Not every gay man has a female best friend, nor does every straight woman have a gay man as her most trusted confidant. But according to a recent article in Evolutionary Psychology, every one should. The authors of this piece, the psychologist Eric Russell and his colleagues from Texas Christian University, claim that the age-old relationship between the homosexual male and the heterosexual female served (and likely continues to serve) a biologically adaptive function.

It’s an ancient alliance, they reason, that is unique among human social bonds for one important reason: the absence of ulterior motives in the domain of sexual behavior. “Straight women may experience increased trust in their relationships with gay men,” explain the authors:

… due to the absence of deceptive mating motivations that frequently taint their relationships with straight men (sexual interest) and other straight women (mate competition).

In terms of having someone to help them to make the most adaptive reproductive decisions, it’s a one-sided friendship. But the authors reason that gay men also derive indirect sexual benefits from having straight female friends:

The sexual interest and competitive motives that may taint gay men’s friendships with each other are notably absent from their relationships with straight women.

And therein lies the win-win for both:

Despite being sexually attracted to the same gender (i.e., men), gay men and straight women are neither potential romantic partners nor mating competition for each other. They are thus uniquely positioned to provide one another with mating-relevant advice and support that is not tainted with ulterior motives borne from intrasexual rivalry or competition.

There’s a lot of talk about ‘tainting’ in the foregoing analysis. That’s shorthand for the ambiguous, deliberate, or awkward sexual tensions that can undermine even the best platonic friendships between a straight woman and a straight man (or between two gay men.) Needless to say, every friendship, no matter the sexual orientations of the parties involved, is different. Yet prior studies have indeed revealed that both straight women and gay men rate their friendships with each other as being qualitatively more meaningful and deeper than other friendships.

Such previous work—which also found that straight women with gay male friends tend to have a positive body image, to feel sexually attractive and secure, and to consider themselves appreciated for their personality—used survey data, thus keeping scientists from drawing any conclusions about the underlying causes. Russell’s study, by contrast, is the first experimental approach to unraveling the mysteries of this distinct type of relationship, and the authors set out explicitly to test their hypothesis that it all boils down to getting unbiased mate advice.

The experiments were in fact quite modest. In the first study, the investigators zeroed in on the vantage point of 88 straight undergraduate females. All of these women read the same hypothetical scenario, which was as follows:

Imagine that you have recently been invited to a party by your friend. It is the night of the party and your friend becomes ill. However, they suggest you attend the party with one of their neighbors. You do not know this person, but you decide to look them up on Facebook before accompanying them to the party.

The participants were then shown a fake Facebook profile of the college-aged neighbor, including a photo and clear information about the person being: (a) a gay male; (b) a straight male; or (c) a straight female. (The authors point out that the photo depicted a person of average attractiveness; for the two male conditions, the image was of the same person, so that only the sexual orientation of the target differed). The women were then asked a series of questions about this target—who, by the way, was given the androgynous name “Jordan” in all three conditions. More specifically, how much would they trust this “Jordan” when it came to making a variety of mating-related decisions? So, for example:

Imagine that you try on something different, and Jordan compliments you on your appearance. What is the likelihood that Jordan is being sincere?

How likely would you [be to] trust Jordan to tell you that you have something stuck in your teeth before talking to an attractive man at the party?

Imagine this attractive man at the party starts flirting with you. He seems really nice and is really interested [in] what you have to say. However, Jordan later tells you that, “He isn’t really interested in you.” How likely would you [be to] trust Jordan?

And so on...

Just as Russell and his colleagues predicted, the straight women who’d been randomly assigned to the “gay male Jordan” condition rated his trustworthiness as significantly higher compared to those answering questions about “straight male Jordan” or “straight female Jordan.” The latter two were seen as being equally (un)trustworthy, supporting the authors’ “ulterior motive” account.

But what happens when the roles are reversed? Do gay men perceive straight women as being similarly trustworthy allies in love and war? Well, yes, apparently so. In the second study, the researchers replicated the party/Facebook experiment, but the participants this time were gay men rather than straight women. “Straight male Jordan” was also replaced with “lesbian Jordan” in the hypothetical scenario. On the one hand, lesbians and gay men have the whole homosexuality thing in common, and their friendships lack ulterior sexual motives. On the other hand, argue the authors, since gay men and lesbians are attracted to different genders, this absence of a common sexual interest may lead gay men to perceive lesbians as less trustworthy than straight women, at least when it comes to relationship and dating advice. And indeed, that’s precisely what they found. Gay men who were randomly assigned to the “straight female Jordan” perceived the target’s trustworthiness to be significantly higher than those who got the “lesbian Jordan” or “gay male Jordan.”

The authors concede that their study was simply an exploratory investigation. And, as such, it has its limits. For example, it’s unknown if these perceptions of the target’s trustworthiness would translate to other adaptive decision-making domains as well. All else being equal, for instance, would a gay man also take a straight woman’s financial advice over that of a lesbian or a fellow gay man? It’s also not entirely clear to me why lesbians and straight men wouldn’t enjoy a similar evolutionary dynamic. But friendships between lesbians and straight men are considerably less common than those between gay men and straight women.

Another point to keep in mind here is that Russell’s study only tapped into perceptions of trustworthiness. Whether or not, say, gay men are actually more trustworthy than straight men (or other straight women) when it comes to doling our mating advice is a very different empirical question. And finally, although we may be more sincere and trustworthy, ladies, that also doesn’t make us right.