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 our ancestors had inherited a couple of genes in a different form - our canonical number, based on our fingers and toes, might be eight instead of ten. This is just one of the oddities of history that Gould deploys in this wonderfully readable book
The theory of evolution stands over modern biology as quantum mechanics and relativity do over modern physics. And few modern scientists are as widely familiar and celebrated as Darwin. Yet most of us remain less than entirely clear as to how evolution by natural selection works and a series of celebrated titles by such writers as Stephen Jay Gould and Richard Dawkins do little to help, being each so partisan of a particular, contentious, view of the subject.