In between the explication of the opening words (""my aim has been to explain...the part that our instincts play in fashioning our lives"") and the inspiration of the closing salvo (""laughter, tears and wonderment as we create together the story of mankind"") this book is pretty clearly defined. Dr. Casson charts the instinctual life from infancy onward and upward through middle age (""the senior citizen""--yes, there is that British inflection) and in terms of sexual drives, aggression, morality, etc. Most of his findings refer back to the staple socio-psychologists, Freud, Margaret Mead, the Kinsey report, and any more knowing reader will be familiar with them. The book's value, like.any instinct, is elementary. It is also salubriously conservative in point of view.