Homology, the similarity between organisms that is due to common ancestry, is the central concept of all comparative biology. However, the application of this concept varies depending on the data being examined. This volume represents a state-of-the-art treatment of the different applications of this unifying concept. Chapters deal with homology on all levels, from molecules to behavior, and are authored by leading contributors to systematics, natural history, and evolutionary, developmental, and comparative biology. Special features include: * Commemoration of the 150th anniverary of Sir Richard Owen's seminal paper distinguishing homology from analogy * Contributors who are renowned leaders in compative biology * Coverage that is both comprehensive and interdisciplinary.