James Lovelock in 2005/Photograph by Bruno Comby

In 1965 the British-born inventor James Lovelock, then working for NASA, had an epiphany.

Thinking about the question of life on Mars, he realized that a major difference between that planet and ours is that the Martian atmosphere is sterile and in a state of unmovable equilibrium, while down here the atmosphere is dynamic, highly atypical, and kept in being by the life it supports. This could be only because planet Earth is in some very real sense a living organism, something that shortly (on the advice of his neighbor the novelist and future Nobel laureate William Golding) he was to call “Gaia.”

Although Lovelock soon gained the support of the biologist Lynn Margulis, she who would win fame as the person who saw clearly that complex cells are symbioses of simpler…