Pharyngula

Textbooks and Haeckel again

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[When I started this weblog, one of the hot topics in the Creationist Wars was Jonathan Wells, a Moonie who had trained as a developmental biologist and written a screed against evolutionary biology titled Icons of Evolution. This book purported to document serious flaws in some of the major examples of evolutionary biology, although what it actually did was parrot old creationist arguments and get much of the science wrong. One of the subjects he focused on was the pharyngula—the embryonic stage that exhibits a common morphology across all vertebrates. This fascinating developmental period has an unfortunate history, in that Ernst Haeckel published some fraudulent drawings of it, and also made exaggerated claims about it. One of Wells' strategies was to condemn every biology textbook that illustrated homologies in pharyngula stage embryos, tarring them with the broad brush of Haeckelism. This got to the point where he was absurdly damning books that even included photos of embryos, and one of the things I've tried to do is document the way he misrepresents science teaching.]

I got a request to document some of Wells’ claims from his execrable book, Icons of Evolution. Specifically, Wells chastises several textbook authors for using modified versions of Haeckel’s drawings:

Starr & Taggart, 10th ed and this was mentioned in
Well’s testimony, p. 315, “slightly simplified version of
Haekel’s original fraudulent drawings”

Raven & Johnson, Biology, 6th ed

“modified version … exaggerates actual similarities” p. 450

I don’t have all of the textbooks he describes, but I do have the 5th and 9th editions of the above books, and I suspect the figures haven’t changed. Below, I’ve scanned in several of the figures that Wells finds objectionable, and for the most part, they aren’t bad at all, and actually make useful pedagogical points. I suspect that the real reason Wells and other creationists dislike them is that they reveal deep homologies that support evolutionary explanations of the origins of animal diversity.

Here’s figure 20.7 from Starr & Taggert’s Biology: The Unity and Diversity of Life, 9th edition:

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Copyright © 2001 Brooks/Cole

That is clearly a reworked version of the Haeckel/Romanes diagram; the fish in particular isn’t very accurate, and there is very little detail. It’s not very good, and doesn’t do a good job of illustrating the point. 20.7b, though, salvages the figure—that is a nice illustration of the homologous layout of the aortic arches.

And here is figure 20.18 from Raven & Johnson’s Biology, 5th edition:

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Copyright © 1999 McGraw-Hill Companies, Inc.

I think this is very nice. These aren’t from Haeckel; these are clearly drawn from real animals. They show the variations that do exist between these animals, for instance in the degree of flexure, the presence of limb buds, and differences in relative size of various structures. There is some exaggeration—for instance, I’ve never seen a photo of a human embryo in which all of those branchial arches are as clearly delineated as that—but that’s the purpose of a drawing. The purple tint isn’t objectionable, since that’s purely to indicate where the structures are.

Another, Guttman’s Biology, 1st edition:

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Copyright © 1999 McGraw-Hill Companies, Inc.

This discussion earned Guttman an “F” from Wells, for using Haeckel’s drawings, and for citing the similarity of early embryos as evidence for common ancestry. Of course, what this textbook is actually doing is discussing the history of this concept, and explaining how the idea has changed from its erroneous 19th form into its current non-recapitulationist version—which makes using Haeckel’s figure quite reasonable. It’s not perfect (I itch to change that last line to “…must resemble the larval cnidarian ancestor”), but these three short paragraphs treat the issue with more honesty and sophistication than Wells’ whole book.

Now here’s something a bit sad, from Campbell-Reece-Mitchell’s 5th edition of Biology:

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Copyright © 1999 Benjamin/Cummings

That’s the best of the four shown here! It’s a pair of good photos (although Wells doesn’t like photos, either—they are “misleading”), that accurately illustrate the point of embryonic homology.

So what’s sad about it? The photos are not present in the 6th edition. The 5th came out in 1999, Wells’ book is from 2000, the 6th is copyright 2002. I hope that is just a coincidence and that Benjamin Cummings (the publisher) had some other good reason for expunging an illustration than criticism from a creationist. I notice that the third edition has even better photographs of embryos; it’s odd that the presentation of this one small subject has been given progressively less attention from Campbell over the years. Rather than creationist pressure, it may be that the increasing amount of information on homologies in vertebrate embryos has made it difficult to do it justice in an introductory textbook.


Here at UMM, we use the textbook Life: The Science of Biology by Purves et al. in our introductory courses. It says nothing about Haeckel or a conserved phylotypic stage at all…but what it does have is an entire short chapter on “Development and Evolutionary Change”. Instead of vertebrates, it uses the example of crustaceans to illustrate how embryonic similarities are useful indicators of homology, and discusses deeper molecular relationships, such as the Hox genes, that unite animal life. It’s strongly pro-evolution, so I’m sure Wells would find some criterion to give this textbook an “F”, anyway.

One thing I have noticed over the last 5 years, though, is an increase in the amount of material on evolution and development in college biology texts. Wells’ book, if it had any influence at all, has not had the effect he might have expected; it’s much more likely, though, that the expansion of evo-devo related content has been a consequence of the success and growing importance of the evo-devo research program.