The History of Human Populations. I. Forms of Growth and Decline (review)

This empirical study of patterns of population growth examines more than 2,000 time series of recorded population sizes for villages, towns, states or provinces, countries, continents, and the whole world. Although this material is uneven, the author spends little time in discussing problems of data quality. He concludes that there are six basic curves that fit the data, the large majority conforming to a so-called G curve that reflects an initial pattern of growth at 3 percent per year, decelerating at a 3 percent rate. Series of exponential growth, or of decline, are comparatively rare. At 3 percent, a population would double in twenty-three years, close to what Benjamin Franklin calculated for the population of the American colonies. Because of the constant deceleration in the G curve, it fits segments of population-growth curves with much lower initial growth. The fit is good, but it is only obtained a posteriori, when the data are complete, by joining parts of curves more or less removed from their theoretical beginning. Breaks in the series are explained by historical accidents or by changes in the economic basis supporting the population. The book has little to tell about population decline, which may become the dominant future trend for developed economies.

The use of mathematical curves to project population sizes has a long history. The logistic curve, invented by Pierre Verhulst in the 1840s, was meant to predict the future course of population in a finite environment. Resurrected by Lowell T. Reed and Raymond Pearl in the 1920s, it was conceived as applicable also to segments of curves, as the limits of the environment were shifting due to economic growth. The present project is not concerned with projections; it has the more limited ambition of being purely descriptive, while also aiming at providing a general theory of population growth, in which deceleration is an almost universal characteristic. This volume is presented as the first of three; the second will examine the fertility, mortality, and migration underlying the growth patterns; and the third volume will analyze their economic underpinning.

Despite its title, the book is not history in any conventional sense. It consists almost entirely of descriptions of curve fittings, and 200 pages could have been deleted without loss. Although the demonstration of empirical regularity in social phenomena is interesting, the author does not offer a systematic explanation of why it is encountered. Presumably, it will come in subsequent volumes. Whereas the quality of time series of population sizes is difficult to ascertain, but probably extremely uneven, the range of variation of plausible vital rates is narrow. The author should have a rough time matching many of his growth series with reliable underlying fertility, mortality, and migration estimates.