From Darwin onward, it has been second nature for evolutionary biologists to think comparatively, because comparisons establish the generality of evolutionary phenomena. Do large genomes slow down development? What lifestyles select for large brains? Are extinction rates related to body size? These are all questions for the comparative method, and this book is about how such questions can be answered. It examines how the comparative method complements other approaches, identifies the biological causes of similarity among species, and discusses methods for reconstructing phylogenetic trees, along with many other topics. The book will interest all students, professionals, and researchers in evolutionary biology, ecology, genetics and related fields.