Friday, March 17, 2006


By goodness, I'm getting close to the end of Dawkin's THE ANCESTOR'S TALE, very close. At the root of the debate below is an organic being called the bacterial flagellar motor which has a rotor mechanism in it. Dawkins shows in another place why larger animals could not evolve a wheel because the blood vessels and neural mechanism would twist themselves into knots as their wheel turns while the world turns. Then he goes on in the passage below to tickle out the reasoning which goes into his conclusions and to debate the clueless IDers who are always looking for things which could not have evolved so that they can say a supernatural power had to be involved in their appearance in the natural world. Wheeeew!

[Open quote.] As it happens, the bacterial flagellar motor itself has recently, in the hands of a species of creationists who call themselves 'Intelligent Design Theorists' been elevated to the status of icon of alleged unevolvability. Since it manifestly exists, the conclusion of their argument is different. Whereas I proposed unevolvability as an explanation for why large animals like mammals don't grow wheels, creationists have seized upon the bacterial flagellar wheel as something that cannot exist and yet does—so it must have come about by supernatural means!

This is the ancient 'Argument from Design', also called the 'Argument from Paley's Watchmaker', or the 'Argument from Irreducible Complexity'. I have less kindly called it the 'Argument from Personal Incredulity' because it always has the form: 'I personally cannot imagine a natural sequence of events whereby X could have come about. Therefore it must have come about by supernatural means. 'Time and again scientists have retorted that if you make this argument, it says less about nature than about the poverty of your imagination. The 'Argument from Personal Incredulity' would lead us to invoke the supernatural every time we see a good conjuror whose tricks we cannot fathom.

It is perfectly legitimate to propose the argument from irreducible complexity as a possible explanation for the lack of something that doesn't exist, as I did for the absence of wheeled mammals. That is very different from evading the scientist's responsibility to explain something that does exist, such as wheeled bacteria. Nevertheless, to be fair, it is possible to imagine validly using some version of the argument from design, or the argument from irreducible complexity. Future visitors from outer space, who mount archaeological digs of our planet, will surely find ways to distinguish designed machines such as planes and microphones, from evolved machines such as bat wings and ears. It is an interesting exercise to think about how they will make the distinction. They may face some tricky judgments in the messy overlap between natural evolution and human design. If the alien scientists can study living specimens, not just archaeological relics, what will they make of fragile, highly strung racehorses and greyhounds, of snuffling bulldogs who can scarcely breathe and can't be born without Caesarian assistance, of blear-eyed Pekinese baby surrogates, of waLking udders such as Friesian cows, walking rashers such as Landrace pigs, or walking woolly jumpers such as Merino sheep? Molecular machines—nanotechnology—crafted for human benefit on the same scale as the bacterial flagellar motor, may pose the alien scientists even harder problems.

Francis Crick, no less, has speculated semi-seriously in Life Itself that bacteria might not have originated on this planet but been seeded from elsewhere. In Crick's fantasy, they were sent in the nose-cone of a rocket by alien beings, who wanted to propagate their form of life, but shrank from the technically harder problem of transporting themselves and relied, instead, upon natural evolution to finish the job once the bacterial infection had taken root. Crick, and his colleague Leslie Orgel, who originally suggested the idea with him, supposed that the bacteria had originally evolved by natural processes on the home planet, but they could equally, while in the mood for science fiction, have added a touch of nanotechnological artifice to the mix, perhaps a molecular gearwheel like the flagellar motor which we see in Rhizobium and many other bacteria.

Crick himself—whether with regret or relief it is hard to say—finds little good evidence to support his own theory of Directed Panspermia. But the hinterland between science and science fiction constitutes a useful mental gymnasium in which to wrestle with a genuinely important question. Given that the illusion of design conjured by Darwinian natural selection is so breathtakingly powerful, how do we, in practice, distinguish its products from deliberately designed artifacts? Another great molecular biologist, Jacques Monod, began his Chance and Necessity in similar terms. Could there be genuinely persuasive examples of irreducible complexity in nature: complex organisation made of many parts, the loss of any one of which would be fatal to the whole? If so, might this suggest genuine design by a superior intelligence, say from an older and more highly evolved civilisation on another planet?

It is possible that an example of such a thing might eventually be discovered. But the bacterial flagellar motor, alas, is not it. Like so many previous allegations of irreducible complexity, from the eye on, the bacterial flagellum turns out to be eminently reducible. Kenneth Miller of Brown University deals with the whole question in a tour de force of dear exposition. As Miller shows, the allegation that the component parts of the flagellar motor have no other functions is simply false. [Close quote.]

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