Reconstructing History

Abstract

This introductory chapter describes the book’s general approach and underlying philosophy. The authors adopt a definition of biological homology that recognizes the hierarchical nature of biological organization and allows for any aspects of a character to change over the course of evolution. The only essential homology criterion is that the characters in question must have been retained from a common ancestor, rather than having evolved independently in multiple lineages. These fundamental ideas are discussed in the context of related concepts, notably “field homology” and the homology of cell types and developmental pathways. Although it is easy to get tangled up in questions about the homology or non-homology of individual characters, the book’s main concern is the evolution and natural history of entire organisms and the lineages to which they belong.