(introduction...)

Expanding megacities will be among the substantial changes that these large population increments will bring. Countrysides will probably be more densely settled, and infrastructure and human services will be either substantially more extensive or under greater stress. The half century of growth since World War II has, for example, seen the Philippines increase from 70 to 226 people per square kilometer of land, and Bangladesh from 290 to 821 people per square kilometer. (At the latter density, the United States would have 7.7 billion people, not 270 million.)

Contrasts between the rapidly expanding developing countries and the steadily growing industrial economies can be extreme. Figure 4, for instance, compares income levels (gross national product, or GNP, per capita), the labor force in agriculture, and infant mortality.³ Average income in developing countries is less than one-twentieth of that in industrial countries. The proportion of the labor force in agriculture is on average more than 10 times as large as in industrial countries. And babies in developing countries die at a rate more than eight times that of industrial countries, producing average life expectancies about a dozen years shorter.

³The groups compared, strictly speaking, are high-income economies versus low- and middle-income economies, as defined in World Bank (1997b). "Europe and Central Asia" includes only the low- and middle-income economies in that region.

Figure 4 - Indicators for High-Income Economies and Low-and Middle-Income Regions

NOTE: Regional averages are weighted by population (or by number of births, for infant mortality) and exclude high-income economies. Data from World Bank (1997b).

How much of the difference in development and human welfare is explained by rapid population growth? A number of previous studies have produced inconclusive and even conflicting results. Cross-national regression analyses with data from the 1970s suggested that population growth did not affect national income, but studies of the 1980s suggested a negative impact.⁴ Population growth, after all, provides not only more consumers of societal resources and services but also more workers and producers of goods, a greater pool of human resources for developing new products and technology. The relevance of expanded pools of consumers and producers may depend on economic and social policies that are often enacted with little attention to population. The net effect of population on development could therefore vary across countries and periods and could be difficult to assess.

⁴See Ahlburg (1996) for a recent review of this general area.

What is clear, however, is that different sources of population growth have different economic implications. A population growing through migration often puts the migrants to work, earning some return from their labor.⁵ A population growing because of substantially longer life expectancies could in principle keep older people working longer to prevent any increase in dependency, although societal preferences and practices may preclude this. But a population growing because of high fertility must accept that those added to the population will spend years as dependents, becoming socialized and educated, before they are productive.

⁵Smith and Edmonston (1997) conclude, for instance, that U.S. residents gain economically from the presence of immigrants because of the additional labor (generally remunerated at lower rates than the average) and the increased specialization.