Testing Socioeconomic Status as a Marker for Condition in the Trivers-Willard Hypothesis within the Human Context

Brandon Wagner, University of North Carolina at Chapel Hill

Applying evolutionary reasoning to reproductive strategy differences between the sexes, the Trivers-Willard Hypothesis suggested that parental resources condition sex differentiation of parental investment. This suggests that socioeconomic status could condition child sex preference in humans. While researchers have tested this possibility, they have neglected the explicit condition that the increases in a child’s reproductive success from parental investment vary between sons and daughters. This paper tests the assumption's validity by examining sex differences in reproductive success, controlling for parental socioeconomic status and multiple dimensions of parental investment. I use fertility-related behaviors to construct a measure of expected births that bypasses modern contraception. The results of OLS regressions find no significant sex differences in reproductive success at any level of parental socioeconomic status. The lack of support for this underlying assumption calls previous research into question and urges closer attention to the use of biological models within social research.