Brown-Eyed Men May Look More Trustworthy

Brown-eyed people may have more trustworthy faces than blue-eyed people, suggests a new study that comes with caveats but also raises fascinating questions about recent human evolution. It wasn't eye color itself that proved more- or less-trustworthy in the study. Rather, it was particular facial features, such as chin shape and mouth position, that happened to cluster with eye color.
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Brown-eyed people may have more trustworthy faces than blue-eyed people, suggests a new study that comes with caveats but also raises fascinating questions about recent human evolution.

It wasn't eye color itself that proved more or less trustworthy in the study. Rather, it was particular facial features, such as chin shape and mouth position, that happened to cluster with eye color.

The findings, based on the reactions of Czechoslovakian college students shown photographs of their peers, shouldn't be extrapolated to explain one's own interpersonal relationships. That said: Even within the confines of the study, why do certain features seem trustworthier than others? And why was it brown-eyed people who had them?

"It was unexpected that some superficial sign like eye color could somehow be linked, by means of genes and hormones, to facial shape," said Karel Kleisner, a history of science professor at the Charles University in Prague and lead author of the new study, published Jan. 9 in PLoS One.

In earlier research, Kleisner and colleagues had noticed an apparent link between face structure and eye color in the Czech population. In the new study, they wanted to see how people perceived those features.

They showed pictures of 40 male and 40 female students, split equally between blue- and brown-eyed, to 238 undergraduate students. Brown-eyed men were consistently judged more trustworthy than blue-eyed men. The same trend held for women, but it wasn't so pronounced.

The researchers then used Photoshop to change brown eyes to blue and blue eyes to brown, and showed the altered photographs to a second group of students. Now the artificially blue-eyed men were judged trustworthy.

Facial shape and not eye color guided viewers' impressions, concluded Kleisner's team, whose analysis of facial shapes returned distinctive profiles for naturally brown-eyed and blue-eyed men. The former had rounder faces, broader chins and wider mouths that turned up at the corners, while the latter had more angular, long-chinned, narrow-mouthed faces.

Perceived trustworthiness of blue-eyed (blue) and brown-eyed (brown) faces by male and female test subjects.

Image: Kleisner et al./PLoS One

A quick, static impression of trustworthiness is not necessarily a guide to real-world, real-time impressions, noted Kleisner. Facial expression and body language are likely far more relevant, though they're not necessarily reliable.

Nevertheless, the ability of a quick glimpse to shape judgment is notable. Kleisner speculates that the generally rounder, wider-mouthed, corner-upturned mouths of brown-eyed men look like they're on the verge of smiling, and happy faces tend to inspire trust.

Harder to explain are the biological underpinnings of links between eye color and face structure, especially the connection between long, angular features and blue eyes, an evolutionarily new trait that arose about 10,000 years ago in Europe.

Genetic theory predicts that links between eye color and facial shape should dissolve over evolutionary time, washed out in the repeated genomic mixings of reproduction. That clearly hasn't happened in this population.

The new study's authors, among them anthropologist Peter Frost of Canada's Laval University, who specializes in recent human evolution, think some as-yet-unidentified link between eye color, prenatal hormone exposures and historical mate preferences could be responsible.

Testing that possibility may prove impossible. Less speculatively, the scientists want to see whether the trends they noted are common across ethnicities and cultures. They've started tests of facial preferences in Cameroon, Romania, Turkey and the United Kingdom.

"The research should be repeated in other age groups, in different countries," explained Kleisner, who said the findings thus far should be considered interesting ideas, not explanations for human behavior. "I'd warn against any social application of the research," he said. "I don't want to cause problems between employers and employees."

Schematic composite images of untrustworthy male features (left), trustworthy features (right) and average features (center) from the study. Image: Kleisner et al./PLoS One

Citation: "Trustworthy-Looking Face Meets Brown Eyes." By Karel Kleisner, Lenka Priplatova, Peter Frost, Jaroslav Flegr. PLoS One, Vol. 8 No. 1, Jan. 9, 2013