The Ash Twins Blog

Kanazawa (2006) makes another correct prediction from sexual selection:

The generalized Trivers–Willard hypothesis . . . proposes that parents who possess any heritable trait which increases the male reproductive success at a greater rate than female reproductive success in a given environment have a higher-than-expected offspring sex ratio, and parents who possess any heritable trait which increases the female reproductive success at a greater rate than male reproductive success in a given environment have a lower-than-expected offspring sex ratio. One heritable trait which increases the reproductive success of sons significantly more than that of daughters in the ancestral environment is the tendency toward violence and aggression. I therefore predict that violent parents have a higher-than-expected offspring sex ratio (more sons). The analysis of both American samples and a British sample demonstrates that battered women, who are mated to violent men, have significantly more sons than daughters.