In our series on academics' rooms, Steve Jones reveals his love of snails to Kate Worsley, but tries to hide his sense of humour

We have come to Steve Jones's study to see his famous collection of artifical snails, so it is rather distracting to stand on the threshold and find broken glass on the carpet, and a neat round hole in the window. What happened? It is an overcast Saturday morning, and there is no one about. But when a taciturn Jones comes back from brushing his teeth - it is early - his noted sense of humour is not much in evidence, and despite his stockinged feet, the glass is not mentioned. So we turn our attention to the L-shaped room that takes up the whole of the first floor.

It is elegant, in that creamy, north London intellectual way. Although snails are indeed everywhere, hundreds of them, it is a quiet display. Arrayed along picture rail, skirting board and shelves, and in tasteful clusters at strategic focal points, they coalesce as an extra layer of decoration, like varicoloured icing on a cake.

Jones, professor of genetics at University College London, curls into a large pale sofa and waits to be questioned. After 30 years working on the ecological genetics of the land snail Cepaea nemoralis he says he's given up research: "I'm as much of a media tart as the next man." He has an award-winning book, The Language of Genes, and his own TV series on DNA, In the Blood, under his belt. His current project is a book called Almost Like a Whale: "a modest proposal, rewriting the Origin of Species". Phew. It seems rather frivolous to be asking him about ornaments.

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He certainly does not need the publicity ("What's your circulation? You're only doing 800 words?"). Rather than use his massive desk he declares he finds it easier to write in his house in the Pyrenees "mostly because there aren't distractions like this". He is not smiling.

A resolutely frivolous question then. Is it true that when geneticists meet they ask each other "fly or worm?". "Fly or worm would cover most of them yes," he says patiently. "Classic genetics is based on fruit flies, and then the mouse became the standard. Worms are the flavour of the month, yeah." Not a flicker.

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He flirted with flies for a while but "snails are ideal for what I do. You can mark them and get them back". As he runs through the basics of snail whorls and neutral variation he seems to come out of his own shell, his fists wave gently above his head and his legs stretch out across the cushions.

The snail collecting started early on when he was doing his PhD in zoology at Edinburgh. His great collecting rivals have been the members of the Caravan Club, whose symbol is the snail, which carries its home with it.

"There's only one rule I stick to: there's nothing here which is real. But speaking as a man who has murdered 400,000 of them I suppose that's my conscience." He had a snail farm himself that "went with the end of the research grant. One hundred iron mesh cages at the top of Wytham Hill near Oxford. These are all land snails, by the way. If I got into sea snails there'd be no end to it."

The longer you look the more snails appear, disguised as candleholder, pepper pot, ashtray and wind chime, jigsaw, door stop and magnet. He looks up slyly. "My favourite is that one there made of dung I got in New York. The idea is you put them in the garden and they dissolve and you buy more."

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The smallest are the specially cast handles on the bookcase doors, and the 150 rubber snails balanced along the picture rail above the door. "From one of these touristy knick-knack places, 5p each. 'How much for the lot?' I said." The largest, whose ceramic tentacles reach nearly to his hip, was Pounds 35 from a "yuppie garden shop". He treats one tentacle like a cane, leaning on it rakishly, but refuses to be photographed like that. Or in the yellow and red stuffed snail slippers.

A friend, Tom Dewhurst, painted the picture over the fireplace of a pair of snails and an earnest crouched man in a cave looking out over a sunny town on a hill. "That's my head and his body. My body, feeble as it might be, is not quite as etiolated as that." Why is he in a cave? "I don't know." It's his first proper laugh that's not a doggy rasp in the throat. "I like it. I really do."

Going to turn round a painting propped by the door he notices the broken glass. He steps about edgily, head down and muttering. "What's most likely is that the guy who's painting the front of the house, his ladder slipped," Jones says at last. "I must ring him and ask."