Gaia, in which James Lovelock puts forward his inspirational and controversial idea that the Earth functions as a single organism, with life influencing planetary processes to form a self-regulating system aiding its own survival, is now a classic work that continues to provoke heated scientific debate. The breath-taking sweep of his central idea - that the earth is a living, self-regulating organism - poses the most dramatic challenge to scientists, politicians, and environmentalists.