Jackson, M. O.
Introduction: Who becomes the most central individual in a society and why? What determines how many friends a given individual has? What determines how clustered or tightly-knit the friendships in a society are? In a set of important and original new findings reported in this issue of PNAS, Fowler, Dawes, and Christakis (1) provide evidence that network characteristics such as those mentioned above are heritable: that is, they show that an increase in the overlap in genetic material in twins corresponds to an increase in the covariation of some of their social network characteristics.