Why do we behave as we do, and how are we to judge this behaviour in terms of right and wrong, good and evil, natural and unnatural? On the answers to these questions, whole systems of religion, law and government have been founded. Now, science has begun to address these same questions, offering data that is both exciting and controversial. Specifically concerned with the biological bases of human behaviour and human emotions, this book is a treatment of materials that have often been misused and exploited for questionable ends.