A new study, led by the University of Michigan, published in the journal Science Advances, revealed that heterosexual males carrying genetic variants associated with bisexual behavior, known as BSB-associated alleles, father more children than average.
Additionally, men who describe themselves as risk-takers tend to have more children and are more likely to carry alleles associated with BSB. Because homosexual sexual behavior does not result in offspring, evolutionary biologists have long wondered how genes associated with this behavior have persisted in the human genome and whether they will remain in the future. To this end, UM researchers analyzed data from more than 450,000 participants of European descent in the UK Biobank database, which contains genetic and health information. Participants responded to a questionnaire that included the question: “Would you describe yourself as someone who takes risks?” These and other observations indicated that male BSB-associated alleles confer reproductive benefits due to genetic variants shared between male bisexual and risk-taking behaviors. “Our findings suggest that male alleles associated with BSBs are likely reproductively advantageous, which may explain their past persistence and predict their maintenance in the future,” said UM evolutionary biologist Jianzhi Zhang, lead author senior of the firm.
“Research also shows that risk-taking is the underlying cause that boosts reproduction in heterosexuals by alleles associated with BSB,” Zhang said. “In other words,” Zhang continued, “the reproductive advantage of BSB-associated alleles is a byproduct of the reproductive advantage of risk-taking behavior.” Risk appetite usually describes the tendency to take actions that require reward despite the possibility of negative consequences. “Although the UK Biobank question on risk taking did not specify the type of risk, it is likely that self-reported risk taking includes unprotected sex and promiscuity, which could lead to more children,” Zhang explained. In analyzing the genetic basis of same-sex sexual behavior, the UM researchers examined both bisexual and same-sex exclusive behavior, which they called eSSB. When they compared the genetic basis of bisexual behavior with that of eSSB, they found that they were significantly different. The scientists also found that genetic variants associated with eSSB are related to fewer offspring, which should lead to a gradual decline in their frequency over time. However, the authors point out that their study examines the genetic basis of same-sex sexual behavior and not the behaviors themselves, which are influenced by both genetic and environmental factors. According to the researchers, in fact, in recent decades the percentage of participants in the UK Biobank who declared having sexual behavior with people of the same sex has increased, probably due to the growing openness and social acceptance of these sexual tendencies and practices. “The results – the authors stated – predominantly contribute to the diversity, richness and better understanding of human sexuality, without suggesting or endorsing discrimination on the basis of sexual behavior.” The new study follows one published in May in the Proceedings of the National Academy of Sciences by Song and Zhang. This analysis also sought to explain the persistence of genetic variants associated with same-sex sexual behavior. In 2021, Australian biologist Brendan Zietsch and colleagues presented evidence that heterosexuals carrying same-sex associated alleles have a greater number of sexual partners than those who do not carry the variants. According to the authors, this could confer a genetic advantage because a greater number of sexual partners could translate into a greater number of children. In their study, which was also based on data from the UK Biobank, Zhang and Song demonstrated that, while the mechanism proposed by Zietsch probably worked in pre-modern societies, it is no longer active today because the widespread use of contraception has decoupled the number of children by the number of sexual partners in heterosexuals. The data presented in the PNAS paper prompted Zhang and Song to look for other potential mechanisms for the genetic maintenance of human same-sex behavior and led the researchers to conduct the most in-depth study reported in Science Advances.
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