Archives for June 2007

Lehigh biochemist and creationist darling Michael Behe, last seen falsely claiming that no evidence exists for an evolutionary origin of the bacterial flagellum, has written yet another book attacking the darwinofascist patriarchy. Writing in Science, molecular biologist Sean Carroll surveys the damage:

The problem is what Behe asserts Darwinian evolution can’t do: produce more “complex” changes than those that have enabled humans to battle malaria or allowed malarial parasites to evade the drugs we throw at them. Behe’s main argument rests on the assertion that two or more simultaneous mutations are required for increases in biochemical complexity and that such changes are, except in rare circumstances, beyond the limit of evolution. He concludes that “most mutations that built the great structures of life must have been nonrandom.” In short, God is a genetic engineer, somehow designing changes in DNA to make biochemical machines and higher taxa.

[…] Behe seems to lack any appreciation of the quantitative dimensions of molecular and trait evolution. He appears to think of the functional features of proteins in qualitative terms, as if binding or catalysis were all or nothing rather than a broad spectrum of affinities or rates. Therefore, he does not grasp the fundamental reality of a mutational path that proteins follow in evolving new properties.

This lack of quantitative thinking underlies a second, fatal blunder resulting from the mistaken assumptions Behe makes about protein interactions. The author has long been concerned about protein complexes and how they could or, rather, could not evolve. He argues that the generation of a single new protein-protein binding site is extremely improbable and that complexes of just three different proteins “are beyond the edge of evolution.” But Behe bases his arguments on unfounded requirements for protein interactions. He insists, based on consideration of just one type of protein structure (the combining sites of antibodies), that five or six positions must change at once in order to make a good fit between proteins–and, therefore, good fits are impossible to evolve. An immense body of experimental data directly refutes this claim. There are dozens of well-studied families of cellular proteins (kinases, phosphatases, proteases, adaptor proteins, sumoylation enzymes, etc.) that recognize short linear peptide motifs in which only two or three amino acid residues are critical for functional activity [reviewed in (7-9)]. Thousands of such reversible interactions establish the protein networks that govern cellular physiology.

Very simple calculations indicate how easily such motifs evolve at random. If one assumes an average length of 400 amino acids for proteins and equal abundance of all amino acids, any given two-amino acid motif is likely to occur at random in every protein in a cell. (There are 399 dipeptide motifs in a 400-amino acid protein and 20 20 = 400 possible dipeptide motifs.) Any specific three-amino acid motif will occur once at random in every 20 proteins and any four-amino acid motif will occur once in every 400 proteins. That means that, without any new mutations or natural selection, many sequences that are identical or close matches to many interaction motifs already exist. New motifs can arise readily at random, and any weak interaction can easily evolve, via random mutation and natural selection, to become a strong interaction (9). Furthermore, any pair of interacting proteins can readily recruit a third protein, and so forth, to form larger complexes. Indeed, it has been demonstrated that new protein interactions (10) and protein networks (11) can evolve fairly rapidly and are thus well within the limits of evolution.

True enough, as always Behe’s declarations sound convincing to anyone who skipped undergraduate biology. For the rest of us, not so much. As an undergraduate I wrote a fairly comprehensive rebuttal of Behe’s book Darwin’s Black Box. It isn’t that hard if you have access to some textbooks and a free database like PubMed or Google Scholar.

As dangerous as Behe’s work might be to people who grow stupider for having read it, I think that Behe poses much more of a danger to the creationist movement itself. The problem is that unlike most other luminaries in the anti-Darwin movement Behe insists on making testable predictions. This passage from Carrol’s review illustrates Behe’s problem:

Behe once wrote, “if random evolution is true, there must have been a large number of transitional forms between the Mesonychid [a whale ancestor] and the ancient whale. Where are they?” (12). He assumed such forms would not or could not be found, but three transitional species were identified by paleontologists within a year of that statement.

Behe makes this same mistake over and over and over. When he declared in Darwin’s Black Box that the bacterial flagellum could not have evolved Behe ignored significant literature that already sketched out a plausible mechanism and subsequent work has almost completely clarified it. We now know that systems as apparently irreducible as our nervous system have clear precursors in species which lack the faintest hint of a neuron or synapse. In fact, Harvard neuroscientist David Linden has just published an engaging book describing how far from representing biological perfection, natural selection instead cobbled our modern brains together from a mishmash of subpar components that had the distinct advantage of being available.

The distinction here is crucial – creation “theory” posits a creator with a near-infinite toolset to work with. Only a cruel or limited creator would create a beloved species using suboptimal components, whereas evolutionary theory demands that a new species can only make incremental changes on the species that came before. Perfect, precursor-free optimization would discredit evolution if it anyone could ever demonstrate it, while suboptimal adaptations, limited by finite precursors, directly contradict the basic tenets of creation. Whenever a creationist proposes a testable hypothesis, creation loses.

Unlike Behe the bright minds behind Ohio’s Kentucky’s new creation museum get the picture.

Early in the museum, the visitor is given advice on the proper mind frame to have for your visit: “Don’t think, just listen and believe”. As you can see in the picture below, Human Reason is the enemy and God’s Word is the hero. Descartes represents Human Reason, saying “I think, therefore I am”. But God tells us there no need to waste your beautiful mind, for God says “I am that I am”.

Answers in Genesis has it exactly right – if you care about creation then check your critical thinking at the door. That should go without saying whenever an inquiry presupposes its own conclusions (are you listening, Doug Feith?), yet somehow doofuses like Behe keep mucking it up.

***

For more thorough swings at this pinata, read PZ Meyers and the Panda’s Thumb.

Own Goal!Post + Comments (42)