The advances made by experimental evolution in the last decade provided the main reason for revising Selection. In the course of revising it, however, the text changed so much that what has emerged is for the most part a new book. The first edition was written from a conviction that selection is a subject unto itself, the basis of a distinct kind of science that requires a separate treatment. To make it accessible to undergraduates, it was organized into sections with declarative headings, written as continuous prose with all the academic furniture relegated to boxes, eschewed mathematical and quantitative arguments, and was twinned with an undergraduate version.