A post at Uncommon Descent offers an innovative way of illustrating the concept of irreducible complexity — one that is likely to be more resistant to Darwinist misrepresentation than Michael Behe’s well-known mouse trap analogy.
The illustration is intended to address the common misconception that irreducible complexity entails that (a) the individual subcomponents cannot be used to serve other functions; and (b) no simpler system exists that can perform the same or a similar function. This caricature of irreducible complexity is seen, for example, in the writings of John McDonald, Kenneth Miller and Nick Matzke.
Contrary to the above misconception, it is not the number of parts needed to perform a function that makes a system irreducibly complex, but rather the irreducibility of a core set of components to achieve the same mechanism of performing that function. The idea is that the different mechanisms of achieving a goal often require too many coordinated changes to jump from one to the other, rendering it immensely unlikely to occur by Darwinian means. In Darwin’s Black Box, Behe notes,
To feel the full force of the conclusion that a system is irreducible complex and therefore has no functional precursors, we need to distinguish between a physical precursor and a conceptual precursor. The trap described above is not the only system that can immobilize a mouse. On other occasions my family has used a glue trap. In theory, at least, one can use a box propped open with a stick that could be tripped. Or one can simply shoot the mouse with a BB gun. These are not physical precursors to the standard mousetrap, however, since they cannot be transformed, step by Darwinian step, into a trap with a base, hammer, spring, catch and holding bar. (p. 43)
Consider the goal of having a glass full of beer stand upright. Now take a look at the following video:
As explained in the video, “the object is to balance the three knives on the three glasses. Each knife can only touch one glass and the fourth glass full of beer has to balance on all three knives.”
Now, obviously there are simpler ways to achieve the same goal of having the glass full of beer stand upright — one could simply sit it on the table. But this particular mechanism of having the glass stand upright is what one might call irreducibly complex.
Furthermore, the individual subcomponents can be used to perform other functions. But here, each of them, in integral fashion, co-operates with all of the other subcomponents to perform a function that none of them can do on their own.
Casey Luskin explains this point using the arch, in a response to Ken Miller:
Miller’s treatment of the bacterial flagellum did not refute its irreducibly complexity, as Miller did not address questions about how the final flagellar systems might arise. The existence of other functions for the TTSS does not imply that the flagellar system would not still require large leaps in complexity (or to use Darwin’s words, non-slight modifications) in order to ultimately achieve a functional flagellum. To use a final analogy to show the deficiency of Miller’s explanation, consider an attempt to build an irreducibly complex arch (Figure A):
Figure A: An arch is irreducibly complex: If one removes a piece, the remaining pieces will fall down. (Note: For the purpose of illustration, I am temporarily ignoring the common objection that an irreducibly complex arch might be made using natural erosional processes. I am aware of no appropriate “scaffolding” analogy within the biological realm, but it is not the present purpose of this discussion to rebut that objection.)
According to Miller, 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:
Figure B: Here an arch has been broken up into sub-pieces. Similarly, Miller has apparently found a flagellar sub-piece (the TTSS) that can perform some other function. The TTSS comprises no more than 1/4 of the total flagellar parts. Similarly, in this arch, there is one large sub-section (labeled “S”) that comprises approximately 1/4 of the total arch. Sub-section “S” can have a function outside of the arch (i.e. here, it can stand on its own). However, this exposes the fallacy of Miller’s test: the ability of sub-section “S” to stand on its own does not therefore dictate that the arch is not irreducibly complex. Thus if one were to remove the top piece (t), the arch crumbles, even if sub-section “S” remains standing (Figure C):
Figure C: Even if sub-section “S” can have a function (i.e. stand) on its own 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, the appropriate test of irreducible complexity asks if the entire system can be built in a step-by-step manner using slight modifications only. It is important to note that the system does not become “reducibly complex” simply because one part remains functional outside of the final system.
(Do Car Engines Run on Lugnuts? A Response to Ken Miller & Judge Jones’s Straw Tests of Irreducible Complexity for the Bacterial Flagellum (Continued–Part II))
Obviously, this is merely an illustration — and, like most illustrations, it has limitations. In order to refute the claim that a given biological system is irreducibly complex one would need to show that it is, at the very least, plausible that a selective advantage could be acquired by the organism at each step involving no more than two or three non-adaptive mutations at a time (depending, of course, on the pertinent population sizes and generation turnover times).
As ID-friendly biologist Douglas Axe discusses in this paper, the number of coordinated changes that can be necessary in order to confer some functional novelty appears to be very limited.