Mega-cities, mega-problems

THE WORLD HAS reached a point of hyper-urbanization: 2007 marks the first year when more than half the global population is "urban," not "rural." Indeed, this is the era of the "mega-city" -- metropolises of 10 million-plus. In 1950, only Tokyo and New York met that threshold. Today there are 20 mega-cities, including Mexico City, Karachi, Manila, Dhaka, Lagos, Jakarta and Chongqing.

This type of drastic population shift isn't without precedent. During the Industrial Revolution, concentrations of people in U.S. and European cities were part and parcel of a factory economy. But that economic and technological progress came with a price -- decades of fetid slums, horrific child mortality, raging epidemic disease. This time around, with cities 10 times bigger and demand for workers uncertain, the costs could be exponentially larger.

In general, an optimist might cheer urbanization as a sign of modernization; Residents of developed countries are much more likely to live in cities than their counterparts in still-developing nations (74% vs. 43%). The city, after all, is the hub of culture, a magnet that draws artists, writers, musicians -- the place where creative spirits create. Great cities have ballet troupes, opera companies, orchestras. The city is, likewise, the hub of industry, generating the bulk of most countries' gross domestic product. Most important, the city is the hub of ideas. The mingling of people spurs the intellectual innovation that fuels thriving societies, at least in the developed world.

But urbanization historically also has spawned an impoverished underclass of the marginally employed, or unemployed, living in a cruel despair. Think of Charles Dickens' London: Scrooge wanted to diminish the "surplus population." Or remember Karl Marx's ruminations on the "lumpen proletariat," doomed to subsistence.

Cholera, typhoid, influenza -- all cut a swath through 19th and early 20th century urban populations. Yet in time those horrors abated as infrastructure -- clean water, enclosed sewers, labor laws, public education, medical advances -- was created. In time, the 19th century cities morphed into exciting places. Today, Dickens or Marx could contentedly sip cappuccino in Florence, take in the opera at London's Covent Garden or peruse the museums of Paris.