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Michael Behe’s Critics Misunderstand Irreducible Complexity and Make Darwinian Evolution Unfalsifiable

Casey Luskin

When Michael Behe published a paper in Quarterly Review of Biology (QRB) in December, 2010, the journal’s editors apparently felt compelled to also publish in the same issue a companion article, titled “Irreducible Incoherence and Intelligent Design — a look into the conceptual toolbox of a pseudoscience.” The title alone gives a hint at its rhetorically charged nature.

The paper apparently serves as QRB‘s penance for publishing Michael Behe’s paper, which had far more measured arguments. The authors of the anti-Behe paper, Maarten Boudry, Stefaan Blancke, and Johan Braeckman, claim that Behe “switches” definitions of irreducible complexity from an absolute argument to a probabilistic argument to avoid criticisms. But they misunderstand that from the very beginning in Darwin’s Black Box, Behe’s argument (like most scientific arguments) was probabilistic.

Specifically they charge:

Precisely because the bacterial flagellum is IC, Behe tells us, it could not have evolved by means of random mutation and natural selection. However, when critics object that the system’s components may well be able to perform other functions in other contexts, thus pointing to the possibility of indirect evolutionary pathways, Behe switches back to the weak definition and claims that his critics have misrepresented his argument.

Reality is very different. Behe’s definition of irreducible complexity was always intended to test a Darwinian explanation where some function is built up gradually over time — a direct evolutionary pathway. Boudry, Blancke and Braekman rightly observe that critics have claimed in response to Behe that indirect evolutionary pathways were possible.

Like their other bluffs, it might sound like the critics explained the origin of irreducible complexity — but that’s only true if such indirect pathways are plausible. In fact, Behe never “switches” arguments: somehow Boudry, Blancke and Braekman miss the conspicuous fact that Behe addresses this very objection on the very next page of Darwin’s Black Box after he defines irreducible complexity. As Behe wrote:

Even if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitively rule out the possibility of an indirect, circuitous route. As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously. And as the number of unexplained, irreducibly complex biological systems increases, our confidence that Darwin’s criterion of failure has been met skyrockets toward the maximum that science allows

(Michael Behe, Darwin’s Black Box, p. 40 (Free Press, 1996).))

The charges of Boudry, Blancke and Braekman are based upon a fundamental misconstrual of Behe’s original argument in Darwin’s Black Box.

Behe’s original argument for irreducible complexity was always probabilistic, meaning that like all claims in science, one never gets 100% proof. You never absolutely rule out with 100% certainty the possibility of an indirect evolutionary route. But science doesn’t deal in the currency of absolutes. Is that Behe’s problem or the neo-Darwinian evolutionists’ problem? It’s the evolutionists’ problem because they claim these structures evolved by unguided mechanisms, and then they promote wildly speculative, perhaps even untestable indirect evolutionary pathways, to back that claim.

If the indirect evolutionary pathway is so unlikely or impractical that it would never occur in nature, then evolutionists have only escaped refutation by irreducible complexity by promoting a widely speculative and untestable hypothesis. In essence, they have put Darwinian evolution in an unfalsifiable position.

Behe’s view doesn’t require absolute falsification. His view is that a direct Darwinian pathway is effectively falsified by the presence of irreducible complexity, not absolutely falsified. Perhaps indirect routes are possible (in the same way that anything is possible), but possible does not mean plausible, or likely.

This has been Behe’s point all along: the inability to achieve 100% refutation of a wildly speculative indirect evolutionary scenario does not mean that irreducible complexity is invalid. To argue such is to hold irreducible complexity to an unreasonably high standard. To the contrary, the fact that evolutionists are forced to respond to Behe with such tenuous and speculative stories of indirect evolution shows the strength of the argument for irreducible complexity. Behe makes this precise point in Science and Evidence for Design in the Universe, Proceedings of the Wethersfield Institute:

[O]ne needs to relax Darwin’s criterion from this: “If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.” to something like this:

If a complex organ exists which seems very unlikely to have been produced by numerous, successive, slight modifications, and if no experiments have shown that it or comparable structures can be so produced, then maybe we are barking up the wrong tree. So, LET’S BREAK SOME RULES!

Of course people will differ on the point at which they decide to break rules. But at least with the realistic criterion there could be evidence against the unfalsifiable. At least then people like Doolittle and Miller would run a risk when they cite an experiment that shows the opposite of what they had thought. At least then science would have a way to escape from the rut of unfalsifiability and think new thoughts.

(Michael Behe, “Answering Scientific Criticisms of Intelligent Design,” Science and Evidence for Design in the Universe, Proceedings of the Wethersfield Institute, Vol 9:146-147 (Ignatius Press, 2000).)

It seems that Boudry, Blancke and Braekman misunderstand both Behe’s argument and the nature of the scientific process: the fact that a theory (in this case, Darwinism) can be saved from refutation by proposing wildly speculative and unfalsifiable scenarios does not mean that theory holds merit. Here, the fact that Behe grants that wildly speculative scenarios involving indirect evolution are still minutely possible does not mean that his argument is invalidated. Rather, it means that the argument for irreducible complexity holds merit, and that Darwinian explanations are effectively falsified.

That that critics refuse to accept falsification it also means that critics are placing Darwinian evolution in an effectively unfalsifiable position, where no level of complexity can falsify it. Proponents of Darwinism are effectively arguing that if an explanation is merely possible, then it defeats counter-arguments. As David Abel writes, this is an unhealthy state for science:

Mere possibility is not an adequate basis for asserting scientific plausibility. A precisely defined universal bound is needed beyond which the assertion of plausibility, particularly in life-origin models, can be considered operationally falsified. … But at some point our reluctance to exclude any possibility becomes stultifying to operational science. Falsification is critical to narrowing down the list of serious possibilities. Almost all hypotheses are possible. Few of them wind up being helpful and scientific ally productive. Just because a hypothesis is possible should not grant that hypothesis scientific respectability. More attention to the concept of “infeasibility” has been suggested. Millions of dollars in astrobiology grant money have been wasted on scenarios that are possible, but plausibly bankrupt. The question for scientific methodology should not be, “Is this scenario possible?” The question should be, “Is this possibility a plausible scientific hypothesis?” One chance in 10200 is theoretically possible, but given maximum cosmic probabilistic resources, such a possibility is hardly plausible. With funding resources rapidly drying up, science needs a foundational principle by which to falsify a myriad of theoretical possibilities that are not worthy of serious scientific consideration and modeling.

(David L. Abel, “The Universal Plausibility Metric (UPM) & Principle (UPP),” Theoretical Biology and Medical Modelling, Vol. 6:27 (Dec. 3, 2009).)

Boudry, Blancke and Braekman seem to anticipate this sort of response, stating:

A first strategy to this end consists of shifting the burden of proof from plausible evolutionary pathways to the actual evolutionary story, and thus to protest that the broad outlines of a plausible evolutionary account amount to nothing more than Darwinian wishful thinking and speculation. The same bait-and-switch technique can be discerned here: IC is constantly boasted as a point of principle for ruling out the possibility of evolutionary explanations, but as soon as it is challenged on that ground through a discussion of plausible evolutionary scenarios, ID creationists contend that they were talking about actual evolutionary pathways all along.

They might have had a point if indirect evolutionary pathways had been demonstrated to actually be plausible scientific arguments. But that’s the problem with the claim that multiple parts can come together from different systems to spontaneously form complex multipart systems: such explanations aren’t scientifically plausible. They do not defeat counter-arguments to Darwinian evolution like irreducible complexity.

The critics need to remember David Abel’s words that “[m]ere possibility is not an adequate basis for asserting scientific plausibility.” Boudry, Blancke and Braekman confuse mere possibility with scientific plausibility. They can’t claim to have explained the evolutionary origin of irreducible complexity when their “explanation” is in fact little more than wishful thinking and wild speculation.

In my final response to Behe’s critics in QRB, I’ll show more evidence that they are not interested in subjecting Darwinian evolution to any realistic form of testing.


Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



Michael Behe