Résumé: "Every animal form is the product of two processes--development from an egg and evolution from its ancestors," writes Sean B. Carroll in his introduction to "Endless Forms Most Beautiful". The new science of "evo devo"--or evolutionary developmental biology--examines the relationships between those two processes, embryonic development and evolutionary changes, despite their radically different time scales. Carroll first offers a recap of how genes express themselves in a growing embryo, then peers into the life histories of real-life examples to explain how those genes have changed (or not changed) over millions of years of evolution. Paraphrasing Thomas Huxley, he asks us to consider evolution and development as two sides of the same coin. We may marvel at the process of an egg becoming an adult, but we accept it as an everyday fact. It is merely then a lack of imagination to fail to grasp how changes in this process that assimilated over long periods of time, far longer than the span of human experience, shape life's diversity." The book's second half is where Carroll really gets at the meat of evo devo, explaining how regulatory genes control such mysteries as individual and population changes in butterfly's spots, jaguar fur, and hominid skulls. Evo devo is one of the hottest areas of study in 21st-century biology, and Carroll's outline of the field is a great place to start understanding it. "--Therese Littleton"