Natural selection presents only half the story of evolution: the fittest survive. The other half has long been presented as "random permutations over millennia eventually hit upon innovations". But this book provides a much more thorough understanding of how and why the fittest arrive. Wagner explains what it is about biological systems that causes evolution to occur, and draws some conclusions about non-living systems as well. A really excellent book that makes a highly technical subject accessible to everyone. Wagner backs up his theory of innovability with a great deal of data and research.