This series began when ENV writer Jonathan M. asked some tough questions of PZ Myers about evolution and embryology at a Skeptics event in Glasgow, Scotland. As a recap of this series, below are links to ENV articles which have appeared on this topic:
• Part 1: Colliding With the Pharyngula: My Encounter With PZ Myers: Jonathan M. gives his firsthand account of what happened at PZ Myers’ lecture.
We’re a little past midway through my series responding to PZ Myers on evolution and embryology, and PZ has already posted a short reply. Unsurprisingly, PZ’s reply is full of his typical name-calling. He writes that my recent article is “embarrassing,” a “cacophany of inanity,” and “stupid.” In case you didn’t get the message, PZ closes his post saying, “Go back to third grade, Casey. You are a very silly, ignorant fellow.”
I’m not angry at PZ for how he’s treating me. Rather, I find it encouraging: When PZ uses incendiary rhetoric like this, it’s a good sign that my arguments are sound. Moreover, his behavior cannot help but show open-minded readers that he’s lacking good scientific and logical rebuttals, and instead is forced to rely on mockery to prevent people from taking ID arguments seriously. Read PZ’s reply to me and you’ll see that he responds to essentially none of my arguments.
PZ’s Two Points
The name-calling aside, PZ makes two points in his short reply:
(1) PZ reiterates his belief that “there are differences between vertebrate embryos,” notes that “the differences have been known for a long time,” and reminds us of his credentials while doing a little academic name-dropping. That’s fine and good and doesn’t contradict anything I wrote. What PZ hasn’t done is explain why he contradicted himself in the past by wrongly claiming that the differences between early vertebrate embryos were merely “superficial.”
(2) PZ’s reply also reiterates his view that Darwinian evolution predicts both similarities and differences, stating: “Look at a cat and a dog. They are different animals; they have different forms and behaviors. However, they also have deep similarities: they are mammalian carnivores, they have the same basic bone structure, they have very similar physiologies. Any theory that purports to explain the existence of these two organisms must account for both the similarities and differences. Evolution would be falsified if it predicted that every organism was exactly the same, or if it predicted that every organism was completely different, because that isn’t what the real world looks like.” Again, PZ’s trivially true second point (which is followed by more personal attacks, in case you were wondering) is not only correct, but also does not contradict anything I wrote.
PZ apparently thinks that I am disagreeing with his description of evolutionary biology, thereby misunderstanding what the theory claims. That’s wrong. In fact, I think his admission that “evolutionary theory predicts differences as well as similarities” is generally accurate. I never denied that this is what evolutionary biology claims. I just said it doesn’t make for a very useful theory (more on this below).
PZ’s point (2) thus completely misses my argument on many levels and does not respond to my arguments. For example:
(a) If you’ve been following this debate, then you should immediately see that PZ has just tried to change the subject. I had previously quoted PZ stating “evolutionary theory predicts differences as well as similarities” in regards to vertebrate development. Since PZ’s reply talks about comparing “bone structures” and “behaviors,” it’s clear that he’s not talking about similarities and differences in early embryonic stages of cats and dogs; he’s making postnatal comparisons. But if we remain on topic, and continue to talk about evolution’s predictions regarding early vertebrate development, my article extensively documents that evolutionary biologists have argued for specific types of similarities between vertebrates in their early embryonic stages. But these similarities haven’t been found.
To review, according to embryologist Michael Richardson, “many biologists” have believed that early stages of vertebrate embryos ought to be similar because those early stages are crucial to organismal development and thereby resistant to evolutionary change. Pro-ID student Jonathan M. was correct to note in response to PZ that many evolutionary biologists have predicted such a “funnel-like model” of development, but that the funnel-like model is not supported by the data.
This funnel-like model is not irrelevant to modern evolutionary thinking and is still perpetuated in many textbooks. Moreover, the failure of the funnel-like model has perplexed a modern evolutionary scientist or two, who assume that embryogenesis was programmed by Darwinian evolution. As a 2011 paper in Nature Communications asked:
One unanswered question in this field is how pharyngular stages became conserved. … [H]ow did vertebrate embryos allow the early developmental stages to diverge while keeping the following stage essentially unchanged? For example, in spite of considerable phylogenetic divergence in the mechanisms of vertebrate germ layer formation and gastrulation among the four species we analysed, all these embryos pass through the conserved pharyngula stage.
(Naoki Irie & Shigeru Kuratani, “Comparative transcriptome analysis reveals vertebrate phylotypic period during organogenesis,” Nature Communications, Vol. 2:248 (2011).)
From an evolutionary vantage, the evolution of vertebrate development almost appears goal-directed, where embryos if many taxa start off developing very differently but then converge on a somewhat similar stage midway. (We’ll talk about challenges to that allegedly conserved pharyngular stage in an upcoming article.) So how could Darwinian evolution preserve a midpoint of development as similar, when embryos start development so differently? The authors aren’t sure, and their article grasps for an evolutionary explanation that almost hints at a goal-directed evolutionary process:
For example, in spite of considerable phylogenetic divergence in the mechanisms of vertebrate germ layer formation and gastrulation among the four species we analysed, all these embryos pass through the conserved pharyngula stage. How did vertebrates establish divergence of early embryogenesis while keeping pharyngular stages conserved? One reasonable deduction from this observation is that early vertebrate embryogenesis reduces the developmental fluctuations, which tend to occur around these stages, much like earthquake-resistant buildings that are built with the ‘flexible structure’.
So early stages of development are “built” to divergently evolve in a way that reduces changes to later stages of development? And we find this same pattern of development repeated throughout many different species of vertebrates? This almost sounds like a goal-directed and non-Darwinian form of evolution, which is precisely why early differences between vertebrate embryos were not predicted or anticipated by many evolutionary biologists.
PZ does not address these problems, and instead tries to save evolutionary embryology from failed predictions by putting evolution in an unfalsifiable position with regards to developmental patterns, denying that the theory makes any real predictions about similarities or differences in embryos. Thus we end up with his claim: “evolutionary theory predicts differences as well as similarities.” Since the theory which can explain anything really explains nothing, he’s left us with a pretty useless theory. But PZ’s prior backpedaling, and present shuffling about cats and dogs, don’t negate the specific failed prediction of many evolutionary biologists that early stages of vertebrate development ought to be conserved. Apart from acknowledging that we were right that the funnel-like model is wrong, PZ has not responded to this point; instead he changed the subject.
(b) Despite PZ’s evasive response that “evolutionary theory predicts differences as well as similarities,” we saw that PZ himself at times buys into the argument that evolution ought to conserve early vertebrate developmental stages. As I documented, PZ has argued: “the phylotype really does represent a literal foundation upon which the rest of development proceeds, and is resistant to evolutionary change, because there are too many later events that are dependent on it.”
PZ has not explained why he has now changed his tune, denying that developmental similarities are predicted by evolution, when in the past he has claimed evolutionary biology predicts certain developmental similarities. PZ didn’t reply to my point that he is trying to have it both ways, where the differences between early stage of vertebrate embryos don’t count as evidence against common ancestry, but the similarities do count as evidence for common ancestry.
(c) PZ also did not respond to my point that he conflated Haeckelian recapitulation with the funnel-like model of development for the purpose of attacking Jonathan M. He also hasn’t explained why he continuously misrepresents our arguments as if we are attacking Hackaelian recapitulation, when we recognize that Haeckel’s recapitulation model was long-abandoned by evolutionary biologists.
As a final point, contra PZ, I’m not saying anything remotely like his false caricature of my position that evolutionary biology predicts “that every organism was exactly the same, or … completely different.” In fact, PZ is wrong to think that I am contesting his description of evolutionary biology. Much to the contrary, I think his admission that “evolutionary theory predicts differences as well as similarities” is exceptionally candid, and is a generally accurate description of evolutionary theory. I’m not saying PZ has misdescribed Darwinian theory. I’m just saying his description shows evolution doesn’t make for a very useful theory.
Darwinian theory, which is grounded in the notion of ‘descent with modification,’ certainly allows species to have both similarities and differences. But such a prediction is so vague and open-ended that evolutionary biologists often have difficulty determining which similarities are the result of descent, and which are the result of modification. This can make it very difficult to reconstruct supposed phylogenetic trees.
While some of the predictions of Darwinian theory are thus fairly useless, the theory does make at least one testable prediction: descent with modification implies that we should be able to categorize those similarities and differences into a nested hierarchy–a tree of life. It turns out the data commonly conflict with such a pattern, and the tree of life has collapsed. (See here for a conversation about this fact.) So in my view, the few useful predictions that neo-Darwinism does make about similarities and differences between species have been proven false by the data.
We’re only midway through my series rebutting PZ Myers, and he’s already responding with statements like we saw above. I’m certainly not upset at PZ, but I think his tone tells us something: PZ has not responded on a scientific level to any of my arguments, instead changing the subject to avoid explaining his contradictions. This provides further evidence that PZ has no logical or scientific rebuttals to our points. Instead, he relies on mockery to deflect from weaknesses in his own arguments.