Wonderful Life: The Burgess Shale and the Nature of History
Stephen Jay Gould
 Gould's thesis in Wonderful Life was that chance was one of the decisive factors in the evolution of life on earth. He based this argument on the wonderfully preserved fossil fauna of the Burgess Shale, animals from around 505 million years ago, just after the Cambrian explosion. Gould argued that although the Burgess animals were all exquisitely adapted to their environment, most of them left no modern descendants and, more importantly, that the surviving creatures did not seem better adapted than their now extinct contemporaneous neighbors. He proposed that given a chance to "rewind the universe" and flip the coin of natural selection again, we might find ourselves living in a world populated by descendants of Hallucigenia rather than Pikaia. This seems to indicate that fitness for existing conditions does not ensure long-term survival, especially when conditions change rapidly, and that the survival of many species depends more on chance events and features, which Gould terms exaptations, fortuitously beneficial under future conditions than on features best adapted under the present environment (see also extinction event). He regarded Opabinia as so important to understanding the Cambrian explosion that he wanted to call his book Homage to Opabinia.