Phyla, Phylogeny, and Embryonic Body Plans

Abstract

This chapter deals with how three related ideas relevant to evolutionary developmental biology (Evo-devo)—phylum, phylogeny, and embryonic body plans—changed during the period after the 1981 Dahlem conference on evolution and development, both in terms of new findings that inform these ideas and how the phenomena they represent provide a platform for evolutionary change (see Valentine 2004 for a general review). My discussion is influenced by Amundson’s book The Changing Role of the Embryo in Evolutionary Thought (2005). One goal of this essay is to bring that historical account, which ends prior to the Dahlem conference, up to the present. While his title uses the word ‘embryo,’ the book does not describe the questions that evolutionary developmental biologists have asked, how they have gone about studying embryos, and why they have concentrated on particular developmental stages. First, I discuss how embryonic body plans were used in classification and phylogenetic reconstruction prior to 1981. Then I show how the utility of embryonic body plans in classification and phylogenetic reconstruction has diminished during the last 30 years, and how our view of their role as a platform for evolutionary change has been enlarged.