The following comes from an essay by Ross Douthat which appeared in the Decmber 1 New York Times.

IN the eternally recurring debates about whether some rival great power will knock the United States off its global perch, there has always been one excellent reason to bet on a second American century: We have more babies than the competition.

It’s a near-universal law that modernity reduces fertility. But compared with the swiftly aging nations of East Asia and Western Europe, the American birthrate has proved consistently resilient, hovering around the level required to keep a population stable or growing over the long run.

America’s demographic edge has a variety of sources: our famous religiosity, our vast interior and wide-open spaces (and the four-bedroom detached houses they make possible), our willingness to welcome immigrants (who tend to have higher birthrates than the native-born).

And it clearly is an edge. Today’s babies are tomorrow’s taxpayers and workers and entrepreneurs, and relatively youthful populations speed economic growth and keep spending commitments affordable. Thanks to our relative demographic dynamism, the America of 50 years hence may not only have more workers per retiree than countries like Japan and Germany, but also have more than emerging powers like China and Brazil.

If, that is, our dynamism persists. But that’s no longer a sure thing. American fertility plunged with the stock market in 2008, and it hasn’t recovered.

Last week, the Pew Research Center reported that U.S. birthrates hit the lowest rate ever recorded in 2011, with just 63 births per 1,000 women of childbearing age. (The rate was 71 per 1,000 in 1990.) For the first time in recent memory, Americans are having fewer babies than the French or British.

The plunge might be temporary. American fertility plummeted during the Great Depression, and more recent downturns have produced modest dips as well. This time, the birthrate has fallen fastest among foreign-born Americans, and particularly among Hispanics, who saw huge amounts of wealth evaporate with the housing bust. Many people may simply be postponing childbearing until better times return, and a few years of swift growth could produce a miniature baby boom.

But deeper forces than the financial crisis may keep American fertility rates depressed. Foreign-born birthrates will probably gradually recover from their current nadir, but with fertility in decline across Mexico and Latin America, it isn’t clear that the United States can continue to rely heavily on immigrant birthrates to help drive population growth.

Among the native-born working class, meanwhile, there was a retreat from child rearing even before the Great Recession hit. For Americans without college degrees, economic instability and a shortage of marriageable men seem to be furthering two trends in tandem: more women are having children out of wedlock, and fewer are raising families at all.

Finally, there’s been a broader cultural shift away from a child-centric understanding of romance and marriage. In 1990, 65 percent of Americans told Pew that children were “very important” to a successful marriage; in 2007, just before the current baby bust, only 41 percent agreed. (That trend goes a long way toward explaining why gay marriage, which formally severs wedlock from sex differences and procreation, has gone from a nonstarter to a no-brainer for so many people.)

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