Pharyngula

This article is part of a series of critiques of Jonathan Wells’ The Politically Incorrect Guide to Darwinism and Intelligent Design that will be appearing at the Panda’s Thumb over the course of the next week or so. Previously, I’d dissected the summary of chapter 3. This is a longer criticism of the whole of the chapter, which is purportedly a critique of evo-devo.

Jonathan Wells is a titular developmental biologist, so you’d expect he’d at least get something right in his chapter on development and evolution in The Politically Incorrect Guide to Darwinism and Intelligent Design, but no: he instead uses his nominal knowledge of a complex field to muddle up the issues and misuse the data to generate a spurious impression of a science that is unaware of basic issues. He ping-pongs back and forth in a remarkably incoherent fashion, but that incoherence is central to his argument: he wants to leave the reader so baffled about the facts of embryology that they’ll throw up their hands and decide development is all wrong.

Do not be misled. The state of Jonathan Wells’ brain is in no way the state of the modern fields of molecular genetics, developmental biology, and evo-devo.

Here’s my shorter version of Wells’ chapter 3, titled “Why you didn’t ‘evolve’ in your mother’s womb.” It may sound familiar to many of you.

The strongest evidence for Darwin’s theory was embryology, but Karl Ernst von Baer, who laid out the laws of development, did not think they supported evolution, and Ernst Haeckel twisted and distorted von Baer’s laws and faked his data to support Darwinism. He was wrong, and the earliest stages of vertebrate embryos do not resemble one another at all, so Darwinism was built on a false foundation, and they’re still using Haeckel’s faked data in our textbooks. Oh, and mutant fruit flies are still just flies.

That’s right, it’s a rather boring rewrite of a premise of his book, Icons of Evolution, which I hammered on over three years ago. He hasn’t learned a thing since, and he’s making exactly the same arguments. I’ll take a different tack this time and expose the sleight of hand he’s pulling.

Here’s the centerpiece of his ploy. It’s a basic concept in evo-devo, proposed in the early 1990s by Duboule and Raff as a summary of 150 years worth of observations, called the developmental hourglass.

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What it illustrates is that we have great diversity in the earliest stages of development, in the blastula and gastrula and neurula, but that they all converge on a more similar form, the pharyngula, at what’s called the phylotypic stage…and then they diverge once again to achieve the diversity of adult forms. This is a great opportunity for a creationist. You see, when you dig into the developmental biology literature, you will find some papers taking about the similarities of embryos at the neck of the hourglass, and you will also find other papers talking in some detail about the great differences before and after that stage. You will also find marvelous possibilities for confusion in the vague and malleable term “early”—to me, for instance, anything before the pharyngula stage is early, and everything after is late and relatively uninteresting. To put that in perspective, though, humans reach that stage at the 4th or 5th week of pregnancy—so I’m basically declaring month two and later of the human pregnancy to be late development. We do tend to throw around the terms early and late as relative measures of the timing of events, but we also name specific stages and processes…the fine details of which Wells leaves out, to make everything that much more confusing.

This is the heart of Wells’ strategy: pick comments by developmental biologists referring to different stages, which say very different things about the similarity of embryos, and conflate them. It’s easy to make it sound like scientists are willfully lying about the state of our knowledge when you can pluck out a statement about the diversity at the gastrula stage, omit the word “gastrula,” and pretend it applies to the pharyngula stage.

Literally. He is actually that dishonest.

Here’s how Wells quotes William Ballard (a well known elder developmental biologist, who has done a lot of work on fish and is therefore familiar to me):

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.”

Always be suspicious when you see partial phrases quoted and strung together by a creationist. Little alarm bells should be going off like mad in your head.

This is from a paper in which Ballard is advocating greater appreciation of the morphogenetic diversity of the gastrula stage—that is, a very early event, one that is at the base of that hourglass, where developmental biologists have been saying for years that there is a great deal of phylogenetic diversity. Here’s what Ballard actually 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.

See what I mean? He has lifted a quote from a famous scientist that applies to the gastrula stage, stripped out the specific referents, and made it sound as if it applies to the pharyngula stage. It’s a simple game, one he repeats over and over in this chapter.

One might argue that maybe Ballard also thought these semantic tricks applied to the pharyngula stage, and so Wells was representing his general views accurately. Alas, this cannot be. The paragraph before his mangled quote says this, rather plainly:

All then arrive at the pharyngula stage, which is remarkably uniform throughout the subphylum, consisting of similar organ rudiments similarly arranged (though in some respects deformed in respect to habitat and food supply). After the standardized pharyngula stage, the maturing of the structures of organs and tissues takes place on diverging line, each line characteristic of the class and further diverging into lines characteristic of the orders, families, and so on.

It’s a classic quote mine. Wells has edited the quote to suit his ends, and has also utterly ignored the sense of the paper, which directly contradicts his claims, to produce a grand lie and tie it to the reputation of a distinguished senior scientist.

I could stop here. With that one example, Wells is exposed as a disreputable scoundrel, a sloppy ideologue whose ‘scholarship’ is untrustworthy and willfully distorted. You simply cannot believe one word he says. I will go on a little further, though, and try to explain some of the ideas he has treated so shabbily.

The developmental hourglass

There is a fair amount of debate in the evo-devo community about the reality of the developmental hourglass, but Wells doesn’t seem to touch on the actual arguments at all—merely these strawman complaints and garbled chronologies that he uses to cast false doubt on the evolutionary process. One serious question is about how wide the waist of the hourglass actually is: an overzealous Haeckelian interpretation would be that it is very narrow indeed, but serious embryology (none of which seems to be done by Intelligent Design proponents) demonstrates that there is a significant amount of variation within the phylotypic period. Michael Richardson relaunched a critical reevaluation on the basis of morphology, and there have been a number of attempts to analyze the molecular basis of the model (several papers are cited at the end of this article; some find no detectable evidence of a consistent molecular pattern, others do.)

If it does pan out as a universal and coherent property of developing embryos that they should have a conserved stage, the next question is “why?” What is it that shelters the phylotypic stage to some degree (as yet unquantified) from the evolutionary divergence so common in other developmental processes? I actually rather like Raff’s explanation: that it is a matter of scope. The diagram to the right below outlines this idea.

i-447cbea02917160cf98ba765931eb172-raff_hourglass.gif

Development is a process of increasing complexity (the grey line). The assembly of an integrated body plan requires, at some time, a pattern of global interaction—there has to be information generated at some point to specify where the head will be relative to the tail, etc., and some processes operate over large areas of the animal. For instance, somites, one of the body elements characteristic of the phylotypic stage, form under the influence of a somitic clock, rhythmic waves of molecular activity that sweep the length of the trunk and tail. One idea is that these ‘whole body’ specification events are conserved and are difficult to uncouple from one another, so all the features for which they are responsible tend to appear together in a coordinated fashion…and that coordination is what we call the phylotypic period. Other processes are more modular and more local, not needing that level of global interaction, and are more free to diverge. The dark line in the graph indicates a peak time of long range interactive processes (and again, the real argument is about how broad that peak might be, and how much are the different fundamental processes, such as myotome and branchial arch formation, unlinked), and how subsequent developmental events become more independent.

That there are active, open questions in this particular area of developmental biology, though, does not suggest the field of evo-devo is wrong. It means that biologists are working on interesting problems, and a survey of the field would show that evolution is the productive framework of choice. Intelligent Design creationists like Wells are reduced to irrelevant carping from the sidelines…and even their criticisms are all wrong.

Darwin’s debt to embryology

Another feature of Wells’ book, and creationists in general, is the obsession with Charles Darwin. I like the guy, I think he was brilliant, and it was his insights that launched modern evolutionary biology. But come on—he’s been dead for 124 years. He didn’t have all the tools we do now: no genetics, no molecular biology. Science has moved on well beyond Darwin’s day, but not for the creationists, who still think they can whimper and whine about errors in a book almost 150 years old and thereby dent work that nowadays depends in large part on molecular and genetic and population genetics…fields that didn’t even exist for Charles!

Darwin did argue that embryology was an important piece of the evidence for evolution, a fact that is still true and probably even more so than in his time. What Wells does, though, is again mislead his readers about Darwin’s views. He claims that:

…von Baer’s view “was confounded with and then transformed into” the evolutionary doctrine that the embryos of higher organisms pass through the adult forms of lower organisms in the course of their development. It was this evolutionary distortion of von Baer’s work that Darwin considered the strongest evidence for his theory.

In the 1860′s, German Darwinist Ernst Haeckel (pronounced “heckle”) made some drawings to illustrate this distorted view, and Darwin relied on the drawings in later editions of The Origin of Species and in The Descent of Man (1871).

There’s that Wells sleight of hand again. Haeckel’s ideas about recapitulation (this idea of embryos passing through the adult forms of ‘lower’ organisms, which even Haeckel did not hold as simple-mindedly as Wells pretends) would be very difficult to find in the Origin of Species, which was published in 1859…note the date of Haeckel’s work. Pore through the Origin, and you won’t find reference to Haeckel’s theory (later editions cite him once), and you certainly won’t find any reliance on his drawings.

Darwin refers to embryology as the “strongest single class of facts” in favor of a change of forms in a letter to Asa Gray, and even there we don’t see the kind of adherence to recapitulation that Wells proposes.

It is curious how each one, I suppose, weighs arguments in a different balance: embryology is to me by far the strongest single class of facts in favour of change of forms, and not one, I think, of my reviewers has alluded to this. Variation not coming on at a very early age, and being inherited at not a very early corresponding period, explains, as it seems to me, the grandest of all facts in natural history, or rather in zoology, viz. the resemblance of embryos.

Hmmm. He’s talking about the timing of the onset of accumulation of variation, not that there is some constraint to follow adult forms. The description above actually fits very well with von Baer’s ideas of development proceeding from the general to the specific, not the “evolutionary distortion” (which is not part of evolutionary theory, anyway!) Wells describes.

In the Origin, we see even more nuance.

We can see why characters derived from the embryo should be of equal
importance with those derived from the adult, for a natural
classification of course includes all ages. But it is by no means
obvious, on the ordinary view, why the structure of the embryo
should be more important for this purpose than that of the adult,
which alone plays its full part in the economy of nature. Yet it has
been strongly urged by those great naturalists, Milne Edwards and
Agassiz, that embryological characters are the most important of
all; and this doctrine has very generally been admitted as true.
Nevertheless, their importance has sometimes been exaggerated, owing
to the adaptive characters of larvae not having been excluded; in
order to show this, Fritz Muller arranged by the aid of such
characters alone the great class of crustaceans, and the arrangement
did not prove a natural one. But there can be no doubt that
embryonic, excluding larval characters, are of the highest value for
classification, not only with animals but with plants. Thus the main
divisions of flowering plants are founded on differences in the
embryo,- on the number and position of the cotyledons, and on the mode
of development of the plumule and radicle. We shall immediately see
why these characters possess so high a value in classification,
namely, from the natural system being genealogical in its arrangement.

Notice: no claim that embryos recapitulate adult forms, an acknowledgment that the importance can be exaggerated and that there are confounding characters, and the citation of well-known authors (Agassiz, by the way, was an opponent of evolutionary theory) that embryology is important for analysis in systematics. This doesn’t resemble Wells caricature in the slightest.

What about later editions? I mentioned that Haeckel was cited once, and here it is:

Professor Haeckel in his Generelle Morphologie and in other works,
has recently brought his great knowledge and abilities to bear on what
he calls phylogeny, or the lines of descent of all organic beings.
In drawing up the several series he trusts chiefly to embryological
characters, but receives aid from homologous and rudimentary organs,
as well as from the successive periods at which the various forms of
life are believed to have first appeared in our geological formations.
He has thus boldly made a great beginning, and shows us how
classification will in the future be treated.

Again, no mention of recapitulation of adult forms, and in fact, the emphasis is on using multiple lines of evidence to build a phylogeny: embryological characters, homologous and vestigial organs, and paleontology. That sounds reasonable to me. Does Wells disagree?

Wells’ treatment of the historical relationship of Darwin and Haeckel is as shoddily done as his discussion of the phylotypic stage. He relies entirely on mangled chronologies and the dishonest attribution of ideas to the targets of his slanders.

Modern developmental genetics and evo-devo

At the end of the chapter, Wells throws away several pages in a common creationist complaint, that mutant flies are still flies, not shrimp or horses. In particular, he focuses on work by McGinnis and colleagues, who have been working out the details of how Hox genes affect morphology; in one well-known work a few years ago, they demonstrated that a fly gene, Ubx, had evolved limb-suppressing properties that are not present in the crustacean version of Ubx. Flies, of course, only have legs on their thoraxes, not their abdomens (where Ubx is expressed), while shrimp do have abdominal limbs. It’s great stuff: it demonstrates how large-scale morphological properties of organisms are regulated by fairly small changes in the sequences of key genes.

Wells response?

…even if they had shown how ancient shrimp lost a few legs, their experiment would not have even begun to explain how a water-dwelling shrimp-like animal could acquire the ability to breathe air and fly.

It’s a classic example of goalpost shifting. The intelligent design creationists are always demanding step-by-step explanations for the evolution of an organism, but when a legitimate researcher uncovers one step, they immediately resort to demanding a grand explanation of the whole leap. McGinnis explained one piece in the process; his goal wasn’t to explain the respiratory system or wings, but the pattern of limbs, and he did an experiment to test his ideas. Wells wants to criticize a study on legs because it didn’t look at wings, but you know that if it had looked at wings, he would have just complained that it didn’t explain legs.

What we have in evo-devo is a promising, exciting field of study that is revolutionizing our understanding of life on earth, and all Wells has to offer is the vapid sophistry of Intelligent Design (the “designer did it”) and no experimental work at all, while making the same crude and ignorant arguments—“mutant fruit flies are still just fruit flies”—that creationists have been making for decades.

It’s all of a piece. I keep looking for a word to summarize this book, and I keep coming back to “dishonest”; devious, unethical, deceitful, underhanded, shifty, false, unethical, and untrustworthy would also fit. I predict that in the coming reviews of other chapters in The Politically Incorrect Guide to Darwinism and Intelligent Design by my colleagues at the Panda’s Thumb, they’re all going to be using permutations of that concept of contemptible fraudulence to express their feelings about Wells. It’s the kind of book that makes knowledgeable people want to wash their hands obsessively.


Ballard WW (1976) Problems of gastrulation: real and verbal. Bioscience 26(1):36-39.

Bininda-Emonds OR,
Jeffery JE,
Richardson MK (2003) Inverting the hourglass: quantitative evidence against the phylotypic stage in vertebrate development. Proc Biol Sci. 270(1513):341-6.

Hazkani-Covo E,
Wool D,
Graur D (2005) In search of the vertebrate phylotypic stage: a molecular examination of the developmental hourglass model and von Baer’s third law. J Exp Zoolog B Mol Dev Evol304(2):150-8.

Poe S,
Wake MH (2004) Quantitative tests of general models for the evolution of development. Am Nat 164(3):415-22.

Richardson MK Hanken J Gooneratne ML Pieau C Raynaud A Selwood L & Wright GM (1997) There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development Anat. embryol. 196 91-106.