Genetic variants underlying male bisexual behavior, risk-taking linked to more children, study suggests

Because same-sex sexual behavior does not result in offspring, evolutionary biologists have long wondered how genes associated with this behavior persisted in the human genome and whether they will remain so in the future.

A new study led by the University of Michigan, published in the journal Scientists progresssuggests that part of the explanation, particularly for bisexual men, has to do with risky behavior.

UM researchers analyzed data from more than 450,000 participants of European ancestry in the UK’s Biobank database of genetic and health information. Participants responded to a questionnaire including the question: “Would you describe yourself as someone who takes risks?” »

The UM analysis found that heterosexual men 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.

These and other observations suggest that male BSB-associated alleles confer reproductive advantages due to genetic variants shared between bisexual and risk-taking male behaviors.

“Our results suggest that male BSB-associated alleles are likely reproductively advantageous, which may explain their past persistence and predict their future maintenance,” said UM evolutionary biologist Jianzhi Zhang, lead author of the study. study.

“These results also suggest that risky behavior is the underlying cause of the promotion of reproduction by BSB-associated alleles in heterosexuals. That is, the reproductive advantage of BSB-associated alleles is a byproduct of the reproductive advantage of risky behavior,” said Zhang, the Marshall W. Nirenberg Collegiate Professor in the Department of Ecology and Evolutionary Biology. The first author of the new study is UM graduate student Siliang Song.

Risk propensity generally describes a tendency to engage in reward-seeking actions despite the possibility of negative consequences. Although the UK Biobank question on risk-taking does not specify the type of risk, it is likely that self-reported risk-taking includes unprotected sex and promiscuity, which could result in more children , Zhang said.

In their analysis of the genetic underpinnings of same-sex sexual behavior, the UM researchers looked at both bisexual behavior and exclusive same-sex behavior, which they call eSSB.

When they compared the genetic basis of bisexual behavior to the genetic basis of eSSB, they found that they were significantly different. They found that genetic variants associated with eSSB are correlated with fewer children, which should lead to a gradual decrease in their frequency over time.

However, the authors emphasize that their study focuses on the genetic underpinnings of same-sex sexual behavior and not on the behaviors themselves, which are affected by both genetic and environmental factors.

In fact, researchers say, the proportion of UK Biobank participants reporting same-sex sexual behavior has increased in recent decades, likely due to society’s increasing openness about it.

Furthermore, the authors claim that their new results “contribute predominantly to the diversity, richness and better understanding of human sexuality.” They are in no way intended to suggest or endorse discrimination based on sexual behavior,” they wrote.

The new study follows one published in May in Proceedings of the National Academy of Sciences by Song and Zhang. This study 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 more sexual partners than those who do not carry the variants. This could confer a genetic advantage, the authors suggest, because a greater number of sexual partners could translate into a greater number of children.

In their PNAS In their study, which also used data from the UK Biobank, Zhang and Song showed that although the mechanism proposed by Zietsch probably worked in pre-modern societies, it is not active today because that the widespread use of contraception has decoupled the number of offspring from the number of children. sexual partners among heterosexuals.

The conclusions presented in this PNAS The paper led Zhang and Song to search for other potential mechanisms for the genetic maintenance of human same-sex behavior.