One set of projections by the United Nations of current demographic trends suggests that the world's population may peak in the middle of the next century and then steadily decline. That course of events would have radical consequences for economics, politics, and family life.

Most of the news from the 23rd General Population Conference, held in October in Beijing, focused on the threat of overpopulation. But this danger may be a myth. Over the past several years, some of the world's best demographers have begun a dramatic reassessment of the world's demographic future. They are now seriously considering the possibility that the world's population will peak in our lifetimes, and then commence an indefinite decline.

The "depopulationist" scenario has been set out most recently in the United Nations Population Division's 1996 revision of its biennial compendium, World Population Prospects--the oldest, largest, and most intensive of various contemporary attempts to outline likely future demographic trends, and a good starting point to outline the demographic revolution that may be in store.

Fertility Trends

All population "projections"--these are not predictions--are built on assumptions. The U.N.'s "low variant" model assumes that life expectancy at birth will rise in "more developed regions" to 81 years in 2050 from roughly 75 today. For the "less developed" regions, average longevity will reach 76 by 2050, vs. 64 today; in the "least developed countries" (mostly in sub-Saharan Africa), it is seen as rising to 72 from 52.

The most important assumptions in the "low variant" model concern future fertility trends. By the U.N.'s estimate, total fertility rates (lifetime births per woman) for the more developed regions have already fallen to about 1.5 from about 1.7 in the early 1990s, and, if this model were to prove accurate, would settle in another decade at about 1.4. For the less developed regions, the rate is thought to have averaged 3.3 in the early 1990s and fallen slightly since; the model projects its declining to about two in 2020, and 1.6 in 2050. For the "least developed countries," where the total fertility rate is estimated to have been over five this decade, it is posited to drop below four by 2010, below three by 2020, and below two by 2035.

With these assumptions about the future--none of them implausible on their face--global depopulation would commence in a little over four decades. Between 2040 and 2050, the world's population would fall by about 85 million. From then on, world population would shrink by roughly 25 percent with each successive generation. To put the matter another way, future world fertility patterns would be similar to those in the "more developed regions" today, where the "net reproductions rate" is already down to about 0.7 (meaning that the next generation, under present patterns of childbearing and survival, and not accounting for immigration, would be about 30 percent smaller than the current one).

The patterns that would result in an ultimate global population decline would also bring about a significant redistribution of world population. In 1995, the ratio of population between "less developed" and "more developed" regions stood at about 4 to 1; in 2050, by these projections, it would be 7 to 1. The balance of population would shift dramatically, not only between given countries but even between entire continents. In 1995, for example, the estimated populations of Europe (including Russia) and Africa were almost exactly equal. In 2050, by these projections, Africans would outnumber Europeans by more than 3 to 1.

An Aging World Population

These same demographic forces--longer lives and falling fertility--would also lead to a radical and inexorable aging of the population. Around 1900, the median age of the world's population was probably about 20; by 1995, it reached about 25 years. By 2050, in the "low variant" world, the median age would be over 42. In some countries, the population would be even older: Japan's median age would be 53; Germany's, 55; Italy's, 58.

As the chart nearby shows, while the number of children around the world would sharply decline, there would be a population boom among the elderly (or, at any rate, among those we would consider elderly today). In the less developed regions, there would be three times as many older people as young children; in the more developed regions, the ratio would be 8 to 1. In Italy, which serves in these projections as the extreme instance of demographic aging, barely 2 percent of the population in 2050 would be under five years old, but more than 40 percent would be 65 or older.

Such a gerontological drift raises basic questions about the health of the societies of this imagined future. Would a depopulating world be a world of wheelchairs--of increasingly infirm senior citizens whose escalating demands for medical services and care seriously burden the rest of society? Or would the revolution in longevity be accompanied by a revolution in health that effectively extends the scope for active, vigorous, and productive existence?

On the whole, the evidence seems to argue that improvements in "disability-free" life expectancy can occur nearly as rapidly as improvements in life expectancy itself. At the same time, the quality of life for older people may at times hinge upon discrete, but expensive, medical treatments--interventions more available in rich countries than in poor ones.

Implications of Depopulation

Negative population growth would have major implications for government, especially for the nationwide, tax-financed, pay-as-you-go pension programs that are the central feature of the modern welfare state. In virtually all of today's industrial democracies, such programs were established in periods of relatively high fertility and relatively rapid population growth. With below-replacement fertility and increasing longevity, the arithmetic of these schemes changes unforgivingly. As the ratio of employees to retirees falls, such programs have only three options for preventing bankruptcy: reduce pension benefits, raise taxes, or restrict eligibility.

One way to begin restructuring such programs is with later retirement ages, as populations make greater productive use of their extended active life spans. But depopulation would almost necessarily presuppose a change from pay-as-you-go financing to self-financing of retirement benefits by individuals over the course of their own lives. Though such a change could involve a full privatization of social insurance, it is also possible to imagine the reformed pension systems operating under the aegis of government. But it is hard to see how self-financed pensions could lend themselves as readily to redistributive or other nonmarket objectives as the pay-as-you-go arrangements have done.

Finally, it is interesting to ponder how the demographic revolution to come will affect the family as most of us have experienced it. The U.N.'s projections imagine a world in which the only biological relatives for many people will be their ancestors.

Consider the possibilities for Italy, currently the country with the world's lowest fertility level. If Italy's current regimen is extended for two generations, almost three-fifths of the nation's children will have no siblings, cousins, aunts, or uncles; they will have only parents, grandparents, and perhaps great-grandparents. Under those same assumptions, less than 5 percent of such a future Italy's children would have both siblings and cousins.

Social Atomization

Projecting the fertility rates for the entire European Union forward two generations only slightly alters the Italian scenario. In time, under "low variant" assumptions, families in the less developed regions would move in this direction. Within another generation or two, a family consisting of siblings, cousins, uncles, and aunts would be anomalous throughout the entire world. For many if not most people, "family" would be understood as a unit that does not include any biological contemporaries. The nuclear family may have marked a radical departure from previous sorts of family arrangements. But, as we have seen, the nuclear family does not begin to approach the limits of atomization that may await us in a depopulating world.

All this represents merely a sketch of a future whose social, political, and economic outlines promise to break sharply with anything in recorded experience. Yet as opaque as these changes may appear today, we may yet manage to discern them very carefully. A good number of us could eventually experience them firsthand: in the U.N.'s "low variant" projections, in fact, half of the world's current inhabitants would still be alive at the time that global depopulation commences.

Nicholas Eberstadt is a visiting scholar at the American Enterprise Institute and the Harvard Center for Population and Development Studies.