Homology

Abstract

Homology is the core concept of comparative biology. Or, better, a variegated flock of concepts about relationships between character states in different biological units, the latter being either modular parts of one biological individual or conspecific individuals differing either in sex or developmental stage or, more commonly, representative individuals of different species. The chapter includes a historical overview of the subject and a definitional characterization of the many concepts of homology proposed since Owen (Lectures on the comparative anatomy and physiology of the invertebrate animals, delivered at the Royal College of Surgeons. Longman Brown Green and Longmans, London, 1843), contrasting non-historical, historical and factorial notions of homology, followed by a detailed analysis of ‘sameness’ across evolutionary time, developmental time and body space. A special section presents a selection of fields of application of the concept, like phylogenetic inference, the study of evolutionary novelties, biological nomenclature and reconstruction of the ancestral taxa. The chapter terminates with some educational suggestions.