The Discovery Institute is so relieved — they finally found a textbook that includes a reworked version of Haeckel’s figure. Casey Luskin is very excited. I’m a little disappointed, though: apparently, nobody at the Discovery Institute reads Pharyngula. I posted a quick summary in September of 2003 that went through several textbooks, and showed a couple of examples where redrawn versions of Haeckel’s diagram were used. More recently, I posted a fairly exhaustive survey by Patrick Frank of the use of that diagram since 1923, which showed that it was rare, and that the concept of recapitulation was uniformly criticized. Really, guys, the horse of recapitulationism is dead. Biologists riddled it with bullets in the 19th century, and have periodically kicked it a few times to be sure. For Intelligent Design creationists to show up over a century later and flog the crumbling bones of a long extinguished horse and crow victory is awfully silly.
So how can you still find any vestiges of Haeckel’s work in textbooks?
That’s an interesting question, actually, and it has a complex answer. None of those answers involve the DI’s preferred explanation, that there is a worldwide conspiracy by biologists to prop up evolution with phony data, and Luskin’s specious “analysis” completely ignores a crucial point: that the textbook is using the diagram to support a valid scientific observation, and to criticize Haeckel’s interpretation.
So why does the infamous diagram still linger?
Conservatism. It’s amazing how much stuff lingers on for edition after edition in biology textbooks. They’re huge, they’re a lot of work, and new editions are in no way rewrites—the team of authors polish up and refine scattered bits, and maybe add a new chapter or two (it’s always “add”, it seems—they grow and grow, year after year.) For a classic example of this phenomenon, read Gould’s “The Case of the Creeping Fox Terrier,” which you can find in the collection “Bully for Brontosaurus”; somehow, most textbooks ended up describing early horse ancestors as being “the size of a fox terrier”.
Specialization. Biology is an immense discipline, and there is a dearth of generalists, of necessity. Darn few of the big textbook authors are developmental biologists, too…so the sections on development don’t usually get the same yearly reexamination that the other sections do. Also, if the Haeckel diagrams are there, they’re in the evolution chapter—and evo-devo experts are even rarer on textbook author bylines.
Historicity. Most textbooks that retain any mention of Haeckel do so because, like him or not, he was a very significant figure in 19th century biology. They keep him in as a symbol of our discipline’s history. The DI shouldn’t complain about that; they seem to be fascinated with him, churning out more stuff about Haeckel than all of the textbooks they complain so bitterly about.
Accuracy. Here’s something the DI never brings up: the image that is used in those textbooks? It’s not the one that Haeckel was accused of faking! It’s clearly been, to put it most charitably, drawn to serve Haeckel’s interpretations — extraembryonic membranes have been removed, for instance , and there are other signs that he emphasized what he thought was important and diminished what he thought wasn’t — but otherwise, it illustrates a real point: vertebrate embryos at the pharyngula stage resemble one another. There are better illustrations out there now, but remember that first point up there—textbook publishers and authors are conservative.
Science. This is one the DI always dodges. The books, even those few that still cling to the old diagram, do not argue for Haeckelian recapitulation. They argue against it. What you’ll usually see is a counterproposal, that the way to explain the similarities is by von Baerian recapitulation, which is a completely different matter. Von Baer argued that the cause of the resemblance is that early embryos express the most common, general morphological underpinnings of the phylum, and that development is a process of adding specializations to that general form. It is therefore to be expected that all members of a phylum will all have embryos with greater similiarity, because the unique features that distinguish the species haven’t been formed yet.
The dead giveaway that the book is endorsing von Baerian recapitulation, not Haeckel’s version, is when they explain that embryos of one species resemble the embryos (not the adults) of other species.
Now look at Luskin’s victory cry. I am vastly amused that in an article that claims that the DI has been vindicated in its insistence that biology textbooks have been indoctrinating children in the Haeckelian lie, he has to use the phrases I have highlighted below.
The text not only discusses “ontogeny recapitulates phylogeny” but also affirms it, albeit in a slightly different form. This entire discussion comes from a subsection entitled “Ontogeny Recapitulates Phylogeny,” in which the authors repudiate Haeckel’s claim but then defend a reformulated version of it: “The developmental instructions for each new form seem to have been layered on top of the previous instructions, contributing additional steps in the developmental journey. This hypothesis, promoted in the nineteenth century by Ernst Haeckel, is referred to as the ‘biogenetic law.’ It is usually stated as an aphorism: ontogeny recapitulates phylogeny; that is, embryological development (ontogeny) involves the same progression of changes that have occurred during evolution (phylogeny). However, the biogenetic law is not literally true when stated in this way because embryonic stages are not reflections of adult ancestors. Instead, the embryonic stages of a particular vertebrate often reflect the embryonic stages of that vertebrate’s ancestors.” (pg. 1228-1229, emphases in original)
Note, too, that last sentence; they don’t mention von Baer, but those words are a clear indication that what they are discussing is von Baerian recapitulation. I would dearly love to see the DI go on a crusade against von Baer, just as they have for Haeckel; von Baer preceded Darwin, and was also probably the premier embryologist of the 19th century. Luskin and his fellows at the DI are so ignorant that they aren’t even aware of the significant differences in these two interpretations, and even think that von Baer’s explanation was a “reformulated version” of Haeckel’s, which would only have worked if von Baer had a time machine. His explanation preceded Haeckel’s by about 30 years.
So in short, the Discovery Institute has found a textbook illustration using Haeckel’s diagram several years after I told them where to look, and that textbook clearly and specifically argues against Haeckel’s biogenetic law, by their own admission. And this is a vindication of their claim?
I want to mention one other point that troubles me. I agree that textbooks should revise their sections on developmental biology extensively — it’s a field that is changing so quickly that there ought to be more effort put into representing it accurately (of course, every representative of every sub-discipline of biology is saying exactly the same thing about their field, but mine must be more important.) If any good was to come from the DI’s carping, it was that maybe the publishers would scrutinize the development sections of their books.
Unfortunately, some of what I’m seeing is the reverse. In my earlier post, I mentioned that the Campbell textbook had actually removed a superb illustration of embryonic homology between editions—and the removal was done for the edition that came out after Wells’ awful book that made bogus criticisms of many textbooks. I’d hoped it was just a coincidence.
But now, the odd thing: I actually praised Raven & Johnson’s Biology, 5th edition for including this nice, clean diagram.
That isn’t drawn from Haeckel, but from contemporary specimens. I like it—it highlights key similarities well.
If you look at the text the DI is now criticizing, though, it’s the 6th edition of Raven and Johnson, from 2002, after Wells’ book was published. I’m baffled. They had a good diagram, and they slid backwards to add an older, poorer one? I don’t have a copy of that edition, but I’m wondering now if they didn’t add it in response to the attention given to Haeckel’s work lately, with a clear explanation of why we don’t accept Haeckel’s explanation anymore.
It would be ironic if the reason they were able to find this illustration in a modern textbook is because the authors were listening to public concerns about it, and added it so they could specifically address the issue, especially since they are explicitly repudiating Haeckel. Apparently, the DI wants biologists everywhere to make a Stalinesque purge of every mention of Ernst Haeckel, even in those cases where we’re plainly disagreeing with some of his ideas, and teaching our students where they are wrong.