Journal of Heredity Advance Access originally published online on September 8, 2005
Journal of Heredity 2005 96(6):725; doi:10.1093/jhered/esi101
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Book Review |
From DNA to Diversity, Molecular Genetics and the Evolution of Animal Design, 2nd edition
Sean B. Carroll, Jennifer K. Grenier, and Scott D. Weatherbee.Blackwell Publishers, Oxford, 2004.
In 2001, Carroll et al. published the first edition of From DNA to Diversity. It was a fascinating book, describing how the fast-paced field of developmental genetics was beginning to impact the field of animal morphological evolution. Now, 4 years later, the second edition has appeared, reviewing additional discoveries that have since been made in the field of evolution and development (evo-devo).
Like the original, the second edition is a pleasure to read; the prose flows in a light engaging style and the descriptions are clear and succinct. It has been kept to about 200 pages, so that one can contemplate reading it over a weekend. The writing has a chatty feel, as if the authors are telling an interesting story they heard the previous day. Useful metaphors that facilitate understanding for the uninitiated are employed. For example, the genetic toolkit denotes the hundreds of conserved genes that are used in animals to control the placement of head and tail, the development of an eye, and so on. This is a book that compellingly transmits the big picture of evo-devo, putting discoveries in their proper context, whether they were originally reported in the pages of Nature or in the pages of a comparatively obscure journal (no names please). It is rare to find a science book that combines information and modest entertainment without seeming puerile, but here it is.
The illustrations are impressive. We primates evolved with an exquisite appreciation for visual representations of the world, and Carroll et al. have wisely exploited this evolutionary quirk. Many figures contain gorgeous pictures of developing embryos, revealing patterns of gene expression with great import for the proper construction of animal form. Others are diagrams that simplify animal architectural principles that have been derived from decades of experiments in molecular genetics.
A great deal of the book is devoted to the role that Hox genes play in the diversification of animal form during animal development and evolution. The Hox genes appear to work as subtle and deeply context-dependent regulators of downstream gene expression patterns, but by acting with this gentle pressure at both high and low levels of the developmental hierarchy, they exert a profound influence on animal form. To anthropomorphize, when you let other genes get the credit for making muscle, bone, and nerve, it is surprising what you can accomplish.
What's new in the second edition? Well the first half of the book, which covers the evolutionary history of animals and the functions of the genes that design animal form, is essentially identical to the first edition. In the latter half, the principal changes are an expansion of the chapter on the evolution of major morphological novelties and the addition of a chapter on the evolution of minor changes that distinguish different species.
The revised chapter on morphological novelties is superb. Of course, nothing is truly novel in evolution, where new structures are cobbled together by the blind watchmaker of random change and natural selection. But similar gene expression patterns can reveal previously hidden relationships and have provided evidence that insect wings evolved from gill-like appendages, that butterfly scales evolved from insect bristles, and that the turtle shell may be a highly modified limb. The new chapter on the evolution of minor morphological changes also is full of interesting stories. There are now plausible molecular genetic explanations for how changes in body color or hair pattern have resulted from alterations in the expression patterns of control genes. It is amazing how comparative gene expression patterns, when interpreted wisely, provide a view into the past we can obtain no other way.
Of course, wise interpretations and cautious conclusions are key in fields like evo-devo, where history plays such an important role, and where most of the evidence is correlative and not subject to experimental testing. In this context, the simplicity and clarity of the prose and figures in this book are won at some little cost, as troubling inconsistencies tend to be swept under the rug. As with all areas of science that involve historical analysis, evo-devo has more than its share of controversy, but you won't find it here. This will not matter to the casual reader, who will benefit from the confident, magisterial tone; and most discerning readers will be well aware that just-discovered scientific "principles" often rest on a stool with just a few legs of supporting evidence, and those legs occasionally collapse.
Who will enjoy reading this book? It would be useful to have a very solid grounding in genetics; others will be baffled trying to decipher the nomenclature and meaning of the developmental genetic toolkit, which is replete with nonintuitive acronyms. But I think anyone who has taken upper level biology courses and is interested in development and evolution will benefit enormously from this book, and may even be inspired. It is exciting and beautiful to witness the development of a new field of science, and the birth and early years of the field of evo-devo are revealed in their splendor in this book.
Section in Cell and Developmental Biology, University of California–San Diego, La Jolla, CA 92093
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