This collection of essays ranges from history to the latest theories in biology, from controversies over palaeontology to the origins of language. The title is a pun and as always with Gould, the joke has a point that illustrates the largest pattern of life's history. For millennia, the animals that populated the Earth had four toes on each foot, or six. If evolution had taken a tiny shift - if man's ancestors had inherited a couple of genes in a different form - our canonical number, based on man's fingers and toes, might be eight instead of ten. Stephen Jay Gould has also written Wonderful Life, Bully for Brontosaurus and Finders Keepers.