MedicalResearch.com Interview with: Robert F. Lynch, PhD Department of Biology University of Turku Turku, Finland  MedicalResearch.com: What is the background for this study? What are the main findings?  Response:  The take home message is that we were trying to experimentally induce something called a Trivers-Willard effect in humans. The Trivers-Willard hypothesis is a theory that uses evolutionary logic to 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.  The logic is that this should be the case 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 found almost nothing supporting this.  Instead we found strong and consistent effects across 4 dependent variables (explicitly stated preferences, implicit associations via IAT tests, actual donations to charities after an experimental prime and a forced choice adoption preference) of women preferring daughters or girls and men having either a slight or no preference for sons or boys. Of course we get into the details of why this may not be so surprising after all from an evolutionary point of view.  And we also discuss how things like sexual genetic conflict might mask TW effects and how cultural changes regarding the expected value of males and females may also play a role in explaining these differences.    (more…)