This is a very good book on how evolution works at the level of DNA. Carroll describes how DNA likely evolved, and how we can analyze DNA to better understand how evolution works. This is the meat and potatoes of the book, with Carroll illustrating how adaptations are gained, selected, and lost, and how all of that evolutionary history is recorded in the DNA of different species. Color vision is his pet example, and it is well-studied enough for him to provide a very detailed, very broad coverage of its evolution in numerous animal species. For anyone interested in genetics or evolution, this book is a very interesting read.
Sadly, the second last chapter is devoted to arguing against those who doubt evolution. While I appreciate the author providing "ammunition" for those who confront such people, what so many evolutionary authors miss is that it isn't an issue of the facts. Those are blatantly obvious and abundant. Rather, it's about faith, which is a much subtler issue. So I don't know how effective this chapter really is. The last chapter is about extinction of the fittest, or how humanity is screwing wildlife across the globe (he focuses primarily on overfishing). That's certainly true, but again, I don't know if more facts is the best solution. Anyone who knows anything knows that we're badly overfishing the oceans.
But I don't want these two preachy, out-of-place chapters to take away from the really good science of the book. I don't even disagree with the content of the two chapters, just their inclusion in an otherwise fact-based exploration of what DNA reveals about the principles of evolution, and its history on Earth. Very interesting stuff indeed!