Owen revisited: a reappraisal of morphology in evolutionary biology

A new analysis within the framework of developmental genetics provides both raw data and theoretical support to the “old” morphology and suggests a new, more predictive, approach to the concept of homology. We distinguish between “positional homologues” and “structural homologues” as independent components of the more general concept of homology. We discuss some general patterns seen in the anatomy of animals and in their morphogenesis. Slack et al. (1993) advanced the concepts of the “zootype”, a particular spatial pattern of gene expression, and the “phylotype”, a particular stage of embryonic development that expresses the zootype. We build upon these concepts and expand them. This allows us to propose some additional phylotypes (arthrotype, cyclotype, platytype, malacotype, trimerotype) that may guide future investigations towards understanding the genesis of metazoan form.