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."
robustness of biological systems increases, other things being equal, diversity increases. The amount of diversity is one measure (after corrections for history and population size) of the effectiveness of the robust adaptable mechanisms that facilitate variation. Finally, the paths of major innovation in human society may parallel the process of major innovations in the core processes in biology. New core technologies may be adapted through a sequence of novelty generation, integration into
random deviation are built into the genetic makeup of the ant. From these rigid rules emerges a highly adaptive strategy applicable to changing environments. Microtubule assembly and ant foraging are conceptually analogous. Both are exploratory processes involving variation and somatic selection. Ants and microtubules move out in random directions and return if they do not encounter a “target.” If they do encounter a target (a stabilizing agent for microtubules or food for ants), the array of
have no way of knowing how often random DNA modification can produce useful outcomes for selection. Without an understanding of how DNA changes are interpreted, we cannot know how much selection molds evolution, or how much the initial variation biases the outcome. It is not enough to know that changes in DNA can in some unknown way cause a change in phenotype; we need to know at least in outline how phenotypes respond to particular changes in DNA. It is this third pillar, an understanding of
negative change in another. If a change is lethal, a favorable change elsewhere can do nothing to overcome it. Compartments mitigate these effects. If bones in the leg are to grow longer than bones in the arm, the expression of genes involved with cartilage and bone in the leg must be endowed with different properties. The arms and the legs are in different compartments. The organism can avoid conflicts over the use of common genes in limb development by using different local selector genes to
to operate in this large-scale patterning role without interfering much in local differentiation. Thus, the individual compartment modifications are selected relative to the conserved and unchanging compartment plan. The compartment plan, because of its anatomical role, is perhaps the most persuasive example of how a robust developmental or physiological process can itself be constrained to change and still deconstrain evolutionary change in other processes. What is the hypothetical alternative