Fertility and sexual selection

Markets are moving, and I’ll have more to say about that in due course, but we before we get to that, I am finally ready to present the third chapter in my running demographics project. The landing page for the project can be found here. You can get the PDF for the third chapter below, or via the landing page.

This chapter kicks off the description, analysis and discussion of fertility and birth rates. It is the first of, I suspect, three chapters on fertility. In it, I try to cover three bases. First, I cover the basics, defining the different ways in which fertility and birth rates are described quantitatively in the literature, and the distinction between these terms. Secondly, I summarise the stylised facts about the global fertility transition, when it began, and how it is going. My objective has been to strike a balance between the big picture and sufficient detail to allow for the discussion individual case studies across individual nations, or groups of countries. The key point, from both an empirical and theoretical perspective, is that fertility does not stabilise at replacement levels in the final stages of the demographic transition. In this way, the fertility transition is an ongoing phenomenon, in contrast to the picture painted by the stylised model of the demographic transition. Thirdly, I run through the theory of sexual selection as described by Trivers (1972), and used in Richard Dawkins’ seminal, The Selfish Gene. There are two reasons for this. First, the basics matter. The game of mate selection, which feeds through to how parents share the costs of reproduction and child-rearing, is crucial to understand why births occur in the first place. The idea that evolved behaviour described by Trivers (1972) can be used to explain phenomena in a modern context invites us to heed F. Scott Fitzgerald’s advice that “the test of a first-rate intelligence is the ability to hold two opposing ideas in mind at the same time and still retain the ability to function.” It is reasonable to expect that many phenomena observed in a modern society can be traced back to core evolutionary processes. But equally, it is unreasonable to go searching for an evolutionary explanation for every phenomenon that social scientists might be interested in, in a modern economy. Whatever the balance between these two positions, the link between modern behaviour and pre-modern evolutionary theorems is a constant source of debate and controversy in the literature on demographics and fertility.

The introduction of the chapter is pasted below;

The fertility transition and sexual selection

The evolution of population growth and structure is intimately tied to the most important decisions individual humans make through their life; when to have children and how many to have. The analysis of reproductive behaviour in humans draws on evolutionary theory and biology, cultural and social sciences, psychology and economics. It is a daunting task to collect all these threads into a coherent framework, but this is what I attempt to do in what follows, all the same. Broadly speaking, the literature treats human reproduction in three ways. In the first, which comes from formal evolutionary theory, reproduction occurs as a result of sexual selection, or more specifically the competition within the human species for a mate. 

This initial condition then gives rise to the second, and main, framework in which the decision on the number of offspring is treated as a resource allocation problem, giving rise to a trade-off between how many children to have, and how much to invest in each child. This model is widely explored in economics and evolutionary biology and theory. In the standard framework, families—or often women alone—solve this allocation problem given a set of external conditions. Generally, in this framework, an increase in resources leads to more children in a traditional society, but not necessarily in a modern post-transition economy. 

The third framework emphasises shifts in norms and culture to explain why fertility trends shift over time. Given that such changes often can be tied back to the same fundamental resource allocation problem mentioned above, it can be difficult to separate the second and third framework. That said, it is possible to imagine forces working independently through culture and norms to affect fertility decisions, a point emphasised by the softer social sciences and evolutionary psychology.

Do you want to read the rest? Click here for the PDF.