Cultural evolution of low fertility at high socio-economic status

Department of Biological Sciences, University of Bristol, UK

Rebecca Pike

Rebecca Pike

Life-history theory predicts that individuals should behave to maximize their lifetime reproductive success, measured by the number of successful offspring. One would thus expect that parents with greater means have more children. Paradoxically, this is not the case: in modern societies socio-economic status is negatively correlated with fertility. As a result, over half of the global population live in countries with below-replacement fertility. Explanations of this pattern based on genetic evolution have traditionally focused on the trade-off parents face between the quantity and quality of their offspring. Reducing the number of offspring allows greater investment in each. Thus, parents may increase their relative reproductive success by producing a small number of high-quality offspring. However, explanations along these lines assume that high-quality offspring will have high reproductive success; the fact that this does not seem to apply in modern societies is the very pattern that needs to be explained.
This project aims to address the paradox by broadening the framing from genetic evolution to cultural evolution. We consider socio-economic status as a cultural equivalent to fitness and the target investment in a child as an individual’s evolving trait. We conjecture that, owing to the highly nonlinear benefits accrued from such investment, high-income parents are constrained by a quality-quantity trade-off and choose a lower number of offspring, whilst low-income parents are not and choose a higher number of offspring. On this basis, we will devise a model in which the number of children can be influenced genetically and culturally. Since genetic evolution is better understood, the main focus of this project will be on the cultural evolution of fertility decisions.

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Last edited: 18 September 2016

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