Kay Hymowitz joins Brian Anderson to discuss how our social instincts, and especially our social networks, affect our behavior and choices, in areas as wide-ranging as divorce, obesity—and even rioting.

Humans are social animals, as the saying goes. Our social nature, Hymowitz writes in her new story, "The Human Network," makes nearly everything contagious, from viruses to behaviors. For example, new research suggests that people can, in effect, "catch" divorce from their friends or extended family. But while network science can be a useful tool for understanding human action, it cannot explain why some are more susceptible to social pressure than others.