A few weeks back at the local library I ran across an interesting book that tied together history, microbiology, ecology, jurisprudence, theology and epidemiology, entitled Justinian’s Flea - The First Great Plague and The End of the Roman Empire. A couple of paragraphs on pages 203/4, dealing with the science of understanding about the bacterium Y. pestis that causes bubonic plague, stood out for me since they dealt directly with something constantly being mentioned here at lgf:

Both advocates of Darwinian selection and their opponents are prone to cite the most benign adaptations as support for their respective positions. Favorite examples of the creationist side — those why style themselves proponents of intelligent design or ID — are must attracted to such complex structures as the human eye or the falcon’s wing, adaptations whose intermediate forms seem to confer no real evolutionary advantage, and therefore have been created ex nihilo. The bacterial equivalent, among ID proponents, is the remarkable organic motor that the tiny organisms use as a propulsive device, the flagellum.

One of the leading lights of ID, Michael Behe, regularly cites the flagellum, a collection of more than forty separate parts including a rotor, bearings, and a spiral-shaped “propeller” that hooks onto one of the outer rings. The engine for the propeller is, like everything invented by bacteria, a triumph of physical chemistry: When a positively charged proton moves across the bacterial membrane, the charge causes the ring to turn, which in turn spins the propeller at speeds of up to 15,000 rpm. Because — in the view of ID, anyway — the flagellum’s components are only useful as a propulsion device once all the pieces are present, it is a challenge to natural selection; a propeller without an engine, or a bearing to turn, is just so much protein. The “irreducible complexity” of the flagellum, goes this theory, is unmistakable evidence of a designing intelligence.

The weakness — one is tempted to write “irreducible weakness” — of intelligent design is the assumption that the component parts of the flagellum (or the eye, or wing) have always had only a single purpose, a purpose that can only be fulfilled with a complement of other parts. One can only wonder what ID makes of the Type III secretion system, a sort of multiple launch artillery system found on the outside of the Y. pestis cell membrane, since the same proton pump that drives the flagella in motile bacteria also serves as the delivery system that the bacterium uses to batter down the walls that protect their victims…and both pumps share a common ancestor.

That bacteria in general, and Y. pestis in particular, have developed such a sophisticated siege engine, using the same parts that can be used to build an outboard motor, is actually testimony to the power of natural selection rather than design.