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Introcluction n Dio~ogy is the most intimate of the sciences. It deals with some of life's most wondrous occurrences, with reproduction and birth' with death and disease, with human abilities and limitations. It seeks scientific explanations for these things, an understancling of how they occur and often why they occur. But explanations do not eliminate the wonder. No matter how much we know about being human, we will always be human. This book describes ground-breaking research in four of biology~s most vibrant fields: genetics, clevelopment, neuroscience, and evo- lution. All of these fields have very long histories, extending back to early human myths and philosophies. At the same time, all of them have experienced tremendous advances in the past few decades. Major questions remain unanswered, but the progress that has been made is . . ~ In many cases aston~s sing. The rapic] accumulation of new knowledge in biology has fundamen- tally changed our views of ourselves ant! the world around us. By revealing the interconnections between human beings ant! other organ- isms' it has reshaped not only science but philosophy and religion. Biological research has also given us an increasing ability to manipulate the biological world, and with that ability has come the necessity of making choices. it has often been a short step in biology from the purely scientific to the ethical, from what one knows or can do to what one believes or ought to clot Progress in genetics, clevelopment, neurosci- ence, and evolution has generated difficult and sometimes agonizing ethical dilemmas, as cliscussed in each of this book's chapters. Bio 1

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logical research has also raised many broader ethical issues, which form the subject matter for the essays that follow each chapter. The Molecular Revolution The most important (levelopment in biology in the past half century (though far from the only important (levelopment) has been the (liscovery of the structure and basic function of DNA, the molecule responsible for the continuity of life. This profound scientific achievement sparked the explosive growth of what has come to be known as molecular bi- ology the study of biological processes on the molecular level rather than the level of cells, organs, organisms, or groups of organisms. Using molecular biology, researchers can trace complex biological processes back to their molecular roots. They can examine the fundamental con- stituents of biological systems and explain those systems in funciamental terms. In the 1970s, molecular biology experienced its most significant advance since the uncovering of DNA's structure and function in the 1950s. Researchers learned how to manipulate DNA on the molecular level. Before the 1970s, molecular biologists were largely limiter] to working with the DNA provicled to them by nature. Researchers could cross two interbreeding organisms to get new combinations of DNA, and they could perform a few relatively clumsy operations on DNA using viruses and bacteria. But their inability to control the structure of DNA at will was a major obstacle to continued rapic] progress. That all changed in the 1970s. Using the new techniques of recom- binant DNA, biologists could isolate virtually any segment of existing DNA anti combine it with other segments of DNA. They could then insert these novel genetic combinations into bacteria, yeast, or even plant or animal cells. They could copy, or clone, DNA segments many times over, creating virtually unlimited amounts of those segments for use in research or other purposes. At the same time, they were devel- oping techniques to sequence pieces of DNA or custom builcl DNA fragments from simple chemical buitcling blocks. Molecular biolo~v had become as much a technology as a science. All four of the fields discussed in this book have been influencer! to a greater or a lesser degree by the growth of molecular biology. Genetics (Chapter 1) has been transformed by the knowledge that the elements of heredity consist of messages encodecl in DNA. The (development of a single fertilized egg into a complex organism (Chanter 2) has come 1 .1 1 . r _ ~ A ~ 1 con - x~ A--- -J ~~~~ ~~~~~~ lo ne seen as tne playing OUt 01 genetic messages. Genetic controls also 2 SHAPING THE FUTURE

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shape the basic structure ant] interconnections within the brain (Chapter 3). And over geologic time the messages in DNA have evolved and become more elaborate to produce the overwhelming diversity of life on earth (Chapter 4~. However, not everything in biology can be explainecl at the molecular level. Many biological processes occur at organizational levels above that of molecules. It is not now possible to describe the development of a human embryo, the higher, more abstract functions of the human mind, or the interactions of organisms in an ecosystem entirely in molecular terms. Current explanations call instead upon the interre- lations among cells, or among organisms, or among groups of cells or organisms. Perhaps it will someday be possible to explain these phe- nomena at the level of molecules (though there are good reasons to think that it may never be possible). But for now, if progress is to be ma(le, explanations must be sought largely at other levels. The emphasis on molecular biology has also ten(lecl to overshadow other developments in biology that have led to important acivances. New methods of visualizing biological systems, such as imaging tech- niques and video technology, have revealed key information about the structure and dynamics of living things. The study of animal behavior has resulted in a much better understanding of how organisms interact with other living things and with their environments. And data storage and computer science have helped researchers make use of the huge amounts of information generated by biological research. Common Themes Although the subjects discussed in this book range widely across biology, several ideas emerge over and over. Perhaps the most important concerns the unity of life, as embodied most succinctly in the univer- sality of the genetic code. All organisms, from plants and animals to the simplest bacteria, use the same molecular mechanisms to read the messages encoded in DNA. This is what makes it possible to extract a . ~ A_ ~ T ~ ~ ~ piece or tJI\A trom a numan cell, insert it into bacteria, and have the bacteria read that DNA just as a human cell would. Plato quotes Protagorus as saying that ``man is the measure of all things," but the unity of biology belies that notion. Among the exper- iments described in this book are ones on fruit flies, toads, mice, monkeys, and canaries. All of these organisms provide insights into human biology, just as the stucly of human biology reflects on the biology of other organisms. INTRODUCTION 3

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Another common theme is the increasing unification anc! interrelation of biological fields. In the 1950s, for example, brain science consisted of three quite separate fields: neuroanatomy (the study of the brain~s parts), neurophysiology (the study of the brain's function), and neu- rochemistry (the study of the brain's chemistry). Then' in the 1950s and 1960s' electron microscopy revealed that there are gaps known as synapses between most nerve cells, and electrical recording of indi- vidual cells showed that nerve signals are related to the chemical events that go on in these gaps. The integrated field] of neuroscience has been a direct result of this linkage between the brain's structure, function, and chemistry. Similar mergers and cross-fertilizations are going on throughout biology. A final common theme is the accelerating pace of biological research. Knowledge builds on knowledge, so that all scientific disciplines un- ~lergo periods of virtually exponential growth. If any science is now undergoing such growth, it is biology. But growth is not an unmitigated blessing. It can require that clifficult ethical choices be macle quickly and without a great deal of prior experience. In a fast-moving area of science, the development of ethics can be harcI-pressed to keep pace. This book does not cover many of the other exciting areas in biology, such as immunology or ecology. But by choosing fielcls that span the range of biology and by focusing on specific research within those fields, this book seeks to give both a broad overview of modern biology anc} a very real taste of how biological research is done. . 4 SHAPING THE FUTURE