Glenn Branch's picture

Falsifiability Dembski-Style, Part 2

Physical model of a bacterial flagellum

Recall that William A. Dembski, in his No Free Lunch (2002), posed the twin questions “Is intelligent design falsifiable? Is Darwinism falsifiable?” and answered, “Yes to the first question, no to the second question.” In part 1, I explained that although the questions are posed in terms of falsifiability, he in fact reformulates falsifiability as refutability (explicitly in The Design Revolution [2004]), claims that “intelligent design” is refutable, and (implicitly) concludes that “intelligent design” is therefore scientific. But, I noted, he fails to ensure that refutability is capable of playing the same role as falsifiability in providing a plausible criterion for what is and what is not scientific. Either it is not so capable (if it is construed so as to classify Popper’s examples of non-sciences as scientific) or (if it is construed to classify Popper’s examples of non-sciences as non-scientific) there is no independent reason to believe that it will classify “intelligent design” as scientific.

Dembski’s answer to the first of his twin questions thus fails. But I thought that I ought to discuss his answer to the second question as well. In No Free Lunch, Dembski claims that “Darwinism” is unfalsifiable “[e]ven with this broadened definition of falsifiability”; in The Design Revolution, he claims that “it seems effectively irrefutable.” Why? The reason is a little hard to understand as given in The Design Revolution:

The problem is that Darwinists raise the standard for refutability too high. It is certainly possible to show that no Darwinian pathway could be reasonably expected to lead to an irreducibly complex biological structure like the bacterial flagellum. But Darwinists want something stronger, namely, to show that no conceivable Darwinian pathway could have led to that structure.

The last sentence is puzzling. It’s hard to understand why a “Darwinist” would want to show that there is no conceivable way for Darwinian processes to produce the bacterial flagellum. Isn’t “Darwinism” all about presuming that Darwinian processes are sufficient unto the day? But if the sentence is understood as making a claim about what the “Darwinist” is willing to acknowledge as a falsification, it begins to make sense.

For Dembski, then, “Darwinism” with regard to the bacterial flagellum is the claim that there is a conceivable way that “Darwinian processes” could have produced the bacterial flagellum. Proving “Darwinism” to be false, therefore, requires showing that there is no conceivable way for “Darwinian processes” to produce the bacterial flagellum. But, Dembski says, “Such a demonstration requires an exhaustive search of all conceptual possibilities and is effectively impossible to carry out.” It would seem to follow that “Darwinism” is unfalsifiable—not necessarily unfalsifiable in the loose sense, i.e. irrefutable in the terminology introduced in The Design Revolution, but at least unfalsifiable in the strict sense. Strangely, Dembski seems never to consider whether “Darwinism,” like “intelligent design,” might be refutable because it is showable to be superfluous; instead, he seems content with the accusation that it’s unfalsifiable.

The problem is that Dembski’s argument for that accusation is precisely the same argument that Behe advanced. Here’s Behe, from “The Modern Intelligent Design Hypothesis” (2001):

The claim of ID is that “No unintelligent process could produce this system.” The claim of Darwinism is that “Some unintelligent process could produce this system.” To falsify the first claim, one need only show that at least one unintelligent process could produce the system. To falsify the second claim, one would have to show the system could not have been formed by any of a potentially infinite number of possible unintelligent processes, which is effectively impossible to do. (emphasis in original)

Here’s Dembski, from chapter 5 of No Free Lunch:

With regard to a particular biochemical system like the bacterial flagellum, intelligent design asserts that “No undirected natural process could produce this system.” By contrast, Darwinism asserts that “Some undirected natural process could produce this system.’’ To falsify the first claim it is enough to exhibit but one causally specific Darwinian pathway capable of producing the system. But how does one falsify the second claim? The Darwinian community seems to assume that to falsify the second claim would require showing that the system could not have been formed by any of a potentially infinite number of Darwinian pathways. Moreover, it places the burden of proof on Darwinism’s detractors, who are then called to run through all those possibilities item by item—clearly an impossible task.

Given the striking resemblance between the passages, it’s reassuring to see that Dembski cites Behe—not “The Modern Intelligent Design Hypothesis,” but a similar discussion that appeared in 2000, in his “Answering Scientific Criticisms of Intelligent Design.”

Now, as I observed in “Falsifia-behe-lity,” Behe’s argument about “Darwinism” involves assaulting a target of straw. Scientists who actually are engaged in investigating the evolutionary history of the bacterial flagellum aren’t interested in what processes could or could not produce the system; they are interested in what processes in fact produced the system. And their hypotheses about those processes are falsifiable; for example, when Mark Pallen and Nicholas J. Matzke suggested in a 2006 paper in Nature Reviews Microbiology that the ur-flagellum arose from mergers between several modular subsystems, they were going out on a limb, empirically: their hypothesis would be falsified by, e.g., the discovery that the flagellum predated those subsystems. Insofar as Dembski’s argument is merely Behe’s, it is not going to fare any better. Is there any added value in No Free Lunch, any extra spin in The Design Revolution?

The only argument, if it can be called that, on offer in Dembski’s books seems to be based on the observation that despite the fact that there is not presently a generally accepted and thoroughly detailed explanation in “Darwinian” terms of the origin of the bacterial flagellum, scientists are confident that such a explanation is in principle possible. (In principle, even if it is ultimately unavailable to us, e.g., if the evidence necessary for distinguishing between alternative scenarios is no longer available due to the passage of time—a common problem in the historical sciences). The observation is reasonable; the conclusion that Dembski bases on it is not. For Dembski regards such confidence as manifesting nothing more than a dogmatic commitment, come what may, to the unfalsifiable doctrine of “Darwinism”: “Darwinism is wonderfully adept at rationalizing its failures and therefore just keeps chugging along.”

But, again, scientists who actually are engaged in investigating the evolutionary history of the bacterial flagellum aren’t interested in “Darwinism” as Dembski and Behe define it; they’re interested in framing and testing hypotheses about what processes in fact produced the bacterial flagellum. Hypotheses that appeal to natural processes are, by and large, testable, so it’s not surprising that those scientists are inclined to concentrate on them. If there were alternatives that were testable, then they would not be necessarily disregarded; there’s no dogma in place. Rather, the proponents of “intelligent design” have consistently failed to present any testable hypotheses of their own, instead hoping to batten on the supposed failures of evolution. In the decision in McLean v. Arkansas (1982), Judge Overton referred to “a contrived dualism” in the creation science movement. It’s alive and well in the “intelligent design” movement.