The prefrontal cortex makes up almost a quarter of the human brain, and it expanded dramatically during primate evolution. This book presents a new theory about its fundamental function. The book argues that primate-specific parts of the prefrontal cortex evolved to reduce errors in foraging choices, so that particular ancestors of modern humans could overcome periodic food shortages. These developments laid the foundation for working out problems in our imagination, which resulted in the insights that allow humans to avoid errors entirely, at least at times.