We cannot, of course, disprove God, just as we can't disprove Thor, fairies, leprechauns, and the Flying Spaghetti Monster. But, like those other fantasies that we can't disprove, we can say that God is very, very improbable.

We, alone on earth, can rebel against the tyranny of the selfish replicators.

Creationists eagerly seek a gap in present-day knowledge or understanding. If an apparent gap is found, it is assumed that God, by default, must fill it.

The physicist's problem is the problem of ultimate origins and ultimate natural laws. The biologist's problem is the problem of complexity.

There is no reason to regard God as immune from consideration along the spectrum of probabilities. And there is certainly no reason to suppose that, just because God can be neither proved nor disproved, his probability of existence is 50 per cent.

We have the power to defy the selfish genes of our birth and, if necessary, the selfish memes of our indoctrination. We can even discuss ways of deliberately cultivating and nurturing pure, disinterested altruism - something that has no place in nature, something that has never existed before in the whole history of the world. We are built as gene machines and cultured as meme machines, but we have the power to turn against our creators. We, alone on earth, can rebel against the tyranny of the selfish replicators.

If there is something that appears to lie beyond the natural world as it is now imperfectly understood, we hope to eventually understand it and embrace it within the natural. As ever when we unweave a rainbow, it will not become less wonderful.