"Anyone would think I was the only atheist around," says Richard Dawkins, in tones of mildly frustrated grievance. He isn't, of course, but if you happen to be in the market for an atheist, there's little doubt that the Charles Simonyi Professor in the Public Understanding of Science at Oxford University is the market leader – a Rolls-Royce of anti-clerical argument, whose contradictions and counter-propositions slam shut with a perfectly engineered thunk.
For the moment, though, he's happy to let the business go elsewhere. "You've no idea how often I turn down invitations to do that kind of controversial stuff," he continues. "Time and again broadcasters will be looking for somebody to say something negative about God and they'll come to me, and nowadays I say no almost always."
This reticence is not the result of second thoughts, incidentally, but of a growing anxiety that his observations on religious faith are obscuring something that matters a great deal more to him – the promotion of scientific method, about which he will speak with a proselytising passion. Whether he likes it or not, it has made him not just the most successful populariser of evolutionary theory in the country, but also a figurehead for scientific scepticism. He has written with genuine indignation about the bad press given to Thomas – the one Disciple who wanted to subject Christ's claims to some kind of clinical verification.
Which is why the publisher of Snake Oil and Other Preoccupations, a book about alternative medicine that John Diamond was working on when he died, naturally turned to Dawkins for a preface – and why he is sitting in his garden in north Oxford talking, among other things, about homeopathy and religion.
We are seated at a vast slab of Devonian Jurassic stone – a roughly hewn square, 10ft by 10ft, resting on three carved- stone Platonic solids, the kind of prodigious jeu d'esprit you can treat yourself to if your books have become global bestsellers. The public appetite that made them so, Dawkins is ready to concede, may not be entirely divorced from the religious instinct that prevailed in Victorian times.
"It is absolutely true that the ecological niche that was filled by religion is now filled by science, and perhaps above all by the evolutionary science that I cling to myself," he says – that word "cling" so hesitantly voiced that I have to rewind the tape several times to make it out. "I do feel that science is absolutely not a religion when you mean it is held on faith, but it fills the same ecological niche as religion in the sense that it answers the same kind of questions as religion, in past centuries, was alleged to answer.
"So I have respect for religious people in so far as they are asking important questions. They want to know why we exist and why the world exists, and they don't just want to know who's going to win Wimbledon and what's for dinner. And to that extent I have great respect. But I get irritated at the way those deep and fundamental and mysterious questions are hijacked – because I think that science can answer most of them, if not all of them."
The "if not all", by the way, is not a revised bid for comprehensive explanation, but a concession that some mysteries will always remain. The "why?" question that is often thrown at Dawkins in public lectures ("everyone who asks it, asks it in the tone of voice that suggests that no one has ever asked it before") is, to his mind, irrelevant: "The mere fact that a question can be put – the mere fact that the English word "why" exists – doesn't mean that it's a legitimate question."
Darwinians ask meaningful "why" questions, he says. Those that ask "why is this leaf this particular shape?" or "why does this animal walk like this?". What about, "why are humans so credulous?" I ask. So happy to pay through the nose for an aura massage or crystal healing. Mustn't gullibility have an evolutionary explanation too?
"I would put it back to childhood and say that there's a Darwinian survival value in children believing what their elders tell them, because the world is too dangerous a place and it takes too long to learn what you need to learn to survive," Dawkins replies. "You've got to have a rule of thumb that's built into the nervous system that says 'Believe what you're told'. And once you've got a rule of thumb like that, it's like having a computer, which is vulnerable to viruses. A good computer will run whatever programme you stick in it, whether it's beneficial or not."
The vulnerability of children to such parental downloads is one source of Dawkins' fierce opposition to religious schools (he recently described government plans to encourage the spread of single-faith schools as "evil"). The subject briefly makes him forget his self-denying ordinance: "I can't bear the religious labelling of children," he says. "Like four-year-old Islamic children or four-year-old Catholic children... If anything makes me see red, that does, because these children are too young to know what they are... Would you ever talk about a four-year-old neo-Keynesian monetarist? Or a four-year-old Gramscian Marxist? Of course you wouldn't. Religion is the one place where opinions about society, about philosophy, about cosmology are grafted on to labels tied round the necks of children."
Dawkins' own label would have read "four-year-old Anglican". His father read Botany at Oxford, and both parents were interested in the natural sciences, so many of the answers to his own youthful questions were likely to have been couched in scientific rather than mythical terms.
"I think I can remember at the age of six regaling my unfortunate younger sister, was three, telling her about the solar system and telling her which planet was further away than which, and the order in which they came... I must have got that from somewhere...
"The first time I understood Darwinism was when my father explained it to me... I understood it but I didn't believe it... it didn't seem to me to be strong enough."
Educated at Oundle, he was confirmed into the Church of England after a brief lapse in faith. He then drifted from the church again as he read more on evolution: "The second time, it was the collapse of the argument from design and the realisation that the beauty and complexity of the living world had a simple explanation. That was a very beautiful revelation".
He revises this word "revelation" later – anxious, I think, that this shouldn't sound too much like a Damascene conversion – but the sense that he had found a credo rather than lost one remains strong. He was never, he says, the kind of biologist who turns their hobby into an academic discipline: "Many students come into biology because they've been bird-watchers or bug-hunters – I was always interested in the more philosophical aspects".
His confidence in evolution as an all-encompassing explanatory framework also allows for doubt: "I've sometimes thought about this. Would I be discomfited if, say, Darwinism turned out to be wrong and the truth about the guiding force of evolution, why things are so beautiful and so – apparently – well-designed, turned out to be something else?" He pauses briefly and then his eyes widen at the thought. "I would be fascinated... Obviously, I can't imagine what that alternative might be, and I'm very sure there isn't one... but I would be totally fascinated if there was one."
The genuine excitement that this speculation arouses marks the difference between a religious and a scientific mindset – this is a man exhilarated at the thought of his conceptual universe being turned upside-down.
In the meantime, though, he continues to fight the good fight against the enemies of reason – the charlatans and the misguided. He did not know John Diamond well, he points out in his preface to Snake Oil..., but he clearly recognised a fellow- combatant, and he salutes him in martial terms. "Although this gallant man is silenced," he concludes, "his guns are not silenced... Open fire, and don't stop."
It may well be that Richard Dawkins is observing a temporary ceasefire on the religious front, but the swords haven't yet been beaten into ploughshares.
'Snake Oil and Other Preoccupations', by John Diamond, is published by Vintage, £7.99Reuse content