The Burgess Shale is a small quarry in the Canadian Rockies, which formed over 500 million years ago. It contains more varieties of fossilized life than any other deposit ever found, but after their discovery, their importance was at first overlooked. However, three Cambridge scientists conducted one of the finest and most detailed palaeontological reconstructions this century. Their findings have shattered many modern theories of early life, for they revealed that the life fossilized in the Burgess Shale was incredibly diverse, yet most forms were wiped out in mass extinctions. Gould's startling interpretation is that it need not have happened; replay the tape of life again, and a different set of survivors emerge. Man would not have existed, but for a unique random set of events.