John T. Cacioppo's groundbreaking research topples one of the pillars of modern medicine and psychology: the focus on the individual as the unit of inquiry. By employing brain scans, monitoring blood pressure, and analyzing immune function, he demonstrates the overpowering influence of social context--a factor so strong that it can alter DNA replication. He defines an unrecognized syndrome--chronic loneliness--brings it out of the shadow of its cousin...