— Can genes explain sexuality? Should we even try to know?

By Katie MacBride

There’s nothing new about being gay, but that hasn’t stopped scientists from trying to understand it.

Over the past two decades, many researchers have become focused on the notion of a “gay gene” — biological proof that one was “born this way.”

It makes sense: Our genes can influence who we are, and psychologists contend sexual orientation is not a conscious choice. It theoretically stands to reason there might be genetic underpinnings to who we become sexually attracted to.

But more recent research has both confirmed and debunked the notion of a genetic basis for sexual orientation. Instead of just one gene (or one marker on one gene) that determines sexual orientation, there are many genes with markers related to attraction to the same sex.

For example, in 2019, the researchers studying those markers and same-sex attraction told Inverse: “This finding suggests that on a genetic level, there is no single dimension from opposite-sex to same-sex preference.”

But that’s just part of the story.

Two new studies published Monday, one in Nature Human Behavior and the other in Scientific Reports, further illuminate the complexities of sexual orientation and how fraught scientific study of the subject is. They also highlight three key factors:

1. Our own sexual orientation may be much more fluid than we thought.
2. The same cluster of genes that may be associated with same-sex sexual behavior may confer some evolutionary advantage.
3. There are inherent dangers in focusing on genetics in relation to sexual orientation.

Genes and sexual behavior — First author Brendan Zietsch, an associate professor of psychology at the University of Queensland in Australia, and colleagues attempted to discover why the genes associated with same-sex sexual behavior continue to flourish. Their study was published in Nature Human Behavior.

In a statement, the study authors report:

“Because [same-sex sexual behavior] SSB confers no immediately obvious direct reproductive or survival benefit and can divert mating effort away from reproductive opportunities, its widespread occurrence across the animal kingdom and human cultures raise questions for evolutionary biology.”

Using information from the UK Biobank, and questionnaire responses about sexual behavior from hundreds of thousands of individuals, the study team analyzed the genome of 477,522 people in the United Kingdom and the United States who had only had same-sex interactions.

They compared that data set to the genome of 358,426 people in the same countries who had only had opposite-sex encounters.

The team found the genes linked to same-sex behavior are also found in straight people. This gene profile across groups is associated with having more sexual partners.

The authors posit that the number of opposite-sex sexual partners could be advantageous from an evolutionary perspective, as it could lead to more children.

In turn, they argue their results help explain why same-sex sexual behavior has persisted throughout the evolution of the human species: These genetic effects may have been favored by evolution as they are associated with more children.

Ultimately and critically, the authors claim, the genes may less have to do with sexual preference and more to do with sexual openness/willingness.

The ethical debate — Other scientists caution against extrapolating information about sexual preference or behavior from genes.

In a commentary piece published alongside the study, ethicists Julian Savulescu, Brian D. Earp, and Udo Schuklenk distill the debate around whether or not this kind of research will lead to societal abuse.

They write:

“One can imagine technologically advanced repressive regimes where homosexuality is outlawed requiring genetic testing of embryos and foetuses, destroying those disposed to SSB, or testing children early in life for their propensities. Others will respond that the world (or at least some parts of it) has become more accepting of homosexuality, so perhaps these worries are overblown.”

What matters, they argue, is creating a society in which this kind of genetic research can’t be abused to further harm anyone, much less already marginalized groups.

They write: “Genes shape, limit, and provide opportunities for who we are and who we can be, both as individuals and as members of communities. To prepare for further research into polygenic behavioral traits including SSB, we must reshape society.”

Ilan Dar-Nimrod, a researcher and professor at The University of Sydney’s School of Psychology, tells Inverse “genes are taking oversize agency” in the minds of sexual behavior researchers.

“Genes code for properties,” he explains. “And although they can predict a lot of things, many people have this one-to-one view: if you have the gene, you’re going to be that and you can’t change it.”

That’s simply not in line with what we know about the science of genetics, he says.

On Monday, Dar-Nimrod and his colleagues also published a study looking at sexual preferences, this one in Scientific Reports. This study’s results support his assertion about preferences being more malleable than genes would suggest.

Sexuality is a spectrum

In their study, Dar-Dimrod and colleagues asked 420 cisgender people ranging in age from 18 to 83 to read literature. The study participants identified as exclusively heterosexual.

“We’ve just changed how they look at it.”

One group read literature about sexual preferences as a fluid spectrum. For example, one of the articles discussed gradations of sexual attraction towards men and women and noted that people can fall anywhere along the continuum. Another article explained that sexual orientation can change over time, shifting throughout one’s life instead of being fixed. The control group read unrelated articles.

After reading the literature about sexual fluidity:

• Twenty-eight percent of the participants in the experimental group were more likely to identify as non-exclusively heterosexual.
• Nineteen percent indicated they would be more likely to be willing to engage in same-sex sexual activities.

The rate of participants identifying as “non-exclusive heterosexual” more than quadrupled after the experiment.

In contrast, in the control group, only 8 percent of the participants identified as “non-exclusively heterosexual” after reading the literature unrelated to sexual preferences.

Dar-Nimrod says there were several results that surprised him:

• How many people in the experimental group identified as “non-exclusively heterosexual” following the experiment
• People actually expressed a willingness to engage in same-sex activities following the experiment
• That even when balanced with literature refuting the idea of sexual preference as a spectrum — one of the articles argued that sexual orientation is indeed fixed — participants still gave more credence to the literature that discussed a sexual spectrum

Dar-Nimord doesn’t believe the literature he had the experimental group read actually changed who the participants were attracted to.

“We haven’t changed the underlying orientation,” he says. “We’ve just changed how they look at it.”

While our genes may predispose us to certain traits and conditions, when it comes to behavior, our society, environment, and relationships all play a huge role in how we behave.

“Do we really need to suggest that [queer people] were born with a certain gene to accept them and their relationships with other consenting adults?” Dar-Nimord says. “I don’t think so.”

Once we realize we’re not in fixed, black and white boxes, we have the freedom to explore the gray area to which most of us belong. At least, that’s what science really can show.

Nature Human Behavior abstract: Human same-sex sexual behaviour (SSB) is heritable, confers no immediately obvious direct reproductive or survival benefit and can divert mating effort from reproductive opportunities. This presents a Darwinian paradox: why has SSB been maintained despite apparent selection against it? We show that genetic effects associated with SSB may, in individuals who only engage in opposite-sex sexual behaviour (OSB individuals), confer a mating advantage. Using results from a recent genome-wide association study of SSB and a new genome-wide association study on number of opposite-sex sexual partners in 358,426 individuals, we show that, among OSB individuals, genetic effects associated with SSB are associated with having more opposite-sex sexual partners. Computer simulations suggest that such a mating advantage for alleles associated with SSB could help explain how it has been evolutionarily maintained. Caveats include the cultural specificity of our UK and US samples, the societal regulation of sexual behaviour in these populations, the difficulty of measuring mating success and the fact that measured variants capture a minority of the total genetic variation in the traits.

Scientific Reports abstract: We examined whether heterosexual individuals’ self‐reported sexual orientation could be influenced experimentally by manipulating their knowledge of the nature of sexual orientation. In Study 1 (180 university students, 66% female) participants read summaries describing evidence for sexual orientation existing on a continuum versus discrete categories or a control manipulation, and in Study 2 (460 participants in a nationally representative Qualtrics panel, 50% female) additionally read summaries describing sexual orientation as fluid versus stable across the life‐course. After reading summaries, participants answered various questions about their sexual orientation. In Study 1, political moderates and progressives (but not conservatives) who read the continuous manipulation subsequently reported being less exclusively heterosexual, and regardless of political alignment, participants reported less certainty about their sexual orientation, relative to controls. In Study 2, after exposure to fluid or continuous manipulations heterosexual participants were up to five times more likely than controls to rate themselves as non‐exclusively heterosexual. Additionally, those in the continuous condition reported less certainty about their sexual orientation and were more willing to engage in future same‐sex sexual experiences, than those in the control condition. These results suggest that non‐traditional theories of sexual orientation can lead heterosexuals to embrace less exclusive heterosexual orientations.

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Being gay no longer holds the stigma it once did, but in evolution, why does a non-reproductive trait persist?

By Tom Whipple

In 1913 George Levick, an explorer, travelled to Antarctica. There, he found something so terrible that he requested his findings not be published. In case the correspondence was leaked or intercepted, he took the further precaution of writing key sections in ancient Greek: these were not letters to be read by the lower orders.

Levick had been studying penguins: birds whose monogamous lifestyle had so impressed the Victorians that they had been held up as models of probity and integrity.

But he had seen something on his trip to the bottom of the world that had caused him to question that assessment. “There seems,” he wrote with palpable shock, “to be no crime too low for these penguins.” Levick’s penguins, you see, were gay.

And if penguins can be homosexual, what was to say that that behaviour, far from being the perversion society presumed it was, was natural in humans too?

These days homosexuals, avian or otherwise, generally have an easier time of it. While we may have accepted that same sex attraction is natural, though, there is a far harder question: why is it natural?

We know that homosexuality is, at least in part, genetic. Studies show, for instance, that identical twins are more likely to be both homosexual than non-identical twins. So it is passed on by evolution. This is a problem, particularly so with men – who for obvious reasons find it harder to fake an interest in sex.

Imagine you had never heard of evolution, and someone described it to you. One of the most basic predictions you would surely make is that a trait that made people less likely to reproduce should die out. Male homosexuality, a trait that, at least among exclusive homosexuals, means people have no interest at all in the act of reproduction, should never have existed in the first place. And yet it does. How?

To answer that question, researchers have gone to a place where homosexuality itself does not exist, at least in the form we know it: Samoa. Here, in the South Pacific, there is a third gender called the Fa’afafine – a group born male who behave as women.

This is not the only place with third genders. There are the “Two-Spirit” people of Native America. There are the Khatoey ladyboys of Thailand. There are the Hijras of Pakistan. In 2004 a Hijra, Asha Devi, was elected mayor of Gorakhpur under the slogan “You’ve tried the men and tried the women. Now try something different”.

Paul Vasey, from the University of Lethbridge in Canada, believes that homosexuality as it manifests itself in most of today’s world is unusual. In more ancient cultures, he thinks you can see homosexuality as it was practised by our ancestors in deep time – as a “third gender”.

And in looking at these third genders – in particular the Fa’afafine – he believes we can find clues as to why this evolutionary paradox of male homosexuality persists.

What is interesting for Professor Vasey is that, firstly, there is no recognised gay identity in Samoa and that, secondly, the Fa’afafine occur at the same proportion as male homosexuals in the west. He believes there is a simple explanation for this.

“I’m gay,” says Professor Vasey. “But if I’d grown up in Samoa I wouldn’t look like this. I’d probably look like a really ugly Fa’afafine.”

Fa’afafine translates literally as “in the manner of a woman”. Boys who appear more feminised in their behaviour will often be classified as a Fa’afafine, and brought up as something between a woman and a man. There is also an analogue for masculinised girls – Fa’afatama.

The fact they also go on to sleep with men is not the only similarity between Fa’afafine and western gay men. “There’s all kinds of traits the two share in common. Both exhibit elevated childhood gender atypical behaviour, both exhibit elevated childhood cross sex wishes, both exhibit elevated childhood separation anxiety, both prefer female-typical occupations in adulthood.”

For Professor Vasey, it seems obvious that being Fa’afafine and being gay is the “same trait, expressed differently depending on the culture.” He even argues that the oddity is the West – that the way homosexuality manifests in Europe and North America may even be an expression of our repression rather than our freedom.

“The part of the brain that controls sexual partner preference, it’s the same for all of us,” he says. “It’s just that if you take that biological potential, put it in Samoa where society doesn’t flip out about male femininity, then feminine little boys grow up to be Fa’afafine. If you take that potential, put it in Canada, feminine boys learn pretty quickly they had better masculinise to survive.” This, he believes, is precisely what he ended up doing.

Whether the “third gender” really is the ancestral form of homosexuality, with the way it is practised in the West today an aberration, is a separate issue. That it can take such widely different forms, shows the impact society can have on sexuality. That its prevalence remains largely the same also shows the limits of such socialisation – that there is something else going on. But what?

Professor Vasey is one of the very few scientists in the world looking at this question, and he does so thanks to the Fa’afafine. There are two specific theories used to explain male homosexuality that he is interested in. The first could be termed the “benevolent uncle hypothesis”.

Alatina Ioelu does not remember not being a Fa’afafine. Yet he does remember not wanting to be one. “You don’t really come out,” he said. “You’re just that. In a way it’s good, in a way it’s not good. When you’re growing up as a kid you’re innocent of your actions, how you move or sound. You’re not aware you are doing something that doesn’t conform to the norms of how society considers boys.”

But he clearly didn’t, because his classmates began to call him a Fa’afafine. “And so you grow up being known as that. I wanted to distance myself from it, I didn’t want to be that.” He couldn’t, though, because he realised it was true. “In the end you’re like, ‘sh*t, that’s what I am.’”

It would be wrong to claim that the Fa’afafine are completely accepted in Samoa. There is a place for them, however, and always has been. “They walk around and nobody says, ‘Oh, that’s a Fa’afafine’. In my family we have a long line going back. I have a great uncle that’s a Fa’afafine, I have four second cousins, a first cousin…”

He realised that this itself was a paradox – all these Fa’afafine going back generations. “How the hell do we have Fa’afafine, and they don’t reproduce? How is it we are still around, when we don’t have children?”

He also realised that Professor Vasey may have the answer. Fa’afafine do not have biological children of their own. Conventionally, from the point Alatina realised who he was, he was taking himself out of the reproductive game. Or was he? Perhaps not entirely.

The benevolent uncle explanation is based on the idea that there is more than one way to pass on your genes. The best way to reproduce, in terms of percentage of genes passed on, is to clone yourself through asexual reproduction. Stick insects can do this. Humans, alas, can’t.

The most efficient method we have to perpetuate our genes is sexual reproduction – passing on half our DNA each time. It is not the only option, though. Your siblings, for instance, share half your genes, which means your nieces and nephews share a quarter. To an uncle each of those nieces and nephews is therefore, from a genetic point of view, worth half a child.

What if simply having an extra man around, a benevolent uncle to provide for the extended family’s children, was enough to ensure more of those children survive to reproduce themselves? This could be where the Fa’afafine come in. Alatina says that there are clear and defined roles for them.

“They become almost like the caretakers of families. They are responsible for taking care of the elderly, parents, grandparents, even their siblings’ children. Because they are feminine they take up this motherly role in families.”

Having an extra hardworking adult without dependants is no minor advantage. Everyone has extra fish, extra firewood – and fuller bellies. It is not implausible that, particularly in difficult times, a childless Fa’afafine could ensure more nieces and nephews reach reproductive age. That is the idea behind the benevolent uncles hypothesis, that good uncling becomes a form of reproduction in itself.

To test the theory, Professor Vasey looks to see if the Fa’afafine are more avuncular – literally, uncle-like. He has found that, compared to single straight men or aunts, they are indeed more likely to want to look after their nieces and nephews. They take more interest in them, babysit more than straight men, buy more toys, tutor more and contribute more money to their education.

Of course, in order for a gay uncle to be useful you need to ensure he actually has nieces and nephews (and preferably a lot of them) to be useful for. There’s no point in being a good uncle with no one to look after. So it would be good for this theory if gay uncles were more likely to pop up in big families. Incredibly, they do.

One of the best-established and more intriguing results in homosexuality research is that the more elder brothers a man has, the greater his chances of being gay. The mechanism, only discovered this year, seems to involve each pregnancy leading the mother to develop antibodies against a protein involved in male foetal brain development.

The result is, as families get more likely to benefit from the services of a gay uncle, the chances of one appearing increases.

Problem solved? Not quite. In order for this to completely explain homosexuality, a lot of extra nieces and nephews would have to be born and survive – probably too many for the genetic mathematics to add up.

But Professor Vasey does not think the benevolent uncle theory needs to be a complete explanation. It can be one of many, and the other leading contender is the “sexually antagonistic gene hypothesis”, more snappily known as the “sexy sisters hypothesis”.

What if the genes for homosexuality persist because despite making non-reproductive (if avuncular) men, when they appear in women they produce excellent breeders? Again the Fa’afafine, and Samoa, have been his laboratory. Professor Vasey took 86 Fa’afafine, and 86 heterosexual Samoan men. He then looked at their grandmothers – who are easier to study than sisters, because all their breeding is already finished.

He found that the grandmothers of the Fa’afafine were indeed better breeders. The theory is simple. By passing on their genes these grandmothers might end up with the occasional grandson who wears dresses and doesn’t reproduce (though always remembers his nieces’ and nephews’ birthdays). But they themselves, thanks to the very same genes, were also better at reproducing – so made enough other grandchildren to make up for it. There is a problem, though, given the way the theory was originally framed. Somehow, the “sexy grandmothers’ hypothesis” just doesn’t have the same ring to it.

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