MedicalResearch.com Interview with:
Robert F. Lynch, PhD
Department of Biology
University of Turku
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.
MedicalResearch.com: What should readers take away from your report?
Response: Readers might want to be more aware of their own either conscious or unconscious biases and preferences. While this may not be a huge problem in intact two parent families because the sex of the other parent may compensate, this may be a problem for single parents (mostly women) or same sex couples raising kids. In the paper we discuss how this could be a problem for intergenerational mobility for kids raised by single parents. We write:
“These results may also have implications for rising income inequality and intergenerational social mobility. A recent study using the tax records of 40 million Americans between 1996 and 2012 showed that the single best predictor of lower intergenerational social mobility was having a single or divorced parent. Because most of these single parents are females, and females prefer daughters, we might expect even lower reduced intergenerational mobility for the sons of these single mothers.“
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: We are planning a follow up study which tests the Trivers-Willard hypothesis in more detail and one in which we use a better design which we think may be better able to detect different preferences for men and women as a function of their socioeconomic status. But in general I think any additional research on sex biased offspring preferences preferences for sons or daughters) as a function of a persons social status, economic resources available or their sex are useful. Sometimes when you do research you are not dead sure if your findings will be able to be repeated. This is not the case here. I am pretty confident of the findings but I think future research might seek to tease apart more of the factors that effect biased sex preferences. It’s obviously not so simple as women prefer daughters and men prefer son or show no preference.
MedicalResearch.com: Is there anything else you would like to add?
Response: Here is the link to the article:
Nature Scientific Reports is an open access journal so anyone can read it and download it for free. The data are all there too. So feel free to use these data to do add to your own research or curiosity.
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