I really should have given this book 5 stars because it is such a complete book on the diversity of life. But I gave it only 4 because it is too complete, each topic worked over and over again until it is just overworked. How many times does it have to be said that we don't know how many species there are? I hold Edward O. Wilson in the very highest esteem and it makes me very uncomfortable to be critical of him. I just wish that he had been more concise and less repetitive.