If beautiful people have more daughters, and if physical attractiveness is heritable, then it follows that, over time, women become physically more attractive than men. This indeed appears to be the case.
The logic of the generalized Trivers-Willard hypothesis (gTWH) suggests that physically more attractive parents are more likely to have daughters than physically less attractive parents. As I explain in earlier posts, the data from both the National Longitudinal Study of Adolescent Health (Add Health) in the United States and the National Child Development Study (NCDS) in the United Kingdom confirm this prediction. Physically more attractive parents are significantly more likely to have a daughter as their first child than physically less attractive parents.
If beautiful parents are more likely to have daughters, and if physical attractiveness is heritable (such that beautiful parents beget beautiful children and ugly parents beget ugly children), then it logically follows that, over many generations in the course of human evolution, the average level of physical attractiveness among women should gradually increase and the average level of physical attractiveness among men should gradually decrease. No matter what the initial sex difference in physical attractiveness (whether men were more attractive than women, women were more attractive than men, or there were no sex differences in physical attractiveness), given long enough time, the outcome should be that women are on average more physically attractive than men are.
Earlier studies indeed show that women are on average physically more attractive than men both in Japan and in the United States. The analysis of the NCDS data replicates the sex difference in physical attractiveness in the United Kingdom.
As the following graph shows, 85.5% of girls in the NCDS sample are described by their teachers at “attractive” at age 7, whereas only 83.1% of boys are. The sex difference in the proportions described as “attractive” at age 7 is statistically significant.
Similarly, 11.4% of girls in the NCDS sample are described by their teachers as “unattractive” at age 7, whereas 12.0% of boys are. The sex difference is in the predicted direction, but, due to the small number of children (both boys and girls) described as “unattractive,” the sex difference here is not statistically significant.
The following two graphs show that the sex difference in physical attractiveness is similar in the United States as it is in the United Kingdom. The data come from Add Health, and physical attractiveness was measured in childhood, in junior high and high school, by an interviewer.
As you can see, girls are on average physically more attractive than boys are. A majority (56.03%) of the girls are either “attractive” or “very attractive,” whereas the comparable figure among boys is much lower (41.75%). In fact, a majority (51.21%) of the boys are “about average.” Nearly twice as many girls (19.53%) as boys (10.51%) are “very attractive.” It therefore appears that, both in the United Kingdom and the United States, women are indeed more physically attractive on average than men are, at least partly because beautiful parents are, and have been, more likely to have daughters.