<p>From 3/9/09 Psychology Today: “Beautiful people are more intelligent” by Satoshi Kanazawa -</p>
<p>"The National Longitudinal Study of Adolescent Health (Add Health), conducted by a team of researchers at the University of North Carolina – Chapel Hill, is one of the very few social science datasets that take biological and genetic influences on human behavior seriously.  As a result, Add Health routinely measures both the intelligence and physical attractiveness of its respondents.</p>
<p>"In the Wave III of Add Health, conducted in 2000-2001, respondents take an IQ test called the Peabody Picture Vocabulary Test.  And then their physical attractiveness is measured objectively by an interviewer, who is unaware of their IQ test scores, on a 5-point scale (1 = Very unattractive, 2 = Unattractive, 3 = About average, 4 = Attractive, and 5 = Very attractive).  The data come from a large (n = 15,197) nationally representative sample of young Americans (mean age = 22).</p>
<p>"[T]here is a clear monotonic positive association between physical attractiveness and intelligence.  The more physically attractive Add Health respondents are, the more intelligent they are.  The mean IQ is 94.2 for those rated “very unattractive,” 94.9 for those rated “unattractive,” 97.1 for those rated “about average,” 100.3 for those rated “attractive,” and 100.7 for those rated “very attractive.”  Due partly to the large sample size, the association is highly statistically significant.</p>
<p>"So it appears that the “stereotype” that beautiful people are more intelligent appears to be true empirically, just as virtually all “stereotypes” are.  But now the question is:  Why?  </p>
<p>"There are two possible explanations for the observed positive association between intelligence and physical attractiveness.  First, the evolutionary psychologist Geoffrey F. Miller suggests that there is a common source of variation between intelligence and physical attractiveness:  the genetic quality of the individual which he calls the general fitness factor (the f factor).  According to Miller’s theory, those who have better-quality genes are simultaneously physically more attractive (because beauty is an indicator of health and genetic quality, as I explain in an earlier post) and more intelligent, hence the positive association between the two traits.</p>
<p>"This is a very plausible theory, but I have doubts that it explains the association between intelligence and physical attractiveness.  If Miller is correct, then the association between intelligence and physical attractiveness should disappear once genetic quality is controlled.  At least in the Add Health sample, however, this does not appear to be the case.  The positive association between intelligence and physical attractiveness is not at all attenuated when measures of genetic quality are controlled.</p>
<p>"Alternatively, the association between intelligence and physical attractiveness may emerge from the process of assortative mating.  If more intelligent men are more desirable to women than less intelligent men, because they achieve higher status, at least in the modern environment, and if physically more attractive women are more desirable to men than physically less attractive women, then there should be assortative mating of intelligent men and beautiful women, and of less intelligent men and less beautiful women.  Because both intelligence and physical attractiveness are heritable, such assortative mating should create an extrinsic (non-causal) correlation between intelligence and physical attractiveness in the next generation.  Children of intelligent men and attractive women should simultaneously be intelligent and beautiful, and children of less intelligent men and less attractive women should simultaneously be less intelligent and less attractive.</p>
<p>“So which theory is correct?  We don’t know yet for sure.”</p>