This book has a glowing review and foreword by Jared Diamond, whose own writing is clear, lucid and readable. Ernst Mayr is well qualified to write a book on evolution, but does not manage nearly so well as most other authors at producing a readable book. (Makes me wonder if Diamond actually read the book!) It starts promisingly enough with a chapter looking at what the evidence for evolution is. Unfortunately Mayr uses a lot of technical terms - these are probably familiar to biologists, but although I consider myself well-read in popular science terms, most of them were not familiar to me.There is a glossary in the back of the book which explains most (but not all) of these terms, but it rather breaks the concentration to have to keep turning to the back of the book.

Chapter 3 outlines how life developed, and I found this particularly hard to get through. The rest of the book explains lots of the finer detail of aspects of evolution. All good stuff, but again I found most of it difficult to wade through, and in fact have still not finished the book. There does not seem to me to be a flow to most of the chapters - I read lots of stuff, but without such a theme or flow it is difficult to put all the information together. Maybe my impression of the disjointedness of the material is because I have read bits of the book and then left it for a while, but this reading pattern is largely due to the style of the writing. I have had to concentrate on other books ('Darwin's Dangerous Idea', by Daniel Dennet, springs to mind, but in that case I could see the point in following the arguments - 'What Evolution Is' does not seem to provide me with enough motivation to persist.) In short, if you want a general introduction to evolution don't buy this book - get something by Dawkins, Zimmer, or one of many other authors who can produce readable stuff. If you already know a reasonable amount, this book may provide a useful summary, but I am not really qualified to judge that.