10. The Role of Ontogeny in Understanding Human Demographic Behaviour

Ontogeny, the development of an organism from conception to maturity, is one of Tinbergen’s two proximate explanations for understanding why we do the things we do. As well as genetic inheritance, the developmental environment, which parents make a large contribution to, is crucial for shaping a child’s life. It shapes not only their physical and psychological development but also influences the adult child’s reproductive strategy and ultimately their life expectancy. Demographers care about fertility and mortality which, when understood within an evolutionary framework, are two entwined processes that influence, and are in turn influenced by, the individual’s developmental trajectory. Here, we provide a summary of how development operates throughout life; from the womb, through childhood, adolescence and puberty, the reproductive years through to menopause and death. We take a life-history approach with a focus on how developmental influences during early life have long-reaching consequences for mortality and fertility. We illustrate each section with theoretical advances, empirical examples, and evaluation of the current literature. We hope to demonstrate that thinking about human demographic behavior in light of ontogeny can be revealing and provide a useful theoretical basis for demographic research.