The Crucible of Creation, The Burgess Shale and the Rise of Animals by Simon Conway Morris Nerdy paleontology stuff focusing on the development of very early life based on discoveries made in Canada in an area know as the Burgess Shale. Far deeper than you can get in popular-science articles but not as dry as a text book. Another book I read on the subject was Wonderful Life, The Burgess Shale and the Nature of History by Stephen Jay Gould. In an odd coincidence, the other day we were watching one on the episodes of Ken Burns' "Baseball" series and S.J. Gould was one of several people featured to tell their baseball stories.