Behe brings up physical precursors, then fails to acknowledge their ubiquity in organisms

NOTE: This was first published here on 8.18.08, and is simply being re-published as a separate post now.

“…Can we evolve a bicycle into a motorcycle? …A motorcycle depends on a source of fuel, and a bicycle has nothing that can be slightly modified to become a gasoline tank. And what part of the bicycle could be duplicated to begin building a motor?” DBB, 44

“A bicycle thus may be a conceptual precursor to a motorcycle, but it is not a physical one. Darwinian evolution requires physical precursors.” DBB, 45

The fact is that in DBB Behe hits on a very important phenomenon in determining whether or not evolution occurs, which is that evolution requires, and predicts, that any complex organ or system needs physical precursors. A designed object, like a motorcycle, does not. He carefully avoids generalizing what he says in the quote, and, as predictably, he avoids testing evolution on the availability of “physical precursors of systems and organs. Yet it is there, he does tell us that a motorcycle cannot evolve because it does not have the beginnings of components that are necessary for an evolution.

And what does he do in the rest of the book? He assiduously ignores or minimizes the importance of the fact that life is made up of modified parts, which he recognizes in the quote above is not the case in designed entities like motorcycles. Right there is a crucial difference between designed and evolved objects, and even though he is willing to bring up the difference in yet another of his ill-suited analogies, he will not mention the importance of the fact that most of his “irreducibly complex” systems are made up of components that, totally unlike a gas tank for a motorcycle, are known to have uses in other systems and pathways (he does point out a few biochemicals that do not have related molecules in other systems–though biomolecules lacking known relatives would not be unexpected in evolved organisms).

For instance, does Behe bring up the fact that the complement cascade is shared by both the adaptive and the innate immune systems, and that there is evidence that these molecules evolved first for the innate system? Certainly not, he writes as though adaptive immunity arose with no antecedents. Does he discuss the fact that adaptive immunity may have arisen to spare symbionts? No. And although I do not know if that hypothesis was well known when DBB was written, his lack of imagination is no argument against evolution. He does in fact bring up “an alternative pathway,” the innate immunity, on p. 134 of DBB, which he notes can active the “membrane-attack complex.” Yet he does not admit that adaptive immunity would therefore indeed have the innate immune system upon which to piggyback the evolution of adaptive immunity (such evolution still has a great many gaps, as might be expected of such an old system, but Behe’s clearly not stating the matter fairly).

I intend to discuss the points in the above paragraph in more detail in a later entry.

Getting back to his pathetic bike to motorcycle “analogy” with evolution, clearly adaptive immunity did have a “gas tank” or “an engine” from which it could evolve step by step. No matter what problems remain, this completely undermines this particular analogy, which is really quite a misleading bit of rhetoric. Notably, there is no meaningful analogy between the designed objects that humans make, which very frequently have components which are taken from an entirely different sort of “conceptual evolution,” and biological evolution, which in many lineages is almost totally incapable of using anything but “physical precursors” coming from direct ancestors.

Other examples are much the same, like the clotting cascade. When I heard him speak, he did admit that many of the molecules involved in clotting do indeed have relatives acting in other pathways, but in DBB this fact is generally smothered over. For, if he were to honestly face up to his own proclamation that “Darwinian evolution” requires physical precursors, while design evolution can make do with conceptual precursors, he would be stuck admitting that Darwinian evolution typically has evidence of such precursors in biochemical (and morphological) relatives–and to the degree that it does not, there are reasonable explanations for this (like the extinction of biochemical relatives–extinction being a prediction of any real evolutionary scenario).

There is little question that Behe slit his own throat by bringing up in DBB the necessity of “physical precursors” in organisms (aside from lateral transfers of genes, that is) under the “Darwinian” scenario, while designed objects like bicycles can make do with “conceptual precursors”. Had he properly analyzed the biochemical pathways in his book according to that crucial distinction, he’d have done nothing but to show, first, that they were not designed, and second, that they in fact evolved. Instead, he ignores, or smothers the importance of, the large number of cases where physical precursors do indeed exist for exactly the kind of evolution that he denies happened, and instead he tries to shift the test for evolution away from his very own criterion on page 45 of DBB, instead insisting that we explain the details of an evolution which happened very long ago and without leaving much evidence regarding its pathways. Making up stuff is the very means of “ID science,” as most of us already know, but it is not the way that real science operates.

There is much more to be said regarding these issues. At this point, it is sufficient to demonstrate that Behe is completely and utterly oblivious (unless he is wittingly dishonest) to the manner in which his very own distinction between “conceptual precursors” and “physical precursors” destroys his design claims, and bolsters “Darwinian” evolutionary theory. Said distinction is probably the single best scientific test for “Darwinian” evolution, and the cumulative evidence is thus very much in favor of life having evolved sans design. So the truth is that Behe and ID are not completely without an understanding of science–they just know enough in order to refrain from applying such tests whenever and wherever they recognize that ID will fail such tests.

This is part of a series of posts that I am combining into one long post, which may be found at Darwin’s Black Box.

Explore posts in the same categories: Darwin's Black Box

Tags: Behe's claims, Conceptual precursors, Physical precursors

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