The Plausibility of Life: Resolving Darwin’s Dilemma
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.”
About the Author(s)
An outstanding introduction, November 6, 2005
The theory of evolution began as an alternative to what is now called creationism. But unlike the advocates of creationism, Charles Darwin did not attempt to build his theory of evolution by refuting the arguments of William Paley and the other creationists of the time. Instead, he based his theory on observations, on the many traits and characteristics that he observed on his long voyage on the Beagle. A successful theory of origins cannot be built merely on sophisticated rhetoric or logical argumentation. Darwin knew this and to his great credit he gave humanity a view of life that is more scientifically justified and based on common-sense observations. Any theory however has its weaknesses, due in part to the limited knowledge of the individuals that propose it. These individuals though usually recognize these weaknesses, and are cognizant that future generations may be able to resolve them, due to the more advanced experimental techniques that are then available.
Darwin knew the weakness in his theory: it could not explain variation. The authors of this book attempt to resolve this difficulty in his theory and account for the enormous novelty in the natural world. And like Darwin, the authors justify their theories with experimental results, particularly in the fields of genetics and embryology. The knowledge from these fields was of course not available in Darwin’s time. The case that the authors make for the origins of novelty is both interesting and very plausible, and even though the book is targeted to a "popular" audience, readers will appreciate the book more if they have a fairly strong background in biology.
The authors emphasize early on that mutation only alters what already exists, and so it is imperative that an explanation be found that shows how one structure can be transformed into another. It must be shown how random genetic changes can result in innovations that have high utility for the evolved organism. The pillar of the authors’ theory for how this is done centers on the notion of `facilitated variation’, and they give detailed arguments throughout the book that support it. Most interestingly, this notion is not based on the genotype of the organism, but rather on its phenotype: random mutations lead to nonrandom phenotypic variation. The authors are careful though to point out to the skeptical reader that this notion is not Lamarkian, but instead refers to the capacity of the organism to generate phenotypic variation as a response to genotypic variation and the nature of this variation. They leave to other researchers the study of the capacity of a particular population to evolve.
Facilitated variation holds that since phenotypic variation is dependent on the modification of what already exists, it cannot be random (even though mutation is itself random). In addition, the variation of the phenotype of an organism, which involves the changes of components and processes, is subject to constraints. However, in this same variation, other components and processes of the phenotype can be deconstrained. There is therefore a trade-off involved, with the result that (less lethal) phenotypic variation can be accelerated when these deconstraints are present. The parts of the organism that are constrained that authors refer to as the `conserved core processes’ of the organism. These processes can be viewed as those that remain fixed under the evolutionary transformations of the organism. Although the authors do not refer to it in the book, and in fact may not be aware of it, this view of conserved processes in evolution is discussed in the mathematical literature under the guise of what are called `evolution strategies.’
The authors give examples of some of these core processes, such as the DNA, RNA processes of replication and protein synthesis. These processes are identical in all living organisms. Other examples given by the authors include the functions of intracellular membranes in eukaryotes, the functions of the extracellular matrix in metazoa, the role of the Hox genes in bilateral metazoa, and the process of limb formation in land vertebrates.
The core processes are specially constructed so that they can be readily linked together to obtain new combinations and can be used at new times and locations. The net result of these changes is the generation of new phenotypes. The authors allude to `weak linkage’ as being one of these special constructions. Weak linkage is primarily involved in signal transduction and transcription, resulting in weak and indirect protein interactions. They also point to `exploratory behavior’ as being one that has the capacity to generate a large number of outcome states. Some of these outputs can then be selected and retained, then becoming stable. The unselected states remain nonfunctional but may be selected in the future. The authors believe that exploratory processes answer the "complexity" objections to evolution, in that they explain how new anatomical structures can arise and how these new structures or systems can repair damage. As an example of this, the authors name the adaptive immune system in vertebrates, but they do not give the detailed reasons for why they believe it is.
The authors’ arguments are fascinating and the length of the book makes its study manageable. Many references are given for readers who need more details. The only part of the book that should probably be omitted entirely is the section entitled "Creationism and Intelligent Design." The proponents of these approaches to explaining novelty need to find constructive examples to substantiate the viability of their theories. Usually one only gets philosophical rhetoric from them, and this does not serve to further the understanding of biological systems. The authors do not need to answer their objections, as it only gives them free press. Emphasis should always be placed on obtaining a true understanding of adaptation and biological processes. Like Darwin, this entails meticulous observation and careful laboratory work. The authors are definitely in this tradition, and have provided the reader with a first look at their theory of facilitated evolution and its observational and experimental support.