ABSTRACT
What will be remembered about the twenty-first century, more than anything else except perhaps the effects of a changing climate, is the great, and final, shift of human populations out of rural, agricultural life and into cities. We will end this century as a wholly urban species. This movement engages an unprecedented number of people-two or three billion humans, perhaps a third of the world’s population-and will affect almost everyone in tangible ways. It will be the last human movement of this size and scope; in fact, the changes it makes to family life, from large agrarian families to small urban ones, will put an end to the major theme of human history, continuous population growth.
