The Spiritual Nature of Man: A Study of Contemporary Religious Experience (1979) by Sir Alister Hardy is a pioneering scientific study analyzing over 3,000 accounts of personal spiritual experiences. As a biologist, Hardy presents a naturalistic inquiry into these phenomena, concluding they are real, common, and often independent of organized religion, suggesting a deeply rooted human spiritual nature. Hardy suggests these experiences are a natural part of human biology and evolution, rather than just superstition.