I first read Michael Behe's book, Darwin's Black Box (DBB), while on vacation in London over 4 years ago. The book has now been available for 9 years and has been the subject of much discussion. I recently re-read much of the book so I could review it here. Although I have certainly absorbed some of my thinking from other sources, I have intentionally not read reviews of Behe's book lately so that I could exercise my own mind. Following my comments on the book I will link to other critical reviews that may add to or supercede mine.
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The goal of DBB is to argue for intelligent design in biology, and provide criteria whereby we may recognize it. Behe is a biochemist at Lehigh University and also a part of the Discovery Institute's Center for Science and Culture. DBB follows books written by other CSC fellows including Of Pandas and People, Darwin on Trial, and others. The apparent goal of DBB was to use science to support the philosophy presented in the previous books (which I have not read).
Behe argues that design in biology can safely be inferred if a system is irreducibly complex (IC). This means that a biological system that performs a specific task has a number of components, each of which are required in order for the system to work. He argues that if a system is IC, it could not have evolved in a step-by-step manner because it would not confer any benefits that could be selected for. Therefore someone or something with intelligence must have designed it.
Behe cites several biological systems as IC. The principal examples are: the biochemical reactions that make vision possible, the bacterial flagellum, the blood-clotting cascade, and the immune system. I will not deal with these systems directly nor will I get into detailed biological systems because others have already done so.
General Impressions:
Behe identifies himself as Catholic so he writes from the perspective of a believer in God. Had the purpose of this book been solely to communicate how he sees the hand of God in biology, I would be less critical. We are all entitled to our own opinions, impressions, and insights, and sharing them can be helpful to others. I think Behe makes a reasonably good argument that the believer need not surrender their faith in the face of science. The book could have helped to calm the conflict between science and religion. Instead, Behe (along with others) is trying to revolutionize science. Instead of calming, the book is an instrument of attack, which helps explain the vigorous response to it.
Argument from ignorance:
As has been pointed out repeatedly, a fundamental problem with IC is that it is an argument from ignorance. Instead of offering positive evidence for design, IC argues that the system under investigation could not have arisen through natural means and therefore must be designed. This is an assumption based on ignorance. Just because the mechanism of the origin of a system is not known today does not mean it will not be discovered in the future. Furthermore, once the label of "design" is applied to a biological system, it would be very difficult to remove because it will be virtually impossible to absolutely prove that a system was not designed--at least to the satisfaction of proponents of design. Also Behe writes, "Design theory has nothing to say about a biochemical or biological system unless all the components of the system are known and it is demonstrated that the system is composed of several interacting parts." To a certain extent this also requires an assumption since, although a system may be well characterized, additional components may be discovered in the future.
Moving goal posts:
Behe discusses several examples of complex biological systems where an evolutionary precursor has been proposed. He then argues that the proposal doesn't prove anything because it does not explain where the components of the system came from. This is a misleading argument because it changes the question. For example, after discussing the argument that pseudogenes are evidence of evolution, one of Behe's objections is that "even if pseudogenes have no function, evolution has "explained" nothing about how pseudogenes arose. In order to make even a pseudo-copy of a gene, a dozen sophisticated proteins are required...Miller has not told us how any of these functions might have arisen in a Darwinian step-by-step process."
My problem here is that the origin of the proteins that make a pseudogene were not the items in question--their ultimate origin is a separate question. This is like saying that the explanation that cars come from factories doesn't really explain anything because it does not account for where the parts of the car came from. An answer to where the parts were made raises the question of where the materials came from, etc. Behe seems to like to play this game until the answer is "we don't know," at which point he invokes design.
Part of the difficulty with some of Behe's arguments is that he does not distinguish between several components of evolution. In the preface he writes that although evolution is a flexible word he uses it to mean "a process whereby life arose from non-living matter and subsequently developed entirely by natural means." This definition encompasses a number of concepts including what may be the most controversial one--abiogenesis. His lack of specificity about the evolutionary process under examination results in broad-brush arguments that are thereby weakened.
Toward the beginning of the book Behe states that he finds "the idea of common descent (that all organisms share a common ancestor) fairly convincing, and [has] no particular reason to doubt it." This statement might lead one to believe that Behe is only discussing the origin of life, and may be an attempt to diffuse criticism at the outset. However, the rest of the book does not seem to support this statement. Behe briefly discusses problems with the fossil record in manner similar to other critics of evolution (including common descent). He also includes quotations from various scientists expressing problems with evolutionary theory, although whether the context is accurate I do not know. The only real success Behe attributes to Darwinism is microevolution--even young earth creationists will concede that.
Appeal to the Masses:
It is apparent that this book is not written for the scientific community; it is written for the layperson. A cynical but not unlikely interpretation of this is that this book fits into the Discovery Institute's strategy of taking ID concepts straight to popular culture in an effort to revolutionize science without having to produce any real scientific evidence.
In order to communicate with laypersons, Behe makes extensive use of analogies. These are sometimes helpful but I believe they are ultimately a hindrance to real discussion. Any analogy will break down if pushed too far and some of Behe's analogies seem near that breaking point. For example Behe uses analogies of a mousetrap, Mount Rushmore, and a trap in the woods to make design arguments. The fundamental problem, it seems to me, is that biological systems are quite different from these examples. None of these examples are naturally common, reproduce themselves, exhibit random variation, or are subject to natural selection. In other words, none of these examples are subject to evolutionary processes--they are fundamentally different. Thus Behe's argument by analogy has severe limitations and flaws, in my opinion.
Why not embrace intelligent design?
Behe proposes a simple hypothesis: a single cell was designed billions of years ago that contained all the information necessary to produce all descended life forms. While the design portion of this hypothesis is not testable, the rest is--and I believe it fails. Having argued that flagella, the biochemical basis for vision, the blood clotting cascade, and the immune system constitute IC systems, Behe's hypothesis predicts that the genes for these systems were contained in the universal common ancestor and only turned on, as appropriate, in descendant organisms. If this were the case then we would expect to find genes for the components of these systems distributed throughout phylogenetic trees with no particular organization.
For example the RAG genes are necessary in order for the adaptive immune system to function. The RAG genes are only present in vertebrates, with the exception of jawless fish such as lampreys. The most straightforward interpretation of this is that vertebrates that existed after the split with jawless fish, acquired the RAG genes that enabled the development of the adaptive immune system in descendant organisms. (Behe might say, "You haven't explained anything because you haven't explained where the RAG genes came from." But that is a different question.)
Behe's hypothesis predicts that all organisms originally had the RAG genes but they were only retained in the vertebrates that now have immune systems. Are we to believe that the RAG genes were carried in organisms for billions of years but were ultimately lost in all organisms except those that now use them--thus giving the illusion of evolution? Are we to believe this for every proposed IC system? Aside from evolution, the only other alternative I can think of is special creation for each taxon that contains a unique IC system, and we are back to explaining the biological world with "because that's how the designer did it."
Conclusion:
The concepts of intelligent design and irreducible complexity may be useful on a personal level in the attempt to harmonize science and theology. However in my opinion they do not belong in serious scientific discourse. Although Behe characterizes molecular evolution as a moribund field, the era of comparative genomics is opening new doors of investigation. As more complete genome sequences become available it will be possible to understand the origins of more genes and biological systems. Although our ability to sequence whole genomes is impressive, a huge amount of work remains. The human, mouse, rat, and chicken genomes are the largest ones completed so far. But a much larger sampling of organisms will be needed in order to definitively answer many questions. It is therefore premature to invoke intelligent design as a force in biology.
Critiques of ID and IC:
Talk.Origins
Talkdesign
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