April 1, 2004 | David F. Coppedge

Validating a Just-So Story: How the Lizard Got Its Horns

As if smarting from criticisms that evolutionists trade in stories instead of evidence, Utah State biologists Kevin Young and Edmund Brodie, Jr and son decided to test an instance of natural selection.  Their subject was the horned lizard of the southwestern United States, the misnamed “horny toad” kids like to catch. 

Many descriptions of evolutionary adaptations are criticized as “just-so stories” that are based more on intuition than on direct tests of adaptive hypotheses.  The elaborate crowns of horns possessed by many species of horned lizards (genus Phrynosoma) are classic examples of intuitively adaptive features that lack direct tests of function.  The bony horns that give horned lizards their name are presumed to function as a defense against predators (Fig. 1B).  Here we present data from the wild showing that natural selection by loggerhead shrikes favors longer horns (fig. S1) in the flat-tailed horned lizard (Phrynosoma mcalli).

So, replete with charts, photographs, equations and scientific names, the trio have pulled off a rare achievement: connecting the selective agent (a loggerhead shrike) to the selected effect (the length of the lizard’s horns).  They showed that lizards with longer horns don’t get attacked by the predatory bird.  Their concluding statement, however, seems to disparage prior work:

Modern methods for analyzing natural selection have increased our understanding of which traits experience selection.  These methods, however, typically cannot identify agents of selection or reveal the functional relations that result in natural selection.  Even most classic data sets demonstrating selection in the wild, including Bumpus’s sparrows and Lande and Arnold’s pentatomid bugs, did not reveal the agents responsible for the observed patterns of survival.  Our results present a rare opportunity to link the statistical form of selection to an identifiable agent, in this case predation by shrikes.  Our study does not show that other agents and forms of selection do not play a role in the evolution of horn size, but clearly illustrates that defense against shrike predation is one factor driving the radical elongation of horns in some species of horned lizards.

Their paper was published in the April 2 issue of Science.1  Though not a just-so story in their opinion, they whimsically gave their paper a Kipling-esque title: “How the Horned Lizard Got Its Horns.”
    The summary in Science Now adds that the horns on the living lizards were less than a millimeter longer, on average, than those of the dead ones.


1Kevin V. Young,1 Edmund D. Brodie, Jr.,1 Edmund D. Brodie, III, “How the Horned Lizard Got Its Horns,” Science, Vol 304, Issue 5667, 65, 2 April 2004, [DOI: 10.1126/science.1094790] (published online April 1).

Well, very nice.  I’m sure father and son and buddy had fun out there in the desert and learned a lot.  This is certainly better empirical research than the typical Darwin Party fare, weaving tales out of pure imagination.  Too bad it’s irrelevant.
    Like the study on peppered mice (see 04/18/2003 entry), this research really doesn’t do much to help prop up Charlie.  Creationists freely admit that existing traits can be emphasized by predation or diet, including finch beaks and fur color.  Even Answers in Genesis has no problem with natural selection at this level.  This paper does nothing to explain how the lucky lizard got horns in the first place, or a head, or running legs, or breathing lungs, circulating blood, seeing eyes, hearing ears, sexual organs, or factories of molecular machines in every cell of its body.
    Researchers who think these kinds of microevolutionary studies support Darwinism commit the fallacy of extrapolation.  They think that if they just add up a large number of little stories about microevolution, they will all add up to macroevolution, and prove that humans had bacteria ancestors.  But like a pendulum on a clock, a lot of little movements do not necessarily add up to vast distances.
    Furthermore, this admirable field work, which must have required a lot of time and effort, raises as many questions as it attempts to answer: why aren’t all the horns long enough on all the lizards by now to prevent all shrike attacks?  Have they connected the acquired characteristics to the gametes and to developmental pathways, to prevent accusations of Lamarckism?  Are the genes for horns subject to pleiotropy or balancing selection?  Do the longer horns cause disadvantages to the lizards?  What other defense mechanisms are at work, like camouflage, better eyesight, faster legs or bad taste?  Perhaps you can think of more.
   The point is, there is just some circumstantial evidence here, with plenty of wiggle room for just-so storytelling, and the relationship, which is probably valid, does nothing to explain the origin of the lizard and the origin of the bird.  The mere sorting of existing information is not what Charlie set out to explain.  The big just-so story is still that.  Swabbing the deck doesn’t make the ship float.
    Science Now contains a Freudian slip that reveals the bad storytelling habit of Darwinians: “Any armchair Darwinist could tell you the lizards’ horns probably evolved to protect it from predators.”  Telling a story with your arms on the recliner was supposed to go out with Aristotle.  Get out there and prove it.

Categories: Terrestrial Zoology

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