Aisling Irwin reports on a project that aims to capture on film the obsessive wonder of scientists for the natural world. Can you remember when, as a child, you were filled with wonder at the world? Your mind raced as you tried to work out what was outside the space that was outside the universe; or as you tried to imagine how long a billion years felt or how small the smallest creature could be?

Some people retain this wonder into adulthood. A new BBC programme has found them - all eminent scientists - and deftly captured on film their amazement about the world. By asking each of them to choose their "seven wonders of the world", the series has a device with which the viewer is scooped up and deposited inside the scientists' minds, looking out at the world through their fascinated eyes.

"People rarely stop to think how amazing fireflies are - that an animal, through an act of will, can produce light," says Julie Theriot, 25, and one of the world's most talented cell biologists.

John Maynard Smith, the evolutionary theorist who brought his mathematics to the study of genetics and sex, says: "It's the comprehensibility of the world that is so extraordinary. And even more extraordinary that it should be understood by mathematics which is so abstract and so weird - these strange marks on pieces of paper with squiggles and arrows ."

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In among the eloquent descriptions, the scientists give impressionistic biographies. Almost all of them grew up obsessed with some aspect of the natural word. James Lovelock would memorise Wades's Organic Chemistry in the lavatory as a child. Maynard Smith spent his childhood devising experiments, which generally failed, "The story of my life is good hypotheses and badly executed experiments". He tested, for example, his theory that new skin was gradually paid out through the navel, by drawing concentric circles around his stomach to see if they moved.

Stephen Jay Gould, professor of zoology and geology at Harvard University, had a childhood wonder of the art deco Akeley Hall Museum of African Mammals in New York.

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"You walk into this hall, with a herd of African elephants in the middle shrouded in shadows. And it's entirely dark except for these wonderful sources of light from the middles of these dioramas . . . . When you read about how Karl Akeley collected the material you see the almost wondrous and inspirational commitment to accuracy . . . . he would send crews to Africa merely to make sure that the plant backgrounds were absolutely accurate in detail after detail."

The theme of obsession permeates the scientists' descriptions. Many, for example, seemed to choose their careers simply in order to pursue their obsessions in peace.

Maynard Smith switched from aeronautical engineer to biologist and has made contributions to fields about which he had known nothing. "You go into a new field and you would think the right thing to do would be to read what everybody else has said about it," he says. "But if you do that you finish up accepting their questions as well as their answers, as being what matters in that subject.

"And maybe they're wrong . . . if you go into it ignorant, like I do, and read as little as possible and plunge in and try to solve things - occasionally you make a complete idiot of yourself . . . . But occasionally I ask a question that other people haven't asked and provide an answer that other people haven't provided and that's much more fun."

Maynard Smith wonders at the flight of the albatross: "There's something particularly moving I think about birds that can fly without ever beating their wings . . . the albatross has worked out a way of flying forever just using the fact that the wind isn't the same speed everywhere - and I think that's rather clever of it.

"For me the wonder is always the combination of a gorgeous piece of natural history like that, with a piece of mathematics . . . a piece of explanation."

The most fascinating parts of this gentle series are when the scientists describe wonders that have absorbed them, as part of their work, for years. Miriam Rothschild, naturalist and fellow of the Royal Society, loves the height of the jump of the jumping flea.

She leans through her rabbit hutches, absorbed with describing how she keeps fleas on the rabbits' ears: "We had a special box for measuring the jump. It was like a drum and it had a recording machine in it. And every time they jumped they made a little bang - and this was magnified. We found that these fleas can jump 30,000 times without stopping.

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"It's really rather a lot . . . they just took off and disappeared because their acceleration was so enormous. It actually turned out to be 20 times the acceleration of a rocket re-entering the atmosphere". She worked out the jumping muscles using photography and dissection: "I cut 6,000 serial sections . . . it was quite a job".

Rothschild also wonders at carotenoids, the chemicals responsible for our being able to see colour: "So many of the very beautiful flowers, the daffodils, buttercups, the canaries, the goldfish, pollen, ripening corn and autumn leaves: all these depend entirely on these marvellous pigments.

"When God said 'Let there be light', he was really saying, as far as we're concerned, let there be carotenoids," she says earnestly. "Because we can't see without them."

Theriot wonders at bower birds, who "do a very extraordinary thing. The males take large sticks and dig them into the ground and then weave twigs in between the sticks . . . and they'll decorate them with flowers and with fruits and with butterfly wings and with colourful fungi . . . and what's amusing about these bowers is that they are not nests: after the birds mate the females go off and they have nothing more to do with each other. The males build these things only to be beautiful . . . it looks like these birds have developed a sort of aesthetic culture.

"We tend to prize things that seem to make us as humans different from other animals," she says, including our ability to recognise beauty without function. "But as we learn more about complicated behaviour of different animals it seems more and more like none of those things is unique to humans."

Sometimes, almost as an afterthought, the scientists marvel at the man-made. Gould says that without marvelling at the man-made "I don't think you could be true to humanism and intellectualism".

Rothschild says: "The whole of nature is so marvellous - and then suddenly you stop and think 'yes, but the man-made things are marvellous too.' I then suddenly remembered the day when I was walking across the sand in Israel and there was a sandstorm which blew up over the hills . . . then, suddenly, before me was this frieze of golden buildings and there beneath the sandstorm was Jerusalem".

Danny Hillis, one of America's leading computer scientists, and Steve Jones, professor of genetics at University College, London, add more wonders, including man's ability to measure the speed of light and supercomputers, and telecommunications.

At the end, one is left with the feeling that these scientists, aged 25 to 75, are still wondering and will wonder till their final day: Gould still cannot grasp the age and ceaseless motion of the earth, for example. "The great geological discovery is that time does not come in thousands but in billions of years. Time is deep. It goes way, way, way back: further back than we ever dreamed that it could."

Theriot reads out a poem by Robert Frost:

Some say the world will end in fire,

Some say in ice

She explains that, if the universe goes on expanding it will gradually cool and end in ice. If it starts to contract it will end in fire. What fascinates her, she says, is that "this poem was published in 1923, but the debate about how the universe is going to end is actually the same today".

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Seven Wonders of the World starts on BBC2 on March 22.