James Lovelock has provided one of the great insights of science, and indeed of metaphysics: that the Earth as a whole and all the creatures on it behave in combination, like some kind of meta-organism. The physical forces at work in the world and the cosmos combine to create the conditions that make life possible. In other words, the Earth and all its organisms are homeostatic; they capture energy from their surroundings and use it to maintain conditions that favour their own continuance. This is what distinguishes living from non-living systems. Lovelock’s friend and neighbour, the novelist William Golding, suggested a name for this metaphorical organism, Gaia, after the Greek goddess of the Earth. Lovelock was at first derided by his fellow scientists, who, though commonly seen as fearless seekers after truth, have as keen a nose for heresy as any medieval zealot. Now, though, Gaia is almost an orthodoxy: the idea is even taught in some universities.

The train of thought that led Lovelock to Gaia began in the 1960s when, as