which generally focused on gay men, often those who were twins or were otherwise related.

“Just the fact that they look at women is hooray,” said Melinda Mills, a professor of sociology at the University of Oxford, who wrote a commentary that Science published alongside the study.


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