Coincidentally, the latest issue of Quarterly Review of Biology, which contains Michael Behe’s paper on microbial evolution in the lab, also has a strong critique of Behe’s ideas about “irreducible complexity” by a group of Belgian philosophers headed by Maarten Boudry. Their paper is called called “Irreducible incoherence and intelligent design: a look into the conceptual toolbox of a pseudoscience”, and you can find a free copy here or here.
The main idea is that Behe (and other ID advocates) have gone back and forth between two views of irreducible complexity to avoid being pinned down and refuted with data. Here’s Behe’s notion of irreducible complexity, as defined in his book Darwin’s Black Box:
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. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition non-functional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution
(Behe 2006, p. 39)
As most of us know, Behe maintains that such irreducibly complex (IC) systems supposedly could not evolve in an adaptive, step-by-step Darwinian way, since the adaptive function supposedly appears only at the end of the process. Ergo an intervening intelligent designer (aka Jesus) must be responsible for such systems.
Boudy et. al, however, show that Behe and his minions have used two distinct interpretations of this notion:
To be sure, it is not difficult to find examples of biochemical systems in which the removal of just one part damages the whole system. But consider Behe’s phrases “effectively ceases functioning” and “by definition non-functional.” There are two possible reconstructions of his definition: 1) the term “functioning” refers exclusively to the basic function currently performed by the whole system (e.g., the rotary motion of the bacterial flagellum) and does not pertain to other possible functions, in other contexts, when one or more components are removed; and 2) the phrases “effectively ceases functioning” and “non-functional” include any function that the impaired system or one of its components may perform in other contexts. In principle, it is not very hard to discover whether a system exhibits IC in the first, weak sense. Leaving aside the ambiguity regarding the natural “parts” into which the system must be decomposed
(Dunkelberg 2003; Sober 2008, pp. 135-160)
, it suffices to knock out these parts one after the other to see if the system can still perform its basic function. Again, evolution by natural selection is perfectly capable of producing complex functional systems exhibiting IC in this weak sense.
. . .
In fact, only an IC system in the second, strong sense would be
to evolutionary theory, because it would rule out evolutionary precursor systems and function shifts of the system’s components. However, it is hard to see how Behe could even begin to demonstrate the existence of such a system without defaulting to the classical “argument from ignorance”
(Pigliucci 2002, p. 67)
. Interestingly, Behe has disingenuously taken advantage of this very ambiguity in answering his critics.
Boudry et al. then recount the history of Behe’s evasions about these two senses and show that “clarifications” by others such as Dembski have in fact made matters worse. It turns out that there are simply no data that Behe and his followers would accept as showing a real Darwinian origin of the biochemical systems they see as “irreducibily complex”. During his testimony at the Dover trial, for example, Behe demanded more than just plausible Darwinian scenarios for the origin of IC; he said he wanted this:
Not only would I need a step-by-step, mutation by mutation analysis, I would also want to see relevant information such as what is the population size of the organism in which these mutations are occurring, what is the selective
value for the mutation, are there any detrimental effects of the mutation, and many other such questions.
No bloody way can evolutionists ever provide that kind of data for systems that evolved in the distant past!
If you’re interested in the notion of “irreducible complexity”, and want an up-to-date analysis of its scientific and philosophical problems, Boudry et al. is a good summary for the layperson.
Boudry, M., S. Blancke, and J. Braeckman. 2010. Irreducible incoherence and intelligent design: a look into the conceptual toolbox of a pseudoscience. Quart. Rev. Biol. 85:473-477.