A comprehensive view of the most heated debate of our time — are genes the primary influence on human personality and behavior? In presenting the recent findings, William Wright argues that in a century dominated by psychoanalytic thought, there has been an insistence that humans, unlike all other species, are brought into the world as blank slates on which personalities are etched by the environment. Wright describes the overthrow of this view by psychologists and geneticists whose discoveries, most dramatically through studies of identical twins separated at birth, have resulted in the recognition of the major role played by genes in personality and behavior. Wright describes how molecular biologists have reinforced these findings by locating the links between genes and behavior in DNA itself. And he explores the exciting future prospects of treating such conditions as depression, addiction, and hyper-aggressiveness that are implicit in the behavioral-genetic revolution.