Epigenetic Mechanisms of Character Origination

TLDR: This work proposes that the present relationship between genes and form is a highly derived condition, a product of evolution rather than its precondition, and helps to explain findings that are difficult to reconcile with the standard neo-Darwinian model.

Abstract: The close mapping between genotype and morphological phenotype in many con- temporary metazoans has led to the general notion that the evolution of organismal form is a direct consequence of evolving genetic programs. In contrast to this view, we propose that the present relationship between genes and form is a highly derived condition, a product of evolution rather than its precondition. Prior to the biochemical canalization of developmental pathways, and the stabilization of phenotypes, interaction of multicellular organisms with their physico- chemical environments dictated a many-to-many mapping between genomes and forms. These forms would have been generated by epigenetic mechanisms: initially physical processes charac- teristic of condensed, chemically active materials, and later conditional, inductive interactions among the organism's constituent tissues. This concept, that epigenetic mechanisms are the gen- erative agents of morphological character origination, helps to explain findings that are difficult to reconcile with the standard neo-Darwinian model, e.g., the burst of body plans in the early Cambrian, the origins of morphological innovation, homology, and rapid change of form. Our con- cept entails a new interpretation of the relationship between genes and biological form. J. Exp. Zool. (Mol. Dev. Evol.) 288:304-317, 2000. © 2000 Wiley-Liss, Inc.