Review: Connected by Nicholas Christakis and James Fowler

THE idea that everyone on the planet is separated by only an average of six degrees sounds a little too elegant to be true, and yet it seems to hold. The first experiment to confirm this came in the 1960s when psychologist Stanley Milgram asked several hundred people in Nebraska to send a letter to a stranger in Boston via someone they knew. On average, it took six people to get the letter to its destination. The experiment was repeated in 2002 by sociologist Duncan Watts on a global scale using email, with the same result. The world…