Book excerpt: This book provides a general introduction to the biological and evolutionary bases of religion and is suitable for introductory level courses in the anthropology and psychology of religion and comparative religion. Why did human ancestors everywhere adopt religious beliefs and customs? The presence and persistence of many religious features across the globe and time suggests that it is natural for humans to believe in the supernatural. In this new text, the authors explore both the biological and cultural dimensions of religion and the evolutionary origins of religious features.