A smaller population? There are benefits.

You can see the hand-wringing from Berlin to Boston, Toronto to Tokyo: Low birthrates and aging populations spell disaster for rich nations. They'll overburden children with financial obligations to their elders, rend social safety nets, and push economies into neutral.

"There's so much hysterical stuff about this issue," says Gary Burtless, an economist with the Brookings Institution. It's worth asking the worrywarts who it is they're really worried about.

Today's parents?

By and large, women have fewer children because they believe it will contribute to their own happiness or that of the children they do choose to have.

Their children?

Over the past 150 years, the next generation has almost always been more prosperous on the whole than the previous generation. Today's children are richer in things and education than their parents were as youngsters.

Future generations?

It may be true that aging slows down an economy. But not necessarily, some economists say. Business, faced with fewer workers, may well invest more in machines and other means for raising productivity and prosperity.

Consider Japan. The Japanese are even more worried than Americans about an aging population. Japanese women, on average, have only 1.35 children, substantially fewer than the 2.05 of American women. Moreover, the Japanese live longer on average than any other nationality on earth.

In the future, though, Japanese workers, ages 20 to 64, will have relatively fewer children to support with food, clothing, housing, education, and so on than Americans will. They don't have anywhere near the share of people in jail that the US does, each inmate costing about $25,000 a year. Nor, do they have America's share of young people incapacitated for work by drugs, alcohol, gangs, and other ills.

"The Japanese do a pretty good job of rearing children," says Mr. Burtless, back from a visit to the island nation. "They have extremely low rates of divorce. Few children are born outside of marriage."

Despite their concern, the Japanese expect to retain a high living standard.

What about Western European nations, most of which are also saddled with extremely low birthrates and populations expected to shrink if not already declining? In Italy, for example, the median age will rise from 42 to 51 over the next two decades. Would they trade places with the people of Mexico - or even China? Would their children?

In the current debate over Social Security in the United States, critics note that by 2042 payroll taxes will cover only 70 percent of promised benefits. What they often don't acknowledge is that this 70 percent will be much greater in real purchasing power than what beneficiaries get today - thanks to greater productivity.

Even if the US kept Social Security fully funded by raising the payroll tax rate, workers toward the end of the century should be "much better off," says Mr. Burtless. "Why should we be feeling sorry for them?"

The aging of populations does have economic consequences, of course. The European and Japanese economies have tended to grow more slowly than that of the US partly because their workforces are not growing as much. Economists debate, however, whether slow or negative population growth will result in less or more output per person.

James Poterba, an economist at Harvard University, suggests that older populations in Japan and Europe may partly account for a political reluctance to make economic "reforms" in the workplace.

The McKinsey Global Institute in New York has just published a lengthy study of the US, Japan, Germany, Britain, and Italy, which account for two-thirds of global financial assets. Its key conclusion is that growth in household financial wealth over the next 20 years will slow by more than two thirds, from 4.5 percent historically to 1.3 percent. So household wealth, instead of growing to $85 trillion in these five countries, will grow to $54 trillion.

Most people in such nations as Italy, Germany, and France depend primarily on their social security system to provide an adequate pension. These pensions are much more generous than the American system provides. But fewer Europeans have pensions from companies or other employers.

Barry Bosworth, another Brookings economist, tells of a visit to Montevideo, capital of Uruguay, a Latin American nation with a shrinking population. The downtown has "block after block of empty buildings," he says. Hotels are empty. "There are apartments which in New York City people would kill for."

So, will aging and thence shrinking populations result in reduced demand for housing and falling home prices?

In Germany, talk of cutting pensions has meant that working Germans have stepped up their savings rate to provide for their old age. The result is an "overhang" of savings and a shortage of spending that is keeping economic growth modest, says Mr. Bosworth.

Contrast that with the US, where for years foreign savings have financed spending. Economists joke that Americans are the world's "consumers of last resort." Possibly today's pension uncertainty, caused by an aging population, will prompt them to save more.

That would not be a bad thing.