There is a growing awareness around the world that national populations are aging. This phenomenon, which was not recognized until the later part of the twentieth century, is sweeping the world at different rates and for a variety of reasons. By itself, the fact that a particular country's population is aging would be of little consequence. In a world with increasing economic ties across borders, the aging phenomenon is likely to have significantly different implications from country to country, which will be heightened by differences in economic and governmental structures. Before we address these latter considerations, we first document the dynamics of population change across several countries.

A Brief Historical Perspective

The history of the human population is rife with uncertainty. National censuses taken at regular intervals are a relatively recent phenomenon. Sweden began the first census in 1750; the United States has conducted decennial censuses since 1790; and France and England have conducted them since around 1800. Using qualitative data, however, statistical demographers have estimated the size of the world population using the observations of historians, archeologists, paleontologists, and anthropologists. Locations of cities and their estimated sizes are important clues. Historical descriptions of peoples and places are used in reconstructing estimates of areas. The ability of ecosystems to support humans in various eras – e.g., pre-agricultural, agricultural, industrial – are important considerations.