On the sixth of June, I had the opportunity to attend a lecture presented by PZ Myers (of the University of Minnesota Morris) to Glasgow Skeptics in the Pub. PZ Myers is probably best known for his popular blog, Pharyngula (which bears the tag line, “Evolution, Development, and Random Biological Ejaculations from a Godless Liberal”). He has also acquired somewhat of a reputation for his militant and aggressive stances on evolution and religious belief. The topic of Myers’ presentation was the embryological/developmental evidence for evolution.
Accompanying me at the event were Dr. Alastair Noble (the director of the Centre for Intelligent Design UK) and David Swift (author of what is, in my opinion, one of the best books on the subject of the debate over ID and evolution, Evolution Under The Microscope).
A week prior to the lecture, I had published a short article on Uncommon Descent issuing a series of questions for PZ Myers, all of them pertaining to developmental biology. PZ Myers responded dismissively on his blog, ridiculing the list and promising answers to the questions the following week. So far, they haven’t been forthcoming: In view of a similar situation involving Paul Nelson, perhaps Sunday 12th June should be denoted “PZ Myers Sunday.”
Myers did mention the questions at the beginning of his lecture (describing yours truly as a “flaming moron”). He did not, however, despite promising to do so, provide satisfactory rebuttals to the questions at all during the course of his presentation (though he did attempt a response to one of the ten questions).
During the course of the Q&A, I raised a question concerning the lack of congruence between homology and developmental pathways, citing several papers to substantiate my claims (which I gave to PZ following the talk). What ensued was an eruption of jeering and mocking from the floor. It became so loud at one point that it was difficult to audibly articulate the point. A few people apologised afterwards.
One atheist sent me a message afterwards saying, “I went along with a sense of fun thinking that there’d be a few jokes on either side, but it got a little like playground bullying there. I suppose that’s what you’d expect since PZ acquired his reputation partly by taking aggressive stances.” A friend wrote to me following the event, commenting “Obviously things were quite heated the other night. I couldn’t believe how hostile the room got to you asking a question. A lot of emotion but no arguments.” David Swift said of the event, “I think PZ’s behaviour last night was outrageous. Just not sure how to respond, if at all. I think any response would just be scoffed at in the same way as any dissenting voice was treated last night. … [T]here was no attempt whatsoever to engage in discussion, not even any acknowledgment that there was any question to answer.”
Homology and Development
The point which I had raised in the Q&A concerned the fact that there exists widespread variation in embryological processes and genetic mechanisms giving rise to apparently homologous organs, and there is also the related problem of homologous structures arising from different embryological sources. I provided several examples of this which have been documented in the literature. Remarkably, Myers seemed to contest my claim that this was actually the case, and I delivered a few papers to him afterwards in support of this contention, and I would also direct my readers to these papers to verify that my claim is both true and very well documented (e.g. Alberch 1985; Scholtz 2005). According to the Alberch paper (the claims of which remain true to this day), it is noted that it is “the rule rather than the exception” that “homologous structures form from distinctly dissimilar sites.”
Moreover, as noted by the preface of the textbook, Gastrulation — From Cells to Embryo (editor Claudio Stern),
Perhaps the most remarkable lesson to come out of this volume concerns the great diversity of strategies that are used by different species to do what appears to be the same thing. Thus, one species forms its mesoderm by ingression of individual cells, another species generates it by involution, yet another by a combination of the two. Genetic pathways are also conserved, but how they are deployed (if at all) to control particular events differs very greatly among different groups of animals. (page x)
Furthermore, David Swift (whom, as I mentioned, was also present at the event) has noted,
Notably, in view of the importance attached to the apparent homology of the vertebrate skeleton, and the weight given to embryology for identifying homology, it is especially relevant that vertebrae – a major component of the vertebrate skeleton – form embryologically in significantly different ways for different classes of vertebrate (such as mammals, birds, amphibians and fish), and even from different groups of early embryonic cells. (For example, see Vertebrates: Comparative anatomy, function, evolution by K. Kardong.) This clearly shows that the vertebrae of these different vertebrate classes are not, in fact, homologous – and hence that these different groups of vertebrate do not in fact share a common vertebrate ancestor, despite their superficial similar appearance and contrary to the commonly held view.
For further discussion, please see Casey Luskin’s comments here.
The only way, it seems to me, to get around this apparent paradox is to postulate that substantial changes in development have occurred — and at very early stages of development. But there seems to be two main problems with this proposal, both of which I mentioned in the Q&A:
1. These changes in very early development would need to have occurred in organisms which were very advanced (i.e. where there was a lot of development following the point at which development changed). But given that it is the final form which is the primary object of natural selection, it is difficult to conceive of what might have led to such changes in early development.
2. Even more damning is the fact that changes in early development , far from being advantageous, are likely to be seriously detrimental if not lethal.
Is There A Conserved Embryonic Stage?
As for the substance of Myers’ talk, there was nothing new. The main thrust of his argument was the apparent similarity of vertebrate embryos at the pharyngula (“phylotypic”) stage of development. Putting up a slide displaying three tetrapod embryos, he announced, “This is a pharyngula,” inviting the audience to try to tell him what species of embryos were being displayed — which turned out to be a human, a dolphin and a cat. His point was that the embryos look so similar at that stage of development that it is difficult to tell them apart without specialised knowledge of embryological anatomy. While Myers is absolutely correct that some vertebrate embryos appear to resemble each other somewhat at the pharyngula stage, one of the main shortfalls of the argument is that the case is only particularly persuasive when you take into account only a very narrow range of species (this was, incidentally, one of the many problems with Haeckel’s notorious depiction as well). The problem is that when you expand the data set to include a much larger sample, the case quickly becomes far less convincing. In the case of Haeckel, the embryos portrayed in the four right-hand columns of his depiction are all from the same order of mammals. In The Politically Incorrect Guide To Darwinism and Intelligent Design, Jonathan Wells observes that “Haeckel omitted embryos from the other two orders of mammals that include platypuses and kangaroos. He also omitted the two classes of vertebrates that include lampreys and sharks, and the order of amphibians that includes frogs–all of which look quite different from the groups portrayed [in Haeckel’s drawings].”
Indeed, in 1997, Michael Richardson and his colleagues published a very famous paper in the Journal of Anatomy and Embryology, which bore the title, “There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development.” The paper reported,
In view of the current widespread interest in evolutionary developmental biology, and especially in the conservation of developmental mechanisms, re-examination of the extent of variation in vertebrate embryos is long overdue. We present here the first review of the external morphology of tailbud embryos, illustrated with original specimens from a wide range of vertebrate groups. We find that embryos at the tailbud stage – thought to correspond to a conserved stage – show variations in form due to allometry, heterochrony, and differences in body plan and somite number. These variations foreshadow important differences in adult body form. Contrary to recent claims that all vertebrate embryos pass through a stage when they are the same size, we find a greater than 10-fold variation in greatest length at the tailbud stage. Our survey seriously undermines the credibility of Haeckel’s drawings, which depict not a conserved stage for vertebrates, but a stylised amniote embryo. In fact, the taxonomic level of greatest resemblance among vertebrate embryos is below the subphylum. The wide variation in morphology among vertebrate embryos is difficult to reconcile with the idea of a phyogenetically-conserved tailbud stage, and suggests that at least some developmental mechanisms are not highly constrained by the zootype. Our study also highlights the dangers of drawing general conclusions about vertebrate development from studies of gene expression in a small number of laboratory species. [emphasis added]
In a more recent (2003) paper in Proceedings of the Royal Society B, titled “Inverting the hourglass: quantitative evidence against the phylotypic stage in vertebrate development,” Richardson and his colleagues report,
… [T]he phylotypic stage has never been precisely defined, or conclusively supported or disproved by comparative quantitative data. We tested the predictions of the ‘developmental hourglass’ definition of the phylotypic stage quantitatively by looking at the pattern of developmental-timing variation across vertebrates as a whole and within mammals. For both datasets, the results using two different metrics were counter to the predictions of the definition: phenotypic variation between species was highest in the middle of the developmental sequence. This surprising degree of developmental character independence argues against the existence of a phylotypic stage in vertebrates. Instead, we hypothesize that numerous tightly delimited developmental modules exist during the mid-embryonic period. Further, the high level of timing changes (heterochrony) between these modules may be an important evolutionary mechanism giving rise to the diversity of vertebrates. The onus is now clearly on proponents of the phylotypic stage to present both a clear definition of it and quantitative data supporting its existence. [emphasis added]
Of particular astonishment to me was Myers’ attempt to defend Ernst Haeckel’s famous embryo diagram, noting that “creationists” (I guess by that he means anyone who disagrees with Darwinism) take strong exception to the inclusion of these diagrams in biology textbooks. He stated that the charge of forgery is somewhat unfair, and — while conceding that Haeckel had a tendency to exaggerate the similarities — also noted that “This diagram is an honest illustration of the developmental stages.”
This claim surprised me. Criticism of these drawings is not limited to creationists and proponents of ID. As I have noted previously on this site, Haeckel’s diagrams have also been criticised by people such as Stephen Jay Gould and Michael Richardson (see also Casey Luskin’s comments here and here). Stephen Jay Gould called Haeckel’s embryo drawings “fraudulent” and wrote: “We do, I think, have the right to be both astonished and ashamed by the century of mindless recycling that has led to the persistence of these embryo drawings in a large number, if not a majority, of modern textbooks.”
And these drawings have been withdrawn from many textbooks — even by notorious ID-critic Brown University biologist Kenneth Miller. In 2008, it was asserted by The New York Times that the “longdiscredited” drawings of Haeckel have not been printed since “20 years ago” (a claim which is, by the way, absolutely false). The anti-ID film “Flock of Dodos” made a similar claim. Why bother to remove them from textbooks if they are “an honest illustration of the developmental stages”? Moreover, given that Haeckel’s drawings were intended to demonstrate recapitulation, it does seem somewhat disingenuous that he omitted the earliest stages in development, at which the various classes of mammals are strikingly different.
Myers then progressed into a discussion of Hox genes, and their role in the regulation of Drosophila development, pointing out that one can find homologous Hox genes ordered in the same way in the chromosome of the mouse and Drosophila fruit fly. I have always tended to view the argument for common ancestry as being quite weak here. Such instances of similarity can surely be explained with reference to common design. And, at any rate, the conservation of these Hox genes and their utilisation in different ways in different organisms perhaps ought to be taken as suggestive of teleology or some kind of front-loaded design (e.g. Sherman 2007).
Moreover, the argument seems to be guilty of cherry-picking. In many cases, similarities are found which are too close for an evolutionary explanation! One particularly clear example is the embryological development of the eye. Back in the 1970s, biologists categoried the eyes of different groups of organisms according to embryonic origin and final structure, and thus determined where it was reasonable to infer that an eye had been inherited from one group to another. They concluded that the eyes must have evolved independently at least 40 different times.
However, we have now learned that in species as different as insects and mammals (which possess compound and camera eyes respectively) — the common ancestor of which, according to evolutionary reckoning, lived so long ago that it did not have eyes — the embryological formation of the eyes uses remarkably similar genes (e.g. eyeless and Pax6 respectively). This becomes particularly problematic for the Darwinist when one considers that the respective developmental mechanisms utilise similar genes (e.g. sine oculus and Six) in later stages of development (rendering implausible the thesis that the common ancestor had some sort of rudimentary eye that used the common gene in its development, the use of which has persisted through the evolution of the different types of eye structure).
Distortions Caused By Yolk?
PZ Myers also claimed that many of the differences we observe during various stages of development can be accounted for in terms of distortions caused by yolk. This claim, however, is incorrect, as a reading of any text on development will highlight. The differences go well beyond the amount of yolk. Actually, as documented by Kalinka et al. (2010), even the patterns of gene expression are very different at the early stages.
Is Jonathan Wells “The Most Contemptable, Despicable, Cruel, And Vicious Evil Liar In The Creationist Movement Today”?
PZ Myers projected a slide displaying a portrait of Jonathan Wells, noting that “I have to single out this man, whom I consider the most contemptable, despicable, cruel, and vicious evil liar in the creationist movement today,” apparently spitting the words out one by one. He paused. And then, as if to emphasise the point, said, “Yes. He’s a nasty, nasty person.” This was met with rapturous applause.
Myers then put up a slide headed “Creationist Claims.” These were:
- Evolution is built on a foundation of Haeckelian Recapitulation
- There is a conspiracy of silence among biologists to hide disconfirmation
- We can thank the brave scientists of the Discovery Institute for exposing the truth.
Myers then noted that we have known for more than a century that Ernst Haeckel was wrong about his principle of recapitulation, and thus Jonathan Wells has got it all wrong.
Generally, when you are claiming that an opponent is misreprseenting literature (as Myers subsequently did), it pays to ensure that you are not guilty of the allegation yourself (though, admittedly, Myers does have a bit of a history of that).
A casual reading of chapter 3 of Wells’ The Politically Incorrect Guide to Darwinism and Intelligent Design (which was cited by Myers) reveals that Wells, in fact, tells us that “Haekel’s fakery was exposed by his own contemporaries, who accused him of fraud, and it has been periodically re-exposed ever since.”
Myers then put up a slide containing a section clipped from page 35 of Wells’ The Politically Incorrect Guide to Darwinism and Intelligent Design, containing a quotation from William Ballard:
It is “only by semantic tricks and subjective selection of evidence,” by “bending the facts of nature” that one can argue that the early embryo stages of vertebrates “are more alike than their adults.”
Myers then noted that nobody thinks that the earliest stages of development are similar. He then put up a slide with the complete quotation which Wells attained from William Ballard, which said,
Before the pharyngula stage we can only say that the embryos of different species within a single taxonomic class are more alike than their parents. Only by semantic tricks and subjective selection of evidence can we claim that “gastrulas” of shark, salmon, frog and bird are more alike than their adults.
Myers thus claimed that Wells has “butchered a quote in order to make this point for himself,” noting that Ballard was talking about the gastrula stage of development. But this seems to me to be disingenuous on Myers’ part, because the gastrulation stage of development is a very early stage. Wells’ point was that, in the context of Darwinism, one would expect to see strong conservation of early developmental stages. Myers also alleged that Wells quoted Ballard in order to argue that “there is no uniform stage in vertebrates.” But if you read the quote from Wells’ book again, you will find that that’s not what Wells was saying at all — he was saying that the early stages are very dissimilar.
When Myers briefly mentioned my set of questions at the beginning of his presentation, he attempted to address the first question which concerned these stark differences. In response, he claimed that Darwinian evolution does not predict that these stages should be highly conserved, thus claiming that such an answer constitutes a satisfactory rebuttal to the question I posed. But it seems to me that Myers is dead wrong here. The reason for this is that modifying the early developmental stages is known to be uniformly detrimental — more often than not lethal — to the organism.
Summary and Conclusions
PZ Myers concluded his talk by alleging that ID proponents never do experiments in order to gather evidence for their theory. Clearly, he hasn’t been paying much attention to the Biologic Institute and Evolutionary Informatics Lab. All in all, it was a rather disappointing event. Myers presented absolutely nothing which was news to me. He claimed towards the end that “you have to be both ignorant and stupid to believe in intelligent design.” But Myers’ presentation was barely about intelligent design. At best, all his case demonstrated was common ancestry — a proposition which is perfectly compatible with intelligent design. It is regrettable that PZ Myers should, in spite of his good intellect and scholarly credentials, distort the facts in such a way. As one person said to me following the event, PZ Myers is another example of a growing band who deliberately plough ahead with their own agenda irrespective of the conclusions suggested by the evidence. And it is not scientific.
You can now watch the full presentation (minus the Q&A) here: