Some don't consider the century's near-quadrupling of population a problem. It's a product of improving human health, improving lifestyles and better nutrition. People are living longer. While others worry that too large a population will exhaust natural resources, Taylor says human ingenuity is the true resource - and that will only increase with more people around. People aren't just mouths to feed.
People can also be surprisingly adaptable.
Last October, U.N. demographers reduced their population-growth estimates by about 2 million a year, saying they hadn't anticipated how quickly women around the world would embrace the notion of having fewer children. In the 1950s, the average woman gave birth five times during her lifetime. Today that global fertility rate is 2.7 births per woman and falling, the United Nations says. Virtually all the gain will occur in the poorer nations. Gordon Hempton answers with a story.