So, getting back to the original question, the bulk of the evidence suggests that smart people are not "usually ugly." In fact, the opposite seems to be true: Either smart people are more beautiful than average, or dumb people are more ugly (or both). And while no facial features within the normal range could ever be that useful as a predictor of intelligence, people can perform better than you’d expect from random chance using nothing more than a head shot.
All of which leaves one great, unanswered question. If smart people tend to be good-looking, that might explain the halo effect. But what led our questioner to get things backward and assume that smart people were ugly? And why are there so many like-minded others, asking the same question—or its inverse—around the Internet? (Here's one, and one more.) Aren't we all familiar with the archetypical nerd, who is both ugly and smart? At the opposite end, what about all those beautiful, airheaded women and beefy, brainless men we see on television? Could the person who wrote in with the 2011 Question of the Year be succumbing to a bias that hasn't yet been documented in the lab—a sort of halo effect in reverse, a "horns effect," perhaps?
Ugly geniuses aren't uncommon in history, of course, and while these anecdotes tell us nothing about the population as a whole, the memory of people who were famously hideous and brilliant might have an outsize influence on our judgments. Jean-Paul Sartre, for example, was short, bespectacled, and wall-eyed. ("I cannot even decide whether [my face] is handsome or ugly," says one of his characters in Nausea. "I think it is ugly because I have been told so.") Ancient sources tell us that the great philosopher Socrates had thinning hair, flared nostrils, widely-spaced eyes, a thick neck, slobby shoulders, and a pot belly. Ludwig van Beethoven was ugly and smelled bad; Abraham Lincoln's face struck the poet Walt Whitman as being "so awful ugly it becomes beautiful."
In addition, Kanazawa points out that a closer look at the data reveals an interesting fact: The very ugliest people in his dataset are dumber on average, but they also tend to be the most diverse when it comes to intelligence. That means that if you're at the low end of the spectrum for looks, you're more likely than anyone else to be at one extreme end for IQ (either very dumb or very smart). If that's the case, then it might provide another reason why Sartre and Socrates types stick out in our minds. We know (consciously or not) that ugly people tend to be a little dim; but at the same time, there are more brilliant brutes running around than we might expect.
For his part, Kanazawa rejects the notion of the horns effect—he doesn't believe the smart-and-ugly stereotype exists at all. (Indeed, it has never been shown in the lab.) Instead, he says, we may be assuming that smart people are nerdy, and that nerdy people tend to lack social skills. Since people with social skills are attractive, there could be an indirect link between at least one kind of "attractiveness" and intelligence. But if you're looking at pure "beauty," as measured by rating photographs or measured facial features, then intelligence and looks go hand-in-hand.
Bonus Explainer: Why might intelligence and looks go hand-in-hand? There are a few different theories. First, it might be that some common genetic factor produces both smarts and beauty. Or maybe there's a combination of genes that make people both dumb and ugly. Kanazawa thinks it's the former, arguing that intelligent men have tended to rise to the top of the social hierarchy and select beautiful women as their mates. Their offspring, contra George Bernard Shaw's supposed quip, would have had both traits together.
Another theory holds that certain environmental factors in the womb or just after birth can produce both facial disfigurements and cognitive impairments on one side, or facial symmetry and high intelligence on the other. A third suggests that attractive children are treated better, and receive more attention from their caretakers and teachers, which helps to nurture a sharper mind. It's also possible that smart people are better able to take care of themselves and their looks.
Explainer thanks Satoshi Kanazawa of the London School of Economics, Joshua Knobe of Yale University, Alina Simone, author of You Must Go and Win, and Leslie Zebrowitz of Brandeis University.
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Correction, Jan. 12, 2012: The original overstated the magnitude of the results of the Ohio and Pittsburgh studies.