Perspectives in Biology and Medicine

With the possible exception of the relationship between our conscious mind and its neurological basis, few problems in modern biology have as much appeal to both professionals and lay people as the process by which a simple egg transforms itself into a complex and autonomous organism. While we now know a great deal about the intricacies of the developmental process in organisms as diverse as soil nematodes and colonial sea squirts, our ignorance is still stupendous. Although the embryology of the king of invertebrate model organisms, the fruit fly Drosophila melanogaster, is better understood than that of any other organism, I think we remain decidedly further removed from fully understanding all the developmental mysteries compressed into the four-day life cycle of Drosophila than we are from putting man on Mars. Couple this nearly numinous ignorance to the realization that every individual animal, large or small, vertebrate or invertebrate, living or extinct, ultimately traces back to a more or less yolky globule of tiny dimensions, and it becomes clear that the wonder of the embryo can also easily beguile those of a more evolutionary bent, such as myself.

For those interested in this intersection of development and evolution, evolutionary [End Page 458] developmental biology, or evo-devo, provides exactly the right discipline. Evo-devo strives to embrace a colossal subject area. Its interdisciplinary and integrative agenda extends far beyond animals to encompass all of life (a distinct animal bias notwithstanding); it goes beyond embryology to include all types of development, including regeneration and asexual reproduction; it oversees a canvas of breathtaking dimensions, encompassing the entire Earth and its history extending as far back as life itself; and its focus ranges freely across all hierarchical levels of life, from the molecular to the environmental. To investigate such a immense subject area, evo-devologists wield an impressive array of concepts, tools, and empirics gleaned from fields as disparate as comparative embryology, comparative (functional) morphology, paleontology, phylogenetics, theoretical (mathematical) biology, and developmental biology. Consciously or not, evo-devo aims to be or become one of the prime interdisciplinary fields in modern science.

Such an ambitious research agenda was not made out of whole cloth. Biologists have long been interested in the multifaceted relationships between development and evolution, or ontogeny and phylogeny. From Embryology to Evo-Devo: A History of Developmental Evolution traces some of the tangled historical roots of modern evo-devo, revealing that the ontogeny of evo-devo is still very much ongoing. The book presents a variety of historical, philosophical, and sociological perspectives on how evo-devo’s central concerns, concepts, and methods have been braided together from a diversity of strands from 19th- to 21st-century biological science. In the space allotted to this review I cannot do justice to the great variety of topics that are so excellently discussed in the 16 chapters of this book; instead, I will provide some highlights that in combination should convey an impression of its general flavor.

For non-aficionados the last two chapters of the book are a good place to start. In “Six Memos for Evo-Devo,” Gerd Müller sketches the emerging outline and conceptual anatomy of evo-devo. This is far from an easy undertaking, because evo-devo’s hulking subject area seems unlikely to yield to any simple scheme of conceptual classification. Nevertheless, Müller manages to boil down evo-devo’s agenda to sound-bite length: “The conceptual focus of Evo-Devo is on the problem of phenotypic evolution.” Its main concern is to understand the evolution of organismal form through a study of the roles that developmental processes play in the generation of form. Since development is the mediator between genotype and phenotype, this focus makes eminent sense.

The relationship between development and evolution can be considered from either perspective. Considered from the viewpoint of evolution, evo-devo is about the evolution of development, or developmental evolution. This much is straightforward and uncontroversial, at least in...