There is no so-called “gay gene”, but a mix of genetic and non-genetic factors which influence sexual behaviour, scientists have said.
Researchers examined the genetics of almost a half a million individuals who self-reported on whether they had experienced same-sex sexual behaviour.
Their findings indicate that like personality and other complex human traits, the behaviour is influenced by a combination of genetic and environmental elements.
The authors analysed survey responses and performed genome-wide association studies (GWAS) on data from more than 477,522 people in databases UK Biobank and 23andMe.
They found five genetic variants were significantly associated with same-sex sexual behaviour.
In total, all tested genetic variants accounted for 8% to 25% of variation in same-sex sexual behaviour.
The variants only partially overlapped between males and females, and do not allow meaningful prediction of an individual’s sexual behaviour, according to the study published in the Science journal.
Researchers could not find any patterns among genetic variants that could be used to meaningfully predict or identify a person’s sexual orientation or behaviour.
They said: “We identified genome-wide significant loci associated with same-sex sexual behaviour and found evidence of a broader contribution of common genetic variation.
“We established that the underlying genetic architecture is highly complex, there is certainly no single genetic determinant – sometimes referred to as the ‘gay gene’ in the media.
“Many loci with individually small effects, spread across the whole genome and partly overlapping in females and males, contribute to individual differences in predisposition to same-sex sexual behaviour.
“All measured common variants together explain only part of the genetic heritability at the population level and do not allow meaningful prediction of an individual’s sexual preference.”
Andrea Ganna, European Molecular Biology Laboratory group leader at the Institute of Molecular Medicine, Finland, and the other authors write: “Our findings provide insights into the biological underpinnings of same-sex sexual behaviour.
“But [they] also underscore the importance of resisting simplistic conclusions because the behavioural phenotypes are complex, because our genetic insights are rudimentary, and because there is a long history of misusing genetic results for social purposes.”
In this study, the term “same-sex sexual behaviour,” was defined as having ever had sex with someone of the same sex.