Indirect Routes and Exaptation

http://www.evolutionnews.org/2012/08/did_michael_beh063271.html

8) Professor Behe excludes, by definition, the possibility that a precursor to the bacterial flagellum functioned not as a rotary motor, but in some other way, for example as a secretory system. (19:88-95 (Behe)).

I certainly do not exclude that bald possibility merely by definition. In fact in Darwin's Black Box I specifically considered those kinds of cases. However, I classified those as indirect routes. Indirect routes, I argued, were quite implausible:

Even if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitely rule out the possibility of an indirect, circuitous route. As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously. (DBB, p. 40)

University of Rochester evolutionary biologist H. Alan Orr agrees that indirect evolution is unlikely:

we might think that some of the parts of an irreducibly complex system evolved step by step for some other purpose and were then recruited wholesale to a new function. But this is also unlikely. You may as well hope that half your car's transmission will suddenly help out in the airbag department. Such things might happen very, very rarely, but they surely do not offer a general solution to irreducible complexity. (Orr, H. A. Darwin v. intelligent design (again). Boston Review [Dec/Jan], 28-31. 1996)

There is no strict logical barrier to a Darwinian precursor to a bacterial flagellum having functioned as a secretory system and then, by dint of random mutation and natural selection, turning into a rotary device. There is also no absolute logical barrier to it having functioned as, say, a structural component of the cell, a light-harvesting machine, a nuclear reactor, a space ship, or, as Kenneth Miller has suggested, a paper weight. But none of these has anything to do with its function as a rotary motor, and so none of them explain that actual ability of the flagellum.

A bare assertion that one kind of complex system (say, a car's transmission) can turn into another kind of complex system (say, a car's airbag) by random mutation and natural selection is not evidence of anything, and does nothing to alleviate the difficulty of irreducible complexity for Darwinism. Children who are taught to uncritically accept such vaporous assertions are being seriously misled.

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