The generalized Trivers-Willard hypothesis proposes that parents who possess any heritable trait that increases male reproductive success at a greater rate than female reproductive success in a given environment will have a higher-than-expected offspring sex ratio (more sons), and parents who possess any heritable trait that increases female reproductive success at a greater rate than male reproductive success in a given environment will have a lower-than-expected offspring sex ratio (more daughters). One heritable trait that increases the reproductive success of daughters much more than that of sons is physical attractiveness. The generalized Trivers-Willard hypothesis therefore predicts that physically attractive parents have more daughters. Further, if beautiful parents have more daughters and physical attractiveness is heritable, then over evolutionary history women on average should gradually become more attractive than men. The analysis of the prospectively longitudinal National Child Development Study in the United Kingdom replicates earlier findings with an American sample and confirms both hypotheses. British children who are rated by their teachers as “attractive” at age 7 have 23% higher odds of having a daughter 40 years later (proportion sons = 0.50127); those who are rated by their teachers as “unattractive” at age 7 have 25% higher odds of having a son 40 years later (proportion sons = 0.56285).
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Kanazawa, S. Beautiful British Parents Have More Daughters. Reprod. Sci. 18, 353–358 (2011) doi:10.1177/1933719110393031
- Evolutionary biology
- generalized Trivers-Willard hypothesis
- offspring sex ratios
- physical attractiveness