No individual gene alone makes a person gay, lesbian or bisexual; instead, thousands of genes likely influence sexual orientation, a massive new study of the genomes of nearly half a million people suggests.
Across human societies and in both sexes, between 2% and 10% of people report engaging in sex with a member of the same sex, either exclusively or in addition to sex with a member of the opposite sex, the researchers said. The biological factors that contribute to sexual orientation are largely unknown, but many scientists suspect that genetics plays a role, given that same-sex sexual behavior appears to run in families and is seen more often in identical twins than in fraternal twins.
But a precise genetic basis for sexual orientation has been elusive, largely because scientists previously had relatively small groups of volunteers to investigate.
“Because it is a controversial topic, funding has historically been limited and recruitment of participants was difficult,” study co-author Fah Sathirapongsasuti, a senior scientist and computational biologist at the genetic testing company 23andMe, told Live Science. Same-sex orientation remains criminalized in more than 70 countries, some with the death penalty, often stifling those willing to disclose such personal information.
The new study, however, included a much larger number of participants, making the results more statistically reliable than those of the previous, smaller studies. In the largest genetic study of sexual orientation to date, scientists studied a group of about 470,000 volunteers in the United Kingdom and the United States who reported on whether they had ever engaged in same-sex sexual behavior. They relied on genetic data from the UK Biobank (a long-term health and genetics study running in the United Kingdom) and 23andMe, as well as responses to surveys asking questions about sexual identity, attraction, fantasies and behavior.