Ron Amundson, The Changing Role of the Embryo in Evolutionary Thought: Roots of Evo-Devo (Cambridge Studies in Philosophy and Biology, Cambridge: Cambridge University Press, 2007), xiii + 280 Pps., $26.99
Ron Amundson is Professor of Philosophy, University of Hawaii at Hilo, a philosopher by training, and a self-styled historian of biology (2). In this title, Amundson examines over 200 years of scientific posits regarding the evolution-development relationship from the perspective of evolutionary developmental biology (stucturalist or evo-devo), a perspective that challenges several long-held and popular views about the history of evolutionary thought. For example, it claims that many (proto)Neo-Darwinian authors in the early twentieth century made history come out right for the Evolutionary Synthesis, in essence tailoring it to be what they desired for it to be. The irrelevance of developmental biology was often argued for during this period on the basis of philosophical, methodological, and even historical grounds. However, in difference to many, if not most, philosophers of science in the twentieth century, Amundson takes his starting point the position of evo-devo versus the Evolutionary Synthesis regarding the study of evolution. As such, this title is a revisionist history, and in what follows I shall highlight the salient points of the text and its chapters.
The book is divided into two main parts, the first of which (five chapters) covers the relations between development and evolution in the nineteenth century, which is set against the backdrop of the traditional narrative of Neo-Darwinian (ND) evolution. In this part, Amundson documents that developmental perspectives on evolution were widely held prior to Darwin, and in the fact the existence of such views were instrumental in Darwin being able to formulate his theory. However, due to the lack of embryological understanding in the period directly following Darwin, the author asserts that it was essentially easier to postulate the existence of some yet-identified entity as the basis of heredity, which would later become known as the gene. I view this perspective on the history of the development of ND thought directly following Darwin himself to be at least possible and very well plausible.
The second part of the book, comprised of five chapters, covers the history the relations between development and evolution in the twentieth century, leading up to and including the formal position of ND thought. This portion of the book largely affirms the positions of ND, and it is intent upon demonstrating how the Evolutionary Synthesis came to be opposed to development within evolutionary explanation, which involves central aspects of the population genetic understanding of evolution and the theory of heredity upon which it is based. It should be noted that proponents of Evo-devo do not deny ND processes. Rather, they deny the sufficiency of these processes to account for the entirety of the complexity to be found upon earth. Instead, they believe additional mechanisms, mechanisms involved with ontogeny rather than population genetics, must contribute to a full understanding of evolutionary biology. Amundson notes that Ernst Mayr is the chief architect of the ND synthesis, and that one of the driving forces of ND thought was its antagonism to the essentialist story, which Amundson describes as the pre-Darwinian belief in the fixity of species.
The ND’s place special emphasis upon transmission genetics instead of developmental genetics. Transmission genetics composes the core of population genetics, which in turn forms the core of ND thought. Genes, in this understanding, are designed to explain the sorting of traits through generation; they do not explain how traits are ontogenetically created within an individual organism. In contrast, the widespread sharing of developmentally important genes justifies a central assertion of evo-devo, i.e. that one must understand how bodies are built in order to understand how the process of building bodies can be changed. As such, a central tenet of evo-devo is that evolution cannot be understood without understanding development. A central theme within the book is that of structure versus function. A second is the large difference in explanatory goals between Darwinian and stucturalist evolutionary theories; Darwinian theories are change theoretic, whereas structuralist theories are form theoretic. A third theme is that there was distinct change in the concept of heredity that occurred in the early twentieth century, prior to this time heredity was considered to be an aspect of embryological development.
All in all, Amundson attempts to answer why developmental biology was for the most part absent from early versions of Neo-Darwinism. He hopes that a way can be found to accommodate both the claims of evo-devo and ND. A weakness of this title, which Amundson himself notes in the introduction, is that the author relies on secondary historical sources, and does not probe into the primary materials (9). In fact, one of the reasons for his composition of this book is that he detected bias in the (secondary source) writings of Neo-Darwinian advocates. But by referring to primary source material, one is left wondering if Amundson could do the very same thing but in the opposition direction? Indeed, although I did not detect any occurrence of this, he could have very well misrepresented some of the primary material unintentionally through the exclusive employment of secondary sources.