Low fertility in humans as the evolutionary outcome of snowballing resource games

For decades, evolutionary biologists and anthropologists have puzzled over the negative relationship that exists between wealth and fertility in humans. Particularly mystifying have been that (1) humans do not appear to translate their reproductive resources into additional offspring, and (2) attempts to model natural selection resulting in a negative relationship between amount of economic resources and fertility have all predicted the opposite relationship. In this article, we use game theory to derive the evolutionarily stable ratio of offspring investment versus resource generation when the continuing survival of offspring lineages is strongly affected by long-term resource accumulation. The model generates the prediction that fertility should be lower when there are more resources available and when more intensive investment in resource generation has the potential to acutely increase the survival probability of descendant offspring lineages. This prediction provides a simple and general evolutionary explanation for why fertility negatively correlates with wealth both within and between human populations. Indeed, this may provide a new understanding of low fertility in contemporary human groups in addition to furthering our understanding the demographic transition in general. Copyright 2005.