The maternal dominance hypothesis: questioning Trivers and Willard

Thirty years ago, Trivers and Willard (1973) hypothesized that parental “condition” could be central in influencing the sex ratio of offspring, “good condition” being associated with the conception of males. However, I argue that “condition” is a distraction in this otherwise useful hypothesis, because it is merely a frequent indicator of dominance (a characteristic which often leads to priority access to resources); and that it is dominance, a biologically-based characteristic underpinned by testosterone, which is of interest. Shifting the focus from good condition to the dominance-testosterone link could help explain otherwise anomalous findings in the literature on the sex ratio. In addition, in female mammals, testosterone is hypothesized to have a role in reproductive processes such that the mother could influence or even control the sex of her offspring, conceiving whichever sex she is, at that time, and in that place, best suited to raise. Such a mechanism would confer an evolutionary advantage on those females able to make use of it.