GET ON THE INTERNET AND READ SOME of the criticisms of Michael Behe's work, and you'll think he is a crank, a fraud and a knave. His work, we are told, has been "thoroughly discredited," "completely demolished" and "utterly destroyed." Critics reluctantly concede that his discussions of biochemistry (Behe's field of expertise) are unobjectionable. But when it comes to his definition and use of irreducible complexity, critics regard him as misguided and safely to be ignored. Critics contend that the biological community has carefully considered Behe's work, found it deeply flawed and therefore rejected it. But in fact the biological community is still coming to terms with Behe's work. Behe has focused attention on a major conceptual problem in evolutionary biology. The problem was noted before, but not in so stark a form.
Behe's challenge has been so unsettling that many in the biological community find it easier to pretend his work has been discredited than actually to engage it. The biology department at one well-regarded evangelical Christian institution is a surprising case in point. Its biology faculty, by last report, remain adamantly opposed to Behe and intelligent design but at the same time have explicitly refused even to read his work lest they dignify it with their time and attention. And so a convenient fiction has emerged in which biologists continually reassure each other that Behe has been refuted but either fail to provide an actual refutation or attack a caricature of Behe's case against Darwinian evolution. Yet to a dispassionate outsider, it's clear that something significant is afoot. If the worst humiliation is not to be taken seriously, then Behe is being taken all too seriously.
Indeed, Behe has attracted a band of vocal and passionate critics who engage him at length. The controversy centers on a book that Behe published in 1996, Darwin's Black Box. This widely influential book opened a great many ideas, central among them the concept of irreducible complexity. As Behe defines it, an integrated multipart functional system is irreducibly complex if removing any of its parts destroys the system's function. Critics have interpreted Behe's use of this concept in one of two ways, neither of which does justice to Behe's project. Thus critics see Behe as making either a purely logical or a purely empirical point. The logical point is this: Certain structures are provably inaccessible to a Darwinian mechanism. They have property P (i.e., irreducible complexity). But certain biological structures also have property P, so they, too, must be inaccessible to a Darwinian mechanism. The empirical point is this: Certain biological structures are awfully complicated. There is not even a suggestion in the literature concerning how the Darwinian mechanism might construct them. So chances are that something beyond natural selection was responsible for their creation.
So stated, these are fundamentally different points and involve very different questions. If Behe seeks to make a purely logical point, then his model needs to be rigorous and mathematical after the fashion of Noam Chomsky's demonstration that, for example, finite state automata are incapable of generating certain languages. If he wishes to make a purely empirical point, then he wastes his time bringing in the notion of irreducible complexity when what he really means is simply that the evolutionary pathways of certain biological objects have yet to be adequately explained. According to critics, the conflation of these two different theses, the logical and the empirical, works rhetorically, but for a bad reason: it suggests in virtue of the sonority of the words irreducible complexity that something rigorous or well-defined is at issue when what is really at issue, provided Behe has abjured the logical point, is what has always been at issue between Darwinists and their critics-the idea that life is simply too complicated to result from a blind, undirected, hit-or-miss, trial-and-error Darwinian process.
According to Darwinists, neither the logical point nor the empirical point nor a conflation of the two poses any challenge to their theory. Let's consider these options in turn. As for the logical point, irreducible complexity clearly cannot close off all logically possible avenues of Darwinian evolution. What irreducible complexity says is that all parts of a system are indispensable in the sense that if you remove a part and don't alter the other parts, you cannot recover the original function of the system. But that leaves the possibility of removing parts and modifying others to recover the original function. Also it leaves the possibility of removing parts and isolating subsystems that serve some other function (a function that could conceivably be subject to selection pressure). Irreducible complexity, treated as a logical restriction, therefore leaves some loopholes for the Darwinian mechanism. (Critics sometimes portray Behe as denying this point, but in fact Behe never denied such logically possible loopholes.)
As for the empirical point, it seems merely to commit the standard fallacy of arguing from ignorance. So what if certain biological systems are incredibly complicated and we haven't figured out how they originated? That doesn't mean the Darwinian mechanism or some other material mechanism didn't do it. It may just mean that we haven't figured out how those mechanisms did it quite yet. And as for conflating the logical and empirical points, that's the most disreputable option of all, for it makes Behe and fellow design theorists guilty of equivocation, of using irreducible complexity to make a logical or empirical point as expedience dictates.
But this is too easy. In fact, Behe's project is more subtle than any of these criticisms suggests. Behe's project is properly conceived as making three key points: a logical, an empirical and an explanatory point. What's more, he conflates none of them. The logical point is this: Certain artificial structures are provably inaccessible to a direct Darwinian pathway because they have property P (i.e., irreducible complexity). But certain biological structures also have property P, so they, too, must be inaccessible to a direct Darwinian pathway. This formulation looks similar to the previous logical point, but it differs in one crucial respect. In the previous formulation, inaccessibility was with respect to the Darwinian mechanism in toto and therefore with respect to all Darwinian pathways whatsoever, both direct and indirect. Here, the restriction is only on direct Darwinian pathways.
A direct Darwinian pathway is one in which a system evolves by natural selection, incrementally enhancing a given function. As the system evolves, the function does not. Thus we might imagine that in the evolution of the heart, its function from the start was to pump blood. In that case a direct Darwinian pathway might account for it. On the other hand, we might imagine that in the evolution of the heart its function was initially to make loud thumping sounds to ward off predators and that only later did it take on the function of pumping blood. In that case an indirect Darwinian pathway would be needed to account for it. Here the pathway is indirect because not only does the system evolve but so does the system's function. Now, as a logical point, Behe was only concerned with direct Darwinian pathways. This becomes immediately evident from reading Darwin's Black Box since in his definition of irreducible complexity, the function of the system in question always stays put.
Does Behe's definition of irreducible complexity render certain structures provably inaccessible to direct Darwinian pathways? As laid out in Darwin's Black Box, Behe's definition actually needed a little fine-tuning. The problem is that Behe didn't address systems that could retain their function by removing parts and then modifying the other parts that remained. (Behe considered only removal, not modification.) But there's a quick fix here, which I describe in chapter five of No Free Lunch, and that is simply to strengthen the concept of irreducible complexity to include a minimal complexity condition. Essentially this condition says that the system cannot be simplified and still retain the level of function needed for selective advantage. With this proviso, irreducible complexity logically rules out direct Darwinian pathways. Note that many of the irreducibly complex systems Behe considers (notably the bacterial flagellum) satisfy this proviso.
In ruling out direct Darwinian pathways to irreducibly complex systems, Behe isn't saying it's logically impossible for the Darwinian mechanism to attain such systems. It's logically possible for just about anything to attain any other thing via a vastly improbable or fortuitous event. For instance, it's logically possible that with my very limited chess ability I might defeat the reigning world champion, Vladimir Kramnik, in ten straight games. But if I do so, it will be despite my limited chess ability and not because of it. Likewise, if the Darwinian mechanism is the means by which a direct Darwinian pathway leads to an irreducibly complex biochemical system, then it is despite the intrinsic properties or capacities of that mechanism. Thus, in saying that irreducibly complex biochemical systems are provably inaccessible to direct Darwinian pathways, design proponents are saying that the Darwinian mechanism has no intrinsic capacity for generating such systems except as vastly improbable or fortuitous events. Accordingly, to attribute irreducible complexity to a direct Darwinian pathway is like attributing Mount Rushmore to wind and erosion. There's a sheer possibility that wind and erosion could sculpt Mount Rushmore, but not a realistic one.
With direct Darwinian pathways ruled out, that leaves indirect Darwinian pathways. Here Behe's point is no longer logical but empirical. The fact is that for irreducibly complex biochemical systems, no indirect Darwinian pathways are known. At best, biologists have been able to isolate subsystems of such systems that perform other functions. But any reasonably complicated machine always includes subsystems that perform functions distinct from the original machine. So the mere occurrence or identification of subsystems that could perform some function on their own is no evidence for an indirect Darwinian pathway leading to the system. What's needed is a seamless Darwinian account that's both detailed and testable of how subsystems undergoing coevolution could gradually transform into an irreducibly complex system. No such accounts are available or forthcoming. Indeed, if such accounts were available, critics would merely need to cite them, and intelligent design would be finished.
Critics of Behe are at this point quick to throw the argument-from-ignorance objection his way, but this criticism can't be justified. A common way to formulate this criticism is to say, "Absence of evidence is not evidence of absence." But as with so many overused expressions, this one requires nuancing. Certainly this dictum appropriately characterizes many everyday circumstances. Imagine, for instance, someone feverishly hunting about the house for a missing set of car keys, searching under every object, casing the house, bringing in reinforcements and then, the next morning, when all hope is gone, finding them on top of the car outside. In this case the absence of evidence prior to finding the car keys was not evidence of absence. Yet with the car keys there was independent evidence of their existence in the first place.
But what if we weren't sure that there even were any car keys? The situation in evolutionary biology is even more extreme than that. One might not be sure our hypothetical set of car keys exist, but at least one has the reassurance that car keys exist generally. Indirect Darwinian pathways are more like the supposed leprechauns that Johnny is certain are hiding in his room. Imagine this child were so ardent and convincing that he set all of Scotland Yard, indeed some of the best minds of the age, onto the task of searching meticulously, tirelessly, decade after decade, for these supposed leprechauns, for any solid evidence at all of their prior habitation of the bedroom. And then imagine that in all those decades, the detectives, driven by gold fever for the leprechaun's treasure, let's say, never flagged in searching out and postulating new ways of catching a glimpse of a leprechaun, a leprechaun hair, a leprechaun fingerprint, any solid clue at all. After these many decades, with not a single solid clue to show for all that work, what should one say to the aging parents of the now aging boy if these parents decided there were no leprechauns in the boy's room? Would it be logical to shake your finger at the parents and tell them, "Absence of evidence is not evidence of absence. Step aside and let the experts get back to work." That would be absurd. And yet that, essentially, is what evolutionary biologists are telling us concerning that utterly fruitless search for credible indirect Darwinian pathways to account for irreducible complexity.
If after repeated attempts you don't find what you expect to find after looking in all the right places and if you never had any evidence that the thing you were looking for existed in the first place, then you have reason to think that the thing you are looking for doesn't exist at all. That's precisely Behe's point about indirect Darwinian pathways. (See his chapter in Darwin's Black Box titled "Publish or Perish.") It's not just that we don't know of such a pathway for, say, the bacterial flagellum (the irreducibly complex biochemical machine that has become the mascot of the intelligent design movement). It's that we don't know of such pathways for any such systems. The absence here is pervasive and systemic. That's why critics of Darwinism like Franklin Harold and James Shapiro (neither of which is an intelligent design supporter) argue that positing as-yet-undiscovered indirect Darwinian pathways for such systems constitute "wishful speculations."
Behe's logical point is that irreducible complexity renders biological structures provably inaccessible to direct Darwinian pathways. Behe's empirical point is that the failure of evolutionary biology to discover indirect Darwinian pathways leading to irreducibly complex biological structures is pervasive and systemic, and that such a failure is reason to doubt that indirect Darwinian pathways are the answer to irreducible complexity. The logical and empirical points together constitute a devastating indictment of the Darwinian mechanism, which has routinely been touted as capable of solving all problems of biological complexity once an initial life form is on the scene. Even so, the logical and empirical points together don't answer how one gets from the failure of Darwinism to account for irreducibly complex systems to the legitimacy of employing design to account for them.
This is where the third main point of Behe's project-Behe's explanatory point-comes in. Scientific explanations come in many forms and guises, but the one thing they cannot afford to be without is causal adequacy. A scientific explanation needs to invoke causal powers sufficient to explain the effect in question. Otherwise, the effect is unexplained. The effect in question for Behe is the irreducible complexity of certain biochem ical machines. How did such systems come about? Not by a direct Darwinian pathway, for irreducible complexity rules that out on logical grounds. And apparently not by indirect Darwinian pathways either, for the absence of scientific evidence here is complete. (Critics who claim otherwise are bluffing.) What's more, appealing to unknown material mechanisms is even more tenuous.
Thus, when it comes to irreducibly complex biochemical systems, there's no evidence that material mechanisms are causally adequate to bring them about. But what about intelligence? It is well known that intelligence produces irreducibly complex systems. (For example, humans regularly produce machines that exhibit irreducible complexity.) Intelligence is thus known to be causally adequate to bring about irreducible complexity. Behe's explanatory point, therefore, is that on the basis of causal adequacy, intelligent design is a better scientific explanation than Darwinism for the irreducible complexity of biochemical systems.
Behe's logical and empirical points are mainly negative: they focus on limitations of the Darwinian mechanism. Behe's explanatory point, by contrast, is positive: it provides positive grounds for thinking that irreducibly complex biochemical systems are in fact designed. One question about these points is now likely to remain. Behe uses the logical point to rule out direct Darwinian pathways and the empirical point to rule out indirect Darwinian pathways to irreducible complexity. But the absence of empirical evidence for direct Darwinian pathways leading to irreducible complexity is as complete as for indirect Darwinian pathways. It might seem, then, that the logical point is superfluous inasmuch as the empirical point dispenses with both types of Darwinian pathways. But in fact the logical point helps tighten the noose around Darwinism in a way that the empirical point can't.
If you look at the best confirmed examples of Darwinian evolution in the literature (from Darwin to the present), what you find is natural selection steadily improving a given feature that is performing a given function in a given way. Indeed, the very notion of "improvement" (which plays such an important role in Darwin's Origin of Species) typically connotes that a given thing is getting better in a given respect. Improvement in this sense corresponds to a direct Darwinian pathway. By contrast, an indirect Darwinian pathway (where one function gives way to another function and thus can no longer improve because it no longer exists), though often inferred by evolutionary biologists from fossil or molecular data, tends to be much more difficult to establish rigorously.
The reason is not hard to see: By definition natural selection selects for preexisting function. It cannot select for future function. Once a novel function is realized, the Darwinian mechanism can select for it as well. But making this transition is the hard part. How does one evolve from a system exhibiting a preexisting selectable function to a new system exhibiting a novel selectable function? Natural selection is no help here, and all the weight is on random variation to come up with the right and needed modifications during the crucial transition time when functions are changing (or, as Darwin put it in his Origin of Species, "unless profitable variations do occur, natural selection can do nothing"). The actual evidence that random variation can produce the successive modifications needed to evolve irreducible complexity is nil.
Behe's logical point about irreducible complexity ruling out direct Darwinian pathways therefore rules out the form of Darwinian evolution that is best confirmed. What's more, it rules out the only form of Darwinian evolution that is open to logical analysis. Indirect Darwinian pathways, by contrast, are so open-ended that no logical analysis is capable of constraining them. (Almost invariably they are left unspecified, thus rendering them neither falsifiable nor testable.) Behe's logical point therefore takes logic as far as it can in constraining the Darwinian mechanism and leaves empirical considerations to rule out what remains. And since logical inferences are inherently stronger than empirical inferences, Behe has made his critique of the Darwinian mechanism as strong and tight as possible. It's not just that certain biological systems are so complex that we can't imagine how they evolved by Darwinian pathways. Rather, we can show conclusively that they could not have evolved by direct Darwinian pathways and that indirect Darwinian pathways, which have always been on much less stable ground, are utterly without empirical support.
To sum up, Behe is significant in the debate between intelligent design and Darwinism because he has taught us how to evaluate the relative merits of each. He has done this by giving us the concept of irreducible complexity and by showing us how to employ it. By carefully analyzing and disentangling the logical, the empirical and the explanatory implications of irreducible complexity for the Darwinian mechanism, Behe has demonstrated that intelligent design is at the very least a viable contender in any attempt to explain the irreducible complexity of biochemical systems. What's more, he has shown how to bridge the scientific theory of design with our commonsense intuitions about design. In media reports on intelligent design, one often hears the following sound bite: "Life is too com plicated to have arisen by natural forces, so it must have been designed." This sound bite captures many people's intuitions about intelligent design, but it is too simplistic for scientific purposes. Behe has shown us how to interpret this claim, substituting the rigorously defined phrase irreducibly complex for the vague and undefined phrase too complicated, and he has shown us how to reason our way properly from the inadequacy of undirected natural forces to design.
THE DESIGN REVOLUTION
ANSWERING THE TOUGHEST QUESTIONS ABOUT INTELLIGENT DESIGN
William A. Dembski
