New research finds bisexual genes for first time – and they are ‘reproductively advantageous’

Scientists have found genetic variations associated with human bisexual behaviour for the first time, and they are linked to risk-taking behaviour and producing more children. 

The University of Michigan-led study, which was published on Wednesday (3 January) in Science Advances, analysed data from more than 450,000 people in the UK’s Biobank database of genetic and health information. 

As part of the research, participants responded to a questionnaire which included a question about whether they are a risk-taker. 

The analysis revealed heterosexual males who have genetic variants associated with bisexual behaviour – known as BSB-associated alleles – have more children. Whilst those who say they take part in risk-taking behaviours have more children than average and have an increased likelihood of carrying the BSB-associated alleles.

The study’s senior author, evolutionary biologist Jianzhi Zhang, said: “Our results suggest that male BSB-associated alleles are likely reproductively advantageous, which may explain their past persistence and predict their future maintenance.” 

Zhang added: “These results also suggest that risk-taking behaviour is the underlying cause of BSB-associated alleles’ promotion of reproduction in heterosexuals. 

“That is, the reproductive advantage of BSB-associated alleles is a byproduct of the reproductive advantage of risk-taking behaviour.” 

The study is part of a body of research into what influences genetics can have on same-sex behaviour. 

‘Nature is complicated’

Zhang, along with study co-author Siliang Song, confirmed the signatures associated with same-sex behaviour and bisexual behaviour are distinct, when previously they had been conflated. 

“We realised that in the past, people lumped together all homosexual behaviour […] but actually there’s a spectrum,” Zhang said. 

The study’s senior author went on to explain that risk-taking behaviour refers to the tendency to engage in behaviour which is reward-seeking despite the possibility of negative consequences. Although the Biobank question on risk-taking did not define the type of risk in question, it is likely the self-reported risk-taking people thought of includes unprotected sex and increased sexual relations – which could result in more children – Zhang said.

“Nature is complicated,” Zhang continued. “Here we’re talking about three traits: number of children, risk taking, and bisexual behaviour: they all share some genetic underpinnings.”

Work relating to human sexuality and genes has long been controversial, with many concerned that if a ‘gay gene’ can be identified, then nefarious interests could use the information to discriminate against queer folks. 

“We want to make it clear that our results predominantly contribute to the diversity, richness, and better understanding of human sexuality,” the authors stressed.

“They are not, in any way, intended to suggest or endorse discrimination on the basis of sexual behaviour.”