Bisexuality may have arisen in humans for a good reason: to help men have more children.
Looking at it only from an evolutionary point of view, the existence of a ‘bisexual gene’ has confused some scientists.
If we are genetically programmed to keep the human race going through having children, and same-sex encounters did not create children before IVF became possible, some wondered why bisexuality existed.
But a study has found ‘bisexual genes’ may play another role – when they are found in heterosexual men, those men have more children.
The study looked at more than 450,000 people in the UK, including heterosexual men who had slight genetic differences more usually seen in bisexual men.
These men were not actually bisexual, but having genes linked to bisexuality meant they had more children on average than other heterosexual men.
These men were not actually bisexual, but having genes linked to bisexuality meant they had more children on average than other heterosexual men
Researchers also found straight men with bisexual genes were more likely to say they took risks in life – so they may have had more sexual partners or unprotected sex, leading to a greater number of children.
If genetic variations linked to bisexuality lead to more children for men, it could explain why they exist and are passed down the generations.
However, the researchers stress that the findings ‘predominantly contribute to the diversity, richness, and better understanding of human sexuality’, adding: ‘They are not, in any way, intended to suggest or endorse discrimination.’
The study found no association between genes linked to bisexuality in women and the number of children they had.
Professor Jianzhi Zhang, senior author of the study from the University of Michigan, said: ‘Although bisexual men have fewer children than heterosexual men on average, heterosexual men carrying bisexual genes have more children than those without such genes.
‘This could potentially keep bisexual genes in the population.
‘As to why heterosexual men carrying bisexual genes have more children than those without such genes, we found that heterosexual men carrying bisexual genes are more willing to take risks and that risk-taking is correlated with more children.’
The study, published in the journal Science Advances, looked at adults involved in the UK Biobank health study whose genes were sequenced.
This helped to identify people with genetic variations that are linked to bisexuality because they are seen more often in people who have sex with both men and women.
Generally, heterosexual people in the study had around 1.9 children on average, with bisexual and gay people having fewer children.
However, an interesting finding appeared when researchers looked only at heterosexual men carrying bisexual genes who were not, in fact, bisexual.
These men had more children and were more likely to answer yes to the question, ‘Would you describe yourself as someone who takes risks?’
Although the question on risk-taking did not specify the type of risk, it is likely this would include unprotected sex and promiscuity, which could result in more children, according to the authors.
