Sunday, May 29, 2005

Dembski on Orr

Well, not everyone liked Orr's article quite as much as I did. William Dembski has weighed in with this response. It doesn't merit a detailed rebuttal, but there is one point that caught my eye:

This last point about the absence of detailed Darwinian pathways is the Achilles heel of Orr’s criticism of Behe. Orr remarks that “Behe and his followers now emphasize that, while irreducibly complex systems can in principle evolve, biologists can’t reconstruct in convincing detail just how any such system did evolve.” To which Orr immediately adds, “What counts as a sufficiently detailed historical narrative, though, is altogether subjective.” This last point constitutes an damning admission — indeed, it gives away the store. Is Orr saying that evolutionary theory is in the business of telling historical narratives that are purely subjective. If so, how can it constitute a science? And if not, where are the detailed Darwinian pathways that could convince any unbiased bystander that the flagellum really did evolve by Darwinian means? Orr suggests that design theorists are tendentiously raising the bar of scientific evidence for Darwinism too high. But this is not the case. Without detailed, testable Darwinian pathways that produce irreducibly complex systems like the bacterial flagellum, why should anyone believe that such pathways exist at all?

Since this is William Dembski we're talking about, I'd feel cheated if Orr had been quoted accurately. Dembski is deliberately misrepresenting Orr's point. Surprise!

What Dembski is not telling you is that his first quote above comes as the last sentence in a paragraph. The second quote, the one about subjective judgements, is the first sentence of the next paragraph. Someone who, unlike Dembski, actually cares about representing his opponent's views accurately and making a good argument in reply, would have quoted considerably more.

In a moment I'll show you what Orr actually said. But first notice that even the fragment quoted by Dembski is enough to show that Dembski is vamping here. Orr's point is perfectly clear. It is not the explanations themselves that are subjective. After all, any proposed scenario for the evolution of a complex system must be consistent with everything that is known about that system. Each bit of data in that regard is one more test for the scenario to pass.

What is subjective is the judgment of whether the scenario is well-enough supported to be accepted as correct. Contrary to Dembski's bleats, the evidence that complex biological systems are the product of evolution is sufficient to convince just about every scientist who has ever considered the matter. In reply the ID folks simply fold their arms and shake their heads and say they are not convinced.

Now, for what Orr actually said:

What counts as a sufficiently detailed historical narrative, though, is altogether subjective. Biologists actually know a great deal about the evolution of biochemical systems, irreducibly complex or not. It’s significant, for instance, that the proteins that typically make up the parts of these systems are often similar to one another. (Blood clotting—another of Behe’s examples of irreducible complexity—involves at least twenty proteins, several of which are similar, and all of which are needed to make clots, to localize or remove clots, or to prevent the runaway clotting of all blood.) And biologists understand why these proteins are so similar. Each gene in an organism’s genome encodes a particular protein. Occasionally, the stretch of DNA that makes up a particular gene will get accidentally copied, yielding a genome that includes two versions of the gene. Over many generations, one version of the gene will often keep its original function while the other one slowly changes by mutation and natural selection, picking up a new, though usually related, function. This process of “gene duplication” has given rise to entire families of proteins that have similar functions; they often act in the same biochemical pathway or sit in the same cellular structure. There’s no doubt that gene duplication plays an extremely important role in the evolution of biological complexity.

That's the point. There are a variety of natural mechanisms (gene duplication is one of many) that can in principle lead to the evolution of so-called irreducible complexity, and there is considerable evidence that those mechanisms have played out in fact. The idea that we must invoke a supernatural intelligence to explain these systems is ridiculous.

Actually, in reading Dembski's reply I was reminded of this quote, from a previous essay by Orr in reply to a similar point from Dembski:

Dembski’s response is to point out that I have merely shown that IC systems can conceivably be built by Darwinism (a point he does not deny), not that such systems were built by Darwinism or even that they were probably built by Darwinism. I am accused, in other words, of having low standards: “Orr, along with much of the Darwinian community, is satisfied with a very undemanding form of possibility, namely, conceivability.” The problem with this is simple. It was Behe who posed the problem in terms of conceivability versus inconceivability. Behe said that Darwinism could not possibly produce IC systems. Behe spoke of “unbridgeable chasms.” Behe asked, “What type of biological system could not be formed by ‘numerous, successive, slight modifications’?” and then answered, “A system that is irreducibly complex.” The discussion has, in other words, taken the following form:

BEHE: Darwinism can’t possibly produce IC systems.
ORR: Darwinism can produce IC systems. Here’s how . . .
DEMBSKI: Orr has merely shown that a Darwinian explanation is possible. What a risibly low standard!

Well said.


At 8:52 PM, Anonymous Anonymous said...

"I'd feel cheated if Orr had been quoted accruately (sic)"
I'm pointing out the typo strictly because I expect IDiots would take your entire line of reasoning as being invalidated by it.
In a previous example of Dembski quote mining, he seemed to be amused when the scientist involved pointed out that he had been quoted in a deceptive fashion, so I don't think Dembski'll acknowledge your posting, valid though it is.

At 8:56 PM, Blogger Jason said...

Thanks for pointing out the typo. It has now been corrected.

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