HISTORIES OF LIFE, in particular human life, usually starts at its far beginnings, and work forwards. This produces a certain attitude of mind. From infinitely small and humble origins developed the amazing creatures which are ourselves. Was it all for us? Was the process divinely ordered? Was it a concatenation of chances? Or was it simply the result of natural selection operating under familiar Darwinian rules? If so, could comparable creatures be found on other planets on similar orbits round similar suns?

The answers to some of these questions can be found more easily if we reverse the process, and work backwards from what we already know. In his lavish new book, Richard Dawkins uses three main resources for tracing life in the past: analysis of fossils,