Developmental Biology, Ninth Edition

Book Preface

It has become increasingly embarrassing for me to ask students to read the Eighth Edition of this textbook. It’s so, well, 2006. Developmental biology has progressed so rapidly in the past four years that my lectures have fundamentally diverged from their reading. My “big” lecture on transcription now focuses on the ability of transcription factors to reprogram cell fates; and my lectures on stem cells and cloning have scrapped the notion of therapeutic cloning altogether, focusing instead on induced pluripotent stem cells. In both instances, we discuss what this means for understanding normal development, as well as what implications these technologies have for the future of medicine. Neither induced pluripotential stem cells nor “transdifferentiation” was established when the last edition of this book was published.

Even my most basic lectures have changed. The lecture on fertilization has to cover the new data on mammalian egg activation. My lectures on sea urchin development— an area of study that has been fundamental to developmental biology for over a century—now include systems theory operations involving double-negative gates and feedforward loops, and my evo-devo talks have led to discussions of mathematical modeling and parasitism. I can’t talk about limb development without including the variations seen in dachshunds and bats, and I can’t discuss sex determination without using the p-catenin model for mammalian ovary production. None of these areas were covered in earlier editions of my book. So this is really a very new edition. My editor tells me it has close to 700 new references; she only wishes I had deleted at least that many old ones.

Developmental biology is in a state of rapid metamorphosis. And, as in insect and amphibian metamorphosis, some old tissues remain the same, some get substantially remodeled, and some old tissues perish altogether; and all the while, new tissues are forming new structures. I hope that I have gotten these correct, and that the added new material will stand the test of time. I have tried to remodel the retained material into new narratives that are more inclusive of the data, and to appropriately jettison the information that was needed for earlier stages of the book’s development but which is no longer needed by undergraduates.

Embryologist John Fallon once wrote me that new data change the story one tells. It is, he said, like putting together a picture puzzle. At first, you think the structure in front of you is a sailboat; but you add another piece, and—no, wait—it’s a mountain. Psychologists call these alterations “Gestalt changes,” and I think that we are seeing these changes in both our day-to-day interpretations of data and in the entire field of developmental biology. We are seeing an inversion of relationships within the biological sciences. Genetics is more and more becoming a subset of development. Similarly, the dynamic of evolution is being studied as a question of gene expression as well as gene frequencies. And developmental biology may be on the threshold of changing medicine as much as microbiology did at the turn of the twentieth century.

I began the Preface of the last edition with a quotation from the Grateful Dead, recalling “What a long, strange trip it’s been.” The epigram for this edition might be Eminem’s “Be careful what you wish for.” We may achieve biological powers that are “tenfold” what we had hoped to have. And it is axiomatic for this generation that “with great power comes great responsibility.”

I hope this Ninth Edition of Developmental Biology presents a better way of teaching and learning (and questioning) developmental biology. The introductory section has been streamlined from six chapters to three—one each on developmental anatomy, the mechanisms of gene regulation during differentiation, and cell-cell communication during morphogenesis. Another new feature is the addition of short part-opening “chaplets” that address key concerns in developmental biology. These provide an introduction to the subsequent chapters, placing the forthcoming information into a specific context. Each chapter ends with a guide to web-based resources relevant to that chapter’s content, and the Ninth Edition is the first to include an extensive glossary of key terms.

During the writing of this edition, I re-read some of the papers written by the first generation of experimental cmbryologists, scientists who were experiencing a Gestalt change as important as what we are experiencing today. What impressed me was not necessarily their answers (although some of them were remarkably good even by today’s standards); rather, it was their asking the “right” questions. Some of their research did not give us any answers at all. But the results told the next generation of biologists what questions to ask. These embryologists stood in awe of the complexity of the embryo; yet they began to remove, transplant, destroy, and recombine cells in order to find out just how the fertilized egg could give rise to a structured body composed of different cell types. They had faith that these were scientific questions and that science would eventually be able to answer them.