The researchers found a strong relationship between how attractive a person was rated, and reviewers' assumptions about how intelligent they were. This relationship was especially strong among women. But when it came to actual intelligence, there was a significant gender gap: reviewers were able to accurately gauge the real intelligence of men, but not of women. They're not exactly sure why this would be, but one possible explanation is that women are simply judged more pervasively on their looks than men are: "The strong halo effect of attractiveness may thus prevent an accurate assessment of the intelligence of women." The finding of a much stronger relationship between attractiveness and perceived intelligence among women seems to back up this claim.
On the other hand, when the researchers looked at perceived intelligence versus actual intelligence, as measured by the subjects' IQ scores, they found no relationship whatsoever. In fact, visual assessments of a persons' intelligence seem to largely be based on stereotypes related, at least partially, to notions of attractiveness. To test this, the researchers constructed "intelligence stereotypes" for both men and women, based on the observers' assessments of subjects' intelligence:
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 intelligence-stereotype shows the same transformations in facial shape space for both men and women. 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.
The images below show the constructed intelligence stereotypes for men and women, using composite photos of the men and women who participated in the study.
Male intelligence stereotypes
Female intelligence stereotypes
These assumptions carry centuries of cultural baggage, and more to the point they're simply wrong: the researchers ran a bunch of regressions and found no relationship between these facial stereotypes and a person's actual intelligence. While "men and women with specific facial traits were perceived as highly intelligent," the researchers conclude, "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." Notably, the study was conducted in the Czech Republic and doesn't say a word about the race or ethnicity of study participants or observers – it would be fascinating to see to what extent these findings are consistent across different cultures.
So in the end, where does this all leave us? While it's comforting to know that there's no real connection between brains and beauty, we nonetheless form opinions of each other as if there were. This can have measureable, real-world consequences: Daniel Hamermesh of the University of Texas found that being attractive "helps you earn more money, find a higher-earning spouse (and one who looks better, too!) and get better deals on mortgages." All told, the lifetime earnings difference between people at opposite ends of the attractiveness spectrum averages out to about $230,000, in beauty's favor.
Finally, the research does suggest one thing we can all start doing to boost others' assessments of our intelligence: smile more. "There seems to be a correlation between semblances of emotions of joy or anger in perceptions of high or low intelligence in faces, respectively," the researchers write. "The ‘high intelligence’ faces appear to be smiling more than the ‘low intelligence’ faces."