Throughout his remarkable career, Donald Pfaff has demonstrated that by choosing problems and methods with care, biologists can study the molecular mechanisms of brains more complex than those of fruit flies, snails, roundworms, and other invertebrates. His half century in the lab, starting with his discovery of hormone receptors in the brains of mammals and leading to the first detailed account of a neural circuit for mammalian behavior, puts him in a unique position to survey the origins and development of behavioral neurobiology and the current state of research. How the Vertebrate...