In April 2008, General Michael Hayden, director of the U. S. Central Intelligence Agency, cited population growth as one of three top destabilizing trends facing the world (the other two were the rise of Asia and the changing relationship between Europe and the United States). While no reasonable expert would argue that there is a simple causal relationship between demography and security--e.g., that a total fertility rate of five children per woman indicates that civil war will break out 20 years from now, or that a country cannot remain stable unless its age distribution resembles a bell curve--demographic trends can clearly interact with poverty, poor governance, competition for natural resources, and environmental degradation to contribute to conflict. As examples, we need look no further than Rwanda, Zimbabwe, Haiti, or Egypt--places where in recent years tensions that led to conflict may have been heightened by demographic pressures.
Those pressures ebb and flow according to demographic circumstance. Current world population trends are varied, with a vast disparity between the experiences of the most- and least-developed countries. Although the global population growth rate is slowing, the planet still gains a net 78 million people per year (roughly the population of Ethiopia). Some analysts and policymakers in developed countries are sounding the alarm about falling birthrates, the economic costs of supporting increased proportions of the elderly, and future population decline, but of the projected increase of nearly 3 billion people by 2050, more than 95 percent is likely to occur in less developed countries. If fertility trends were to stay constant at current levels, for example, the population of Yemen will surpass that of Russia--a country currently seven times its size--by 2050.
The majority of the global population lives in countries whose populations will continue growing for the long term, based on current trends. Fifty-seven percent of the world's people, including nearly all of Africa, live in countries where fertility rates are higher than "replacement level," the rate of 2.1 children per woman at which population neither increases or decreases. More than 800 million people live in countries in which fertility averages four or more children per woman--a level that, if sustained, will lead these populations to double in less than 35 years.
Meanwhile, 42 percent of the world's people live in countries in which the average family size is below the number needed to maintain a stable population level. These countries have reached the end of the "demographic transition"--the decades-long shift from high mortality and fertility rates to longer lives and then smaller family size. So far, 16 countries are losing population, all in Eastern and Southeast Europe, including Russia. However, while the countries with the highest rates of negative population growth could decline by a maximum of 15 percent by 2025, the most rapidly growing populations are likely to nearly double over the same two decades.
Because many national populations have undergone significant declines in fertility rates (resulting in new emphasis on the economic and social concerns of population aging), some observers assume that such progress is inevitable. On the contrary, the dramatic fertility declines occurring in countries in Europe, East Asia, and parts of Latin America, which stem from a complex mix of socioeconomic conditions and access to health and education, have not been universal. Although some degree of fertility decline is under way almost everywhere, in sub-Saharan Africa the pace of these declines is hardly changing. Among 19 African countries for which survey data are available, fertility rates have stalled at four children per woman or higher.
United Nations population projections show overall improvements in countries' progress through the …