Demography is the study of human populations. It is an important part of sociology and the other social sciences because all persisting social aggregates—societies, states, communities, racial or ethnic groups, professions, formal organizations, kinship groups, and so on—are also populations. The size of the population, its growth or decline, the location and spatial movement of its people, and their changing characteristics are important features of an aggregate whether one sees it as a culture, an economy, a polity, or a society. As a result some anthropologists, economists, historians, political scientists, and sociologists are also demographers, and most demographers are members of one of the traditional social science disciplines.

A central question for each of the social sciences is: How does the community, society, or whatever, seen as a culture, an economy, a polity, or whatever, produce and renew itself over the years? Formal demography answers this...