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Answering Massimo Pigliucci's Critique of Icons of Evolution

Pigliucci.jpgAn email correspondent recently wrote to me citing various challenges to Jonathan Wells's book Icons of Evolution, including a critique by evolutionary biologist and philosopher Massimo Pigliucci in his 2002 book Denying Evolution: Creationism, Scientism, and the Nature of Science. This provided a welcome reminder to me to go back and consider Pigliucci's criticisms. He gives a chapter-by-chapter response to Wells's book, but I must confess that I found the substance to be extremely inadequate to show Wells was wrong.

Before Pigliucci even begins his analysis, we see the kind of rhetorical attacks that are typical of evolution-defenders. Of course the title "Denying evolution," has ugly overtones and suggests that skeptics of Darwinian theory are close-minded, or worse. He calls Wells an "intelligent design creationist" and claims his own goal in responding to Wells is to show how we can "produce a rational population that will be naturally immune to creationist and other pseudoscientific nonsense." (Denying Evolution, p. 252) He then states that the icons have been converted into bookmarks "with the explicit purpose of 'embarrassing' ... teachers." (p. 252) There's a footnote at the end of the sentence where he quotes comments by those he calls "Discovery Institute creationists." However, the comments say nothing about "embarrassing" anyone, and in fact quote a parent, Mark Hartwig, who praises his daughter for challenging a teacher's evolutionary claims: "She did it very politely."

But Pigliucci's initial rhetorical posturing doesn't get to the substance of the scientific questions. Is Jonathan Wells right to maintain that many of the common lines of evidence enlisted to support biological and chemical evolution are flawed?

Icon 1: The Miller-Urey Experiment

Here, Pigliucci correctly states Jonathan Wells's argument, namely that the Miller-Urey experiment "was based on an incorrect hypothesis concerning the chemical composition of the early earth." (Denying Evolution, p. 252) Pigliucci says that Wells is wrong because "The origin of life is not a field of research within evolutionary biology." (p. 253) That may be true, but Wells never claims otherwise. His book is a critique of how evolution is taught in textbooks, and since most textbooks teach about the Miller-Urey experiment, often calling it evidence of "chemical evolution." Therefore, it is legitimate for Wells to discuss the origin of life in a book about "evolution," and Pigliucci's comments don't touch upon Wells's arguments.

Pigliucci acknowledges that "Scientists still disagree on the composition of the early atmosphere" -- basically conceding one of Wells's central points. The problem, Wells explains, is that textbooks often discuss the Miller-Urey experiment as if it was valid, when in fact there are many scientists who feel it is irrelevant to conditions on the early Earth. Finally, Pigliucci states, "The origin-of-life field is not in disarray as Wells implies" and instead "new hypotheses and experiments are being produced at a rapid pace." This seems like an odd statement to me, given that the very next year Pigliucci admitted:

We really don't have a clue how life originated on Earth by natural means.

(Massimo Pigliucci, Where Are We Going?, page 196, in Stephen C. Meyer and John Angus Campbell, eds., Darwin Design and Public Education (East Lansing Michigan: Michigan State University Press, 2003).)

Given this admission from Pigliucci, it's safe to say that Wells isn't off-base to question the adequacy of theories of chemical evolution.

Icon 2: The Cambrian Explosion and the Tree of Life

On the Cambrian explosion, Pigliucci's main response is to assert that it "occurred over tens of millions of years, very likely more than that." (p. 253) As I discussed here, numerous recent mainstream scientific sources date the Cambrian explosion to 5 to 10 million years, just as does Jonathan Wells.

Pigliucci then states that there are "Precambrian forms," but they are "difficult to relate to modern phyla precisely because they show mixed characteristics, which is what one would expect from evolutionary theory." He's right that Precambrian organisms are difficult to connect to modern phyla, but he's wrong that they look like evolutionary precursors. Earlier in the book Pigliucci had cited the Ediacaran fauna, but as Stephen Meyer explains in Darwin's Doubt, many experts doubt that these organisms were ancestral to the Cambrian animals. Meyer quotes Cambrian specialists Valentine, Erwin, and Jablonski stating that the Ediacaran fossils "do not tend to share definitive anatomical details with modern groups." Meyer quotes other experts: "It is genuinely difficult to map the characters of Ediacaran fossils onto the body plans of living invertebrates." Or as Nature stated, the Ediacaran fossils "bore little or no resemblance to any other creatures, either fossil or extant."

Pigliucci makes another common evolutionary explanation for the Cambrian explosion -- the artifact hypothesis -- claiming that, "The Precambrian fossil record is still too sparse, and all of the ancestral storms were softbodied animals, which rarely fossilize." (p. 253) Meyer also deals with this objection, noting that the late Precambrian geological records do contain soft-bodied fossils, as well as the kind of strata that ought to preserve soft-bodied fossils -- they just don't preserve specimens that could have been evolutionary ancestors to the Cambrian animals. Chapters 3 and 4 of Darwin's Doubt explain this in detail.

Finally, Pigliucci tackles horizontal gene transfer (HGT), noting that it "complicates, but does not negate, evolution." Jonathan Wells never denies horizontal (or "lateral") gene transfer, and discusses it in his chapter on the tree of life. So what's Pigliucci's point? He may be correct that HGT doesn't make evolution impossible, but it does conspicuously produce a pattern that is incompatible with a "tree of life," long cited by evolutionary biologists as evidence for evolution. As my co-authors and I explain in Discovering Intelligent Design:

To attempt to explain this non-treelike pattern, materialists like Doolittle appeal to a process called horizontal gene transfer (HGT). In this process, microorganisms obtain genes through mechanisms other than inheritance from a parent, specifically by sharing and swapping genes with their neighbors. For example, they might swap segments of DNA with neighboring cells.

The HGT process has been observed in nature -- for example, it can spread beneficial traits like antibiotic resistance between bacteria. But evolutionary biologists have extrapolated this process -- claiming it applies also to much more complex organisms. This means that when genes appear to invalidate a phylogenetic tree, evolutionists often think they can ignore the conflict, instead blaming it on horizontal gene transfer.

But there are two main reasons why HGT does not validate common descent:

  • A number of the tangled pathways at the base of the tree of life (see Figure 13-3) result from genes that encode fundamental cellular machinery. While HGT can occur with some bacterial genes, it is highly unlikely that it could occur with all these essential genes.
  • Conflicts within the tree of life are also prevalent among more complex organisms -- such as plants or animals -- where such geneswapping is not directly observed.
Evolutionary biologists claim that HGT can cause conflicts in phylogenetic trees. They then use circular reasoning to claim that conflicts between phylogenetic trees are evidence for horizontal gene transfer. They ignore the possibility that the conflicts exist because common descent is false.

Consider this analogy: A store manager tells the owner that the cash register is infested with money-eating microorganisms. "In fact," he insists, "money missing from the cash register is proof that that these bugs exist." Perhaps this is possible, but a responsible owner would not ignore other possible explanations. (Discovering Intelligent Design, pp. 148-149)

Icon 3: Homology

Next Pigliucci tackles Wells's arguments about homology, saying: "Wells does not understand basic concepts in philosophy of science." Pigliucci claims, "A perfectly noncircular way to think about homology is that similarities among organisms that cannot be explained by functional commonalities (i.e., same usage of similar organs) are the result of common descent." But Wells tackles this definition in his book, using as his primary example of homology the similarities among vertebrate limbs, which are said to result not from functional constraints, but from common descent. Wells points out that "biologists have known for decades that homologous features are not due to similar genes" (Icons, p. 62). This throws Pigliucci's definition of homology into doubt.

Pigliucci also says, "Alternatively, common descent can now be established by independent means (through the use of molecular data, for example), again avoiding circularity." (Denying Evolution, p. 254) But Wells anticipates this argument in his book, noting "The third (and currently most popular) way to deal with the problem is to define homology in terms of common ancestry and then seek evidence for descent with modification that is independent of homology. Such evidence may come from pattern (DNA sequence comparisons or the fossil record)." (Icons, p. 66) So have molecular data established common ancestry? Again, we turn to Wells's previous chapter, which notes that biologists have all but given up on trying to sequence the DNA of microorganisms to reconstruct the base of the tree of life. In fact, since Wells wrote in 2000, problems in the tree of life have only gotten worse. Stephen Meyer writes about this in Chapter 6 of Darwin's Doubt. Or see here: "A primer on the tree of life".

I'll have more to say on Pigliucci's critique in subsequent posts.