Demography is not destiny, as is sometimes claimed. The human race could be wiped out by a plague or an asteroid, or transformed by some new technology. But no matter what, today's patterns of fertility, migration, and mortality fundamentally determine how much society will or can change for many generations to come.
And what demography tells us is this: The human population will continue to grow, though in a very different way from in the past. The United Nations' most recent "mid-range" projection calls for an increase to 8 billion people by 2025 and to 10.1 billion by century's end.
Until quite recently, such population growth always came primarily from increases in the numbers of young people. Between 1950 and 1990, for example, increases in the number of people under 30 accounted for more than half of the growth of the world's population, while only 12 percent came from increases in the ranks of those over 60.
But in the future it will be the exact opposite. The U.N. now projects that over the next 40 years, more than half (58 percent) of the world's population growth will come from increases in the number of people over 60, while only 6 percent will come from people under 30. Indeed, the U.N. projects that by 2025, the population of children under 5, already in steep decline in most developed countries, will be falling globally -- and that's even after assuming a substantial rebound in birth rates in the developing world. A gray tsunami will be sweeping the planet.
Which countries will be aging most rapidly in 2025? They won't be in Europe, where birth rates fell comparatively gradually and now show some signs of ticking up. Instead, they'll be places like Iran and Mexico, which experienced youth bulges that were followed quickly by a collapse in birth rates. In just 35 years, both Iran and Mexico will have a larger percentage of their populations over 60 than France does today. Other places with birth rates now below replacement levels include not just old Europe but also developing countries such as Brazil, Chile, China, Lebanon, Tunisia, South Korea, and Vietnam.
Because of the phenomenon of hyper-aging in the developing world, another great variable is already changing as well: migration. In Mexico, for example, the population of children age 4 and under was 434,000 less in 2010 than it was in 1996. The result? The demographic momentum that fueled huge flows of Mexican migration to the United States has waned, and will wane much more in the future. Already, the net flow of illegal Mexican immigration northward has slowed to a trickle. With fewer children to support and not yet burdened by a huge surge of elders, the Mexican economy is doing much better than in the past, giving people less reason to leave. By 2025, young people on both sides of the border may struggle to understand why their parents' generation built this huge fence.