It’s my impression that many straight people believe that there are two types of gay men in this world: those who like to give, and those who like to receive. No, I’m not referring to the relative generosity or gift-giving habits of homosexuals. Not exactly, anyway. Rather, the distinction concerns gay men’s sexual role preferences when it comes to the act of anal intercourse. But like most aspects of human sexuality , it’s not quite that simple.

I’m very much aware that some readers may think that this type of article does not belong on this website. But the great thing about good science is that it’s amoral, objective and doesn’t cater to the court of public opinion. Data don’t cringe; people do. Whether we’re talking about a penis in a vagina or one in an anus, it’s human behavior all the same. The ubiquity of homosexual behavior alone makes it fascinating. What’s more, the study of self-labels in gay men has considerable applied value, such as its possible predictive capacity in tracking risky sexual behaviors and safe sex practices.

People who derive more pleasure (or perhaps suffer less anxiety or discomfort) from acting as the insertive partner are referred to colloquially as “tops,” whereas those who have a clear preference for serving as the receptive partner are commonly known as “bottoms.” There are plenty of other descriptive slang terms for this gay male dichotomy as well, some repeatable (“pitchers vs. catchers,” “active vs. passive,” “dominant vs. submissive”) and others not—well, not for Scientific American , anyway.

In fact, survey studies have found that many gay men actually self-identify as “versatile,” which means that they have no strong preference for either the insertive or the receptive role. For a small minority, the distinction doesn’t even apply, since some gay men lack any interest in anal sex and instead prefer different sexual activities. Still other men refuse to self-label as tops, bottoms, versatiles or even “gay” at all, despite their having frequent anal sex with gay men. These are the so-called “Men Who Have Sex With Men” (or MSM) who are often in heterosexual relations as well.

Several years ago, a team of scientists led by Trevor Hart at the Centers for Disease Control and Prevention in Atlanta studied a group of of 205 gay male participants. Among the group’s major findings—reported in a 2003 issue of The Journal of Sex Research —were these:

(1) Self-labels are meaningfully correlated with actual sexual behaviors. That is to say, based on self-reports of their recent sexual histories, those who identify as tops are indeed more likely to act as the insertive partner, bottoms are more likely be the receptive partner, and versatiles occupy an intermediate status in sex behavior.

(2) Compared to bottoms, tops are more frequently engaged in (or at least they acknowledge being attracted to) other insertive sexual behaviors. For example, tops also tend to be the more frequent insertive partner during oral intercourse. In fact, this finding of the generalizability of top/bottom self-labels to other types of sexual practices was also uncovered in a correlational study by David Moskowitz, Gerulf Reiger and Michael Roloff. In a 2008 issue of Sexual and Relationship Therapy, these scientists reported that tops were more likely to be the insertive partner in everything from sex-toy play to verbal abuse to urination play.

(3) Tops were more likely than both bottoms and versatiles to reject a gay self-identity and to have had sex with a woman in the past three months. They also manifested higher internalized homophobia—essentially the degree of self-loathing linked to their homosexual desires.

(4) Versatiles seem to enjoy better psychological health. Hart and his coauthors speculate that this may be due to their greater sexual sensation seeking, lower erotophobia (fear of sex), and greater comfort with a variety of roles and activities.

One of Hart and his colleagues’ primary aims with this correlational study was to determine if self-labels in gay men might shed light on the epidemic spread of the AIDS virus. In fact, self-labels failed to correlate with unprotected intercourse and thus couldn’t be used as a reliable predictor of condom use. Yet the authors make an excellent—potentially lifesaving—point:

Although self-labels were not associated with unprotected intercourse, tops, who engaged in a greater proportion of insertive anal sex than other groups, were also less likely to identify as gay. Non-gay-identified MSW [again, “Men Who Have Sex With Men”] may have less contact with HIV prevention messages and may be less likely to be reached by HIV-prevention programs than are gay-identified men. Tops may be less likely to be recruited in venues frequented by gay men, and their greater internalized homophobia may result in greater denial of ever engaging in sex with other men. Tops also may be more likely to transmit HIV to women because of their greater likelihood of being behaviorally bisexual.

Beyond these important health implications of the top/bottom/versatile self-labels are a variety of other personality, social and physical correlates. For example, in the article by Moskowitz, Reiger and Roloff, the authors note that prospective gay male couples might want to weigh this issue of sex role preferences seriously before committing to anything longterm. From a sexual point of view, there are obvious logistical problems of two tops or two bottoms being in a monogamous relationship. But since these sexual role preferences tend to reflect other behavioral traits (such as tops being more aggressive and assertive than bottoms), “such relationships also might be more likely to encounter conflict quicker than relationships between complementary self-labels.”

Another intriguing study was reported in a 2003 issue of the Archives of Sexual Behavior by anthropologist Mathew McIntyre. McIntyre had 44 gay male members of Harvard University’s gay and lesbian alumni group mail him clear photocopies of their right hand along with a completed questionnaire on their occupations, sexual roles, and other measures of interest. This procedure allowed him to investigate possible correlations between such variables with the well-known “2D:4D effect." This effect refers to the finding that the greater* the difference in length between the second and fourth digits of the human hand—particularly the right hand—the greater the presence of prenatal androgens during fetal development leading to subsequent “masculinizing” characteristics. Somewhat curiously, McIntyre discovered a small but statistically significant negative correlation between 2D:4D and sexual self-label. That is to say, at least in this small sample of gay Harvard alumni, those with the more masculinized 2D:4D profile were in fact more likely to report being on the receiving end of anal intercourse and to demonstrate more “feminine” attitudes in general.

Many questions about gay self-labels and their relation to development, social behavior, genes and neurological substrates remain to be answered—indeed, they remain to be asked. Further complexity is suggested by the fact that many gay men go one step further and use secondary self-labels, such as “service top” and “power bottom” (a pairing in which the top is actually submissive to the bottom). For the right scientist, there’s a life’s work just waiting to be had.

*Editors' note (9/17/09): The article originally stated in error that the shorter the difference in length between the second and fourth digits of the human hand—particularly the right hand—the greater the presence of prenatal androgens during fetal development.