The Plausibility of Life: Resolving Darwin's Dilemma
Marc W. Kirschner, John C. Gerhart
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In the 150 years since Darwin, the field of evolutionary biology has left a glaring gap in understanding how animals developed their astounding variety and complexity. The standard answer has been that small genetic mutations accumulate over time to produce wondrous innovations such as eyes and wings. Drawing on cutting-edge research across the spectrum of modern biology, Marc Kirschner and John Gerhart demonstrate how this stock answer is woefully inadequate. Rather they offer an original solution to the longstanding puzzle of how small random genetic change can be converted into complex, useful innovations.
In a new theory they call “facilitated variation," Kirschner and Gerhart elevate the individual organism from a passive target of natural selection to a central player in the 3-billion-year history of evolution. In clear, accessible language, the authors invite every reader to contemplate daring new ideas about evolution. By closing the major gap in Darwin's theory Kirschner and Gerhart also provide a timely scientific rebuttal to modern critics of evolution who champion “intelligent design."
variation, even if it did not exactly correspond to the questions the creationists asked, can now be seen as one of the strengths of a general theory of evolution. Largely because they derive from experiment, the mechanisms proposed for phenotypic variation have both great explanatory power and great verifiability. Molecular and cellular data can be added to the results of prior biologists and assembled into a coherent theory addressing the specific evolutionary problems of novelty and variation.
unchanged. Indeed, many conserved proteins and genes exist in the phenotype. In general, though, constraint was considered a minor effect, or trivial, for example, in explaining why mollusks and echinoderms were less able to evolve wings than vertebrates. Novelty, Time, and Random Mutation What if evolutionary biologists were wrong to think of phenotypic variation as random and unconstrained, even though genetic variation was random and unconstrained? How much would it matter if we really
conserved core processes. When a significant change occurs in evolution, do radically new behaviors developor does the cell use its existing repertoire in different ways? To understand evolutionary change in Wright’s terms, we want to know the historical changes that have occurred in cell behaviors and trace these modifications to the large-scale changes in anatomy that have traditionally been used to document evolutionary history. Yet information about alterations in cell behavior cannot be
widely used in the cytoskeleton of nondividing cells, such as nerve cells. The other two major filament types, actin and intermediate filaments, along with microtubules, play structural roles in the cell—a different role for each. The cytoskeleton is both rigid, giving any specific cell stability against mechanical deformation, and versatile, capable of being reassembled and used over and over again to support different shapes. The key to the adaptability of microtubules is their dynamics. In a
modification of existing processes is likely to be less lethal and generate more phenotypic change, for an input of random mutation, than would be gained by inventing new structures or physiology. 10. The core processes are built in special ways to allow them to be easily linked together in new combinations, and to be used at new times and places, to generate new phenotypes. These special properties include: a. Weak linkage, a property particularly of signal transduction and transcription. In