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From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design (review)
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Perspectives in Biology and Medicine 46.1 (2003) 148-153

From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design. By Sean B. Carroll, Jennifer K. Grenier, and Scott D. Weatherbee. Malden, MA: Blackwell Science, 2001. Pp. xvi+214. $44.95 (paper).

If Stephen Jay Gould and Niles Eldredge are right that evolution proceeds in short periods of rapid phenotypic change followed by periods of prolonged stasis, and, for a moment, we apply this model to the history of science, then, without any doubt, we are witnessing a period of extremely rapid evolution in the field of evolutionary developmental biology ("evo-devo" for short). What had been a trickle of experimental and theoretical contributions during the 1970s and a small but sustained flow of studies during the 1980s and early 1990s has now turned into an outburst of scientific advances that truly revolutionize our understanding of phenotypic evolution.

All this intellectual activity has also been accompanied by a concentrated effort to establish evo-devo as a biological discipline in its own right. In the last two years alone we witnessed the formation of a new division within the Society of Integrative and Comparative Biology, the establishment of two new journals specifically devoted to evo-devo (Evolution & Development, edited by Rudolf Raff, and Molecular Developmental Evolution, edited by Günter Wagner), academic departments running searches designated evo-devo, the publication of an increasing number of evo-devo papers in mainstream journals, several symposia and panels devoted to the new discipline, and now the first textbook for advanced undergraduates as well as for readers from other disciplines, who want to inform themselves about this new and exciting field.

With all this excitement, one would almost be tempted to evoke Thomas Kuhn's notion of a paradigm shift, were it not for the fact that attempts to combine explanations of evolution and development have a long history that dates back to the very beginnings of evolutionary thought in the first decades of the 19th century. Even earlier, the very name "evolution" actually referred to a developmental process of the unfolding of what was thought to be a preformed organism already present in the egg (or alternatively the sperm). Besides this historical connection, the temporal processes of development and evolution are also logically linked; after all, changes in the phenotypic appearance of organisms have to originate in the sequence of developmental events that produce them. Consequently, all mechanistic explanations of phenotypic evolution have always considered developmental events to be the immediate (or proximate) causes of these changes. Integration of the processes of evolution and development is thus nothing new, however, what sets the current incarnation of evo-devo apart from its predecessors is the inclusion of molecular genetics.

In light of the dynamics of post-WWII biology the emergence of such a synthesis was somewhat surprising. By the 1950s, developmental biology, evolutionary biology, and genetics, which were closely linked at the beginning of the 20th century, had separated, and the centrifugal forces between them only grew stronger with the advent of molecular biology and genetics. While the success of molecular biology had largely been predicated on technological advances and an analytic and reductionistic research agenda, developmental biology continued to struggle with more holistic processes, such as pattern formation, regulation, differentiation, or induction, and evolutionary biology, with the exception of paleontology, was largely concerned with micro-evolutionary processes, such as speciation. But, ironically, it was a series of discoveries within molecular genetics that initiated the dramatic realignment of research agendas that has led to present-day evolutionary developmental biology.

During the 1970s and early 1980s, Ed Lewis, Eric Wieschaus, and Christiane Nüsslein-Volhard (who shared the Nobel Prize in medicine and physiology in 1995) isolated homeotic genes, genes that controlled the development of large developmental modules, such as insect legs or antennae. Soon thereafter, in 1984, Walter Gehring and his collaborators discovered that these regulatory genes shared a specific sequence element, the homeobox, and that homologous sequences are also present in vertebrate genes. In the following years, Hox genes, as they were commonly called, were found in all major phyla of animals. The fact that a rather small set of regulatory genes...

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