Book excerpt: Written by two of the premier cell biologists of our time, this important new book takes the reader toward an understanding of how on a cellular and developmental level, organisms came to be different. For 150 years we have had a good theory of natural selection in biology and for explaining the genetic differences on which selection acts. This book explores the missing link: how genotypic change produces phenotypic change. Cells, Embryos, and Evolution is richly illustrated with examples drawn from modern paleontology, developmental biology, and cell biology. It attempts to establish a coherent basis for evaluating the role of cellular and embryological mechanisms in evolutionary change.