Scott F. Gilbert
Jean Rostand, the French embryologist and essayist, wrote, "Today my book is done. Will it be done tomorrow?" The answer, of course, is "No way in developmental biology!" Developmental biology has not stood still for a minute, and its new ideas and explanations have pushed it to the frontiers of our knowledge. Indeed, if you seek the intellectual challenges of building new concepts, developmental biology is the place to be. There is a twofold revolution going on in developmental biology. This present text is a document of that revolution.
The first phase of the revolution began in the 1970s. At that time, developmental biology began to make use of the new recombinant DNA technologies to explain how the genetic instructions specified phenotypes composed of different cell types and organs. This remains one of the great projects of developmental biology. The first edition of this book (1985) was written in response to the start of this revolution. Although hardly a gene was mentioned in that edition, the techniques of DNA cloning were discussed, and the first work from the Nusslein-Volhard laboratory was mentioned. By the second edition (1988), the book discussed homeobox genes, enhancers, and promoters, and in situ hybridization was on its cover. Transcription factors made their appearance in the third edition (1991, and the fourth edition (1994) detailed paracrine factors. Subsequent editions went into the signal transduction pathways linking paracrine factors with transcription factors. This newly empowered science identified molecular mechanisms for the two most central processes of developmental biology: differentiation and induction.
During that time frame, the second phase of the revolution began. Developmental biology looked outward to other fields, applying recombinant DNA techniques and even newer technologies (bioinformatics and genomics) to bring developmental biology into areas that it had abandoned during its history. There are four fields of expansion and reconciliation: evolution, embryology, ecology, and medicine.
We have returned to evolutionary biology (just as Wilhelm Roux predicted we would) with a new paradigm for the causal mechanisms of evolution, seeing evolution as changes in gene expression as well as changes in allele frequency. The third edition of the textbook inaugurated the chapter on evolutionary developmental biology. Developmental biology had also abandoned the questions of morphogenesis in embryology, thinking it was largely a subset of differential gene expression. We are now returning to this area with new molecular and computational tools to analyze the cellular mechanisms that enable organogenesis and the mathematical constraints that permit only certain phenotypes to occur. The fourth edition (1994) highlighted these concerns. In addition, as the genetic mechanisms underlying such morphogenetic questions as axis specification became illuminated, the ubiquity of similar mechanisms became awe-inspiringly apparent. Even plant morphogenesis, long seen as so distinct from animal development as to constitute virtually a separate field, became part of this new incarnation of developmental biology. The sixth edition of this textbook (2000) saw the addition of a chapter on plant development.
Some of the first experimental embryologists were interested developmental plasticity and how the development was modified by the environment. Today we are once again bringing developmental biology to bear on issues of ecology. This ecological developmental biology seeks to find the proximate causes for the life history strategies well known to ecologists. The fifth edition of this book (1997) inaugurated our chapter on ecological developmental biology.
Many of the early investigations of experimental embryology were performed in order to discover the mechanisms of congenital birth defects. Today, after a long absence, developmental biology, with its new tools and insights, is reclaiming its medical heritage. We are identifying the causes for inherited malformations of development, seeking the ways by which exogenous chemicals disrupt normal development, and looking at developmental cures for such anomalies. This present edition inaugurates our chapter on the medical implications of developmental biology.
"To explore strange new worlds"
Along with the revolution in developmental biology has come the revolution in information technology. The information revolution has become integrated with the revolution in developmental biology and has greatly facilitated the merging of developmental biology with ecology, evolution, and medicine. This influence is also seen in this book. Developmental Biology may have been the first science text to have a website (in 1994), and in this edition, devbio.com has expanded to include an entire volume on the ethical issues of developmental biology. These may be useful for starting discussions in the laboratory while we wait for the gels to run or the embryos to cleave.
The Vade Mecum CD has undergone its own metamorphosis and has become even more integrally connected with the book. Not only has its coverage expanded, but it has incorporated an entire laboratory manual as well. just as this is the first edition of the book to integrate all the diverse areas of developmental biology, it is the first edition to include a laboratory manual and a bioethics pamphlet in its electronic augmentations.
This is the first edition of the book that has brought together all these strands, and I hope it does justice to developmental biology and to the revolution that is changing our professional and personal lives. 'Throughout all this revolution, however, one always returns to the embryos. They are the source of both our curiosity and our awe. Some of us are lucky enough to be paid to think about them and to even get into the laboratory to see if our ideas are possibly correct. As Jean Rostand proclaimed, "What a profession this is--this daily inhalation of wonder."
I am once again indebted to the many colleagues who vetted early versions of these chapters for errors and who steered me to new and important research papers being done in their respective specialties. Kathryn Anderson, Adam Antebi, Bruce Baker, Hans Bode, Donald Brown, Ann Burke, Blanche Capel, Judy Cebra-Thomas, Eddie De Robertis, Charles Emerson, John Fallon, David Gardiner, Laurinda Jaffe, Ray Keller, Marta Laskowski, Kirsti Linask, David McClay, Anthony-Samuel Lamantia, Philip Meneely, Mary Montgomery, Lisa Nagy, Fred Nijhout, John Opitz, Rudy Raff, Kirsi Saino, Hannu Sariola, Gary Schoenwolf, Billie Swalla, Carl Thummel, Kathy Tosney, Rocky Tuan, Mary Tyler, Adam Wilkins, Christopher Wright, and Christopher Wylie all provided valuable input, often including reprints and sketches of improved figures-the most concrete kind of help an author can ask for! Persisting errors are mine alone.
My editors Andy Sinauer and Carol Wigg shepherded the project to another successful completion while somehow managing (at least as far as I know) to maintain their sanity. The Sinauer production staff, including Chris Small, Jefferson Johnson, Janice Holabird, and Joanne Delphia worked their magic using modern digital publishing software to design and produce the pages, making changes and updating right up until the book "hit the presses." Fraser Tan provided back-up proofreading for a harried author. And as always, my thanks to Anne Raunio for her help with the medical chapter and especially for putting up with me during the past year.
Published by Elsevier Science under Auspices of Society for Developmental Biology
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