THE 'OLD ONES' HAVE FLAGELLA, TOO

People, if you've been following the intelligent design (ID) movement, you've heard about the bacterial flagellum. This corkscrew-like structure (shown at left) is embedded in the cell walls of bacteria and essentially functions as a rotary motor. The rapidly-spinning motor is connected to an assembly of microtubules (ahem--tiny tubes), and the rotation of this assembly propels the bacteria through the local environment. Pretty cool!

b

Now, the bacterial flagellum's remarkable function and complex shape (it has more than twenty distinct components) has not gone unnoticed by ID advocates. The chemist Michael Behe has gone so far as to claim that the flagellum's structure is 'irreducibly complex'. By this, Behe means that the flagellum could not have been produced by natural selection, due to the alleged fact that there are no functional intermediates between the present flagellum structures and simpler arrangements of the proteins that form it. If there is no way that such a structure could've been produced by a series of modifications, ID advocates argue, then the existence of such structures at the molecular level exhibits design, and hence a Designer.

b

This particular line of reasoning is so well-known and so widely-accepted by ID advocates that Ken Miller has described it as "the poster child of the modern anti-evolution movement" or, more humorously, as one of the "icons of anti-evolution." Miller's analysis demonstrates, however, that there is abundant evidence for the evolution of flagella.

b

A similar feat has now been accomplished for another domain of life! Rather than looking at conventional bacteria, workers have focused on the Archae ('the old ones'), a diverse group of microscopic organisms that often inhabit extreme environments hostile to most other forms of life. As you might imagine, the Archae differ in significant ways from conventional bacteria, both in terms of their genes and their biochemistry. It should come as no surprise, therefore, that they have come up with their own sort of 'flagella', distinct from that of conventional bacteria.

b

What is somewhat surprising, however, is what you learn when you compare the genomes of different Archae. Workers have performed such an analysis, described here, that provides powerful evidence that the genes for building 'archaeal flagella' are highly conserved within Domain Archaea, to the extent that a fairly detailed phylogenetic tree showing the relationship between different archaeal species is possible, and that this analysis not only suggests the steps that led to the evolution of the 'archaeal flagella', but point to an event of horizontal gene transfer between two widely-separated lineages. Apparently, there is more than one way to skin the flagellar cat, but in all cases examined evolution by natural selection is up to the task!