PRINCIPLES OF DEVELOPMENT UNDERLIE A MODEL FOR MORPHOLOGY

Development controls the construction of morphology and, by extension, structures how morphological features change through time. In the past few decades, developmental evolutionary biology has made great headway in elucidating both the components and the organization of the gene regulatory networks that build morphology. We now recognize that developmental networks are highly conserved, and are often tightly associated with particular features; conversely, different types of generic network structure can specify similar morphological patterns and character arrangements. These developmental patterns can serve as a basis for studying living and fossil morphologies, and for organizing morphological data for phylogenetic analysis. I describe how the developmental underpinnings of morphology may be used to reorganize discrete morphological character data, focusing on how network structure translates into a separation of character identity from character states. This reorganization recognizes the biological distinctiveness of both “traditional” characters, such as appendages, and of patterning mechanisms which may be re-deployed across multiple body regions, and extends homology beyond a position-specific designation. Because the complex wiring of developmental networks can impose lineage-specific constraints upon the pattern and rate of morphological character evolution, this approach provides a first step in forming a probabilistic model for the evolution of morphology, as well as future application to phylogenetic methods utilizing morphological characters.