Photo: Matthias Ritzmann/? Corbis. All Rights Reserved.

When it comes to the study of relationships, few topics serve up as much rich fodder as jealousy. It can be a frustrating, destructive force — and therefore one that’s worth understanding better.

A recent study in Archives of Sexual Behavior seeks to understand some of the gender differences in jealousy that have been previously observed. Specifically, the researchers, David Frederick of Chapman University and Melissa Fales of UCLA, were curious whether a big data set would replicate a common previous finding about heterosexual dating: Men are more upset by the prospect of sexual infidelity (even when there’s no emotional connection), and women are more upset by the prospect of emotional infidelity (even when there’s no sex taking place).

The researchers took data from a survey posted on the former msnbc.com back in 2007. A total of 63,894 people filled it out, making for a large and useful sample, and they answered a wide variety of questions about relationships and dating.

Frederick and Fales were interested in one section in particular:

Participants were presented with the following scenario: “Take a moment to imagine which of the following situations would be MOST upsetting or distressing to you.” They then chose between the following options: “You found out that your partner is having a sexual relationship with someone else (but has not fallen in love with this person)” or “You found out that your partner has fallen in love with someone else (but is not having a sexual relationship with this person).”

There was one group, and one group alone, for which the concept of a partner having sex with someone but not falling in love was more upsetting than the reverse: straight men. Fifty-four percent of them said they’d be more upset by that, “more so than heterosexual women (35%), gay men (32%), lesbian women (34%), bisexual men (30%), and bisexual women (27%).”

What can account for this? Evolution, say the researchers. This question of sexual versus emotional cheating touches upon two big problems humans faced back in the day (and still do, sometimes) — one unique to men, the other unique to women.

Men who were helping a partner raise a kid, at least before the days of DNA testing, could never be 100 percent sure the kid they were raising was theirs. From an evolutionary perspective, it’s a really big commitment of time and energy to stick around and raise a kid — and one only “worth it” — in that crude evolutionary sense — if you get to help ensure the survival of your DNA in the process, not some random dude’s. So for men, the idea of a female partner sleeping with another man summons the unpleasant idea of inadvertently raising his kid. Emotional infidelity without the sex part doesn’t pose the same threat.

Women have always faced a different problem: the possibility that the man helping them raise a kid will take off, reducing the odds that the child will survive (and that mom’s genes will be passed on). Here, emotional infidelity is a bigger risk factor in terms of the man actually leaving — it doesn’t actually matter if the guy is stepping out (again, in that crude evolutionary sense) if at the end of the day he’s around to take care of the kid.

Okay, back to reality for a second. The problem with theories like these, of course, is that they reflect a bygone world, and it’s almost impossible to suss out exactly how the psychological imprint of evolution and a million modern influences interact with one another and come to shape our behavior. It’s easy, after all, to imagine that various cultural or technological innovations have muted the influence of evolutionary factors (to take the obligatory example, some of us eat much less fat than evolution “wants” us to, because we have access to modern health information and therefore know better). Are these factors as important when a couple has no plans to have kids, for example? Or in countries that are so good on the gender-equality front many women are unlikely to ever have to rely on men?

As the researchers note, while men seem to be more worried about sexual infidelity in most places where the question has been asked, the actual numbers vary quite a bit from country, suggesting that in past studies “there were clearly cultural ecological, and/or contextual factors that produced variation regarding the degree to which men and women were bothered most by sexual infidelity versus emotional infidelity.” (There’s also, of course, the question of how all these worries about reproduction factor in when reproduction in the “old-fashioned” manner isn’t even on the table — that is, couples with gay or bisexual members.)

All this stuff is really, really complicated, and none of the evidence suggests that individual men or women might not have different views. We’re talking about averages here: plenty of men were more upset by emotional infidelity, and plenty of women by sexual infidelity.

Even though the researchers think evolution is the best explanation for the data, they acknowledge throughout the paper that a variety of other factors are in play. Better understanding these factors — and how they reinforce or push back against whatever cards evolution dealt us — is a monumental challenge.