A Short History of Nearly Everything

by Bill Bryson

Each of these massive transformations, as well as many smaller ones between and since, was dependent on that paradoxically important motor of progress: extinction. It is a curious fact that on Earth species death is, in the most literal sense, a way of life. No-one knows how many species of organisms have existed since life began. Thirty billion is a commonly cited figure, but the number has been put as high as 4,000 billion13. Whatever the actual total, 99.99 per cent of all species that have ever lived are no longer with us. ‘To a first approximation,’ as David Raup of the University of Chicago likes to say, ‘all species are extinct14.’ For complex organisms, the average lifespan of a species is only about four million years15 – roughly about where we are now.