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Darwinian evolution is widely advertised to be a fact, as firmly established as the shape of the Earth. Defenders of the theory insist that there is no scientific controversy over it, and people who question or criticize it are typically accused of being ignorant or religiously motivated. Yet every few years a book comes along—written by scientists—claiming to remedy some major flaw in evolutionary theory.
by Marc W. Kirschner and John C. Gerhart Yale Univ. Press, 2005 314 pp., $30 |
The Plausibility of Life, by Marc W. Kirschner and John C. Gerhart, is such a book. Gerhart is an eminent cell and developmental biologist, now retired after a distinguished career at the University of California at Berkeley; Kirschner—once Gerhart's graduate student (as was I)—is an equally eminent biologist, now a department chair at Harvard University. According to the book's jacket, the authors close "a major gap in Darwin's theory" and thereby provide "a timely scientific rebuttal to critics of evolution who champion 'intelligent design.'"
The "major gap" in Darwin's theory is the origin of novelty: new variations, physiologies, anatomies, and behaviors. According to Kirschner and Gerhart, Darwin's theory rests on three pillars: natural selection, heredity, and variation. Darwin provided the first, and Mendelian and molecular genetics provided the second, but until now "a major weakness remained, casting all else in doubt." That weakness has been the origin of new variations: "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." Indeed, the "cardinal issue in evolution is the origin of complex and heritable variations," and the authors maintain that until now no one has dealt adequately with this issue. "The plausibility of life," they write, "rests on the plausibility of generating novelty, and that in turn rests on mechanisms newly uncovered in biology."
Such variations must arise in the embryo, so Kirschner and Gerhart write that "understanding the organization, growth and development of the organism is essential to complete Darwin's theory." Although Darwinists largely ignored embryology for a hundred years, many biologists in the late 20th century realized that we need to understand embryo development before we can hope to understand evolution. This realization led to the field of "evolutionary developmental biology," or "evo-devo." The Plausibility of Life is a contribution to this field.
To overcome the weakness in existing evolutionary theory, Kirschner and Gerhart propose what they call "a major new scientific theory: facilitated variation." The authors note that organisms consist of "core processes" that have apparently been "conserved" since their evolution from a common ancestor. The most basic of these are found in all living organisms from bacteria to humans; for example, dna replication, protein synthesis, and metabolic pathways. Kirschner and Gerhart acknowledge that they have no explanation for the origin of these in the first living cell. "Evidence is completely lacking about what preceded this early cellular ancestor," they write. "Everything about evolution before the bacteria-like life forms is sheer conjecture."
There are other major transitions in the history of life that Kirschner and Gerhart also concede remain unexplained. One of these was the "invention" of the first eukaryotes, cells with nuclei that are very different from bacteria. "Generating the first eukaryotic cell was a major and enduring accomplishment," they write. "Extensive innovation showed up in the complexity and organization of the eukaryotic ancestor." Another major transition was the origin of multicellular organisms, which require complex mechanisms for cells to aggregate and communicate with each other. Still another unexplained transition was the origin of animal body plans in the Cambrian explosion. "Once again," write Kirschner and Gerhart, "a new suite of cellular and multicellular functions emerged rather quickly and was conserved to the present."
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