This book takes us on a pilgrimage backwards in time, being joined by other living things along the way. Each chapter represents the organism at a joining in the evolutionary tree, which Dawkins calls a concestor.Thus we go from concestor 1 to concestor 39. There are also 'Tales' from various animals, each being an essay on some relevant topic in evolution. I felt that the structure of the book helped to remember what was read, and that Dawkins deals with a complex subject in a non-technical way. Certainly this book would make an impressive addition to anyone's bookshelf.
One problem some readers might have is deciding how much of the book to read at a time. The Concestor sections vary in length from 2 pages to 75 pages (when we are joined by the insects). The book emphasises the use of cladistics in classification, that is classifying organisms in terms of clades - groupings of animals with a common ancestor. Also Dawkins shows how decoding the DNA of organisms has lead to a new method of classification, and he makes it clear that he follows this route if there is a conflict with previous classifications. The last two chapters speculate on the origin of life and what might happen if evolution were rerun, which will be of interest to those who have read other books on these subjects.