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Most people have some interest in embryos; this probably results, in part, from their interest in understanding the biological origins of themselves and their offspring and, increasingly, concerns about how environmental change such as pollution might affect human development. Obviously, et- cal considerations preclude experimental studies of human embryos and, c- sequently, the developmental biologist has turned to other species to examine this process. Fortunately, the most significant conclusion to be drawn from the experimental embryology of the last two decades is the manner in which orthologous or closely related molecules are deployed to mediate similar - velopmental processes in both vertebrates and invertebrates. The molecular mechanisms regulating processes fundamental to most animals, such as axial patterning or axon guidance, are frequently conserved during evolution. (It is now widely believed that the differences between phyla and classes are the result of new genes, arising mostly by duplication and divergence of extant sequences, regulating the appearance of derived characters. ) Other vertebrates are obviously most likely to use the same devel- mental mechanisms as humans and, within the vertebrate subphylum, the - parent degree of conservation of developmental mechanism is considerable. It has long been recognized that particular vertebrate species offer either d- tinct advantages in investigating particular stages of development or are - pecially amenable to particular manipulations. No single animal can provide all the answers because not all types of experiments can be carried out on a single species.

The new third edition of Gene Activity in Early Development reflects the ten years of technological progress since the last edition. Providing a unique blend of classical and molecular knowledge, it discusses all major embryonic systems from both a comparative and mechanistic point of view. In deriving overall interpretations of developmental phenomena, it brings into play all the disparate forms of evidence, including genetic, molecular, and cytological.**This book is written for any serious student or scholar entering the field, whether his or her background is in genetics, molecular biology, or embryology.

Nearly 10 years have elapsed since I finished writing the first edition of Intro duction to Molecular Embryology. During this period, molecular embryology has made great strides forward, but without undergoing a major revolution; there fore, the general philosophy and outline of the book have remained almost un changed. However, all the chapters had to be almost completely rewritten in or der to introduce new facts and to eliminate findings which have lost interest or have been disproved. There was a major gap in the first edition of this book: very little was said about mammalian eggs despite their obvious interest for mankind. Research on mammalian eggs and embryos is so active today that this important topic deserves a full chapter in a book concerned with molecular embryology. Therefore, I am very thankful to my colleague Dr. Henri Alexandre, who has written a chapter on mammalian embryology (Chap. 9) and has prepared all the illustrations for this book.

Technological systems become organized by commands from outside, as when human intentions lead to the building of structures or machines. But many nat ural systems become structured by their own internal processes: these are the self organizing systems, and the emergence of order within them is a complex phe nomenon that intrigues scientists from all disciplines. Unfortunately, complexity is ill-defined. Global explanatory constructs, such as cybernetics or general sys tems theory, which were intended to cope with complexity, produced instead a grandiosity that has now, mercifully, run its course and died. Most of us have become wary of proposals for an "integrated, systems approach" to complex matters; yet we must come to grips with complexity some how. Now is a good time to reexamine complex systems to determine whether or not various scientific specialties can discover common principles or properties in them. If they do, then a fresh, multidisciplinary attack on the difficulties would be a valid scientific task. Believing that complexity is a proper scientific issue, and that self-organizing systems are the foremost example, R. Tomovic, Z. Damjanovic, and I arranged a conference (August 26-September 1, 1979) in Dubrovnik, Yugoslavia, to address self-organizing systems. We invited 30 participants from seven countries. Included were biologists, geologists, physicists, chemists, mathematicians, bio physicists, and control engineers. Participants were asked not to bring manu scripts, but, rather, to present positions on an assigned topic. Any writing would be done after the conference, when the writers could benefit from their experi ences there.

The first edition of Embryos, Genes and BirthDefects, edited by the late Peter Thorogood, was a radicalnew book aimed at bridging the gap between the medical disciplinesof embryology and dysmorphology, and recent advances in cellular,molecular and developmental biology. This new edition remainsunique in its breadth and brings up to date our understanding ofbirth defects and of the strategies utilized to gain suchknowledge. It features new chapters on human cytogenetics,mutagenesis and the eyes and ears. The book presents key topics in developmental biology andexplains how they provide the foundations for understandingclinical birth defects. The first six chapters introduce conceptsand strategies adopted to elucidate developmental anomalies leadingto birth defects. The book then focuses on specific organs andreviews the cellular and molecular mechanisms affecting theirdevelopment and how disruption of these mechanisms by genetic orenvironmental factors may underlie certain birth defects. Thechapters are concise and provide up-to-date coverage of topics in aformat that is easily accessible and yet at the forefront ofresearch. Written primarily for paediatricians, obstetricians, clinicalgeneticists and allied workers, this book guides the reader throughthe contribution of modern molecular biology to our understandingof human development. Developmental and cellular biologists willlearn how errors in the cellular and genetic mechanism can lead toclassical disorders, diseases and syndromes.

The fifth in a series of five histories of the Carnegie Institution of Washington, offering an exciting exploration of a century of scientific discovery.