Dreams puzzled early man, Greek philosophers spun elaborate theories to explain human memory and perception, Descartes postulated that the brain was filled with "animal spirits," and psychology was officially deemed a "science" in the 19th century. The Fourth Edition of Hergenhahn's best-selling text continues to provide students with a comprehensive view of the history of psychology by showing that most of the concerns of today's psychologists are manifestations of themes that have been a part of psychology for thousands of years.