Intelligent Design Arguments



A reader points me to a collection of links that purport to debunk the intelligent design arguments based on the supposed irreducible complexity of the flagellum. I have had a chance so far to look at one such paper, Kenneth R. Miller's "The Flagellum Unspun: The Collapse of 'Irreducible Complexity'," and it doesn't impress me.



The irreducible complexity argument is that a flagellum consists of about thirty discrete components, each of which is individually of no value to a cell, and therefore if it came about because of mutation, it would provide no advantage. Miller accurately portrays this argument in his paper:

In the case of the flagellum, the assertion of irreducible complexity means that a minimum number of protein components, perhaps 30, are required to produce a working biological function. By the logic of irreducible complexity, these individual components should have no function until all 30 are put into place, at which point the function of motility appears. What this means, of course, is that evolution could not have fashioned those components a few at a time, since they do not have functions that could be favored by natural selection. As Behe wrote: " . . . natural selection can only choose among systems that are already working" (Behe 2002), and an irreducibly complex system does not work unless all of its parts are in place. The flagellum is irreducibly complex, and therefore, it must have been designed. Case closed.

Certainly, one component might show up in a population, and if it gave no competitive disadvantage, there is no reason for it to leave the gene pool--but neither would you expect its frequency to rise, either. (A point that neither Miller nor intelligent design advocates seem to have raised is that the mutation might be genetically linked to some other trait that is advantageous.)



Of course, one component caused by mutation might remain in the gene pool until another mutation took place that created another component, and then another component, and so on. But it doesn't do any good for the second component to show up in the gene pool unless it ends up in individuals that have the first component. Ditto for all the rest of the components required for a complete system--until the point is reached that some competitive advantage accrues to individual organisms from this collection of components coming together, these mutations are just random events, scattered across the gene pool for this species.



Consider what happens if the mutation for the first component happens. It will happen in one individual of the species. There is no advantage to this mutation, so its percentage of the gene pool doesn't change--it remains rare. If you have a billion individual proto-bacteria in an early ocean of Earth, and one of them gets this mutation, a million years later, that one mutation will have reproduced as fast as the other 999,999,999 non-mutants. To get that fully functional flagellum means that one of mutant bacteria has to get the mutation for component 2. One of its descendants must get the mutation for component 3, and so on, until you get the fully functional flagellum. Do the math: this is a serious problem.



Mutations are random; you should not get the exact same mutation (caused by a cosmic ray zapping an AT or CG pair in DNA, for example) in multiple individuals of a species. In several billion pairs along the double helix, what are the chances that a radiation source is going to cause the exact same positive mutation? Even if you admit the possibility that the same pair gets hit in two different individuals, remember that DNA contains a parity check that looks for and corrects coding errors. What are the chances that two different individuals, getting the same one in a billion mutation, are going to have their error checkers resolve base mismatches identically? (Note that radiation-induced cancers are a somewhat different situation. A cancer is a runaway process, while a positive mutation requires a much more precise change.)



Miller's argument is essentially that the irreducible complexity claim about the flagellum falls apart because of "type III secretory system (TTSS)":

However, molecular studies of proteins in the TTSS have revealed a surprising fact - the proteins of the TTSS are directly homologous to the proteins in the basal portion of the bacterial flagellum.



...



According to the doctrine of irreducible complexity, however, this should not be possible. If the flagellum is indeed irreducibly complex, then removing just one part, let alone 10 or 15, should render what remains "by definition nonfunctional." Yet the TTSS is indeed fully-functional, even though it is missing most of the parts of the flagellum. The TTSS may be bad news for us, but for the bacteria that possess it, it is a truly valuable biochemical machine.

Miller's argument is that the TTSS is the basal portion of the bacterial flagellum, and here is an example of a basal portion of the bacterial flagellum performing some other useful function that might explain its existence, even before the other ten to fifteen parts come into existence. However, making the claim that the TTSS is homologous to the basal portion of the flagellum is not the same as saying that they are same. Homologous means "having the same evolutionary origin but serving different functions; 'the wing of a bat and the arm of a man are homologous'." The author is asserting that the TTSS and the basal portion of the bacterial flagellum have the same evolutionary origin. How does he know this? This is merely an assertion, a form of teleology.



An adequate refutation of irreducible complexity would require demonstrating that all, or nearly all of the ten or fifteen components exist in parallel forms as the author argues that TTSS is. It might indeed be the case that this can be done. The author's next statement seems to acknowledge the inadequacy of his claim:

A second reaction, which I have heard directly after describing the relationship between the secretory apparatus and the flagellum, is the objection that the TTSS does not tell us how either it or the flagellum evolved. This is certainly true, although Aizawa has suggested that the TTSS may indeed be an evolutionary precursor of the flagellum (Aizawa 2001). Nonetheless, until we have produced a step-by-step account for the evolutionary derivation of the flagellum, one may indeed invoke the argument from ignorance for this and every other complex biochemical machine.

Aizawa can suggest it all he wants; this doesn't make it necessarily true. What Miller calls the "argument from ignorance" is the claim that once we have all the information, and understood all the processes adequately, we will have enough knowledge to refute the claim of irreducible complexity with respect to the flagellum. Very true; once someone has all the data to show that all the thirty components that make up the flagellum exist in other forms, used for different mechanisms, and that these components provided a competitive advantage to the individual mutant bacterium in isolation, he will be right. But this requires biologists to do so, or at least demonstrate that many of these thirty individual components fit this pattern. One example--and TTSS, from Miller's description, isn't even clearly in that category--doesn't destroy the irreducible complexity argument. It only reduces the number of components that must be explained from thirty to twenty-nine.