Helen Scales is a marine biologist, diver, surfer, broadcaster and writer who's spent hundreds of hours underwater watching fish.

A familiar voice for the oceans, she's pondered the mysteries of the deep sea with Robin Ince and Brian Cox on BBC Radio 4's The Infinite Monkey Cage and donated an imaginary tank of seahorses to The Museum of Curiosity. She's a regular writer for BBC Focus and BBC Wildlife magazines.

Among her radio documentaries she's explored the dream of living underwater and followed the trail of endangered snails around the world and back again.

Helen's recent book, Spirals in Time, is a Guardian bestseller. It was shortlisted for the Royal Society of Biology book prize, picked as a book of the year by The Economist, Nature, The Times and the Guardian and was BBC Radio 4's Book of the Week.

Sir David Attenborough is a broadcaster and naturalist whose television career is now in its seventh decade. After studying Natural Sciences at Cambridge and a brief stint in publishing, he joined the BBC in 1952 and spent ten years making documentary programmes of all kinds, including the Zoo Quest series. In 1965, he was appointed Controller of a new network, BBC2, and then, after four years became editorially responsible for both BBC1 and BBC2.

After eight years of administration, he returned to programme-making to write and present a thirteen-part series, Life on Earth, which surveyed the evolutionary history of animals and plants. This was followed by many other series which, between them, surveyed almost every aspect of life on earth.