Answering Massimo Pigliucci’s Critique of Icons of Evolution

[This article was adapted from a series of articles originally published on Evolution News & Views. For the original articles, please see: Part 1, Part 2, and Part 3.]

An 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“.

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 “naïve 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: Galápagos 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 Galápagos 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 Galápagos 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.

Icon 8: Four-Winged Fruit Flies

Pigliucci doesn’t contest Wells’s critiques of the treatment of four-winged fruit flies. Instead he states that, “Only a few misguided molecular biologists (ignorant of evolution)” have claimed that “There are no known beneficial morphological mutations.” (Denying Evolution, p. 257) One would therefore expect Pigliucci to give examples of such, and he thinks he does. He writes: “There are countless examples of beneficial morphological and behavioral mutations in the technical literature.” (p. 257) No citation is given. He goes on: “If he would only stop and think for a second, Wells would realize that he carries many of these mutations himself, which is in part why he looks different from other human beings.” (p. 257)

Here Pigliucci is begging the question. No one contests that human beings have genetic differences from other species that give us our unique body plan and intellectual abilities. The question is whether random mutations can produce the kinds of changes in organisms necessary to create new body plans. Wells points out that creating four-winged fruit flies requires multiple mutations, and even then they lack flight muscles. This implies that multiple coordinated mutations are necessary to build new body plans. It would help Darwinian theory to provide evidence of mutations radically changing body plans. Pigliucci must provide this evidence, and not just assert that it exists. He thinks he can provide this evidence, and here’s the example he gives:

A typical example of a morphological mutation that is beneficial (conditionally on the specific environment encountered by the organism) is the change in skin coloration that has happened several times during the course of human evolution. (Denying Evolution, p. 257)

Pigliucci is apparently aware that increased (or decreased) melanin in the skin of humans simply means producing more (or less) of something you already can produce. He seems to anticipate that this might not be considered by Wells to be a “morphological mutation.” He thus writes: “this example also shows that the distinction that Wells makes between morphological and biochemical mutations is entirely artificial; the morphological mutations that affect the color of the skin are in fact biochemical mutations that change the rate of production of the skin’s pigment, melanin.” (Denying Evolution, pp. 257-258) Pigliucci simply asserts that this is a “morphological mutation” even though what Wells means is a mutation capable of changing the organism’s body plan. Wells explains that he’s looking for mutations that show “large-scale variation” which produce “a gain of structures” that can “supply the raw materials for morphological evolution.” (Icons, pp. 177, 186-187, 188) Can changes in skin color provide this large-scale variation and gain of new structures required for morphological evolution? Of course not. In fact, it’s noteworthy that when evolutionary biologists try to show how developmental mutations can lead to evolution, they often involve small-scale changes in coloration.

Stephen Meyer notes this in Darwin’s Doubt. He observes that the National Center for Science Education (NCSE) cited a paper in the Proceedings of the National Academy of Sciences USA to show the power of evo-devo to explain morphological evolution. He writes:

The paper did not show what the NCSE claimed, however. It did assert that changes in regulatory DNA produce “both relatively modest morphological differences among closely related species and more profound anatomical divergences among groups at higher taxonomical levels.” But the study only showed how changes in the cis-regulatory elements in fruit fly DNA might have affected the coloration of wing spots in several different types of flying insects. It did not report any significant change in the form or body plan of these insects. Instead, the study highlighted a clear case of a viable mutation generating merely a minor or superficial change. (Darwin’s Doubt, p. 317)

The same critiques could be made here: If changing the skin color in human beings amounts to the kind of “morphological mutation” that can fundamentally change the body plan or lead to new species, then Massimo Pigliucci must believe that human individuals with different skin pigments are like different species in the wild. I certainly don’t believe this is the case, and I strongly doubt that he does either.

In any case, if changes in pigment levels in humans — which he admits merely “change the rate of production of the skin’s pigment, melanin” (i.e., changing the rate at which you produce something you already have) — is his best example of a “morphological mutation,” we can rest assured that evolutionary biology cannot provide the kind of morphological mutations Wells is looking for.

Icon 9: Horses

Pigliucci claims that Wells “acknowledges that the current view of the evolution of horses is very likely to be correct” (p. 258), not noting that Wells discusses chronological inversions that afflict the horse series. But it also seems that Pigliucci doesn’t contest Wells’s central claim that Darwinian evolution implies materialistic conclusions. Pigliucci concedes, “General statements by evolutionary biologists that natural selection is a purposeless and directionless process are consistent with the evidence, since nobody has been able to demonstrate either a purpose or a direction in it.” (p. 258) Pigliucci plainly states: “There is simply no empirical evidence … to support either purpose or direction in nature.” (p. 258) So what is wrong with Wells’s claim? According to Pigliucci, the materialistic assumption that evolution is purposeless and directionless “has worked very well in practice, and Wells provides no reason to abandon it.” (p. 258) Except, I suppose, for all of the evidence Wells has shown throughout his book that the evidence does not support the claims of neo-Darwinian theory.

Icon 10: Human Evolution

Here, Pigliucci acknowledges that Wells is correct that the Piltdown story was a hoax, but once again the only point he can make is that the “hoax was actually uncovered by evolutionary biologists, not creationists.” (Denying Evolution, p. 258) I don’t know if his claim is true, but once more, what matters isn’t who made a discovery but whether the discovery is true. Yet again, Pigliucci is committing the genetic fallacy, suggesting that the truth of a claim depends on who is making it. Pigliucci then claims that Wells “admits in his book, the hominid fossils discovered after Piltdown are genuine and do show intermediate stages of human evolution.” (p. 259) I’ve looked through Chapter 10 of Icons of Evolution and I can find no such admission. Instead, I see Wells stating the following — written in the subjunctive:

In the twentieth century, the ultimate icon seemed to acquire the evidence it initially lacked. Numerous fossil discoveries supplied what appeared to be transitional links in the evolutionary chain leading to modern humans; experiments on peppered moths and other organisms seemed to provide the missing evidence for natural selection; and geneticists thought they had found the raw materials for evolution in DNA mutations. (Icons, p. 211)

Now we already know that Wells doesn’t believe that the peppered moth or similar stories provide evidence for natural selection. Nor does he think that geneticists have discovered raw materials for evolution in DNA mutations. Thus, given Wells’s use of subjunctive, it’s safe to assume he also doesn’t really think that fossils have shown the “transitional links” leading to modern humans. The rest of the chapter bears this out. He notes that supposed intermediate fossils have been called “bones of contention” where “each new discovery seems to add to the problem rather than alleviate it.” (Icons, p. 218) Wells challenges the idea that one can show human evolution using fossils — and he certainly doesn’t make the concessions Pigliucci claims he does. In any case, for a lengthy discussion of how the fossil evidence doesn’t support human evolution from ape-like creatures, see our book Science and Human Origins.

Pigliucci closes by acknowledging “the abysmal state of the textbook publishing industry.” He agrees that biology textbooks can contain “mistakes and inaccuracies.” (Denying Evolution, p. 259) Having reviewed his treatment of Jonathan Wells’s book, I can’t find a single legitimate problem that Pigliucci has identified with Icons of Evolution. Instead, I see that Pigliucci has conceded that many of Wells’s complaints about biology textbooks are valid, including Wells’s central point that textbooks can be highly inaccurate. When Pigliucci disagrees with Wells, he repeatedly puts words in in the latter’s mouth and cites evidence or data that doesn’t actually refute Wells’s argument. The icons of evolution remain problems for Darwinian theory, some 14 years after Jonathan’s book was written. Icon by icon, I would say that makes a solid, if not a perfect ten.

Casey Luskin

Associate Director and Senior Fellow, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.