Department of Biochemistry
University of Iowa, Iowa City, IA 52242
One of the profound gifts that accompanies a life in biology is a deep and continually growing reverence for the intricacy and beauty of life. Many biologists are moved to awe in the face of such grace and power; biologists who are also Christians see in the loveliness of life an image of the loveliness of its Creator. In Darwin's Black Box: The Biochemical Challenge to Evolution, Behe has explored whether some parts of life are sufficiently intricate or inherently complex that the most parsimonious explanation for them is the action of a Designer.
This is a valuable book for two reasons. In it, Behe has done a very good job of making accessible several examples of the beauty and complexity of biochemical systems. It seems likely that anyone who reads this will come away with an increased appreciation for the glorious order of living things, and that can only be a gain for both science and faith. He has also made an explicit statement of neglected, but important, questions. He has drawn attention to two areas that have not been extensively examined: the evolution of complex biochemical systems and the evolution of regulation. These are genuinely challenging questions. If his book stimulates more thought about them, then that will be a real gain.
There are several aspects of the necessary background where Behe and I disagree. These need to be discussed before his central thesis because one's judgment of these points will considerably affect how one weighs the absence of convincing evolutionary scenarios.
First, I believe that Behe overestimates biochemists' interest in evolution. I am a cell biologist in a department of biochemistry. My formal background in evolution includes both undergraduate and graduate study, including quantitative population genetics. This means I have more formal background in evolutionary questions than the average biologist (with particular emphasis on cellular evolution) but less than a real evolutionary biologist. I would guess that this may also reflect my relative level of interest in evolutionary questions.
Now, the most likely person to generate a good evolutionary scenario for the systems that Behe talks about would be a biochemist. The biochemists I know well (from fifteen years working together) don't think about evolution very much; they resemble chemists much more closely than they do evolutionary biologists. They are very capable people who know a great deal about NMR, enzyme mechanisms, transcription factors, and protein structure (much more than I do), but most of them know nothing about even the simple descriptive facts of evolution. For many, I doubt they think about evolution from one year to the next.
As evidence for their lack of knowledge, I get called on occasionally for simple facts about evolution. Based on these requests, typical biochemists don't know the following descriptive aspects of evolution: when the dinosaurs died; the difference between protostomes and deuterostomes; which came first, vertebrates or flowering plants; the relative time that the procaryotes and eucaryotes appeared within a factor of five; why the end of the Permian is even more exciting than the end of the Cretaceous; and why the similarities in homeobox genes between mice and humans are satisfying, between mice and fruit flies amazing, and between mice and plants astounding. Readers who know what these mean will appreciate how little of the simple pattern of evolution has caught their attention. Readers who don't know what these mean are offering evidence of how little the descriptive facts of evolution are known in general, much less the theories of how it occurred. If biochemists know so little of what is known about the evolutionary pattern, is it reasonable to expect them to ask probing new questions about its mechanisms?
Second, I believe that Behe has seriously underestimated how hard it would be to produce a good scenario for the evolution of the kinds of systems he wants explained. Evolutionary studies are never easy, and the kind he wants done are harder than the comparative anatomy that most evolutionary scientists do, for two reasons:
The biochemists would have to work with fewer data. When people do comparative anatomy, they have fossils, real examples of at least some intermediates that may have played a role in the evolution of the structures they are thinking about. When biochemists attempt an evolutionary scenario, they have, at best, "living fossils" which may or may not have preserved the real primitive state. Often the intermediates will be lost because the newer form was more efficient (that's what a Darwinian explanation is, after all, and it is the case for structures that fossilize). When this is true, the biochemists are reduced to what the linguists do in thinking about the origins of languages. They look at a number of existing languages, try to note similarities, use those to reconstruct the precursor, and then perhaps repeat the process to reconstruct that language's ancestor. Now, linguists mostly agree about Indo-European, some have attempted to reconstruct Indo-European's ancestor (with less unanimity), and at least one person has tried to reconstruct elements of the "mother of languages," but few people are persuaded by this because it involves so many nested reconstructions. Yet, that is what would be needed for an evolutionary account of these complex biochemical systems.
The biochemists have more to explain in the face of harder experimental conditions. If we think about a comparative anatomist examining a cube 10 cm to a side, he or she is unlikely to want to account for details less than a millimeter across. When we go down to finer levels of resolution, every decrease in scale involves an increase of detail. However, the difficulty also goes up with the decrease of detail, because the things being studied are smaller, less massive, etc. Therefore, there may be something like the Heisenberg uncertainty principle here, with a tradeoff between resolution and information.
In any case, to obtain the data for comparative studies, the original biochemistry largely has to be repeated; it may be 20% as difficult the second time, but it can be even harder on the second organism than on the first just from idiosyncrasies of the organism. There is no way to know in advance which organism on which to repeat the biochemistry; perhaps one in three or as few as one in ten guesses will be right, but the biochemist won't know until most or all of the work is done. All these combine to make my estimates of the difficulty of such studies considerably more pessimistic than Behe's.
Behe's Central Thesis
Behe makes three main points: (1) Darwinian explanations have not been given for "irreducibly complex" systems, (2) Darwinian explanations cannot account for "irreducibly complex" systems, and (3) intelligent design is the best explanation for "irreducibly complex" systems.
Behe's definition for an "irreducibly complex" system is a system that is "composed of several well-matched interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning." At first, this definition seems clear, but I think there are problems with it that only appear later.
1. Darwinian explanations have not been given for "irreducibly complex" systems.
This claim is probably true. My primary research focus is not in evolutionary studies, but I am not aware of any system with the degree of complexity that Behe discusses for which there is a complete (or even substantial) account. Behe interprets this as the failure of an attempt; I interpret it as the combined result of the low level of interest in and knowledge of evolution by biochemists and the increased difficulty of such explanations for biochemical systems.
2. Darwinian explanations cannot account for "irreducibly complex" systems. Here is where trouble begins (for me) in being clear about what Behe wants to claim. Taking all his examples together, an "irreducibly complex" system is not just one with an essential element in it, because he discusses some cases which to him do not seem "irreducibly complex" but which do have an essential element. Therefore, there only seem to be two possible senses for this claim: either (A) Darwinian explanations cannot account for "irreducibly complex" systems because we can't think of such explanations, or (B) Darwinian explanations cannot account for "irreducibly complex" systems because they cannot work without all the parts there.
If A is his claim, then this is a claim about all conceivable explanations. Behe shows that several scenarios he tries won't work, but just showing that several don't work isn't the same as showing that none can. If B is his claim, then it amounts to affirming the consequent, i.e., making the thing you want to prove part of the definition. Finally, it is still not clear how to identify which systems are "irreducibly complex" systems and which ones aren't. It would seem that unless this is unambiguous, most of his arguments are hard to support.
3. Intelligent design is the best explanation for "irreducibly complex" systems.
Although it is not clear to me just what qualifies as an "irreducibly complex" system, Behe's claim here is that for such systems intelligent design is the best explanation. Again, this claim depends upon some confidence that we know what the set of possible explanations is, and the relative probabilities of each. Furthermore, Behe wants to claim that "intelligent design" is a meaningful attribute in the absence of any statements about the designer. But it seems that without some specification about what constitutes "a designer" or how "a designer" would act, attributing complex structures to "a designer" is like saying that opium makes you sleepy because of its "soporific powers."
There remain two other concerns about this argument. Behe makes extensive use of referring to the scientific literature itself to give a sense of whether or not scientists examine these questions and what kind of answers they come to. However, it was very surprising to see no discussion of Cairns-Smith's "Seven Clues to the Origin of Life," an excellent book about the origins of life, written several years ago by a senior, and very thoughtful, scientist. Cairns-Smith faces the difficulties of complex systems straightforwardly, and proposes that intermediate steps might be quite different from the final product. He also used analogies well, and his analogy for this part is that of an arch with a keystone. Seeing it standing, you might wonder how it came to stand free of support. However, there could have been an intermediate stage where there was a scaffold that was later removed, and there might be no traces of that scaffold now. Another analogy he used for the transition between types is that of a rope that might be all hemp at one end and be gradually replaced with nylon along its length until by the other end it was all nylon.
I am not saying that Cairns-Smith's book answered all of Behe's concerns. It did, however, address the concerns directly and has a proposed strategy for approaching them. Behe did not discuss it. If it is because the Lehigh library doesn't have it, then Behe's search may be seriously incomplete. If Behe knew about it and did not discuss it, it is a serious shortcoming in his discussion.
I also see considerable potential for misuse of the thesis that Darwinian explanations cannot account for "irreducibly complex" systems. There is an enormous amount known by someone about a great many systems; the last time I looked, Bioabstracts was covering 100,000 articles a year. If people who do not allow any room at all for Darwinian evolution pick Behe's thesis up without thinking hard about it, they may range over the whole body of biological thought, picking up examples incompletely and then claim to have confirmed the argument when that particular point is not answered. The more likely explanation is that people who know enough to answer all, or even most, points that might be raised didn't happen to see the claim made.
In short, an interesting book, a
potentially valuable one if it convinces biochemists to start the hard work of
evolutionary analysis, but in the end one that did not convince me that a new paradigm of
explanation is justified.