• Darwin’s Doubt – Chapter 12 – Part 1 (Guest Post)

    In order to help me out a little bit a reader (who is a professional scientist) offers this take on another of Meyers… curious interpretations of scientific literature. The post is below. I’d just like to point out that the paper Meyer is quoting from is from 1970.  If you take a careful count, that’s 44 years ago. That’s right in the middle of the big molecular biology revolution and well before Evolutionary developmental biology. This is roughly akin to telling a modern aeronautical engineer that flying faster than the speed of sound is impossible because propellers would tear themselves apart.

    Without further ado, Darwin’s Doubt Chapter 12 – Part by Christine Janis, Professor of Biology.

    In Darwin’s Doubt, Meyer expresses the notion that evolutionary change in morphology would be impossible because “to change such systems [i.e., complex morphological structures] requires altering each of the many independent parts upon which their functions are based” (p. 231). In support of this conjecture he cites morphologist Thomas Frazetta as saying that evolutionary mechanisms necessarily involve gradual change, and that evolutionary mechanisms can be viewed “as a sort of continuous change, where one structural difference melts gradually into another” (Frazetta, The American Naturalist, 1970: pp. 62-63)*. Frazetta is discussing the evolution of the upper jaw (maxilla) in a group of rather obscure Madgascan snakes (the boyerines), in which a moveable joint developed in what in most snakes is a single, unjointed bone (as it is in our own upper jaws).

    Meyer also quotes the following sentence in that paragraph: “In the framework of such a view, bolyerines are clearly difficult. A movable joint dividing the maxilla into two segments seems to have either a presence or absence, with no intermediate to connect the two conditions.”

    Such a direct quote begs the question: What exactly did Frazetta mean by this apparent denial of the possibility of evolution in these snakes? First of all, these quotations come from a section with the heading “Evolutionary Appearance of the Joint”, which might lead one to suspect that Frazetta was not quite so set against the evolutionary viewpoint as Meyer implies.

    Following this initial quote the rest of the paragraph from Frazetta’s paper reads as follows:

     “The overall similarities of the bolyerine skull with that of terrestrial boids do not suggest a major overhaul in cranial structure. Instead, it appears that the significant evolutionary changes in the upper jaw were fairly direct.”

    Hmm. Interesting. If one reads the entire paragraph that Meyer is quoting a portion of, it appears that Frazetta is not at all supporting of the notion that complex morphological change is impossible in evolution.

    Meyer goes on to say: “As Frazetta himself observed: ‘I thus find it difficult to envision a smooth transition from a single maxilla to the divided condition seen in bolerines’.” Meyer continues to expostulate about the impossibility of all necessary parts evolving at once, as if morphology were determined by individual genes for each part, not a developmental cascade. He further describes what Frazetta says about “the problems for Neo-Darwinian theory” — without actually providing quotations, so that the reader would naturally assume that what Meyer is saying here (about the impossibility of changing any one part of an organism) follows from what Frazetta actually said.

    Reading what Frazetta does actually say in this article, while it is indeed true that he does not envisage a smooth, gradual transition from a maxilla without a joint to one with joint, he clearly does not think that such a change is impossible under an evolutionary framework. Indeed, functional intermediate forms of such a gradual transition would be difficult to envisage. Instead, he proposes some other mechanisms. Right after the second above quoted sentence he says:

     “The previous discussion leads to another possibility. A maxilla that through accident is broken shortly behind the prefrontal bone may have difficulty in healing. Damaged ends of the now-separated maxillary segments would be moved against one another during the drawing forward of the palatomaxillary arch and during the collision between prey and predator. Reuniting of the two maxillary pieces would be impeded, and a pseudarthrosis might appear between them.”

    And a little later:

     “This set of possibilities is not very different from the case considered by Bock (1959) in his analysis of the evolution of secondary mandibular joints in certain bird species. In both instances there is hypothesized a gradual morphological change, under selective direction, which results in a rather sudden structural and functional “leap ” to a novel adaptive type.

    A further possibility regarding the origin of the joint is that, in an ancestral population of snakes, one or a few individuals suddenly appeared with a divided maxilla, a result of mutation or of extreme inbreeding on a small island (Breder 1954, reports the birth of a jawless teleost, structurally and mechanically an even greater freak than a snake with a divided maxilla, that may have resulted from excessive inbreeding in captivity). Thus, to summarize, it seems to me that with respect to the origin of the intramaxillary joint, the evidence allows three possibilities: 1. Acquisition of the joint started as a gradual process, involving a continuous thinning of the posterior portion of the maxillary bone. But it seems that, if this occurred, it would eventually lead to a condition in which the bone would be broken when used. This direction of structural change would lead to the next possibility: 2. Selection for a thinned maxilla results in a high probability of intramaxillary breakage. When an “injured”‘ individual develops a pseudarthrosis connecting the separated maxillary pieces, he is selectively favored. Continued selection would result in a population of snakes where thinning had reached the ultimate extreme, that is, complete division of the maxilla. 3. There suddenly arises in the population an individual possessing an intramaxillary joint, without there having been any particular selective influence on the individual’s ancestors to make such an event more probable. Since the first alternative seems to lead to the second, it might be legitimate to examine possible ramifications of a tentative conclusion: the bolyerine maxillary adaptation came into existence by a discontinuous transition from an ancestral condition-it appeared with a certain degree of suddenness.”

    In his Summary, Frazetta says:

     “It is difficult to devise a scheme whereby this adaptation evolved in smooth, uninterrupted fashion from an ancestral condition. Several possibilities are presented, all of which lead to the conclusion that the maxillary modification arose suddenly. The sudden appearance of a bizarre, adaptive type has certain implications in common with Goldschmidt’s concept of the “hopeful monster.” These are discussed. A definition of adaptive precision is proposed, and the selection values of crudely fashioned organic machinery-as might characterize a hopeful monster-is regarded in terms of simplified, hypothetical considerations.”

    Whether or not the reader might find Frazetta’s explanations fanciful (and it must be remembered that Frazetta was writing almost half a century before our current knowledge of evo-devo, and our current understanding of how rapid morphological transitions can be effected by changes in regulatory genes), one thing is certain: he is *not* making a case that the morphological change in bolyerid snakes could not be achieved by evolutionary means. He is merely saying that it would have to involve some other mechanism besides small, gradual changes.

    Let’s make it quite clear what Meyer is doing in this book. He is making a case that the evolution of coordinated morphological systems is impossible, and using as his back-up misleading quotes from a respected morphologist to make it look as if he agrees with him about the impossibility of evolutionary change. It is one thing to look at scientific data and to claim that you think that this means that evolution is impossible. It is quite another issue to selectively quote from a noted scientist to make it appear like he is agreeing with your interpretation. This is just one more piece of frank dishonesty and manipulation of scientific information in this book.

    * http://www.jstor.org/discover/10.2307/2459073?uid=3739888&uid=2134&uid=2&uid=70&uid=4&uid=3739256&sid=21103862971593

    The rest of the series.

    Category: Book ReviewCreationismEvolutionfeaturedScience


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