In the course of that life detection experiment work, there was a day at Jet Propulsion Labs in 1965 when I was in an office overlooking the hills at the back there, and with the people present were Carl Sagan, now sadly dead, and Diane Hitchcock, a very competent philosopher who was advising on life detection experiments, and myself. Oh, yes, there was one other person, that was an astronomer called Lou Kaplan and Lou ha just brought in the latest results from the Pic du Midi Observatory in France, which had a multiplex interferometer attached to the telescope that could analyse the compositions of Mars' and Venus's atmospheres quite remarkable. Now, it so happens that that interferometer was invented by a friend of mine, Peter Felgate [?], who lives only a few miles from here. But what the results showed was that both Mars and Venus had atmospheres dominated by carbon dioxide and very close to the equilibrium state and therefore according to my theory, Mars was lifeless.

But in order to sort of prove the notion one had to look at a life-bearing planet and compare it. And of course the Earth's the only one we know and when you look at the Earth's atmosphere and compare it with Mars, it's astonishingly different. Mars looks like the exhaust gas that comes out of your car - mostly carbon dioxide. Very little oxygen, bit of nitrogen. The Earth's atmosphere, you've got this strange mixture of lots of oxygen mixed with hydrocarbons like methane. It's the sort of gas that goes into the intake manifold of your car, a reactive gas. In fact, if the composition were different it would be combustible or explosive.

And this begun to intrigue me as I sat thinking there, and I thought, well if you've got an unstable atmosphere like the Earth, hydrocarbons and oxygen mixed, and other gases that are stable, how on Earth does it stay constant? Something must be regulating it. And then it suddenly dawned on me. Well, obviously life produces these gases, life is regulating it. And sure, nobody said it very much, they mostly tended to be somewhat doubtful, you know, they thought this was a flight of fancy.

But then Carl Sagan, when I shared an office with him, said to me afterwards, he said you know, I don't agree with what you've said, but there might be something in it because did you know that one of the great puzzles of astronomy is how is the Earth kept a constant temperature when the sun has been warming up steadily since it begun? The sun was something like 25-30% cooler when life started on the Earth nearly four billion years ago than it is now. So, why wasn't the Earth frozen then and all the evidence suggests that it wasn't, or if it was warm enough then why isn't it boiling now, sort of thing. And, so immediately in my mind there came the thought, oh, so if life regulates the chemistry of the atmosphere then it must be regulating the climate also. And that was when the notion of the self-regulating system was, you know, firmly established.

Now, when I got back to England, living in the village called Bowerchalke in Wiltshire in those days, a near neighbour was the novelist William Golding. And most people don't know that he was trained in science when he was at university. And he was very interested in what was going on at JPL and those other places and we would often talk about it, and one day on a walk with him I told him about this idea of a self-regulating planet and he turned to me and said, 'Well if you're going to produce ideas, you know, about the whole Earth, large like that you better give it a proper name'. So I said, 'What do you suggest?' He said 'You call it Gaia, that's the right name'. We walked on for 20 minutes talking at crossed purposes because I thought he'd said G, Y, R, E, one of the great whirls that feed back on themselves and that would have been a natural thing to think about because it's a fed-back system I was talking about. And then it suddenly dawned on both of us that we… We were talking to the wind. And Bill said, 'No, no, no, no I mean Gaia the classical Greek goddess. And of course then all was light.

And I was very grateful to him, it was not often you get a wordsmith like Golding to give you the name for your theory and… but again, the biologists have hated it. And John Maynard Smith said at a recent Royal Society meeting, 'What a dreadful name to call a theory'. I don't know why they don't like it. You see, somebody might think it was metaphor envy. After all, the biologists, very hot at metaphors. I mean there's a selfish gene, the spiteful gene - they make a big thing of that - and I could go along and say how ridiculous, how could a gene possibly take thought and be selfish, it's an absurd idea, it's an anthropomorphic notion. But, I don't, because I think it's a jolly good metaphor, I think it has taught millions of people around the world, because Richard Dawkins writes so well, just the very nature of Darwinian Natural Selection. I think it's a splendid metaphor. So why are they so unkind to me with my metaphor of the living Earth? I don't think that the Earth reproduces. I never did. I think the living Earth is no different from the selfish gene. They're both good metaphors.