A Review of Darwin's Black Box: The Biochemical Challenge to Evolution, by Michael J. Behe
This review originally appeared in the September-October 1997 issue of American Scientist.
Darwin's Black Box: The Biochemical Challenge to Evolution Michael J. Behe. 307 pp. The Free Press, 1996. $24.50.
"Will you honestly tell me (and I should be really much obliged) whether you believe that the shape of my nose was ordained and 'guided by an intelligent cause?'" In exasperation, but not without humor, Charles Darwin posed this question to Charles Lyell in 1860, the year Darwin dealt with the maelstrom unleashed by the publication of The Origin of Species. In both the popular and the scientific press, Darwin had to contend with the wrath of those for whom the notion of a living world based on accident, time and natural selection was simply too disquieting. Look around, Darwin's critics argued, and see the evidence of design. And where there is design, there must be a designer.
One hundred thirty-six years later, this argument makes a reappearance in Michael Behe's Darwin's Black Box. Adorned this time around with the language of molecular biology, spiced up with charges of a conspiracy of scientists, masquerading as an appeal for truth and not for theology, it is nonetheless the same old thing: There cannot be design without a designer. Although I do not doubt the sincerity of the author, nor scoff at his unease with a world apparently lacking purpose, the case for intelligent design put forth in Darwin's Black Box is built on some deep misunderstandings about evolution, molecular organization and, ultimately, about the nature of scientific inquiry. Because of these misperceptions, not a blow is landed on the central, radical claim of Darwinian thinking: Biological order and design emerge from the workings of the evolutionary process and not from the hand of a designer.
This book will, no doubt, find its defenders. Those who are uneasy with a materialist explanation of the living world will welcome this attack on the Darwinian worldview. But as a practicing biologist, and a card-carrying molecular evolutionist, I cannot but find the premise of this book—that molecular discoveries have plunged a wooden stake through the heart of Darwinian logic—ludicrous. This book tells me that the field of molecular evolution has "grown stale from a lack of viable solutions to dead end problems." Worse yet, it appears that the endeavor "has been moribund for decades" and that "molecular evolution is not based on scientific authority ... the assertion of Darwinian molecular evolution is merely bluster." And all this time I have been thinking that this is probably the golden age of evolutionary biology (although 1860 and the early years of the Modern Synthesis in the 1940s were probably not bad, either). For the first time we have molecular methods that allow the generation of massive amounts of detailed data relevant to a host of evolutionary questions. We have techniques that allow us to follow the control and expression of single genes in living organisms. We can now move genes from one species to another to test their function in a novel genetic context. Computational power now allows us to compare tens of thousands of DNA sequences to one another in search for conserved motifs, shared functions and common ancestry. We can carry out simulations of complex biological phenomena and find solutions to quantitative problems that seem to defy analytic solutions. Not bad at all, I thought.
What then is Behe's argument? The central point of Darwin's Black Box is not always easy to spot, but it appears to rely on Behe's notion of irreducible complexity. Molecular systems, defined to include both linked sets of biochemical reactions (the clotting cascade) and aspects of cellular organization (cilia and flagella), for example, are apparently "irreducibly complex": They only work when all the pieces are in place and finely tuned. Any single component, on its own, is useless. If there is a single missing piece, the whole apparatus ceases to function, like a mousetrap without a spring. Such complex mechanisms, argues Behe, could not have arisen "in a Darwinistic manner." Their complexity shows an intelligent designer at work. But this is a conclusion reached only by stacking misunderstandings of the evolutionary process upon misrepresentations of the practice of evolutionary biology. I emphasize six fallacies inherent in Behe's claim, although there are many others where these came from.
Fallacy one: There is a boundary between the molecular world and other levels of biological organization.
By the author's own admission, the Darwinian argument appears to suffice in accounting for design at visible levels of organization—bird flight or the hydrodynamic design of aquatic organisms. Only at the molecular level does the argument somehow fail. But, in fact, there is no fundamental discontinuity between the molecular and the supramolecular level in biology. The traditions, tools and approaches of the molecular biologist may differ radically from those of the functional morphologist, but the fabric of living systems is seamless. There is nothing that makes design at the molecular level any more special than design or organization at any other level in biology. If anything, molecular design may be somewhat easier to account for, because the components of molecular machines are frequently the products of identifiable genes.
Fallacy two: The current utility of a given feature (molecular or otherwise) explains "why" the feature originally evolved.
By this logic, if a particular protein is part of a complex system—say, the eye—that protein must have arisen to play a role in the incipient eye. But we know this is not the case. Many of the proteins in the eye lens, for example, begin their careers doing something completely different and unrelated to vision. Evolution is a creative scavenger, taking what is available and putting it to new use. The correct metaphor for the Darwinian process is not that of a First World engineer, but that of the Third World auto mechanic who will get your car running again, but only if parts already lying around can be used for the repair. Ironically, it is at the molecular level that this recycling of available parts is most apparent. My current favorite example (of many available) is the discovery that a gene complex originally involved in specifying the pattern of segmentation in insects has now been found to assist in the proper development of the vertebrate hindbrain (a structure that has no counterpart in segmented insects). This homeotic complex of genes is an exquisite piece of molecular machinery, precisely of the sort that the author finds so imponderable in a Darwinian world. Once the origin and the current role of the homeotic complex are disentangled, the problem vexing Behe—"...biochemical systems cannot be built up by natural selection working on mutations: no direct gradual route exists to these irreducibly complex systems"—simply disappears. Then we can see that just as the aging home-run hitter is drafted to be the designated hitter, the homeotic complex that helps guide the development of the vertebrate hindbrain predates the vertebrates by hundreds of millions of years. The homeotic complex did not evolve to regulate hindbrain development, it was recruited. In fact, homeotic complexes have been recruited over and over again wherever delicate control of gene expression is required. Design-from-scratch and direct routes are not luxuries afforded to the evolutionary process.
Fallacy three: Unless we can identify advantages for each imaginary gradual step leading to a contemporary bit of biochemistry, we cannot invoke a Darwinian explanation.
There has always been a version of popular evolution that consists of identifying some curious feature of the living world, speculating on why that feature might be "good for the organism" and imagining how that feature may have come to pass. Any one of us can come up with multiple, plausible stories concerning the evolution of a given biological feature. But plausibility is about the weakest criterion one can apply to an evolutionary hypothesis. Evolutionary biology may finally be coming of age precisely because we are moving away from particularistic, speculative scenarios—the just-so stories. The rigorous testing of evolutionary hypotheses depends on the use of comparative data, on an understanding of mechanism and, increasingly, on the experimental manipulation of components of the system. It does not (see fallacy two) depend on inventing an "advantage" for a partially evolved flagellar motor. In a narrow sense, Behe is correct when he argues that we do not yet fully understand the evolution of the flagellar motor or of the clotting cascade. Unsolved questions, however, are the hallmark of an exciting science.
Fallacy four: Molecular evolution: "a lot of sequences, some math, and no answers."
In a peculiar quest for an article or book that "tells us how specific biochemical structures came to be," Behe has made glancing contact with the literature of my field. What he has found apparently dismays him. The basic tools of the trade—the comparative analysis of sequences and structures, the mathematical modeling of the evolutionary process and the experimental generation of biologically relevant molecules in abiotic systems—are summarily dismissed. What then is left? Would the accumulating evidence that myriad novel molecular functions for proteins and nucleic acids can be evolved (not engineered) in vitro count as evidence against intelligent design? How about the observation in real time of the acquisition of antibiotic resistance by bacteria? Drug resistance by viruses? Herbicide resistance by weeds? I suspect that in the end nothing would cause the author to abandon his commitment to intelligent design.
Fallacy five: There is a conspiracy of silence among scientists concerning the failure of Darwinian explanation.
Anyone who has ever attended a scientific meeting will find the notion of a conspiracy of silence—well, unlikely. The meetings I go to are usually characterized by N scientists voicing at least N+1 opinions on the topic at hand. When Behe reviews the indices of several major biochemistry textbooks and finds that fewer than one percent of the entries deal with evolution, I fear he may be onto something: Molecular biologists and biochemists often have no training in evolution. Given my conference experience, however, that does not always stop them from voicing a personal opinion about the evolutionary process. But like my personal opinions about the analysis of detailed crystallographic data, such opinions should not be mistaken for expertise.
Fallacy six: The evolution of complexity is unaddressed and unexplained.
The very definition of complexity, and the rules that govern its emergence, are indeed critical issues in evolutionary biology. But the problem becomes deeply uninteresting if the only legitimate approach to solving it is the demonstration of "a direct, gradual route [leading to] irreducibly complex systems." We are still deciding how to measure complexity, debating whether the history of life shows a tendency toward increased complexity and arguing about whether biological organization is but a subset of the larger problem of order and complexity. We do not as yet know what form the answers will take, but mathematical models, computational simulations and, increasingly, experimental results suggest that complexity and organization may be inexorable outcomes in multicomponent systems. If our hypotheses about complexity are to be of any use, however, they will have to be materialist explanations grounded in material cause.
I've often wondered why the argument from design so appeals to engineers and chemists. I suspect that the problem derives from the day-to-day experience of these professions. Engineers and chemists know that they do not get a desired outcome—stable bridge or purified compound—from random inputs, time and a statistical principle for differential representation. In these professions, there is no design without a designer, no desired outcome without careful and intelligent planning. But personal experience is not always the best guide.
Behe's argument for intelligent design ultimately fails because it is a belief and not a potential explanation. The hand of God may well be all around us, but it is not, nor can it be, the task of science to dust for fingerprints.