Endless Forms Most Beautiful. Sean B. Carroll. (2005, W. W. Norton.) $25.95. ISBN 0-393-06016-0

Endless Forms Most Beautiful. Sean B. Carroll. (2005, W. W. Norton.) $25.95. ISBN 0-393-06016-0. In the run-up to the completion of the sequencing of the human genome, many biologists engaged in a modern-day parlor game (via the internet) of guessing the likely number of genes. The genome of Drosophila had already come in at some 13,000–14,000 genes, and since some theories suggested that two whole-genome duplications (albeit with some subsequent gene loss) had occurred between the last common ancestor of Drosophila and vertebrates, guesstimates of 60,000 to 80,000 were common. The announcement in 2003 that the draft human genome sequence indicated a relatively paltry 20,000–25,000 genes was met with some incredulity (and a few refuse to believe it to this day). How could humans, in all our diversity of cell types and complexity of neurons, require essentially the same number of genes as a fly, or worse, a worm (the nematode Caenorhabditis elegans)? I half expected Republicans in Congress to demand that NIH find the missing genes to assuage this affront. That the astonishing morphological diversity of the animal kingdom can be constructed from such a limited number of genes is indeed remarkable, but far more surprising has been the elucidation, over the past two decades, of the developmental mechanisms underlying the construction of this diversity. Sean Carroll, professor at the University of Wisconsin, Madison, and an investigator at the Howard Hughes Medical Institute, has been at the forefront of this revolution since its inception. In Endless Forms Most Beautiful, Carroll brings this story to a general readership in an insightful and enthusiastic fashion, weaving together a childhood friend’s fascination with horror movies; mutant lambs born with a single eye after their mother ate a lily, Veratrum californicum, which secretes cyclopamine; and master regulator genes responsible for major components of body patterning. More importantly, however, Carroll uses these studies in comparative evolutionary developmental biology (known to initiates as evo-devo) to argue for its central role in what he believes is an emerging new evolutionary synthesis. Over the whole the range of topics, Carroll’s writing is witty and engaging, and pulls the reader into the intricacies of Hox genes, Pax-6 as a master gene controller for eye formation, what the Cambrian ‘‘big bang’’ of animal evolution says about the evolution of development, and a remarkable chapter on making black animals, or more prosaically, the evolution of dark coloration. Carroll focuses on four questions: the developmental rules underlying the generation of animal form, the specific mechanisms for generating these forms, how animal diversity has evolved over time, and the developmental explanations underlying large-scale trends in the evolution of form. Throughout the book Carroll moves seamlessly from discussing the morphology of living and fossil animals to the developmental mechanisms underlying them. The first section of the book moves from a discussion of the diversity of animal architecture, including the importance of serial homology and modularity, through the aforementioned discussion of master control genes, to the range of genetic techniques that underlies the genetic toolkit of metazoan development. This background