Sexual conflict and the Trivers-Willard hypothesis: Females prefer daughters and males prefer sons

Abstract

Because parental care is expected to depend on the fitness returns generated by each unit of investment, it should be sensitive to both offspring condition and parental ability to invest. The Trivers-Willard Hypothesis (TWH) predicts that parents who are in good condition will bias investment towards sons, while parents who are in poor condition will bias investment towards daughters because high-quality sons are expected to out-reproduce high quality daughters, while low-quality daughters are expected to out-reproduce low quality sons. We report results from an online experiment testing the Trivers-Willard effect by measuring implicit and explicit psychological preferences and behaviorally implied preferences for sons or daughters both as a function of their social and economic status and in the aftermath of a priming task designed to make participants feel wealthy or poor. We find only limited support for predictions derived from the TWH and instead find that women have strong preferences for girls and men have preferences for boys.

Figure 1

The preference for adopting a boy is lower for females than for males across all conditions. Males who experience more poverty in childhood are more likely to express a preference to adopt females. The plot holds all the other variables (see Table 1) in the top models constant (i.e. holds them at their mean values) across each level of poverty in childhood (Shading around line is 95% CI).

Figure 2

Both sexes, but especially females, donated more to charities supporting girls. Males who reported higher perceptions of their own status donated more to charities supporting boys.

Figure 3

Both sexes showed implicit preferences for same sex children but females showed a stronger preference than males.

Figure 4

Each sex showed a weak, but statistically significant explicit preference for same sex offspring.

Figure 5

Theoretical predictions made by sexual conflict and TWH for the reproductive success of sons and daughters as a function of mother and fathers sexually antagonistic genes (a) and (b) [adapted from] and the condition of both parents (c) [adapted from].