https://news.abs-cbn.com/life/...Researchers have discovered genetic variants linked to human bisexual behavior for the first time, and they have discovered that when these markers are carried by heterosexual men, they are associated with risk-taking and having more children.
Senior author of the new study Jianzhi "George" Zhang, a professor at the University of Michigan, told AFP that the findings contributed to the resolution of a long-standing evolutionary puzzle: why natural selection has not eliminated the genetic basis for attraction within the same sex.
Based on data from over 450,000 individuals of European descent who joined the UK Biobank, a long-term genomics project that has been a huge help for medical research, the study was published on Wednesday in Science Advances.
It expands on a growing body of research, notably a groundbreaking 2019 Science paper that discovered environmental factors had a greater influence on whether an individual engaged in same-sex behavior than genetic variants.
Zhang said, "We realized that in the past, people lumped together all homosexual behavior...but actually there's a spectrum," elaborating on part of the inspiration behind the work.
Zhang and his co-author Siliang Song were able to verify the signatures linked to same-sex behavior and bisexual behavior were, in fact, different by examining the whole sets of DNA, or genomes, of participants and fusing that data with survey responses.
NATURE IS COMPLICATED
Because they could now be examined independently, it was discovered that male heterosexuals who carried the markers, known as bisexual behavior (BSB)-associated alleles, fathered more children than usual and hence passed on those genes to their progeny.
Furthermore, men who identified as risk-takers also tended to be more likely to carry alleles linked to BSB and to have a higher birth rate.
"Our results suggest that male BSB–associated alleles are likely reproductively advantageous, which may explain their past persistence and predict their future maintenance," the researchers wrote.
Although the UK Biobank survey only asked participants if they thought of themselves as risk-takers, it is likely that risk-taking behavior involves having more partners and more unprotected sex.
Zhang remarked, "Nature is complicated," considering the idea that different traits can be influenced by a single gene, a phenomenon called "pleiotropy."
"Here we're talking about three traits: number of children, risk taking, and bisexual behavior: they all share some genetic underpinnings."
Conversely, heterosexual men who carried alleles linked to exclusive same-sex behavior (eSSB) correlated with having fewer children, indicating that these traits will eventually disappear.
Nonetheless, the UK Biobank data also showed that, likely as a result of increasing societal acceptance, the percentage of people reporting bisexual and homosexual behavior has been rising for decades.
For example, the authors estimated that 60 percent of a person's behavior is influenced by their environment and 40 percent is determined by their genes.
"We want to make it clear that our results predominantly contribute to the diversity, richness, and better understanding of human sexuality," they stated. "They are not, in any way, intended to suggest or endorse discrimination on the basis of sexual behavior."