Darwinism, Naturalism and Falsification
Well, PZ Myers has yet again expended his time and energy, not on conducting scientific research, or educating his students, but instead trashing anyone – intelligent design proponents especially – with the temerity to doubt his own blinkered metaphysical interpretation of natural history. Intelligent design theorists, he says this time around, are "flailing about trying to emphasize their pretense of scholarliness," whose ideas "haven't worked so well" and whose arguments "fall flat." So if intelligent design proponents are really just a bunch of dolts whose arguments are hopelessly ineffectual, why does Myers not move on to more important things and simply let their ideas die a natural death? Why devote endless hours combating them, as if they represented a genuine threat?
That's just it. He can't afford to ignore intelligent design, because with no one like him standing in the way some observers might actually (and often do in fact) find it persuasive. At the same time he can't afford to treat intelligent design seriously, because some observers again might find the arguments for it persuasive quite regardless of his best efforts at a serious refutation. Contemptuous insults are pretty much the only strategy left for someone determined to defend orthodoxy without the aid of substantive arguments and explanations. Say what we will about the ad hominem tactic being a fallacy; it's almost always effective. In the hands of a skilled academic bully like Myers, it routinely badgers uncommitted observers (or the "hapless ignorati" as he affectionately terms them) into intellectual submission. After all, most of us would rather not be labeled an idiot, or a pathological liar or a deluded religious crackpot if we can avoid it.
Now aside from all that Myers does make a point that appears legitimate on its face. That is, if intelligent design promoters have wrongly defined Darwinism* in terms of "randomness and unguided evolutionary processes" on one hand, and "adaptation and fitness" on the other, then they should find out which view actually represents Darwinism and stick with that. The problem there is that just about everything already represents Darwinism. So in the case at hand, Darwinists happily explain examples of seemingly useless non-adaptive characteristics like junk DNA as evidence of unguided randomness; but they also explain stunning examples of functional complexity (like the mammalian eye or echolocation in bats) as evidence of boundless adaptability. Similarly every biological eventuality is explainable in terms of "descent with modification," where extremely wide levels of taxa-spanning variation and diversity are evidence of modification, but shared characteristics like homologous structures and identifiable body plans are evidence of (common) descent.
In short, there's no conceivable biological feature that Darwinism cannot explain in principle. But if there's nothing that it cannot adequately explain in principle, there's also no way in principle to falsify it. So on this I have to agree with Myers, Dawkins, Coyne, et al: Because his particular brand of evolution is not falsifiable there is nothing in biology that "could not have evolved." But ordinarily science doesn't accept mere possibility as its burden of proof. Under this sort of methodological libertinism the evidence for Darwinism is indeed overwhelming – so overwhelming that it explains not only all the biological evidence currently at our disposal but any biological evidence we can imagine.
This uncritical acceptance of Darwinism may be inspired by the naturalistic metaphysics that arguably drives Darwinism in the first place. For many naturalists, after all, even the strongest conceivable evidence for a miracle would not be strong enough to falsify naturalism. Keith Parsons, for example, says, "Perhaps if all the galaxies in the Virgo cluster were instantly rearranged so that when viewed from earth they spelled out 'PREPARE TO MEET THY GOD' this would be a good candidate for the scientifically inexplicable." But then he hedges his bets: "It nonetheless remains that we do not have, and have little prospect of getting, an adequate criterion for distinguishing the inexplicable from the merely extraordinary." (Science, Confirmation, and the Theistic Hypothesis, 1986).
In other words there may yet be a naturalistic explanation for even the most clearly miraculous event. But at least Parsons grants the possibility of a miracle in principle. Myers is unequivocal: "There is no valid god hypothesis, so there can be no god evidence, so let’s stop pretending the believers have a shot at persuading us." To recap: All possible evidence confirms Darwinism by default, while no possible evidence is sufficient to confirm that God exists. It looks as if Myers has created for himself the best of all possible atheistic worlds.
* As I use it here, "Darwinism" means belief that the entire range of biodiversity is readily explicable in terms of descent with modification from an original common ancestral stock, by purely natural mechanisms like selection.