Wednesday, January 12, 2005

Discovery Institute Responds to Derbyshire

Not everyone is so pleased with Derbyshire's posts, however. The Discovery Institute has weighed in with this reply. After a brief introduction they write:


There are lots of arguments for ID in a variety of scientific disciplines, from various areas of biology and the origin of life, to physics, astronomy, and cosmology. (Go here to find out more.) But the only argument Derbyshire seems willing to identify with intelligent design is Mike Behe’s. And he doesn’t even describe it accurately. Behe focuses on features of certain “molecular machines.” Behe argues that there are certain structures in biology that are “irreducibly complex.” They’re like a mousetrap. Without all of their fundamental parts in place, they don’t work. Darwin’s mechanism of natural selection and random variation must build systems one small step at a time, by traversing a path in which each step provides a present survival advantage. It can’t select for a future function. So the Darwinian mechanism isn’t a good explanation of such structures.

On the other hand, we do know of causes that can exercise foresight, that can produce irreducibly complex structures. We usually know the effects of such causes when we see them. We call them “intelligent agents.” Such agents can use foresight, can conceive of a plan and implement it. They would be causally adequate to explain such structures. So intelligent design is a better explanation for them than the Darwinian mechanism.


Derbyshire's description of Behe comes from this post and goes as follows:


As I understand Intelligent Design theory, it rests on the idea that there are phenomena, especially in biological evolution, that can only be explained by the intercession of a directing intelligence. Behe's “irreducible complexity,” for instance, says: “You can't get from HERE to HERE (in the evolution of an organism) by any conceivable natural process, because the intermediate steps make no functional sense.”


If you can discern any important difference between Derbyshire's description of Behe and the Discovery Institute's description of Behe, please let me know.

Since the DI has chosen to repeat Behe's argument once again, perhaps I will be forgiven for reminding people why this argument is very, very stupid. As the DI blogger points out, Behe examines certain molecular machines and finds that if they are missing any one of their parts then they cease to function. This is said to rule out the possibility that it formed gradually via the prolonged action of natural selection.

But this claim is false, and for an obvious reason. The fact that every part in its current form is needed for the machine to function in its present context does not imply that every part has always been necessary in every ancestral organism in which it appeared. In other words, as biologist H. Allen Orr first pointed out, you could have the following scenario: Initially you have a simple system performing some function. Later a part gets added that improves the functioning of the system, but is not necessary. Later still, a change to the original system renders the added part essential. The result will be a system that formed gradually, yet satisfies Behe's definition of irreducible complexity.

This is hardly the only scenario. Irreducible complexity can also arise when you have redundancy in a system. If two parts are performing the same function within a machine, and one of those parts then develops some different function, then the remaining part will be essential.

Now, even if these scenarios were pure speculation they would be sufficient to refute Behe's argument. It is Behe (and his blogging defender) who are claiming that it is so implausible to think that such irreducibly complex systems evolved gradually, that we do better to invent out of whole cloth an intelligent being capable of creating them. It is for them to show that such scenarios as I have described are not plausible.

As it happens, however, the scenarios I described above are not pure speculation. To pick one of many known examples, we know, from both fossil evidence and embryological evidence, that the bone structure of our inner ear (which satisfies Behe's definition of irreducible complexity) evolved from similar bones in the reptilian jaw as the result of a redundant jaw joint. The literature contains numerous other examples of the same phenomenon. Indeed, none of the systems Behe has chosen to focus on in his writing (such as the human blood clotting cascade or the immune system) are as difficult to explain as Behe wants you to believe.

Furthermore, experiments in artificial life have routinely shown that irreducibly complex structures can form via gradual selection acting on randomly generated variations. ID folks sneer at such demonstrations. They are wrong to do so. All of the relevant features of natural selection are accurately modelled in such experiments. They show decisively that any assertion that natural selection is fundamentally incapable of generating irreducible complexity is completely wrong.

We should also point out that when it comes to making an affirmative case for ID in biology, the argument from irreducible complexity is all they have. Everything else is either a criticism of evolution, or is based explicitly on Behe's work. William Dembski's musings about complex specified information, which in creationist fantasy land is said to provide a mathematical foundation for ID, contributes absolutely nothing to the discussion (and is totally wrong to boot). The fact is, when it comes time for him to produce the probability calculation that will prove the bacterial flagellum could not have evolved, he bases the calculation explicitly on the assumption that Behe's argument is correct.

That's ID in a nutshell. Their one affirmative argument is false as a matter of logic. It only gets worse for the ID folks when you consider the actual scientific literature.

That is why Derbyshire, and all other people not blinded by religious wishful thinking, have little trouble seeing through it.


5 Comments:

At 10:58 PM, Anonymous Anonymous said...

I was taken by this paragraph from the DI response:

"Next, contra Derbyshire, there’s nothing in Behe’s argument that says that “certain features of the natural world CAN ONLY be explained by the active intervention of a designing intelligence.” It’s a matter of comparing hypotheses, and picking the best one — the one with the most explanatory power, the one that most increases the likelihood of the evidence in question, and so forth."

Perhaps someone should tell the blogger that Dembski strenuously argues against any statistical approach that considers the likelihoods that the several hypotheses confer on the evidence. Dembski opted for Fisherian hypothesis testing specifically in order to avoid having to consider the merits of the ID conjecture directly by making 'chance' the null and ID the alternative hypothesis implied by a probability calculated to be in the rejection region.

RBH

 
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