The largest study to date on the genetic basis of homosexuality has revealed five spots on the human genome that are linked to same-sex sexual behavior — but none of the markers are reliable enough to predict someone’s sexual orientation.
The findings, which were published in science.org on 29 August 2019, were based on the genomes of nearly 500,000 people, and shore up the results of earlier, smaller studies confirming the suspicions of many scientists: while sexual preferences have a genetic component, no single gene has a large effect on sexual behaviors.
“There is no ‘gay gene’,” says lead study author Andrea Ganna, a geneticist at the Broad Institute of MIT and Harvard in Cambridge, Massachusetts.
“This is a solid study,” says Melinda Mills, a sociologist at the University of Oxford, UK, who studies the genetic basis of reproductive behaviors. But she cautions that the results may not be representative of the overall population — a limitation that the study authors acknowledge. The lion’s share of the genomes comes from the UK Biobank research program and the consumer-genetics company 23andMe, based in Mountain View, California. The people who contribute their genetic and health information to those databases are predominantly of European ancestry and are on the older side. UK Biobank participants were between 40 and 70 years old when their data were collected, and the median age for people in 23andMe’s database is 51.
“Whatever genes are involved represent predispositions, not predeterminations,” said Professor Francis Collins, director of the National Center for Human Genome Research.