Homology in the Age of Developmental Genomics
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
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Homology in the Age of Developmental Genomics Günter P. Wagner
Chapter vignette artwork by Brigitte Baldrian. © Brigitte Baldrian and Andreas Wanninger. G.P. Wagner Department of Ecology and Evolutionary Biology, Yale Systems Biology Institute, New Haven, CT, USA Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University, New Haven, CT, USA e-mail: [email protected]
A. Wanninger (ed.), Evolutionary Developmental Biology of Invertebrates 1: Introduction, Non-Bilateria, Acoelomorpha, Xenoturbellida, Chaetognatha DOI 10.1007/978-3-7091-1862-7_2, © Springer-Verlag Wien 2015
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INTRODUCTION The homology concept was introduced into preDarwinian evolutionary biology by Richard Owen as referring to “the same organ in different animals regardless of form and function” (Owen 1848). 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 (Donoghue 1992; Amundson 2005). 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 (Lankester 1870). 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 a species or a 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 (Wake 2003), a move that is hardly feasible. Morphological evidence for phylogenetic relationships among extant organisms is increasingly replaced with molecular data, which seems to make controversies around morphological homology obsolete. I think, however, that abandoning the homology concept would be counterproductive, since it still has an important role to play in both evolutionary and developmental biology and also in other branches of organismal biology (Wagner 2014). Why, then, is homology still necessary and important in the twenty-first-century biology? There are two broad reasons why homology is still central to evolutionary and developmental biology. First, homology reflects a broad pattern of biological diversity, and, second, a deeper
G.P. Wagner
understanding of the nature of homology (i.e., character identity) is essential for research into the origin of evolutionary novelties (Müller and Wagner 1991; Müller and Newman 1999; Wagner and Lynch 2010) and thus is essential for understanding of how complex organisms (and charact
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