The Intellectual Challenge of Morphological Evolution: A Case for Variational Structuralism

This chapter explores variational structuralism, whose core idea is that organisms and their parts play causal roles in shaping the patterns of phenotypic evolution. Drawing on the work of pioneers such as Ron Amundson, it discusses the conceptual incompatibilities between two styles of thinking in evolutionary biology: functionalism and structuralism. It proceeds by explaining the meaning of developmental types and structuralist concepts arising from macromolecular studies. It also examines facts and ideas about bodies, Rupert Riedl's theory of the “immitatory epigenotype,” and Neil Shubin and Pere Alberch's developmental interpretation of tetrapod limbs. Finally, it looks at the emergence of molecular structuralism and the enigma of developmental variation. The chapter argues that typology naturally emerged from the facts of evolutionary developmental biology and that it would be seriously problematic to try to avoid it.

Lessons and Challenges

This book has argued for the reality of a class of biological entities that have a hard time finding their place in a theory of evolution based on genetics and population biology. These entities, or developmental types, include cell types, homologs, and body plans. The book has also provided examples that already have empirical data to see whether such ideas are contradicted by known facts about certain well-studied organ systems, like limbs, skin appendages, and flowers. This concluding chapter summarizes the book's central claims about homology, characters and character identity, and cooperativity in gene regulatory networks. It also discusses some of the lessons derived from reviewing the literature on these paradigms of devo-evo research as well as the challenges inherent in this perspective of developmental evolution.