The adage “demographics are destiny” is increasingly being replaced by a notion that population trends should actually shape policy. As the power of projection grows, governments around the world find themselves looking to find ways to counteract elaborate and potentially threatening population models before they become reality.

Nowhere is this clearer than in China’s recent announcement that it was suspending its “one child” policy. The country’s leaders are clearly concerned about what demographer Nicholas Eberstadt has labeled “this coming tsunami of senior citizens” with a smaller workforce, greater pension obligations and generally slower economic growth.

A second example is Europe’s open migration policy. Despite widespread opposition by its own citizens, and cost estimates that run to a trillion euros over 30 years, Europe’s political and business leaders regard migration as critical to address the Continent’s aging demographics. Germany knows it may not be able to keep its economic engine running without a huge influx of workers.

In defense of the migration policy, European Union economists project that refugees from the Middle East, Africa and Central Asia could boost Europe’s GDP by 0.2 percent to 0.3 percent by 2020.

This all speaks to a kind of demographic arbitrage between countries with aging demographics and those with youth to spare. Half the world’s population already lives in countries with fertility rates below replacement level (2.1 per woman).

By 2050, according to United Nations projections, the number of countries with below-replacement-level fertility rates is expected to nearly double, to 139 nations, accounting for 75 percent of the world’s population at that time. These countries are being forced either to try restoring their fertility rates to sustainable levels or to welcome masses of people from those parts of the world that still produce demographic surpluses.

Crisis of low-fertility countries

Most affluent countries and those on the way to prosperity, such as China, all face the same basic dilemma: an aging population and shrinking workforce. China, notes the U.N., by 2050 will suffer a net loss of 60 million people under 15 years of age, approximately the size of Italy’s population. China at the same time will gain nearly 190 million people age 65 and over, approximately the population of Pakistan, which is the world’s sixth most-populous country.

It seems likely that the policy shift away from “one child” may be too late to have much impact. Gavin Jones, a demographer based at the National University of Singapore, traces China’s demographic implosion less to government policy and more to factors such as rapid urbanization and skyrocketing housing prices. Indeed, expensive, prosperous cities like Shanghai and Beijing now have among the lowest fertility rates ever recorded – near 0.7 children per woman, or one-third the replacement rate.

Chinese couples reluctant to have one child do not seem likely to opt for two. Indeed, a 2013 easing of restrictions on family size for limited populations elicited far fewer takers; barely 12 percent of eligible families even applied to take advantage of the change.

Overall, governments are notoriously unsuccessful at getting people to change their basic behaviors. Like China, other East Asian countries – South Korea, Taiwan, Singapore – used to worry about overpopulation. Now, they try to encourage births by offering elaborate cash gifts, subsidies and pro-family changes in tax policy, but they still have failed to halt the decline of the the traditionally familial culture that long defined Confucian-infused societies.

Japan is the poster child for this East Asian demographic transition. Fertility there has been well below replacement level for a generation. The resulting economic effects of its plunging workforce and lack of new families are painfully clear, and the trajectory is not promising. Japan since 1990 has had more people over age 65 than under 15, but by 2050 there will be three times as many.

More remarkable still, there will be more Japanese over age 80 than under 15. Japan’s population – now 127 million – is expected to fall to 108 million by 2050. By 2100, according to the U.N., the population could be 84.5 million, but Japan’s National Institute of Population projects a drop to roughly 60 million.

Not-so-dissimilar demographics might be evolving in other prosperous areas of the world, if not for migration. Immigrants and their children have allowed the U.S. and Australia to stay close to the replacement rate, and have kept Canada’s from imploding.

European countries, logically, also are seeking out new labor sources. But this strategy clearly threatens the long-term social harmony and political stability of these traditionally homogeneous countries. Germany within a few years could be 20 percent Muslim, which would represent, notes Uwe Brandl, president of the Bavarian Association of Municipalities “a demographic shift of epic proportions, one that will change the face of Germany forever.”

The youth-bulge countries

The primary source for migration today comes from what may be defined as “youth bulge” countries – places with large populations of young people. The most important example is India, which, although its fertility rate is falling, is still twice that of China. China’s population is due to peak in the 2020s, but not until the 2060s for India.

India is not likely to run out of labor – even with significant migration to other countries – in the foreseeable future. By 2022, according to U.N. estimates, India should pass China as the world’s most-populous country. This could help set the stage for India arguably to emerge as the next global economic superpower, along with China and the United States.

The outlook, sadly, is not so promising in the Middle East, where fertility rates are now generally near or below replacement level. A huge generation of young people, born when birth rates were still high, face little opportunity to advance at home. Made up mostly of young men, this cohort could meet the European demand for labor, but also come from countries that are primary incubators of terrorism in the world and represents a potential threat to the social stability of these host countries.

African Genesis

It is widely believed that humanity originated in Africa, and that continent now also represents the future of humanity. Yet unlike many other youth-bulge areas, Africa’s fertility rates remain high even today. This means that, between now and 2100, that continent, and mainly its sub-Saharan areas, will supply some 83 percent of the world’s population growth. Impoverished Niger, Mali, the Democratic Republic of the Congo and Somalia now possess some of the highest fertility rates in the world. In 2050, roughly a quarter of Africa’s population, notes the World Bank, will be ages 15 to 30, twice the percentage in developed countries.

Unlike the aging parts of the world, Africa’s dilemma remains too many babies and not enough money. Projections of the continent’s demographic future can be downright frightening. By 2100, according to the U.N., Nigeria will replace the United States as the third-largest nation, with approximately 750 million people, more than quadrupling its present population.

Hopefully these projections will prove overblown, as similar forecasts have in much of the developing world. Fertility in more economically evolved South Africa already is now close to replacement levels. As Africa urbanizes, its birth rates can be expected to drop significantly, and its population may grow less rapidly than currently predicted.

Demographic Interdependence

Varying global demographics argue for some changes in both migration and foreign investment patterns that are responsive to the fundamental interdependence of aging and more youthful countries. This is most clear in the demographic dependence on migration in Europe, the United States, Canada and Australia.

Japan, and likely other East Asian countries, may take another approach, relying on robots to do those things for which labor lacks. The Japanese government is focusing efforts on creating artificial beings to help care for its soaring senior population. European countries, if they become disenchanted with the current migration wave, eventually may also seek to emulate this strategy.

A more hopeful approach however might be to steer more investment – employment-generating as opposed to only resource-stripping – toward the poorest countries. This may ease migration pressures and slow down population growth as people move to cities for work.

Wealthy countries might also want to steer investment toward educating more women and promoting well-planned, dispersed urbanization. Humanity’s demographic problems may be addressed in the short term by changes in policy, but the real solution lies in spreading the blessings of economic growth and technology to more of the world.

Joel Kotkin is the R.C. Hobbs Fellow in Urban Studies at Chapman University in Orange and executive director of the Houston-based Center for Opportunity Urbanism.