Mothers prefer daughters and fathers prefer sons

Specifically, the authors sought to test the Trivers-Willard hypothesis which predicts that parents in good conditions will bias investment towards sons, while parents in poor conditions will bias investment towards daughters.

"However, our study failed to show that the parents' preferences for the offspring's gender are affected by their status, wealth, education or childhood environment. Instead, parental preferences were best predicted by their sex. Women from all socioeconomic backgrounds expressed implicit and explicit preferences for daughters: they chose to donate more to charities supporting girls and preferred to adopt girls. In contrast, men expressed consistent, albeit weaker, preferences for sons," explains lead author, Postdoctoral Researcher Robert Lynch from the University of Turku, Finland.

The researchers tested the Trivers-Willard effect with an online experiment by measuring implicit and explicit psychological preferences and behaviourally 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.

The results of the research help to make sense of the often contradictory findings on offspring sex preferences. The effects of parental condition and status, competing genetic interests between males and females, economic constraints on families, and the effects of cultural practices all conspire to complicate the evolutionary outcomes of parental investment strategies.

"Frequently, the impact of one factor, for example, the genetic sexual conflict between males and females, can mask the impact of another, such as the Trivers-Willard Hypothesis. This can make it difficult to parse their effects and make clear predictions about 'optimal' parental investment strategies from an evolutionary perspective. We hope that our study can shed new light on these strategies and provide a better understanding of evolutionary biology in humans," states Lynch.