Researchers in Canada believe there could be a biological component to what makes a gay man a top or bottom in penetrative anal sex.

The divide between dominant and passive sex roles is, of course, laden with baggage, both within the gay community and in the larger heteronormative world: For most of history, being penetrated has been associated with being a woman, and therefore a sign of weakness. And of course sexual practices are influenced by the availability of partners, and the preferences of both parties involved.

But two studies of out of University of Toronto found some interesting correlations among men who have anal sex with other men. Researchers contacted more than 240 men at the 2015 Toronto Pride festivities, asking them to fill out an online survey about their sex positions—both in practice and in preference.

They were further questioned about how gender-conforming they were as children, whether they were left or right handed, and the number and type of siblings they had.

While the survey found bottoms identified as being more gender-nonconforming, they were also more likely to be left-handed and to have more older brothers. The studies also found that non-right-handed men were more likely to be bottoms in actual practice rather than personal preference, while fraternal birth order was more linked to preference. There was also a correlation between between being versatile and having older sisters.

Whether any of these factors is based in biology is hard to pin down: A man who grew up among more women may feel more comfortable expressing what is stereotyped as a “feminine” sex role.

“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,” study author Doug P. VanderLaan told Jezebel’s Rick Juziak.

The question of right/left-handedness is particularly useful, he says, as its evident very early on in life and is generally not affected by social or cultural mores. But VanderLaan doesn’t expect to find a smoking gun, as it were.

“Sex role identity development is a complex process that unfolds over decades,” he says. “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 late… seems potentially a little too simplistic and we certainly don’t have demonstrative evidence that that sort of scenario is indeed the case.”