Money and Sex, The Illusory Universal Sex Difference: Comment on Kanazawa

Kanazawa tests the hypothesis, derived from Evolutionary Psychology, that men's income enhances their ability to engage in copulation with more partners and at a greater frequency. However, the results presented in Kanazawa's article fail to appropriately test for interaction effects and some of the analyses may suffer from sample-selection bias. I reestimate the equations appearing in Kanazawa's study and find (given the author's original methodological decisions) evidence in support of the evolutionary prediction in only two of the four original analyses. Had the same methodological decisions been consistently applied in the original study, then only one of the four analyses provides very weak evidence in favor of a sex difference in the returns to income. Furthermore, I conduct cross-national analyses with International Social Survey Program data from four other industrialized nations: Australia, Bulgaria, Ireland, and Poland. In only one of the nations (Ireland) and for only two of the four dependent variables is there any compelling evidence that men with higher incomes have more sex partners. Since the term "sex partner" may be ambiguous, I also use data from the National Health and Social Life Survey where detailed questions were asked that may better measure evolutionarily significant forms of copulation. The data are not consistent with the evolutionary psychological theory of sexual behavior.