Read: The Steady Destruction of America’s Cities

New York is the poster child of this urban renaissance. But as the city has attracted more wealth, housing prices have soared alongside the skyscrapers, and young families have found staying put with school-age children more difficult. Since 2011, the number of babies born in New York has declined 9 percent in the five boroughs and 15 percent in Manhattan. (At this rate, Manhattan’s infant population will halve in 30 years.) In that same period, the net number of New York residents leaving the city has more than doubled. There are many reasons New York might be shrinking, but most of them come down to the same unavoidable fact: Raising a family in the city is just too hard. And the same could be said of pretty much every other dense and expensive urban area in the country.

In high-density cities like San Francisco, Seattle, and Washington, D.C., no group is growing faster than rich college-educated whites without children, according to Census analysis by the economist Jed Kolko. By contrast, families with children older than 6 are in outright decline in these places. In the biggest picture, it turns out that America’s urban rebirth is missing a key element: births.

Cities were once a place for families of all classes. The “basic custom” of the American city, wrote the urbanist Sam Bass Warner, was a “commitment to familialism.” Today’s cities, however, are decidedly not for children, or for families who want children. As the sociologists Richard Lloyd and Terry Nichols Clark put it, they are “entertainment machines” for the young, rich, and mostly childless. And this development has crucial implications—not only for the future of American cities, but also for the future of the U.S. economy and American politics.

The counties that make up Los Angeles, Chicago, New York City, and Philadelphia shed a combined 2 million domestic residents from 2010 to 2018. For many years, these cities’ main source of population growth hasn’t been babies or even college graduates; it’s been immigrants. But like an archipelago of Ellis Islands, Manhattan and other wealthy downtown areas have become mere gateways into America and the labor force—“a temporary portal,” in the words of E. J. McMahon, the founder of the Empire Center for Public Policy. “The woman from Slovakia comes to Queens, lives in her second cousin’s basement, gets her feet on the ground, and gets a better apartment in West Orange, New Jersey,” he said. Or a 20-something from North Dakota moves to Chicago after school, works at a consultancy for a few years, finds a partner, and moves to Missoula.

But if big cities are shedding people, they’re growing in other ways—specifically, in wealth and workism. The richest 25 metro areas now account for more than half of the U.S. economy, according to an Axios analysis of government data. Rich cities particularly specialize in the new tech economy: Just five counties account for about half of the nation’s internet and web-portal jobs. Toiling to build this metropolitan wealth are young college graduates, many of them childless or without school-age children; that is, workers who are sufficiently unattached to family life that they can pour their lives into their careers.