New research published in PLoS One has found that a man’s facial characteristics contain some clues about his intelligence. Surprisingly, the same can’t be said for women’s facial traits. And the particular male facial characteristics linked with intelligence are a mystery.

“Our raters were able to estimate intelligence with an accuracy higher than chance from static facial photographs of men but not from photos of women. At the same time, we found no differences in the abilities of men and women to assess intelligence from static facial photos: the ratings of both sexes were highly correlated,” Karel Kleisner of Charles University in Prague and her colleagues wrote in their study.

For their study, the researchers recruited 80 students, who completed an IQ test and had their face photographed with a neutral expression. Another 160 students rated the 80 photographs in random order for either perceived intelligence or attractiveness.

The researchers found that people who were perceived as more attractive also tended to be perceived as more intelligent by both male and female participants. This link between perceived attractiveness and perceived intelligence was stronger for women’s faces than men’s faces.

The researchers also found that the participants rated men with a high IQ as more intelligent based solely on their facial photograph. For women, however, the researchers found no statistically significant link between perceived intelligence and their actual IQ.

Naturally, the findings raised the question of why people could predict men’s intelligence based on their face, but not predict women’s intelligence based on their face. The researchers proposed a number of explanations to be tested by future research.

“One possible explanation is that cues of higher intelligence are sexually dimorphic and are thus apparent only in men’s faces, e.g. due to some genetic and developmental association to sex steroid hormonal agents during puberty,” Kleisner and her colleagues wrote.

“Another option is that women are pervasively judged according to their attractiveness. The strong halo effect of attractiveness may thus prevent an accurate assessment of the intelligence of women,” the researchers added.

By examining the geometric features of the faces, the researchers were able to determine there was a link between certain facial characteristics and perceived intelligence for both men and women.

“Our data suggest that a clear mental image how a smart face should look does exist for both men and women within the community of human raters,” the researchers explained. “In both sexes, a narrower face with a thinner chin and a larger prolonged nose characterizes the predicted stereotype of high-intelligence, while a rather oval and broader face with a massive chin and a smallish nose characterizes the prediction of low-intelligence.”

But these facial characteristics were only associated with perceived intelligence. The researchers found no link between these facial traits and actual IQ scores.

“This means that our raters accurately assessed intelligence from faces of men based on visual cues that simply are not explicable from shape variability in men’s faces,” the researchers wrote.

But the correlation between these geometric traits and perceived attractiveness suggests there is an intelligence stereotype.

“These faces of supposed high and low intelligence probably represent nothing more than a cultural stereotype because these morphological traits do not correlate with the real intelligence of the subjects,” the researchers said.