Sometime in the next year or two, a woman will give birth in the Lagos slum of Ajegunle, a young man will flee his village in west Java for the bright lights of Jakarta, or a farmer will move his impoverished family into one of Lima’s innumerable pueblos jóvenes. The exact event is unimportant, and it will pass entirely unnoticed. Nonetheless it will constitute a watershed in human history, comparable to the Neolithic or Industrial revolutions. For the first time, the urban population of the world will outnumber the rural.