Behe’s bait and switch: on the falsifiability of intelligent design

Michael Behe. Image from Uncommon Descent.

Michael Behe. Image from Uncommon Descent.

In a post on Evolution News and Views, Michael Behe sidesteps criticisms that intelligent design is not scientific with a bit of verbal judo. By conflating falsification of particular claims with falsification of intelligent design in general, he seems to back his critics into a rhetorical corner:

Now, one can’t have it both ways. One can’t say both that ID is unfalsifiable (or untestable) and that there is evidence against it. Either it is unfalsifiable and floats serenely beyond experimental reproach, or it can be criticized on the basis of our observations and is therefore testable. The fact that critical reviewers advance scientific arguments against ID (whether successfully or not) shows that intelligent design is indeed falsifiable.

However, the examples he gives are of people trying to falsify particular arguments, and this is a monumental difference.

In fact, my argument for intelligent design is open to direct experimental rebuttal. Here is a thought experiment that makes the point clear. In Darwin’s Black Box (Behe 1996) I claimed that the bacterial flagellum was irreducibly complex and so required deliberate intelligent design. The flip side of this claim is that the flagellum can’t be produced by natural selection acting on random mutation, or any other unintelligent process. To falsify such a claim, a scientist could go into the laboratory, place a bacterial species lacking a flagellum under some selective pressure (for mobility, say), grow it for ten thousand generations, and see if a flagellum — or any equally complex system — was produced. If that happened, my claims would be neatly disproven.

Okay, first of all let’s look just how unreasonable that last suggestion is: 10,000 bacterial generations is a few years…in E. coli, in the conditions of Richard Lenski’s Long Term Evolution Experiment, that would be a bit over four years. Let’s say that ancient bacteria living in suboptimal conditions reproduced a hundred times slower. No one who actually understands the concept of deep time has ever seriously claimed that the bacterial flagellum evolved in a few hundred years. The time available for bacteria to evolve a flagellum, given the constraints of the geological record, was probably on the order of hundreds of millions of years. Even if we remove a few orders of magnitude for shorter generation times, consistent selective pressures, etc., we’re talking about an experiment lasting hundreds of thousands of years. I don’t know of any funding agencies that award grants that long.

More to the point, though, falsifying intelligent design as a factor in the origin of bacterial flagella would not falsify intelligent design in general. Dr. Behe anticipates this criticism:

How about Professor [Jerry] Coyne’s concern that, if one system were shown to be the result of natural selection, proponents of ID could just claim that some other system was designed? I think the objection has little force. If natural selection were shown to be capable of producing a system of a certain degree of complexity, then the assumption would be that it could produce any other system of an equal or lesser degree of complexity. If Coyne demonstrated that the flagellum (which requires approximately forty gene products) could be produced by selection, I would be rather foolish to then assert that the blood clotting system (which consists of about twenty proteins) required intelligent design.

This answer is totally unsatisfying. I think if one of Dr. Lenski’s former postdocs evolved a bacterial flagellum in the lab, shifting focus to another complex system is exactly what cdesign proponentsists would do. But that’s not the point. The point is that intelligent design, as Behe himself describes it, is in principle impossible to falsify:

By “intelligent design” I mean to imply design beyond the laws of nature. That is, taking the laws of nature as given, are there other reasons for concluding that life and its component systems have been intentionally arranged? In my book, and in this essay, whenever I refer to intelligent design (ID) I mean this stronger sense of design-beyond-laws. [emphasis added]

By redirecting the argument about falsifiability from intelligent design in general to particular claims, Dr. Behe has attributed to his critics a contradiction that does not exist. Arguments and evidence that the bacterial flagellum evolved through natural processes could not possibly falsify intelligent design; at best, they could falsify the claim that ‘design beyond the laws of nature’ was involved in the origin of the flagellum. Ditto for water balance, sodium content, potassium content, cardiovascular function, blood pressure, blood flow, blood clotting, the adaptive immune system, glucose control, thermoregulation, bone formation, male sexual function, female sexual function, kidney function, thyroid functioneyes, ears, balance, reflexes, ATP synthaseserpin antithrombin IIIFlavobacterium motility, Archaeal motilityCRISPR-associated complex for antiviral defense, the Type IV secretion systemmRNA regulation, ribosomesbacterial sporulation, and insect metamorphosis, Does anyone really believe that if one of those systems were re-evolved in the lab, everyone at the Discovery Institute would say “Well, I guess we were wrong”? Of course not.

Falsifying a supernatural role in each of those cases would falsify intelligent design only for that case. And how would you do that in the first place? Dr. Behe admits (in The Edge of Evolution) that there is “…great evidence that random mutation paired with natural selection can modify life in important ways,” so his view is that life’s diversity and complexity are best explained by a combination of natural and supernatural processes. In fact, I think that’s a fair summary of intelligent design in general. So to falsify intelligent design for a particular example, it’s not enough to show that natural processes are mainly responsible for its origin. No, you’d have to show that supernatural causes played no role at all, no matter how minor.

Even if you had the complete evolutionary history of a trait – if you knew when each relevant mutation occurred, in which individual, and had the complete genealogy showing how each spread through the population – how could you demonstrate that some, or even one, of those mutations weren’t caused by supernatural intervention? And if you could, you’d only have ruled out a supernatural role in the origin of that trait. To falsify intelligent design, you’d have to show that supernatural causes had no role, not just in the origin of a given system, but in any component of any system, in any species, ever.

And what about Dr. Behe’s counterclaim, that it’s Darwinism, not intelligent design, that is unfalsifiable:

Let’s turn the tables and ask, how could one falsify the claim that, say, the bacterial flagellum was produced by Darwinian processes?

Show that a supernatural cause was involved. Ever. In any system. In any species. Demonstrate that a mutation involved in the origin of a complex system was triggered by a supernatural cause. That one of its bearers survived or found a mate because of a supernatural cause. That a sperm bearing the mutant allele reached the egg first because of a supernatural cause. If you could do that, we would have to admit that life’s diversity and complexity are best explained by a combination of natural and supernatural processes.

But no one ever has.


Stable links:

Behe M J 2001. Reply to my critics: a response to reviews of Darwin’s Black Box: The Biochemical Challenge to Evolution. Biology and Philosophy 16:685–709.

Behe M J 2007. The Edge of Evolution: The Search for the Limits of Darwinism (New York: Free Press).


  1. sonofrojblake says

    My hobby: going into bookshops, taking Michael Behe books from the “Popular Science” section (where they’re typically found) and reshelving them in the “Religion and Spirituality” section where they belong.

  2. Menyambal says

    I just worked out a series of viable steps from a fixed cilia to a rotary flagellum, and I’m still in bed with one eye open.

  3. Anton Mates says

    One can’t say both that ID is unfalsifiable (or untestable) and that there is evidence against it.

    Sure one can, because ID involves more than one claim.

    The claim that living organisms were designed by an intelligent supernatural being (or an intelligent being whose powers and intentions are completely unspecified, which amounts to the same thing) is unfalsifiable.

    The claim that there exists scientific evidence supporting the previous claim is falsifiable, and many instances of this have been falsified.

    Without the second claim, it’s not ID; it’s just theism, and of course plenty of theists accept evolutionary theory. It’s the second claim that takes it from irrelevant to wrong, scientifically speaking.

  4. EnlightenmentLiberal says

    I’ll take the stronger position that you can falsify intelligent design outright, and that is has been falsified, along with the rest of supernatural claims.

    The following paper includes the simple and obvious argument that every supernatural explanation in the past has never born out, or it’s been falsified, and investigations into “natural” causes and mechanisms has worked out pretty well, and therefore, the only reasonable conclusion is that there are no supernatural forces.
    > How not to attack Intelligent Design Creationism: Philosophical misconceptions about Methodological Naturalism
    > (final draft – to appear in Foundations of Science)
    > Maarten Boudry, Stefaan Blancke, Johan Braeckman

    In the following blog post, PZ Myers makes much the same argument through metaphor.

    Sean Carroll makes a particular and stronger form of this argument, which is that with the discovery of the Higgs Boson, the standard model of physics is complete, and the fundamental physics of everyday life is entirely known, and there is no room in known physics for supernatural forces due to the math and rules of quantum field theory and the standard model. The only way to insert supernatural forces is to invoke special pleading, contrary to all accumulated evidence. Sean Carroll makes this argument in several places IIRC, including this public talk / lecture:
    > Particles, Fields and The Future of Physics – A Lecture by Sean Carroll

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