Illustration: Jim Cooke / GMG

While a single factor (the elusive “gay gene,” for example) has yet to emerge in the ongoing scientific investigation of what determines sexuality, there are a host of theories. Genetic factors, hormonal factors, immunological factors, and more have been posited as possible biological causes. However, many experts argue that it’s most likely a confluence of factors, as Barbara L. Frankowski and Committee on Adolescence did in a 2004 article in Pediatrics: “Sexual orientation probably is not determined by any one factor but by a combination of genetic, hormonal, and environmental influences.”

Regardless of how wide-ranging these studies are, they tend to have one thing in common: they treat gay men as a monolithic group. But now a research team out of the University of Toronto Mississauga (Ashlyn Swift-Gallant, Lindsay A. Coome, D. Ashley Monks, and Doug P. VanderLaan) has investigated variation within the population of gay men based on their anal-sex roles (that is bottom, or receptive, top, or penetrative, and versatile, or both receptive and penetrative depending on circumstance). The results of two of their studies suggest there very well could be biological subgroups of gay men, which is to say that one’s biological makeup could possibly (and most likely, indirectly) influence whether or not he likes to fuck or get fucked (or both).

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When it has been studied, anal-sex role has been viewed as a result of social factors (more on that in a minute). Despite every study I’ve read that asks about the anal-sex role of its respondents has found that the majority men who have sex with men identify as versatile (including the two studies at hand from the University of Toronto team) as well as my own anecdotal experience suggesting as much, the top/bottom binary persists in gay culture. It comes with predictable cultural baggage for those who firmly fit on either pole (pun intended—but only for the bottoms). Tops are stereotyped as masculine, taking up the male tradition of putting their dicks in things, while bottoms are regarded as more feminine (despite the overwhelming evidence to the contrary in porn, and the preponderance of self-identified “masc bottoms” in sex-app profiles). And with the assumptions of femininity in men come insults (“bottom” as a pejorative amongst gay men) and with those come a specific kind of shame in addition to the shame many gay men already experience merely living in a heterosexual world.

But perhaps if the variation among gay men has biological basis, it could help make one’s desires, not to mention those of others, less fraught or intimidating, for one thing.

“What’s interesting about this work is even among a group of individuals who are pretty similar in terms of their sexual preference—that is, gay men preferring men—there could be a diverse set of processes that lead them to exhibit that same sexual orientation outcome,” explained VanderLaan, an assistant professor in the University of Toronto Mississauga’s Department of Psychology, and the senior author on two recent papers: “Handedness is a biomarker of variation in anal sex role behavior and Recalled Childhood Gender Nonconformity among gay men,” published on PLOS One, and “Gender Nonconformity and Birth Order in Relation to Anal Sex Role Among Gay Men,” published in Archives of Sexual Behavior.

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Both studies built on previous research suggesting that gay men are more likely to be gender-nonconforming (“less interested in, say, male-typical activities...and [exhibiting] less masculine personality characteristics,” said VanderLaan), are more likely to be non-right handed than their straight counterparts, and are more likely to have older brothers (in what’s known as the fraternal birth order effect, which technically posits that the more older brothers a man has from the same mother, the more likely he is to be gay). The University of Toronto team contacted what would become their sample of men during the 2015 Toronto Pride festivities and asked them to fill out online surveys regarding their sexual positioning (both in preference and behavior—there was discernible variation between the two), their recalled childhood gender nonconformity (which was assigned a number through a regularly used 23-item questionnaire The Recalled Childhood Gender Identity/Gender Role Questionnaire, which asks questions like “As a child my best or closest friend was 1-always a boy, to 5-always a girl,” and “In fantasy or pretend play, I took the role 1-only of boys or men, to 5-only of girls or women), their handedness, and their amount of siblings (the samples of the two studies were almost identical, with 91 straight men surveyed in both studies, and 242 gay men in the handedness study versus the 243 men of the birth order study).

“One thing about handedness is we know it’s related to brain organization and we know that it takes place really early,” said VanderLaan. “People very early in life—infants and children—will show hand preference for activities. That’s what makes handedness such a valuable marker is that it tells us about a particular developmental window.”

The team’s ultimate findings pointed to statistically significant variation amongst the gay men, with bottoms being more likely within the sampled populations to be gender-nonconforming (Table 1) and non-right handed (Table 2), as well as to have a higher proportion of older brothers (Table 3):

Table 1 (Graph: Lindsay Coome)
Table 2 (Graph: Lindsay Coome)
Table 3 (Graph: Lindsay Coome)
Table 4 (Graph: Lindsay Coome)

Note that the handedness study found the strongest links in terms of behavior (i.e. what actually happens during sex) as opposed to preference (i.e. what would ideally happen during sex), whereas the fraternal birth order study found statistical significance in terms of preference (and additionally, it found a correlation between between being versatile and having older sisters). (Contrast Table 3 with Table 4.)

“That was an interesting discrepancy,” said VanderLaan. “Behavior is generally more constrained by what your partner is willing to do with you. Whereas attraction is a more personal aspect of sexuality. You can have a fantasy about whoever you like. This is part of the reason why I feel like there probably isn’t a direct relationship between these early-life developmental biological developmental experiences and these later-life sex role behaviors. There’s probably some set of circumstances that these biological factors are having an indirect effect on anal sex role behavior.”

Additionally, bottoms and versatiles were so similar in terms of reported childhood gender nonconformity as well as handedness that they were grouped together in that study; they differed in terms of birth order, though (bottoms had more older brothers; versatiles had more older sisters) so in that study they were not grouped together.

VanderLaan said that he’d like to see if these studies could be replicated, as they’re the first to look at biomarkers differing between anal sex groups. As with all self-reported studies, this one had its limitations (we can never ignore how sex-based shame may color some gay men’s responses regarding their sexual interests and practices, for example). And VanderLaan concedes that it wasn’t necessarily representative of the entire population as it wasn’t a national probability sample, and it certainly seems that way: The respondents were overwhelmingly white with 301 in the handedness study identifying as such and 302 in the birth order. (Of the remaining 32 in each study, one identified as black, two as Chinese, eight as Asian, two as aboriginal, three as Latin American, 15 as “other,” and one declined to answer.) Additionally, what’s entirely missing from the conversation these studies are attempting to start is why such variation may be occurring.

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“Sex role identity development is a complex process that unfolds over decades, so the idea that some early life developmental experience that happened in the womb has a direct impact on someone’s sex role behavior decades later,” VanderLaan explains, “that seems potentially a little too simplistic and we certainly don’t have demonstrative evidence that that sort of scenario is indeed the case.” Nothing about these findings is meant to be all-encompassing; indeed, this very post has been written by a right-handed gay man with only younger sisters and who identifies as militantly versatile. And I still find it to be interesting as hell.

Instead, though, VanderLaan and his team are looking to biomarkers to get a broader picture of people’s decision-making and that complex process of identity formation. Until now, the vast majority of the research regarding the development anal sex roles in gay and bisexual men has focused on social factors. For example, in a fascinating paper from January’s Archives of Sexual Behavior, “Recognition and Construction of Top, Bottom, and Versatile Orientations in Gay/Bisexual Men,” Northwestern University’s David A. Moskowitz and Northwestern University’s Michael E. Roloff, examined a variety of factors including “attitudinal constructs suggested by previous literature as important” and found that “sexual position self-label was learned over a 15-year timespan.” The attitudinal constructs investigated were: finding bottoming pleasurable, sexual anxiety when bottoming, sexual anxiety when topping, strength/control of a partner, gender typicality of a partner, penis size as a factor, and race/ethnicity of partner as impactful. Though a number of indirect connections were postulated after examining the results, “finding bottoming to be pleasurable and the importance of sexual control dynamics were the only two direct predictors,” according to the paper’s abstract.

I reached out to Moskowitz, whose work has captivated me for years, to ask if the University of Toronto’s biological findings necessarily opposed that of his social-based research or if they could operate in conversation. He emailed back this response:

I specifically conducted [the “Recognition and Construction of Top, Bottom, and Versatile Orientations in Gay/Bisexual Men”] study to try to prove that anal penetrative role was far more innate than ever thought. We wanted to suggest that role, not unlike sexual orientation, was predetermined by biological factors. People could be born a top or a bottom, and that was that. However, we found both in the chronology of gay and bisexual men’s self-labeling of their penetrative roles and in their attitudinal measures, evidence to suggest that understanding and assigning a role developed over time. Role orientation was essentially socialized by reactions to sexual trials, with adjustments made in label according to positive and negative outcome efficacies. Put simply, the more good or bad sexual experiences, over time, lead people to a role.

But despite my study, I am convinced that it is more complicated than that, as the authors of the University of Toronto study suggest. Our studies don’t rule each other out. I still ardently believe that biology plays a vital role in predisposing individuals towards more of a bottom or top orientation, with social maturation and sexual experience accrual potentially doing the rest… shaping the inherently sociopolitical process of self-assignment of a label in a community that LOVES labels.

And that, perhaps, is why Moskowitz (who considers VanderLaan a “great colleague and friend”) is so enthusiastic about the University of Toronto team’s work. “The study is pretty ground-breaking in that no studies to-date have looked at actual biological determinants of penetrative sex roles,” he writes. “For years now, we have anecdotally and empirically understood that some association roughly exists between gender typicality and anal sex roles. Most of us in the field have scrambled to understand the underlying influences of that relationship. The authors of the article provide some well-needed insight into the more innate characteristics that lead to top or bottoming behaviors.”

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Additionally, VanderLaan says that his research provides a window into the formation of the nervous system, and that it starts to help answer the question that many queer people ask of themselves: “How did I come to be the way that I am?”