DARWINISM GONE WILD: Neither sequence similarity nor common descent address a claim of Intelligent Design
Metal mousetrap parts
Okay, so one day a guy walks up to you and says irreducible complexity is no problem for a random, Darwinian-like evolutionary process. In fact, he can explain how a mousetrap could be made step by step. That's great, you reply, tell me. Easy, says he. He has just finished a detailed analysis of the standard mechanical mousetrap and discovered that, except for the wooden base, all the parts are made of metal! What's more, he's even looked at non-standard mechanical traps, and their pieces are all made of metal, too! Also, after much sleuthing he's noticed that the mousetrap spring has a lot in common with the spring inside his ballpoint pen -- both are made of metal, and both are curled into spirals.
Fascinating, you reply, please go on. Go on? What, are you blind? Don't you see? asks he. The mousetrap spring must have arisen from something like the pen's spring, to make the beginning of the mousetrap. Then the spring duplicated to form the other metal parts, which were added one by one to make the trap we see today. What more could a reasonable person ask for?
You point out that it isn't quite obvious to you how that helps, that the function of the mousetrap would seem to be missing from all those parts, and that while all the parts were being added, the system still wouldn't work like a trap. In fact, you note that the scenario says nothing at all about how the mouse-trapping function arose.
IDiot!, he mutters.
Common descent versus random mutation/natural selection
That's pretty much the scenario being played out after the recent online publication of a paper by Liu and Ochman (1) in the Proceedings of the National Academy of Sciences. The gist of the paper is that the workers compared the sequences of the dozens of proteins of the flagellum of the gut bacterium E. coli to each other, to other E. coli proteins, and to the flagellar proteins of other kinds of bacteria. They noted plausible sequence similarities among the flagellar proteins to each other, but not so much to other bacterial proteins. So Liu and Ochman concluded that all 24 proteins of the flagellum core must have descended from a single gene for a single protein!
As I'll mention below, other people find that claim very dubious, but let's leave that aside for now. Let's concentrate on the fact that this is being touted as an answer to claims of intelligent design. As I've pointed out many times, beginning with Darwin's Black Box over a decade ago, the argument for intelligent design in biology has little to do with protein-sequence similarity or common ancestry, for the same reason that knowing all the parts are made of metal doesn't explain the mousetrap. Even if all those parts are made of metal, and even if they derived serially from each other or from some primordial piece of metal, that doesn't even begin to explain how a mousetrap could be built step by step by a random process. In the same way, even if all the proteins of the flagellum derived serially one from the other, or from some magical precursor protein, that doesn't even try to explain how a flagellum could be built step by step by a Darwinian process.
Let me emphasize the point: Common descent is one thing. Random mutation and natural selection is something completely different. Evidence for common descent is NOT evidence for RM/NS. At the very best, protein sequence comparisons may say something about common descent, but they aren't support for Darwin's crucial claim that the startlingly elegant, functional complexity of life arose by random mutation culled by natural selection. The PNAS paper is quite irrelevant to that. The bottom line is that, despite the authors' apparent confusion, the paper does not even try to address the irreducible complexity of the flagellum or its need for intelligent design.
The PNAS paper reaches conclusions that other workers find very questionable. Nicholas Matzke of the pro-Darwinian National Center for Science Education and Panda's Thumb blog declares the work to be of "canine quality", that is, "a dog." (2) (Although a geographer by training, Matzke has acquired some skills in the area and earlier published his own sequence comparisons of flagellar proteins in Nature Reviews Microbiology.) The bottom line is that Matzke is quite skeptical that the two dozen kinds of proteins in the flagellum core could be derived from a single protein. His point is well taken. Yet neither of the scientists that Science magazine journalist Jennifer Cutraro called for comments expressed any curiosity concerning that startling claim. (3)
Nor were they curious about other some pretty obvious points: 1) What kind of amazing protein would it take to actually be able to give rise to the disparate physical parts of the flagellum? 2) The authors of the paper find few homologies between flagellar proteins and other proteins; yet if that primordial protein were indeed so plastic, why hasn't it been co-opted to perform many other functions in the bacterial cell? 3) In their scenario, the prodigy protein gave rise to all the core parts of the flagellum billions of years ago, before the common ancestor of major classes of bacteria. Yet since that time it has not been heard from. A single protein which blossoms to give one coherent, astoundingly complex structure and then, its work complete, is never heard from again -- that hardly seems like what one should expect on Darwinian grounds.
Grandioser and Grandioser
It seems that the grandiosity of Darwinian claims against ID is rapidly accelerating. Just one year ago the supposed big breakthrough was a paper by Thornton (4) showing that, if he himself personally changed a couple amino acids of a receptor protein in his lab, he could slightly alter the ligand it bound. So just last year, one worker strained to account for a couple amino acid changes to a single protein affecting one property. Yet twelve months later, the PNAS paper blithely claims to account for dozens of whole proteins with many different functions.
All in all, this paper is a marvelous example of Darwinism-gone-wild, where imagination does almost all the work, experiment none of it. I'm hopeful that my new book, The Edge of Evolution, will provide a sorely needed reality check when it comes out in June. It will demonstrate the enormous difficulty of putting together by random mutation and selection even two coherent amino acid changes, let alone a multi-protein complex.
1. Liu,R. and Ochman,H. 2007. Stepwise formation of the bacterial flagellar system. Proc. Natl. Acad. Sci. U. S. A., http://www.pnas.org/cgi/content/abstract/0700266104v1
2. Matzke, N. Flagellum evolution paper exhibits canine qualities, http://www.pandasthumb.org/archives/2007/04/flagellum_evolu_1.html
3. Cutraro, J. A Complex Tail, Simply Told, http://sciencenow.sciencemag.org/cgi/content/full/2007/417/3
4. Bridgham,J.T., Carroll,S.M., and Thornton,J.W. 2006. Evolution of hormone-receptor complexity by molecular exploitation. Science 312:97-101, http://www.sciencemag.org/cgi/content/full/312/5770/97