Behe's Critics' Scaffolding Falls Down
In their response to Michael Behe in Quarterly Review of Biology, Maarten Boudry, Stefaan Blancke, and Johan Braeckman raise a common objection to irreducible complexity, claiming that even if an irreducibly complex system cannot function if it loses parts, it might still function if it gains parts. The problem is that this "scaffolding" argument lacks biological analogues.
If we trace backward along the evolutionary pathway, perhaps the system first gains parts until there is a sort of "scaffolding" supporting the final structure, and then it loses parts until the scaffolding is gone. They write:
As early as the beginning of the 20th century, geneticist Herman Muller explained how biological systems that depend on the complex "interlocking" actions of many different components could come about by evolutionary processes: "Many of the characters and factors which, when new, were originally merely an asset finally became necessary because other necessary characters and factors had subsequently become changed so as to be dependent on the former" (Muller 1918, pp. 463-464). Thus, redundant complexity can eventually generate IC (under the weak interpretation). More recently, biochemist and molecular biologist A. G. Cairns-Smith proposed the analogy of "scaffolding" in the construction of an arch to explain the evolution of systems that are IC according to Behe (Cairns-Smith 1986; see also Orr 1997; Pennock 2000). A classical stone arch is IC in the weak sense, because the structure will collapse as soon as one removes either the keystone or one of the other stones. The support of scaffolding is necessary in building a stone arch, but once the arch is completed, the scaffolding can be safely removed. In a similar vein, a biochemical structure may have functioned as a scaffold in the evolution of an IC system before becoming dispensable and disappearing. That is, "Before the multitudinous components of present biochemistry could come to lean together they had to lean on something else" (Cairns-Smith 1986, p. 61).
This argument makes a valid point insofar that gradual evolution can remove parts in addition to adding them. However, I've heard this point made before, and in each case I've asked evolutionists to give me a biological analogue for the "arch" or scaffolding. It sounds nice in theory, but I have never been provided with a single specific real world example where this argument might actually have some relevance to the real world of biology.
And there's another problem with the scaffolding objection. Behe defines irreducible complexity as requiring as requiring not just one part, but "several well-matched, interacting parts." Even if you end up with an irreducibly complex system by removing parts from scaffolding, you still had to build the scaffolding. How does unguided evolution build the scaffolding by adding parts?
In that regard, adding parts to build scaffolding may be more complicated than ID critics would admit. Adding a part isn't always that simple, even if it isn't indispensible. Sometimes simply getting a functional protein-protein interaction is beyond the reach of Darwinian evolution. In 2004, Behe and Snoke published a paper in Protein Science reporting results of computer simulations and theoretical calculations. They showed that the Darwinian evolution of a simple functional bond between two proteins would be highly unlikely to occur in populations of multicellular organisms. The reason, simply put, is because too many amino acids would have to be fixed by non-adaptive mutations before gaining any functional binding interaction. They found:
The fact that very large population sizes--10^9 or greater--are required to build even a minimal [multi-residue] feature requiring two nucleotide alterations within 10^8 generations by the processes described in our model, and that enormous population sizes are required for more complex features or shorter times, seems to indicate that the mechanism of gene duplication and point mutation alone would be ineffective, at least for multicellular diploid species, because few multicellular species reach the required population sizes.
(Michael J. Behe & David W. Snoke, "Simulating Evolution by Gene Duplication of Protein Features That Require Multiple Amino Acid Residues," Protein Science, Vol 13:2651-2664 (2004).)
According to this data, chance mutations are unlikely to produce even two required non-adaptive mutations in multicellular diploid species within any reasonable timescale. This answers the third question: getting multiple specific non-adaptive mutations in one individual is extremely difficult, and more than two required but non-adaptive mutations are likely beyond the reach of multi-cellular organisms. Studies like this show that the actual ability of random mutation and unguided selection to produce even modestly complex new genetic functions is insufficient.
In other words, there is too much complex and specified information in many proteins and enzymes to be generated in humans by Darwinian processes on a reasonable evolutionary timescale, even given the actual age of the earth. Simply adding a functional part in the hopes of building scaffolding might be far beyond the reach of Darwinian evolution.
An Absurd Charge
In my previous critique, I explained that Boudry, Blancke and Braekman would effectively place neo-Darwinism in an unfalsifiable position. To further give a sense of the mindset of Behe's critics, consider the following:
Boudry, Blancke and Braekman charge that Behe makes an "absurd demand" simply for stating: "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."
Apparently for these critics, Behe is "absurd" for actually expecting neo-Darwinian evolution to present a convincing case. Thankfully, some scientists are interested in actually testing these questions, even when they are difficult. As discussed above, Michael Behe and David Snoke have performed tests that address the plausibility of Darwinian processes producing new protein-protein interactions under reasonable timescales and population sizes. Doug Axe's recent paper in BIO-Complexity also addresses such questions. Both papers are showing that to simply produce modestly complex features that require multiple mutations to yield any function, one quickly exhausts the probabilistic resources available in the history of the earth.
In contrast, it seems that Boudry, Blancke and Braekman would just give up and say (my paraphrase): "if neo-Darwinian evolution is too hard to test, we should just assume it's true."
Only a die-hard ID-critic would find it "absurd" to actually test neo-Darwinian explanations on a mathematical level.