Currents

It's no secret that over the past decade, the number of people who identify as LGBT has increased. As I’ve covered previously, in 2012, 3.5% of Americans said they were LGBT. By 2022, it was 7.2%. Among Gen Z, it’s nearly 20% — two-thirds of whom are bisexual. This increase in self-identification has led some skeptical commentators, from scholars like Eric Kaufmann to pundits like Bill Maher, to conclude that the reason greater numbers of young people are coming out as LGBT in general, and bi in particular, is largely due to social trends. Underlying such skepticism is the tacit assumption that “actual” bisexuality must be very uncommon, owing to the basic evolutionary logic that same-sex behavior does not result in offspring and must therefore necessarily be limited to a small minority of the population. But groundbreaking new research on the genetics of bisexuality deals a serious blow to this reasoning. The genes associated with bisexual behavior, it turns out, correlate with having more children, not fewer.

The study, just published out of the University of Michigan in the journal Science Advances, analyzed data from over 450,000 people of European ancestry and identified, for the first time, the genetic variants associated with human bisexual behavior. The authors, Siliang Song and Jianzhi Zhang write that “male [bisexual behavior] is genetically positively correlated with the number of offspring.” This is because the genes associated with male bisexuality are also associated with “risk-taking behavior”, which correlates with having a greater number of children. Even among people who exhibit exclusively opposite-sex behavior, the presence of these “bisexual” genes is linked to having more offspring.

The novelty of these findings stems, in part, from the fact that genetic research has tended to study either heterosexuality or homosexuality, often merging bisexuality with homosexuality instead of examining it as its own distinct orientation. "We realized that in the past, people lumped together all homosexual behavior [...] but actually there's a spectrum," Zhang explained to the AFP. “Here we're talking about three traits: number of children, risk-taking, and bisexual behavior: they all share some genetic underpinnings."

This correlation between bisexuality and having more children accords with primate research from 2022 which found that among rhesus macaque monkeys, same-sex behavior, which was observed to be almost entirely bisexual, was a predictor of greater numbers of offspring. Indeed, data from across the animal kingdom shows that over 1,500 known species exhibit same-sex behavior, though almost never exclusively — in other words, bisexual behavior.

When it comes to humans, research going back nearly a century has indicated that bisexuality is far more prevalent than popularly believed. The question of why has baffled scholars and commentators for many years, leading to all manner of speculation. This new genetic study is beginning to fill in some of the explanatory gaps. In doing so, it renders prior notions of bisexuality over the past decade as a “social or political identity” far less persuasive.

Of course, trends, peer influence, and social incentives play a role in the number of people who identify as LGBT, as these factors influence almost everything people do in life. It comes as no surprise that societies who view same-sex behavior as shameful or even deserving of death will have lower rates of self-identification than societies with full legal protections and in which LGBT people are not only accepted, but celebrated. In this sense, it’s perfectly true to say that the social environment plays a significant role in whether a bi person comes out or chooses to act on their desires — but not whether they are bi in the first place. Indeed, Song and Zhang estimate that whether a person engages in bisexual behavior is “40% influenced by genetics and 60% by the environment.” As Zhang told me via email, “I believe that the recent increase in bisexual identification is due to [...] the openness of society to sexual minorities.”

Even so, it may be that in the West, some few openly bi folks are fibbing about their sexual orientation, or perhaps just confused. It may also be that many folks who see themselves as “mostly straight” (which is, by definition, bisexual) are similarly confused, or pressured by their specific communities to stay in the closet. However, this new research shows that bisexuality is not some evolutionary aberrance that can only be rationally explained in small numbers. Rather, the data powerfully demonstrates that bisexual behavior and its associated genes are “reproductively advantageous.” This should cause us to rethink our assumptions about a supposed natural upper ceiling for “legitimate” bisexuality. If it correlates with increased offspring, then using evolutionary logic, we’d be better off supposing that bisexuality is, if not the norm, then at least quite widespread.

Published Jan 9, 2024