Just last week an article turned up at the Australian Broadcasting Corporation, “The bacterial flagellar motor: brilliant evolution or intelligent design?,” by a biophysicist named Matt Baker, claiming to refute irreducible complexity. Has Baker finally solved the riddle of answering Behe’s challenge to Darwinian evolution? No, it’s pretty much the same stuff we’ve heard before, with maybe a variation or two that are original to Matt Baker.

Well, since these perennial objections are indeed perennial, I would like to answer them again, using Dr. Baker as my example. We’ll see that IC remains as potent a weapon in ID’s arsenal as it was in 1996.

The article purports to explain how the bacterial flagellum is the result of Darwinian evolution rather than intelligent design. But the author badly misunderstands both how we test for irreducible complexity and what it means to provide a Darwinian explanation. He is also apparently unaware of the many reasons why the Type III Secretory System could not have been a precursor to the flagellum.

The article’s first error comes in the sub-headline, which states:

"Luckily, individual components of the bacterial flagellar motor have indeed been found elsewhere. And they work. So the motor is ‘reducible’, and certainly not ‘irreducibly complex’."

First of all, it’s not the case that all “individual components” of the flagellum have been found elsewhere. But even if they had, that would not necessarily mean that the motor is “reducible” and “not ‘irreducibly complex.'” In any case, Baker goes on to state:

"A central tenet of this theory is the notion of ‘irreducible complexity’. This asserts that some biological machines — like the flagellar motor — must be the product of design, because if you were to remove one or two components from the motor it would not function properly, or at all. The logic being, this motor was designed as a whole construction — it didn’t evolve through a series of steps, so the individual parts of the motor would serve no purpose on their own.So the creationist argument relies on us finding no evidence of individual parts of the motor having a role outside of bacterial flagella."

Ignoring the gratuitous “creationist” jab, his argument is self-contradictory. On the one hand he says (correctly) that irreducible complexity means that a system “didn’t evolve through a series of steps.” But he then wrongly claims that this implies “the individual parts of the motor would serve no purpose on their own” or that irreducible complexity “relies on us finding no evidence of individual parts of the motor having a role outside.”

The former claim is a great description of irreducible complexity; the latter is a straw man test, which has nothing to do whatsoever with the concept. Dr. Baker should read my article “Do Car Engines Run on Lugnuts? A Response to Ken Miller & Judge Jones’s Straw Tests of Irreducible Complexity for the Bacterial Flagellum,” which addresses this common misconception. I explain there that Michael Behe formulates irreducible complexity as a test of building an entire system in a stepwise manner. IC relates to the functionality of a collection of parts, not the function (or possible functions) of each individual part. Even if a separate function could be found for a sub-system or sub-part, that would not refute the irreducible complexity of the whole, nor would it demonstrate the evolvability of that entire system. Here’s how Behe defines IC:

"In The Origin of Species Darwin stated:

“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.”

A system which meets Darwin’s criterion is one which exhibits irreducible complexity. By irreducible complexity I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.(Michael Behe, Darwin’s Black Box, pg. 39 (Free Press, 1996).)"

According to Darwin himself, Darwinian evolution requires that a system be functional along each small step of its evolution. One could find a sub-part that could be useful outside of the final system, yet the total system would still face many points over its “evolutionary pathway” where it could not remain functional through “numerous, successive, slight modifications.” Thus, Baker mischaracterizes Behe’s argument as one that focuses on the non-functionality of sub-parts, when in fact, Behe actually focuses on the ability of the entire system to assemble in a stepwise fashion, even if sub-parts can have functions outside of the final system.To further understand how Baker’s test fails, consider the example of a car engine with its nuts and bolts. Car engines use many kinds of bolts, and a nut or a bolt could be seen as a small “sub-part” or “sub-system” of a car engine. Under this logic, if a vital nut in my car’s engine might also perform some other function — perhaps as a lug nut — then it follows that my car’s whole engine system is not irreducibly complex. Such an argument is obviously fallacious.

In assessing whether an engine is irreducibly complex, one must focus on the function of the engine itself and whether it can be built in a stepwise fashion, not on a possible function that one particular sub-part could have elsewhere. Of course a nut or bolt could serve some other purpose in my car. It could probably serve many purposes. But this does not explain how a variety of complex parts such as pistons, cylinders, the camshaft, valves, the crankshaft, sparkplugs, the distributor cap, and wiring came together in the appropriate configuration to make a functional engine. Even if all of these parts could perform other functions in the car (which is doubtful), how were they all assembled properly to construct a functional engine? The answer must be intelligent design.

To offer another analogy, consider how you would build an irreducibly complex arch (Figure A):

image
Figure A: An arch is irreducibly complex: If one removes a piece, the remaining pieces will fall down.

According to Baker, if we can find a function for some sub-piece, then a system is not irreducibly complex. Now, let’s now break this arch into sub-pieces:

image
Figure B: Here an arch has been broken up into sub-pieces.

Baker has apparently found a flagellar sub-piece (the T3SS) that can perform some other function. The T3SS comprises no more than a quarter of the total flagellar parts. Similarly, in this arch, there is one large sub-section (labeled “S”) that comprises approximately a quarter of the total arch. Sub-section S can have a function outside of the arch (i.e., it can stand on its own). However, this exposes the fallacy of Baker’s test: the ability of sub-section S to stand on its own does not therefore dictate that the arch is not irreducibly complex. If one were to remove the top piece (t), the arch crumbles, even if sub-section S remains standing (Figure C):

image
Figure C: Even if sub-section S can have a function (i.e., if it can stand) outside of the arch, this does not imply that the arch as a whole is not irreducibly complex — capable of being built in a step-by-step manner.

Thus, we see that a system does not become “reducibly complex” simply because one part remains functional outside of the final system, and Baker has followed many others in proffering a straw-man test of irreducible complexity.

So can we properly test the flagellum to show that it is irreducibly complex? Yes, we can. Scott Minnich’s genetic knockout experiments on the E. coli flagellum have shown that it fails to assemble or function properly if any one of its approximately 35 structural parts are missing. That’s prima facie evidence that it’s irreducibly complex, and it’s a proper test of the model.