AT SOME point in 2008, someone, probably in either Asia or Africa, made the decision to move from the countryside to the city. This nameless person nudged the human race over an historic threshold, for it was in that year—according to the United Nations, at least—that mankind became, for the first time in its history, a predominantly urban species.
It is a trend that shows no sign of slowing. Having taken around 200,000 years to get to the halfway mark, demographers reckon that three-quarters of humanity could be city-dwelling by 2050, with most of the increase coming in the fast-growing towns of Asia and Africa. Migrants to cities are attracted by plentiful jobs, access to hospitals and education, and the ability to escape the enervating boredom of a peasant’s agricultural life. Those factors are more than enough to make up for the squalor, disease and spectacular poverty that those same migrants must often at first endure when they become urban dwellers.