Homology in the age of developmental genomics

Abstract

The homology concept was introduced into pre-Darwinian evolutionary biology by Richard Owen as referring to “the same organ in different animals regardless of form and function”. Since then, it has played not only a fundamental role as an organizing idea in comparative anatomy but also an important role in preparing the way for evolutionary biology. Homology is the primary evidence for phylogenetic relationships among organisms, and whenever we project experimental results from a model organism onto humans, we assume homology among the mechanisms in humans and the model organism. Homology was fully integrated into the Darwinian tradition through Lankester’s redefinition as an organ in two species that is derived from the same organ in the most recent common ancestor of the two species. Nevertheless, the homology concept remains controversial primarily because it seems to escape a simple rigorous definition. Homology shares this attribute with other fundamental concepts like that of species or gene. In addition, homology is hard to pin down mechanistically. Apparently, homology is among the concepts biologists have a hard time living with but certainly can’t live without. This situation often leads to considerable frustration among biologists, and some have suggested abandoning the concept altogether and may even result in proposals to abandon the concept altogether, a move that is hardly feasible.