Melvyn Bragg and his guests discuss the cell, the fundamental building block of life. First observed by Robert Hooke in 1665, cells occur in nature in a bewildering variety of forms. Every organism alive today consists of one or more cells: a single human body contains up to a hundred trillion of them. The first life on Earth was a single-celled organism which is thought to have appeared around three and a half billion years ago. That simple cell resembled today's bacteria. But eventually these microscopic entities evolved into something far more complex, and single-celled life gave rise to much larger, complex multicellular organisms. But how did the first cell appear, and how did that prototype evolve into the sophisticated, highly specialised cells of the human body?With:Steve Jones Professor of Genetics at University College LondonNick Lane Senior Lecturer in the Department of Genetics, Evolution and Environment, University College LondonCathie Martin Group Leader at the John Innes Centre and Professor in the School of Biological Sciences at the University of East AngliaProducer: Thomas Morris.