People can predict with modest accuracy whether a man (but not a woman) has cheated before based solely on the appearance of his face, according to a recent study published in Royal Society Open Science. In other words, we seem to have a limited ability to pick out men who have committed infidelity just by looking at them.

In this study, 1,516 heterosexual adults (of whom 61% were female and all were White) viewed facial pictures of either male or female adults of the same race as them. The people in these pictures had neutral expressions and the photos were cropped such that most of the hair, neck, and ears weren’t visible—in other words, faces were the main focus.

For each photo they saw, participants were asked to answer the question“How likely is this person to be unfaithful?” on a scale ranging from “not at all likely” to “extremely likely.” The people who provided their photos for this study previously reported on both their cheating and “poaching” behaviors. Specifically, these people reported how many times they had been in a relationship and had sex with someone else (i.e., cheating) as well as how many times they’d had sex with someone else they knew was already in a relationship (i.e., poaching).

It turned out that both male and female participants were able to predict whether men had engaged in cheating and/or poaching based only on looking at their faces. However, neither male nor female participants were able to predict whether women had cheated or poached before based on looks alone.

What was it specifically that was cluing people into whether men had cheated? Facial masculinity appeared to be the key. Men with more masculine-looking faces (think guys with more squared rather than rounded faces) were rated more likely to be unfaithful—and, indeed, these men had committed more acts of both cheating and poaching.

That said, there are some important limitations and caveats here. Perhaps most importantly, we’re talking about a relatively small effect. So although people can predict men’s odds of cheating and poaching at rates higher than chance guessing, they were far from perfect. In other words, just because a man has a more masculine face doesn’t mean he’s destined to cheat. The authors of this study therefore caution that people shouldn’t use this information to judge men’s likelihood of infidelity in everyday situations. Keep in mind that cheating is a complex behavior that occurs for a wide range of reasons (learn more about people’s reasons for cheating here).

Also, this study only looked at White, heterosexual adults and the people pictured in the photos were relatively young. As a result, it’s not clear whether the results would generalize to more diverse populations.

Furthermore, we should be careful to avoid concluding that female infidelity cannot be predicted by appearance given that the women in the photos had relatively low rates of reported cheating and poaching. This may be due to their younger age and/or to underreporting of these behaviors. Again, we need more research and more diverse photo sets before drawing too many conclusions.

That said, these provocative results suggest the possibility that we might have some limited ability to infer whether someone is likely to commit infidelity based on appearance alone.

So why is that? We can’t say for sure, but the study’s authors suggest an evolutionary explanation: perhaps it was adaptive for humans to develop this kind of detection ability in order to reduce the odds of winding up with an unreliable partner.

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To learn more about this research, see: Foo, Y. Z., Loncarevic, A., Simmons, L. W., Sutherland, C. A., & Rhodes, G. (2019). Sexual unfaithfulness can be judged with some accuracy from men's but not women's faces. Royal Society Open Science, 6(4), 181552.

Image Source: 123RF/Andriy Popov

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