Thursday, November 17, 2005


The End of Irreducible Complexity

When he's not quacking like a duck, Lehigh University biochemist and intelligent design guru, Michael Behe, sometimes speaks of irreducible complexity, the notion that:
... a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. (Darwin's Black Box, p. 39)

As an example, Behe likes to cite the bacterial flagellum, that whip-like tail that propels an organism through its environment, as an example of irreducible complexity, which he sees as a powerful challenge to Darwinian evolution.

Ken Miller, a professor of biology at Brown University, has already supplied an elegant response to Behe's nonsense. In an article, "Answering the Biochemical Argument for Design," Miller notes:
In 1998 the flagella of eubacteria were discovered to be closely related to a non-motile cell membrane complex known as the Type III secretory apparatus (Heuck 1998) These complexes play a deadly role in the cytotoxic (cell-killing) activities of bacteria such as Yersinia pestis, the bacterium that causes bubonic plague. When these bacteria infect an organism, bacteria cells bind to host cells, and then pump toxins directly through the secretory apparatus into the host cytoplasm.

This means that a portion of the whip-like bacterial flagellum functions as the "syringe" that makes up the Type III secretory apparatus. In other words, a subset of the proteins of the flagellum is fully-functional in a completely different context – not motility, but the deadly delivery of toxins to a host cell. This observation falsifies the central claim of the biochemical argument from design – namely, that a subset of the parts of an irreducibly complex structure must be, "by definition nonfunctional."

In other words, evolution has adapted a previously existing structure, the bacterial syringe, to another use, a flagellum that propels the bacterium.

But, what if the old function, such as the syringe, is still required for an organism's survival? How can evolution account for that?

Now, there's new evidence from Howard Hughes Medical Institute investigator Sean Carroll and HHMI predoctoral fellow Chris Todd Hittinger. Their report appears in the December 1, 2005, issue of the journal Development.
For an animal to acquire a new form during evolution, the proteins that control its physical development sometimes take on new or altered functions through changes to the genes that encode them. But these proteins often carry out many essential roles that must be preserved for the animal to survive, and the function of most developmental proteins has been conserved throughout evolution. Now HHMI researchers have shown how those proteins can evolve new functions while retaining their old ones—enabling new animal forms to arise.

As the gaps narrow, it won't be long before they're so small, intelligent design activists like Behe won't be able to draw breath.


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