Human sexual nature today experiences many unanswered questions. Why does woman respond more slowly than man in arousal? What is the significance of the human orgasm? Why does sexual experience so often fail to form a lasting relationship? When is the most vulnerable time for a relationship in the process of formation? These and other questions are supported to find answers in our evolutional history. In this wide ranging and penetrating study the author finds human sexual nature to be basically inclined to committed relationships. The deepest evolutional trend, having early vertebrate origins, he finds to be the increasing biological investment in the unit young of each new generation.