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Icon by Icon: Responding to Massimo Pigliucci on Jonathan Wells's Icons of Evolution

Pigliucci.jpgI've been analyzing philosopher Massimo Pigliucci's critique of Jonathan Wells's book Icons of Evolution, icon by icon. (See here for yesterday's post.)

Icon 4: Haeckel's Embryos

In his 2002 book Denying Evolution: Creationism, Scientism, and the Nature of Science, Pigliucci does not contest that Haeckel's drawings are flawed. He concedes that "The drawings in question were indeed fudges." (p. 254) Yet he thinks it matters that "the fact of their being fudged was discovered by biologists, not creationists."

A fraud is a fraud regardless of who discovered it, and if evolutionary biologists discovered it, then good for them. But it turns out that some of the earliest scientists who critiqued Haeckel's drawings were in fact "creationists," as Pigliucci calls them. As Richardson et al. (1997) note: "Haeckel's ideas soon came in for strong criticism. His drawings are also highly inaccurate, exaggerating the similarities among embryos, while failing to show the differences (Sedgwick 1894; Richardson 1995; Raff 1996)." The aforementioned Sedgwick is Adam Sedgwick, who even Wikipedia admits "was an outspoken opponent of Darwin's theory of evolution."

Next, Pigliucci claims that Wells wrongly says Stephen Jay Gould was "silent" on Haeckel's fraud. But Wells doesn't say that. In fact, Wells quotes Gould extensively in Icons on this topic: "Writing in the March 2000 issue of Natural History, Stephen Jay Gould noted that Haeckel 'exaggerated the similarities by omissions' and concluded that his drawings are characterized as inaccuracies and outright falsification." (Icons, pp. 93-94) Wells also notes that Gould called them instances of "scientific fraud." (p. 108) Pigliucci is incorrect to claim Wells called Gould "silent" on this topic. This also refutes another one of Pigliucci's claims, that the drawings shouldn't be called "complete fakes." (Denying Evolution, p. 254)

Pigliucci goes on to make a common argument: "Modern evolutionary and developmental biology do not rely on the work of a nineteenth-century scientist to make their case any more than physicists still consider Newton's work the latest rage." (pp. 254-255) It's true that concepts like Haeckelian ideas about recapitulation have largely been rejected by modern embryology. But if Haeckel's work is totally irrelevant, someone should tell it to Donald Prothero, who uses Haeckel's original drawings in his 2013 textbook to promote evolution, as he did in his 1998 and 2004 textbooks. Tell it also to other recent biology textbook authors who have used Hackel's drawings. Given that Wells's book is about how textbooks misuse evidence to advocate for Darwinian evolution, it seems entirely appropriate that he critique Haeckel's work.

If Haeckel's work is completely irrelevant today then why do biology textbooks continue to use his drawings?

Pigliucci closes by noting that development supports common descent because "more closely related animals have more similar developmental systems." But Pigliucci must be aware that there are serious exceptions to that rule. For he adds, "When exceptions occur, these are also predicted by evolution because they often turn out to be the result of adaptation." Thus we see Pigliucci adopting PZ Myers' position that "evolutionary theory predicts differences as well as similarities."

This is another way of saying that, according to Pigliucci and Myers, evolutionary theory predicts whatever it finds. Such logic might help save their theory from falsification in light of all the differences between vertebrate embryos across many stages of development, but it doesn't help to construct a robust theory that makes testable predictions.

Icon 5: Archaeopteryx

Pigliucci claims that Jonathan Wells "completely misunderstands cladistics" (Denying Evolution, p. 255). How so? Because Wells claims cladistics is "based only on similarity among organisms" whereas in reality, says Pigliucci, it is based "only on shared derived characteristics." Pigliucci is of course correct that cladistics only considers shared derived characteristics when constructing cladograms, but that doesn't mean Wells contradicts him. Indeed, I tried to find in Icons where Wells said that cladistics is based upon mere "similarity," but I couldn't. Instead, I saw Wells alluding to Pigliucci's position by stating that under cladistics, "Organisms can only be grouped together if they share a common ancestor, and every group includes a common ancestor and all its descendants," groups called clades. (p. 118) The problem, of course, lies in determining which characters are homologous, unique only to organisms within a clade -- i.e., which are shared derived characteristics. Since by this point in the book Wells has adequately discussed difficulties associated with determining whether a trait is "homologous," his critique is apt.

Next, Pigliucci notes that it doesn't matter that Archaeopteryx isn't an "intermediate between two forms along their direct line of descent" because expecting that would hold Darwinian theory to "a standard of proof that is not required in historical sciences because it is sufficient to show that related forms appeared in the right temporal sequence and that they were intermediate to each other." (Denying Evolution, p. 255) That's an interesting claim, given that Archaeopteryx appears millions of years before its supposed theropod dinosaur ancestors, a point Wells establishes in the book, representing a highly contradictory temporal sequence.

As if Pigliucci has forgotten the argument he just made, he then says that Wells "also does not understand that ancestors can live simultaneously with their descendants." This is puzzling: Hadn't Pigliucci just said that the fossil sequence matters when establishing an intermediate form? In any case Wells, as if anticipating Pigliucci, writes:

The obvious objection that an animal cannot be older than its ancestor is discounted by assuming that the ancestral form must have been there before its descendant, but its fossil remains cannot be found. In other words, advocates of cladistics cite the imperfection of the geological record -- the very same reason Darwin gave for the troubling absence of transitional forms. As a result, however, gaps in the fossil record become more pronounced than ever before. Immense stretches of time are left with no fossil evidence to support cladistics phylogenies. (Icons, pp. 121-122)
So adherents of cladistics aren't bothered by chronological inversions in the fossil record implied by their theories. That makes it very difficult to test their theories. How ironic, therefore, that Pigliucci accuses Wells of "na�ve falsificationism" when it's just about impossible to overturn the sort of cladistics-based theories promoted by Pigliucci by referring to the chronological order of fossil evidence. In important ways, these models are unfalsifiable.

Icon 6: Peppered Moth

After stating Wells's critique on this point, Pigliucci writes that "the peppered moth case has been revised by evolutionary biologists, not by creationists." As we saw earlier with regards to Haeckel's embryo drawings, scientific discovery is true (or false) based on the evidence, not who makes it. Pigliucci is committing the genetic fallacy, thinking that the origin of an argument has some bearing on whether it's true.

In any case, he basically concedes Wells's point that the traditional moth story has problems. Pigliucci critiques the concerns raised by Wells that the pictures were staged. He writes: "There is nothing wrong with staging pictures for illustrative or didactive purposes; it is done all the time to understand certain scenarios better by seeing them reenacted, and it is done in physics and other disciplines as well." (Denying Evolution, p. 256) Here, Pigliucci is exactly right -- provided that what you're staging represents reality. Thus, as Wells points out, the problem with the photos of moths on tree trunks that are common in textbooks isn't that they were staged, but rather that they are staging something that isn't known to happen in reality -- namely, that moths rest on tree trunks where they are eaten by birds. If the staged photos represented something that really happened, then there's no problem at all. The problem is that there's great debate -- debate that's rarely disclosed to students -- about whether peppered moths actually spend time on tree trunks where they are predated by birds. Wells wrote a nice summary of the question in 2012.

The debate over moths itself has evolved quite a bit since Icons and Denying Evolution were written, and frankly in my mind it doesn't really matter much whether moths rest on tree trunks or not. Assuming the entire classical story of the moths is correct, the most that it can show are small-scale changes in the relative allele frequencies for light or dark colored moths. The fact that this story is such a staple of biology textbooks shows that some the best examples of natural selection involve trivial levels of biological change.

Icon 7: Gal�pagos Finches

Pigliucci starts off here by conceding one of Wells's central points -- that textbooks often over-extrapolate. After noting that extrapolation can be a legitimate tool of science (something neither Wells nor anyone else would disagree with), Pigliucci writes: "However, it does need to be used carefully, which was not the case in the textbooks cited." (Denying Evolution, p. 256) Pigliucci then argues that the finches "show that natural selection can cause meaningful morphological changes over a fairly brief period of time." (p. 256) Here, it's not clear exactly what Pigliucci means. The finches have been on the Gal�pagos islands for some 13 million years, and many of the "species" can still interbreed and are difficult to tell apart. Or, he may be saying that the Grants' research shows that beak sizes can change quickly, in a matter of years. Of course we're talking about millimeter-sized differences -- changes that by Pigliucci's own admission can't be extrapolated to show large-scale evolutionary change.

Pigliucci tries to claim that there are "several distinct species of finches." Yet he then undercuts this assertion, conceding that Wells is correct to state that "some of the species of finches do hybridize." (Denying Evolution, p. 256) If they can interbreed, can it be said they really are different "species"? In any case, with new information coming out that the various Gal�pagos finch "species" naturally interbreed, recent evidence doesn't support Pigliucci's claims.

Pigliucci closes by saying that "countless examples of natural selection have been measured in the field." However, in 2009, Nature collected what it thought were the best examples "to spread awareness for of evidence for evolution by natural selection." As seen in our response, many of those examples involved nothing more than trivial biological change.

I'll continue, icon by icon, in a subsequent post.