Homology in Character Evolution

AbstractHomology forms the basis of organisation for comparative biology. Richard Owen's simple definition of homology as the ‘same organ in different animals under every variety of form and function’ takes on new meaning in light of Darwin's concept of descent with modification. The modern study of comparative biology and phylogenetics is grounded in the notion that organisms share a greater proportion of homologous (i.e. ‘derived’) characteristics the more recently they share a common ancestor. Instead of solely being the purview of anatomical study, homology of these characteristics can be applied at the level of molecular evolution, genomic organisation and modern evolutionary developmental biology (‘evo/devo’). Aspects of homology help us formulate hypotheses about the meaning of changes in homologous structures in the inference of evolution of organisms at all levels of biological organisation.Key Concepts:Homology was originally a measure of correspondence between anatomical structures.Descent with modification explains homology as a result of shared ancestry that reflects modifications in characteristics within related lineages.Comparative methods use changes in homologous characteristics to infer evolution within groups (phylogenetics).Recent advances in molecular biology allow for the comparison of homologous characteristics at more diverse levels, including DNA sequences, genomic arrangements and developmental pathways.Recent work highlights homologous characteristics at a fundamental or ancient level, termed ‘deep homology’.