Dawkins was born in Africa, where his father, John, worked in the Colonial Service. ''For generations,'' the son writes, ''sun-browned Dawkins legs have been striding in khaki shorts through the jungles of empire.'' At seven, Richard was sent away to The Eagle - a boarding school in the Vumba Mountains of what was then Southern Rhodesia. In the early mornings he would imagine the matron on her rounds ''would somehow be magically transformed into my mother''. ''I prayed incessantly for this.'' Jean Dawkins tells me later that she didn't want to send her son away to school: ''But it's what you did in those days. He was rather a nice little boy and brave; he never made a fuss about going.'' A year later the family returned to England, where John had inherited the Oxfordshire family estate Over Norton Park from a distant cousin. He resigned his post in Nyasaland and set about restoring the estate to a working farm. He died three years ago but four generations of the family - Dawkins' mother, his sister and her husband, their three adult children and 10 grandchildren - still live there: ''It's a sort of mini-Dynasty, or Dallas,'' he jokes. Transposed from the African plain to this pastoral landscape, the young Richard devoted himself to talking to animals, in the manner of his then-hero, Dr Doolittle: ''I wished and prayed and willed all the animals from miles around to converge on Over Norton Park, and me in particular, so that I could do good works for them. I did this kind of wishful praying so often, I must have been deeply influenced by preachers telling me if you wanted something strongly enough you can make it happen.'' At eight, he was sent away again - to prep school and then, at 13, to public school, where he suffered with an intermittent stammer. When he got full marks in class tests, he would report a nine so he didn't have to tackle the initial ''t'' of 10. Was life more upsetting than he lets on? He frowns: ''Hmmm, well, yes … I chose not to make this a misery memoir or talk about my feelings too much. I do go into bullying a bit; I wasn't bullied but I am ashamed of having not stood up to bullies on behalf of others. I wasn't beaten a great deal but when I was it damn well hurt.'' He doesn't blame the headmaster who inflicted the beatings and had two canes - one more painful for greater crimes. ''They all did it and it's wrong to judge the past by the standards of today. For example, my childhood was thoroughly racist in a benign, paternalistic sort of way. The Africans were all 'boys' - nice and funny but you couldn't actually trust them to do any sort of competent job.''

At school the young Dawkins' faith in the existence of a divine Creator was boosted by the discovery that his new hero, Elvis Presley, was also a believer. Several generations of Dawkins ancestors had been clergymen and he admits that had he been born in their centuries, he might have been one, too. ''Because I have always been interested in the deep questions of existence, the questions that religion aspires, and fails, to answer.'' But what he calls his period of ''religious frenzy'' didn't last: by 16 he was a signed-up Darwinist, refusing to kneel during school chapel service as a mark of rebellion. He is, however, all for teaching children about religion: ''You can't understand European history at all other than through religion, or English literature either if you can't recognise biblical allusions. No child is educated who doesn't know about it. But telling a child, 'You belong to religion X and this is what you believe', I think is wicked.'' Dawkins has a daughter, Juliet, 28, from his second marriage, to Eve Barham. When Juliet was 10 he published a letter to her in his book A Devil's Chaplain stressing the importance of truth based on evidence and the unreliability of tradition or revelation. It ended: ''Next time somebody tells you that something is true, why not say to them: 'What kind of evidence is there for that?' And if they can't give you a good answer, I hope you'll think very carefully before you believe a word they say.'' Recently Dawkins has been attacked for claiming teaching a child about the fires of hell is worse than child sexual abuse. On Twitter people have said things such as, ''Oh Richard, I'm such a fan of yours but you really have gone too far …'' He frowns: ''I just don't get that. I think the reason is that when people think of sexual abuse they think of a horrendous experience like being raped or buggered violently. But I was talking about things like what happened to me - a master at school stuck his hand down my trousers and had a little fiddle and that was it. It was unpleasant but not the same thing.'' But what about a father persistently going into his daughter's bedroom for years? ''Oh yes, awful. But there is a spectrum of awfulness and the horror of telling a child about hell is somewhere in the middle: you burn forever, your skin peels off and you grow another so it can burn off again. If you were a child who really believed that, wouldn't it traumatise you more than having someone stick his hand up your skirt?''

It is seven years since The God Delusion but Dawkins can't stop writing, lecturing, blogging and tweeting about the iniquities of faith. He comes out at the sound of the bell every time; he rings the bell himself. ''I do, I do. But I get fed up with being treated as though I was a nasty, humourless, negative person. I feel that if people can't argue with you, the best they can do is criticise you as a person.'' But his own attacks are often ad hominem too - he is contemptuous of people who disagree with him. ''I'm contemptuous of their ridiculous beliefs, but not of them as individuals.'' In his autobiography he writes entertainingly of family, school, friends and undergraduate days in Oxford; but once he starts postgraduate work, we are plunged into detailed descriptions of research, early forays into computer programming, complete with diagrams, and some fancy linguistics. I enjoyed the book, I tell him, up until he disappeared into the laboratory. It is, in a sense, a book of two halves. ''Well, yes,'' he says, ''perhaps two-thirds and a third, but I am a little bit uneasy about whether others will have the same reaction as you; though the last part is not solid science.'' True, he writes joyfully, if briefly, of friendships with contemporaries in the Animal Behaviour Research Group where he met and married his first wife, Marian Stamp (colleagues recall him as the brightest of the bunch and ''daunting'' in argument). And of his two-year term as a precocious assistant professor at Berkeley in the ''politically seething'' late 1960s when he worked on the anti-war campaign of Eugene McCarthy. At one point in the book he mentions losing his virginity to a ''sweet cellist'' and muses on the ''glory'' of sex, ''reinvented afresh and the heart leaps up every time''. But then he vows that he won't write any more on the subject - ''it isn't that sort of autobiography''. Oh dear, really?

He looks anxious: ''You're disappointed in that, are you?'' Well, not because I hoped for a frenzy of kiss-and-tell, but because while he writes about male friends, family, teachers and mentors, there is almost total silence on girlfriends and wives - and he's had three of those and reputedly a good few lovers, too. Will the second volume be any more of ''that sort of autobiography''? ''Well, now,'' he says, ''I need to think about this. It's a question for me to resolve. I thought that having been quite intimate in the childhood part of the first volume, I wanted volume two to be at least sexless. However, I do take your point that I haven't written about women. In those cases where a lover has been influential on my work, I would not wish to deny her.'' So, women only in the context of work? Readers may be disappointed. ''Well, um, yeah. OK, you can help me with this.'' Well, if I were his editor I'd encourage him to be more forthcoming about relationships, emotions, home - life in the round. He squares his shoulders: ''OK, yes … I will definitely think about it.'' Dawkins once wrote an impassioned piece about sexual jealousy, arguing that we should rise above it. ''Why are we so obsessed with monogamous fidelity?'' he asked. ''Why should you deny your loved one the pleasure of sexual encounters with others?'' In his new book he writes about his parents' 70-year marriage, seeming to value such constancy. What does he think about the possibility of enduring, monogamous married love in the modern age? ''I'm sceptical about it,'' he says. ''People are different: some happy for years together, some not, but I don't want to be personal about this.''

Fine. Let's talk about the Ashes. He looks surprised. Days earlier he had tweeted that when the Australians looked like winning the third Test it was bad form for the British to wish for rain. ''Yes, I was shocked that not everyone agreed with me. People said I didn't understand international sport. Well, I do bloody well understand it and I don't like it.'' Music has always been important and he was recently given an EWI, an electric wind instrument that looks much like a clarinet, the instrument he played as a boy. ''The fingering is much the same and this wire goes into the computer, which makes the sound, but it's a proper instrument.'' Will he show me? He looks startled: ''Really? Are you sure?'' We go into his study, an enviably spacious and orderly room, where he plugs into his laptop and starts playing the Trumpet Voluntary. Then he presses a button, plays the instrument and out comes Danny Boy, this time on violin. Apparently this little miracle can mimic most of the orchestra and he plays several more snatches of classics from memory. What makes him happiest? He says it's an odd question. ''What sort of answers do people give?'' I tell him: one person nominated fossicking about on his own in an archaeological dig in hot sunshine. Another said she was at her happiest when family and friends gathered around her table to eat together. ''Well, they're lying,'' he says. What would be his answer? ''I wouldn't dream of telling you.''