Crime, congestion and pollution mar all cities, from Los Angeles to Mumbai. But another force trumps the drawbacks of urban living: cities bring opportunities for wealth and for the creative inspiration that can result only from face-to-face contact with others. In fact, the crush of people living in close quarters fosters the kind of collaborative creativity that has produced some of humanity’s best ideas, including the industrial revolution and the digital age. In the years ahead such collaborations can be expected to help solve the world’s most pressing problems--poverty, energy shortages, climate change--and to promote the type of fundamental political transitions seen in Cairo that recently astonished the world.

Why do cities bring out the best in us? Technology lets us hold virtual meetings, and the Internet keeps us in touch 24/7, but neither can be a substitute for the types of social cues (a facial expression that signals comprehension or confusion) when people meet in an office, bar or gym. Cities deliver the random exchanges of insight that generate new ideas for solving the most intransigent problems [for more on this mechanism, see “ Bigger Cities Do More with Less ,” by Luís M. A. Bettencourt and Geoffrey B. West]. Young workers, whether they are on Wall Street or in Google’s New York City offices, succeed by picking up unexpected bits of knowledge from the successes and failures of those around them. It has always been so.