November 13, 2008 | David F. Coppedge

Polishing Darwin’s Icons

Finch beaks, peppered moths, transitional forms – the standard props for evolution have been scrutinized ad infinitum for decades.  Can anything new be said about them?  Find out in these recent articles.

  1. Peppered moths:  The peppered-moth story just about collapsed when investigators realized that the famous pictures that adorn textbooks were staged, because the moths do not normally reside on tree trunks, but in the branches.  Other critics pointed out that no evolution occurred – just shifts in abundances of existing varieties of the same species.  Moreover, it was never proved that changes in coloration were related to predation by birds.  Seeing this icon under assault was enough to make staunch evolutionist Jerry Coyne feel like discovering Santa Claus was really his dad (07/05/2002).
        Nevertheless, another peppered-moth paper appeared in PNAS recently.1    The authors did not add anything of substance; they only provided evidence that a shift in populations across a region requires many generations.  The notable aspect is what was lacking: no mention of the controversy, no mention of the critics who found flaws in the previous studies (like Judith Hooper, 06/25/2004), and no indication that the peppered moth evidence is useless for evolution anyway.  Quite the contrary.  Kettlewell (who glued moths to tree trunks) was cited favorably, and the article began triumphantly, “Historical datasets documenting changes to gene frequency clines are extremely rare but provide a powerful means of assessing the strength and relative roles of natural selection and gene flow.”
  2. Darwin’s finches:  The Galapagos finches are to Darwinism what the Statue of Liberty is to America: the leading light of evidence for natural selection.  What they are not, Jonathan Wells argued in Icons of Evolution, is evidence for macroevolution, because the changes oscillate back and forth with no real trend either way.  Furthermore, after all the flutter of scientific papers, the finches are still finches.  Most varieties on the islands are still interfertile.
        It seems it would be hard to add anything to the work of David Lack and Peter and Rosemary Grant, work that covers decades of observations (03/04/2008 bullet 4, 07/14/2006).  Nonetheless, PhysOrg reported on work by a team from University of Massachusetts at Amherst that “Offers Rare Glimpse Into How Species Diverge.”  What else is new?  Previous researchers had already shown that environmental changes can trigger adaptive changes, primarily in beak size and shape.  The team must have had fun figuring this out again, because one said, “Witnessing this dynamic tug of war among environmental factors is very exciting.”
        The punch line that deflates the excitement came at the end of the article:

    The behavioral ecologist points out that this process has been known to change in the other direction; one species can emerge where once there had been two, if environmental factors press in that direction.  Thus Podos and colleagues have not necessarily witnessed the birth of a new finch species at El Garrapatero.  In wetter years with more abundant food, selection may be less intense and medium-beaked populations may rebound.  But the researchers suggest that understanding the relative strength of disruptive selection in different environmental directions could provide key insights into the speciation process.

    They speak of “key insights” in future tense.  What, exactly, was demonstrated that was not already common knowledge?  Finch beaks change slightly depending on the food available.  That claim is not controversial even to creationists.  This team just stated two conclusions unhelpful to Darwin: that they didn’t observe any new species coming into being, and that two species can merge into one.  How did finches arise in the first place?  No researcher at the Galapagos has answered that question.  But that was Darwin’s question: the origin of species.

  3. Tiktaalik again:  Among the alleged transitional forms demonstrating “great transformations” in evolutionary history, Tiktaalik is a relative newbie.  Neil Shubin’s 2006 discovery of an alleged tetrapod ancestor made a splash on TV and became the centerpiece of his book, Your Inner Fish.  This fossil, however, is only one contender for the title (e.g., 10/20/2006).  Shubin’s pet fish-a-pod is not wholeheartedly endorsed by other paleontologists; nor do paleontologists look for a straight-line series leading from one body form to another as they did in the days of belief in orthogenesis.  As with other alleged transitional forms, Tiktaalik contains a confusing mosaic of features evolutionists consider primitive and derived.  Casey Luskin on Evolution News showed reports of other scientists claiming that the quality of this evolutionary icon is poor in retrospect.
        Last month’s paper on Tiktaalik in Nature2 did not make as much of a splash.  Shubin and team claimed more transitional features in the cranium.  National Geographic endowed it as the fish with the first neck, and Science Daily dressed it up in a series declaring the hyomandibula is shrinking toward becoming an ear bone (cf. 03/19/2007).  Other than that, very few mentioned this latest claim.  We’ll have to wait and see if the quality of the icon has improved.

Not one of these papers mentioned the controversial aspects of the icons.


1.  Saccheri et al, “Selection and gene flow on a diminishing cline of melanic peppered moths,” Proceedings of the National Academy of Sciences USA, October 21, 2008 vol. 105 no. 42 16212-16217, doi: 10.1073/pnas.0803785105.
2.  Downs, Daeschler, Jenkins and Shubin, “The cranial endoskeleton of Tiktaalik roseae,” Nature 455, 925-929 (16 October 2008) | doi:10.1038/nature07189.

Leftovers again.  High-profile criticisms, not just from creationists, have been leveled at these so-called proofs of evolution.  It would seem in the interest of publishers to air the controversies and deal with them, rather than present the icons as news.

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