Scientists Discover First Genetic Variation Associated with Bisexual Behavior in Humans

In a recent scientific study, scientists have for the first time identified genetic variations associated with bisexual behavior in humans, a finding that not only provides insight into the diversity of sexual orientations, but also reveals the link between these genetic markers and the ability of heterosexual men to engage in risk-taking behaviors and produce more offspring. The study, led by University of Michigan professor Jianzhi Zhang, was published Wednesday in the journal Science Advances.

The study is based on data from over 450,000 people of European descent registered with the UK Biobank, a long-term genomics project with significant benefits for health research. The research builds on a groundbreaking paper published in Science in 2019, which found that genetic variation influences whether a person engages in same-sex behavior to some extent, although environmental factors have a greater impact.

Professor Chang explained that past studies have tended to lump all homosexual behavior into one category, but in reality there is a range. By studying the complete DNA or genome of participants and combining this information with survey results, Chang and his co-author Siliang Song were able to confirm that the characteristics associated with homosexual and bisexual behavior are actually different.

The study reveals that male heterosexuals who carry these markers, called bisexual behavior (BSB)-related alleles, pass on these genes by having more children than average. In addition, men who describe themselves as adventurous tend to have more children and are more likely to carry the BSB-associated allele. This suggests that male BSB-related alleles may have a reproductive advantage, which could explain their past persistence and predict their future maintenance.

However, alleles associated with exclusive same-sex behavior (eSSB) are associated with fewer children being born to heterosexual men, suggesting that these traits will disappear over time. Data from the UK Biobank also show that the proportion of people reporting bisexual and homosexual behavior has been rising for decades, possibly due to increased openness in society.

The study estimated that whether a person's behavior is bisexual has 40% to be influenced by genetics and 60% by environment. The researchers emphasized that their findings mainly contributed to the diversity, richness and better understanding of human sexuality and were not intended to imply or endorse discrimination on the basis of sexuality.

This study not only provides new insights into the genetic basis of sexual orientation, but also emphasizes the natural phenomenon of complexity and pleiotropy, whereby a single gene can influence multiple traits. The findings of this study provide an important perspective for understanding the evolutionary context of human sexual behavior and open new avenues for future research.