Thursday, October 14, 2010

Refutation and Evidence

It's a truism that arguments for creationism or ID somehow always turn out to be arguments against evolutionary theory: "evolution can't explain this," usually.  A distinctive feature of intelligent design apologetics is the assumption, or the assertion, that arguments for evolutionary theory consist purely of arguments against "design."  Such is the burden of Casey Luskin's follow-up to his earlier article on the recurrent pharyngeal nerve.  He argues on the assumption that the nerve's circuitous path functions as evidence for evolution only because it is "bad design," and indignantly suggests that bad design is still design, and still evidence for a Designer.

One might, in passing, wonder how far Luskin would be willing to push that argument.  The Discovery Institute is promoting a book asking if "Darwinism" is compatible with traditional theism; one must wonder if traditional theism is any more compatible with a blundering, clumsy Deity Who settles for "good enough for (divine) government work."  But that's a side issue.  Luskin, after all, goes on to argue that at least the recurrent pharyngeal nerve is really good design.

Luskin observes that evolution is compatible with both apparent good design and apparent bad design, and goes on to wonder, then, what sort of predictive value evolutionary theory can have.  Since he is dealing with quote mines and slogans rather than trying to comprehend his opponents' arguments, he doesn't grasp that the point of "bad design" is not so much their supposed lousiness, but the way that they are more explicable as results of descent with modification than as results of independent design.  Likewise, the point isn't that the laryngeal nerve innervates other organs besides the larynx.  The point is, why would a Designer, already (to judge by the rest of nervous system anatomy) committed to using multiple nerves and branches, choose one particular nerve and send it along a circuitous path to supply this particular list of organs?  Common descent with modification, from a common ancestor in which this nerve in fact traced a more or less straight line, makes sense of this structure; separate designs don't.

Now, Luskin points out (and again, one wonders whether he would like it if ID supporters took him up on this suggestion) that ID is compatible with common descent: if common descent is the best explanation for the path of the nerve, then it's still compatible with ID.  But in that case, what does ID add to the explanation?  The recurrent pharyngeal nerve would be one piece of evidence for (not "proof of") common descent; what evidence would there be that intelligent design played a part in modification in the course of descent?  His assumption seems to be that any reasonable person would assume design until is has been proved not to be involved.


  1. The recurrent laryngeal (not "pharyngeal") nerve has been the main subject of my research and clinical career for almost forty years, as I am an academic Otolaryngologist. Its strikingly circuitous course is readily explained by study of embryology, whose basic maxim "Ontogeny recapitulates Phylogeny", should be among the strongest arguments for the reality of evolutionary speciation. The simple observation that both giraffes (with exceedingly long necks), and primates or any other mammal (with much shorter ones) have the same circuitous arrangement and that the early stage embryos of all mammals and other cordates have identical internal anatomy in the earliest stages of development should make this abundantly clear. Although these facts do not automatically refute the possibility of ID, they also (IMO) cannot possibly be used as an argument in support thereof. This seems to be just another example of "fact mining and selection" by people with superfifcial understanding of scientific fact in an effort to suggest that ID and evolution can co-exist.

  2. While it is true that following the development of embryos explains how this nerve starts as a somewhat straight nerve in most tetrapod embryos analyzed, and then diverges according to the organism under development, it is not true that "ontogeny recapitulates phylogeny."

    Never is our embryo a fish. Never is our embryo a reptile. We don;t go through our phylogeny as our embryo develops.

    Stages in common in our embryology do show our common ancestry (the evo/devo paradigm), but we should not mistake that for phylogenetic recapitulation.