Nicholas Christakis, MD, PhD, is a Harvard professor with joint appointments in Care Policy, Sociology and Medicine, who has been studying social networks for the last ten years. His work has been covered by numerous publications including the New York Times, Newsweek and Time magazine, which recently voted him one of the 100 Most Influential People in 2009.

James Fowler, PhD, is a political scientist who specialises in the study of social networks, human cooperation and political participation. His projects on obesity and the genetic basis of political behaviour have been covered by media outlets including the Washington Post and the BBC.