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This book is about the origins of novelty in evolution. The brain, the eye, and the hand are all anatomical forms that exquisitely serve function. They seem to reveal design. How could they have arisen? The vast diversity of organisms, from bacteria to fungi to plants and animals, all are of different design. How did they originate? Nothing in the inanimate world resembles them. All are novel. And yet novelty implies the creation of something from nothing—it has always defied explanation. When Charles Darwin proposed his theory of evolution by variation and selection, explaining selection was his great achievement. He could not explain variation. This was Darwin’s dilemma. He knew only that variation was indispensable as the raw material for selection to act on, and random with respect to the particular selection at work. Genetics provided important clues about the dependence of variation on genetic change and in particular about how change is inherited. What has eluded biologists is arguably the most critical: how can small, random genetic changes be converted into complex useful innovations? This is the central question of this book.
To understand novelty in evolution, we need to understand organisms down to their individual building blocks, down to the workings of their deepest components, for these are what undergo change. Insights into these components have come only in the past few years. A theory of novelty was impossible to devise until the end of the twentieth century; experimental evidence was incomplete on how the organism uses its cellular and molecular mechanisms to build the organism from the egg and to integrate the genetic information into functional processes. Ignorance about novelty is at the heart of skepticism about evolution, and resolving its origins is necessary to complete our understanding of Darwin’s theory.
The last 150 years have seen Darwin right and Darwin wrong; Darwin doubted, Darwin ignored; Darwin demonized, and Darwin idolized; but in the end we may have the true worth of his accomplishment. He came up with a single transcendent idea, variation and selection, and he demonstrated that idea through intense observation. This science is the simplest to appreciate; one might even say it is science at its purest. So convinced was Darwin of variation and selection, based on his empirical evidence, that he was willing to ignore or contrive mechanisms to explain it. The course for biologists has been ever more clear: to see if we can understand the mechanistic underpinnings of his transcendent idea.
Evolutionary biologists and paleontologists in their search for more evidence of selection and common descent have done their part, though their task is hardly complete. Geneticists, achieving spectacular success at the end of the twentieth century in solving the mechanism of heredity for all of life, have done their part. Still, they can do more with the modern tools at their disposal.
Developmental biologists, cell biologists, biochemists, and now genomicists have begun the arduous job connecting the bewildering amount of genetic change to the variation on which selection has acted. It is their insights that we report here. An understanding of the connection between the gene, on the one hand, and the anatomy, physiology, and behavior of the organism, on the other, can provide the explanation for novelty. Knowing the ease with which novelty can arise in turn helps us determine whether it is plausible that life is a product of evolutionary change.
In this book we propose a major new scientific theory: facilitated variation that deals with the means of producing useful variation. From an explanation of how such variation emerges comes an appreciation of the facility of evolutionary change. We present facilitated variation not only for the scientist, but also for the interested nonscientist who is ready to explore ideas at the forefront of biological theory. Recognizing how difficult it is to speak to such a diverse audience, we owe both groups an explanation.
To the scientist, we ask forbearance that we have largely skirted the jargon and qualifying phrases emblematic of scientific writing. Yet many of our scientific colleagues who read drafts of this book strongly encouraged us to keep the language simple while making no concessions in the ideas. Even if we had tried to confine the message to professional biologists, we would have had problems. In which subfield would this book be understood? If it were addressed primarily to those who study molecular biology, would the ideas be familiar enough to those who study natural history? If addressed strictly to evolutionary biologists, our assumptions would disenfranchise most molecular biologists, who would find the questions peculiar and the examples exotic. We decided that a common, straightforward vocabulary was essential just to reach scientists as a group. To move beyond scientists to the lay public required further adjustments, but fewer than one might expect.
To the nonscientist, we would say that you have already revealed your deep interest in evolution and your appreciation that evolution affects your sense of self as a biological creature. In record numbers you have bought books, visited museums, traveled to exotic habitats, and attended courses and debates about evolutionary theory. Your intense demand for knowledge has been met by interpreters of science, often journalists, who have contributed to your understanding. But the barrier of ignorance of the molecular sciences has handicapped the lay public, as it has in fact handicapped many scientists as well. To be forced to occupy the worst seats in the theater for one of the most meaningful dramas in the history of human exploration seems tragic, especially if it is avoidable. The nineteenth-century discoveries in evolution filled museums with towering fossil skeletons of dinosaurs, which inspired children and adults alike. Zoos, arboretums, and animal programs on television have thrilled millions with the diversity of life on earth.
We are not sure that we can succeed as well in portraying the molecular and cellular understandings that complement and ultimately explain this diversity. But we know from experience that a vivid real drama can be much more engaging than a paraphrased retelling. We have done what we could: reduced the jargon, emphasized the universal concepts, stayed true to the narrative of evolutionary history, and provided a glossary and ongoing explanations. What we have not done is dilute the ideas or turn arguments and demonstrations into uncorroborated assertions. We have tried to provide conveniences and aids, but there is no shortcut to understanding. We hope we have succeeded in both explicating a significant new theory in evolution and embracing a broad audience.
As an original, far-reaching recasting of evolutionary theory, our book has much to convey. We have high drama: the union of molecular, cellular, and developmental biology with evolutionary history; the story of how novelty was generated in evolution; the paradox of the conservation of fundamental mechanisms of the cell but the extraordinary diversity of organisms; a new cast of evolutionary mechanisms all based on trading constraint for deconstraint; and the completion of Darwin’s theory with new evidence as to why his original idea of variation and selection works on the variation side as well as on the selection side. We hope that the magnitude of a retold story of creation will hold the interest of readers—specialists and generalists alike.
Ours is a journey from molecule to cell to organism to life’s diversity. It is up to the reader to traverse the nearly four billion years of life embedded in our account. We have invoked the latest results from the molecular sciences, pressing chemistry, cell biology, developmental biology, biochemistry, and genetics into the service of evolutionary biology.
Understanding life is not a conquest, but a slow lesson in appreciation. Most of what we, the authors, have learned we learned from others; our own contributions are small enough that they rarely appear in this book. We, as scientists, have been and continue to be active participants in the process of discovering how the organism constructs itself. We continually confront the surprising admixture of conservation and diversity found in all organisms. Our lifelong pursuits of the conserved processes of life led us inexorably to the question of the origin of novelty in evolution. Novelty by definition is always a surprise, but when the surprise is too great, it is completely implausible. The plausibility of life rests on the plausibility of generating novelty, and that in turn rests on mechanisms newly uncovered in biology.
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