The continued use of the idea of homology is questionable on philosophical and scientific grounds. It is based on the widespread idea that a "homologue" in extant taxa can be "traced back" to a feature in common ancestor. In contrast, Richard Owen, who first used the term in 1846, saw homology (homologue) differently, as "sameness": "the same organ in different animals under every variety of form and function." At that point in time, he was not influenced by evolutionary thinking, and more focused on the details and approaches to biological comparison and description. His was a perceptive approach to comparison. This paper argues that the concept of homology no longer plays a useful role in comparative biology. It is a conceptual idea with little or no empirical implications for modern comparisons among phenotypes. Comparative biology now uses formal phylogenetic analysis in which similar features in individuals of two or more taxa are treated as characters on a tree and tested for historical "sameness" in terms of the concept of synapomorphy. If we are to understand the complexities of phenotypic evolution, applying this method to detailed comparative data will be essential. At the same time, a deep understanding of the phenotype and its history will emerge only through the use of multidisciplinary approaches that address historical changes at different hierarchical levels.
Keywords: characters; comparative biology; evo-devo; homology; phenotypic change.
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