Beautiful people have higher intelligence than ugly people, especially if they are men.

In a previous post, I show, using an American sample from the National Longitudinal Study of Adolescent Health, that physically more attractive people are more intelligent.

As I explain in a subsequent post, the association between physical and intelligence may be due to one of two reasons. Genetic quality may be a common cause for both (such that genetically healthier people are simultaneously more beautiful and more intelligent). Alternatively, the association may result from a cross-trait assortative , where more intelligent and higher status men of greater resources marry more beautiful women. Because both intelligence and physical attractiveness are highly heritable, their children will be simultaneously more beautiful and more intelligent.

Regardless of the reason for the association, the new evidence suggests that the association between physical attractiveness and may be much stronger than we previously thought.

The National Study (NCDS) includes all babies born during the week of March 9, 1958 in Great Britain (England, Wales, and Scotland), and has followed them for more than half a century throughout their lives. When the children were 7 and again when they were 11, their teachers were asked to describe them physically. For the purpose of the analysis below, the children are defined to be attractive if they were described as attractive at both age 7 and age 11. They were defined to be unattractive otherwise.

Sixty-two percent of the NCDS respondents are coded as attractive. Their intelligence is measured with 11 different cognitive tests at three different ages (7, 11, and 16). NCDS has the best measure of general intelligence available in any large-scale survey data.

As the graph below shows, attractive NCDS respondents are significantly more intelligent than unattractive NCDS respondents. Attractive NCDS respondents have the mean IQ of 104.23, whereas unattractive NCDS respondents have the mean IQ of 91.81. The difference between them is 12.42. This mean difference implies a correlation coefficient of r = .381, which is reasonably large in any survey data.

By pure coincidence, the correlation between physical attractiveness and intelligence in NCDS is exactly the same, down to the third decimal point, as the correlation between intelligence and . Both correlations are .381. Everybody knows that intelligence and education are very highly correlated. What they don’t know is that physical attractiveness is equally highly correlated with intelligence as education is. If you want to estimate someone’s intelligence without giving them an IQ test, you would do just as well to base your estimate on their physical attractiveness as you would to base it on their years of education.

As the following two graphs show, the association between physical attractiveness and intelligence is stronger among men than among women. In the NCDS sample, the attractive women have a mean IQ of 103.64, and the unattractive women have a mean IQ of 92.25. The difference between them is 11.39. This mean difference implies a correlation coefficient of r = .351.

In contrast, the attractive men in the NCDS sample have a mean IQ of 105.00, and the unattractive men have a mean IQ of 91.39. The difference between them is 13.61, which is almost one full standard deviation in the IQ distribution (σ = 15). This mean difference implies a correlation coefficient of r = .414, which is very large in any survey data.

Now, given that it was the children’s teacher who was asked to assess their physical attractiveness, there is a possibility of a halo effect, where teachers believe that better, more intelligent students are physically more attractive.

The halo-effect explanation for the association between physical attractiveness and intelligence, however, runs into three different problems. First, it presumes that the judgment of physical attractiveness is arbitrary and subjective. As I explain in an earlier post, however, beauty is not in the eye of the beholder; it is an objective, quantifiable trait of someone like height or weight. Second, as I note in the previous post, the association between beauty and intelligence has been found in the American Add Health sample, where physical attractiveness of the respondents is assessed by the interviewer who is unaware of their intelligence.

Most importantly, however, the halo effect explanation simply leads to another question: Where does the teachers' belief that more intelligent students are more attractive come from? The notion that more intelligent individuals are physically more attractive is a stereotype, and, just like all other stereotypes, it is empirically true, as both the American and British data show. Teachers (and everyone else in society) believe that more intelligent individuals are physically more attractive because they are.