2 - Demographic perspectives on human population dynamics

Summary

Introduction

This chapter describes a formal demographic perspective on human population dynamics. It first attempts to summarise the way in which human population dynamics are treated in the more technical and theoretical demographic literature. The next section considers some demographic fundamentals, including population structure (especially the age and sex composition) and the three components of population change: fertility, mortality and migration. The third part looks at some of the formal models which demographers have developed to help understand population change. These models make several assumptions in order to simplify a complex reality. One of these is that migration is zero: populations with zero migration are said to be closed. An attraction of this is that, if migration can be ignored, simple relationships exist between fertility, mortality, the population growth rate and the age structure.

In the fourth section population dynamics in the short to medium term are considered. The age and sex structure of a population is itself a dynamic feature, containing a record of the population's past fertility, mortality and migration. Moreover, the future age–sex structure is determined by past and current events. Discussion of these aspects of population dynamics leads naturally in the fifth section to a consideration of population momentum, or what is sometimes, inaccurately, called the ‘demographic time bomb’. The origins of population momentum are explained.

Finally, in the sixth and seventh sections long-run population dynamics are explored in the context of the demographic transitions in Europe and contemporary Africa.