This book explores ways in which systematic patterns are used to infer evolutionary processes. Among evolutionary biologists and systematists there is a constant interchange between those that study the process of evolution (e.g., mutation, selection, speciation) and those that study its patterns (e.g., variation, geographic distribution, ontogeny, phylogeny). Because patterns influence the development of theories, and processes yield patterns, it is not always easy to distinguish one from another. This book is dialectic and helps crystallize a continuing debate over the relationship of patterns to process theories.