The largest ever study of its kind examined data and DNA information about 500,000 people and found there were thousands of genetic variants linked to same-sex sexual behaviour, most of the them having a minor impact.
The researchers said non-genetic factors, including upbringing, personality, and nurture, had far more influence on a person’s choice of sexual partner.
The researchers, writing in Science, suggested genetics may account for as much as one-third of the various factors that determine whether someone is attracted to same-sex partners.
“We scanned the entire human genome and found a handful – five to be precise – of locations that are clearly associated with whether a person reports in engaging in same-sex sexual behaviour,” said Andrea Ganna, a biologist at the Institute of Molecular Medicine in Finland who co-led the research.
The study looked at survey responses and performed analyses known as genome-wide association studies (GWAS) on data from more than 470,000 people who had given DNA samples and lifestyle information to the UK Biobank and to the genetics testing company 23andMeInc, which is based in the US.
Asked why they had wanted to conduct such research, the team told reporters on a teleconference that previous studies on this topic had mostly been too small to offer robust conclusions.
“Previous studies were small and underpowered,” Mr Ganna said.
“So we decided to form a large international consortium and collected data for [almost] 500,000 people, [which] is approximately 100 times bigger than previous studies on this topic.”
Sexual rights campaigners welcomed the study, saying it “provides even more evidence that being gay or lesbian is a natural part of human life”.
“This new research also re-confirms the long established understanding that there is no conclusive degree to which nature or nurture influence how a gay or lesbian person behaves,” said Zeke Stokes of the US-based LGBT+ rights group GLAAD.
Additional reporting by Reuters