Does he love you so? Maybe it really is in his face …

Many people believe they can, according to a U-M study published in the December issue of Personal Relationships, a peer-reviewed academic journal.

U-M social psychologist Daniel Kruger conducted a series of online experiments showing 854 male and female undergraduate students versions of composite male faces that had been altered to look more or less masculine by adjusting, for example, the shape of the jaw, the strength of brow ridges and the thickness of lips.

Participants were asked which of the men they preferred as mates, dates, parents of their children or companions for their girlfriends. They also were asked which men were most likely to behave in certain ways—starting a fight or hitting on someone else’s girlfriend, for example.

“It’s remarkable that minor physiological differences lead people to pre-judge a man’s personality and behavior,” says Kruger, a research scientist at the School of Public Health and the Institute for Social Research. “But even though physiognomy (the attribution of personality to faces) is thought to be a pseudoscience, a lot of people believe there’s a link between looks and personality.”

In terms of evolutionary psychology, there may be a kernel of truth in that belief, Kruger says. Facial masculinity is related to levels of testosterone during development, and testosterone levels are related to rates of infidelity, violence and divorce.

“Facial masculinity may serve as a visual cue in female mate choice, much as the tail of the male peacock signals females about male fitness to reproduce,” Kruger says.

In one study, participants linked more masculinized faces with riskier and more competitive behaviors, higher mating effort and lower parenting effort in comparison with less masculine faces.

Men with highly masculine faces were judged more likely to get into physical fights, challenge their bosses, sleep with many women, cheat on their partners and knowingly hit on someone else’s girlfriend. Those with more feminine faces were judged to be more likely to be good husbands, be great with children, work hard at their jobs even though they didn’t like them and be emotionally supportive in long-term relationships.

“Men picked the less masculine-looking men to accompany their girlfriends on a weekend trip to another city,” Kruger says. “And both men and women would prefer the less masculine versions as dating partners for their daughters.”

Together, the studies show that highly masculine faces are associated with riskier and more competitive behavior, higher mating effort and lower parenting effort in comparison with less masculine faces.