It’s hard to pin down the precise moment the world’s center of gravity shifted. For thousands of years, people lived in the countryside. They worked on farms or in villages, knew little of the world beyond their immediate families and neighbors, and generally got by on their own. Slowly, they began to congregate. It happened in Mesopotamia and Egypt, later in Greece and Rome, and also in Europe and the Americas. More recently, we’ve seen fast growth in Africa and, most spectacularly, in Asia. And then, by 2008, according to the United Nations, the balance finally tipped: in the ebb and flow of daily births and deaths, the number of people who inhabit the world’s cities ticked into the majority, for the first time ever.
The milestone itself isn’t nearly as significant as the trend. In the 20th century cities grew more than 10-fold, from 250 million people to 2.8 billion. In the coming decades, the U.N. predicts, the number of people living in cities will continue to rise. By 2050 the world population is expected to surpass nine billion and urban dwellers to surpass six billion. Two in three people born in the next 30 years will live in cities.