A commenter named Brad, who is apparently a creationist, left a comment to one of my recent posts.  In that post, “Creationist foists “fraudulent” embryo picture on his readers“, I talked about how creationist Brian Thomas ironically used a biologically inaccurate picture of a human embryo to illustrate his article in which he denies the evidence for evolution from developmental biology and implies that all such evidence is based on the supposedly fraudulent embryo drawings 19th century biologist Ernst Haeckel.

Not wanting it to be neglected in the comments section, I have moved my response to Brad up to a full post.

Brad: Wow, evolution is like magic. It turns gills into ears, tonsils, and glands (and part of the larynx).

There is no magic involved in evolution, you’re thinking of creationism, the very heart of which is the claim that living things are the miraculous creations of a supernatural being.

Brad: Calculate the odds…

Since by all available evidence it did in fact happen, the odds are 100%.

Brad: Granted, it was a bad choice with the stock photo; however, that’s possibly an oversight vs. the intentional use of known fraudulent drawings for decades in school textbooks.

I would suggest that it was an “oversight” brought on by ignorance of the subject and a lack of curiosity to even check. As for the recycling of Haeckel’s embryo illustrations in textbooks (as illustrations of evidence rather than as a historical reference) this due to the regrettable and all too common laziness on the part of textbook publishers who often recycle not just images but even language as well. See: Stephen Jay Gould’s essay “The Case of the Creeping Fox Terrier Clone” (Gould 1991).

I agree that some* of Haeckel’s drawings exaggerated overall similarity of the embryos they depict and that more accurate illustrations should be used. However, I am unaware of any fundamental anatomical inventions in the illustrations that if corrected would affect the evidence from comparative embryology for evolution.

So, please explain in your own words exactly what anatomical details were altered in Haeckel’s drawings that created evidence for evolution where none exists in actual vertebrate embryos.

Remember, specific anatomical details and in your own words. I don’t want quotes of vague generalities from other people. You’ll note that in my post on pharyngeal clefts at no point did simply I quote some scientists opinion that the pharyngeal apparatus of amniote embryos are homologous to the pharyngeal apparatus of “fish”. Instead I pointed to the anatomical and genetic evidence for this.

If you are going to argue against this, then you are going to have to do likewise.  And if you want to present an alternative scientific explanation you are going to have to present something that is logical, coherent, makes reference to the empirical evidence at hand and does not rely on untestable miracles or divine fiat.

Brad: O’Rahilly and Müller stated that ‘the pharyngeal clefts of vertebrate embryos … are neither gills nor slits’.1

I don’t have this reference handy and I don’t know when I’ll get a chance to get to my local university’s science library (whose website says they have it) I was able to find a later edition on Amazon with a free preview which allowed me to get what seems like the relevant section.  If the older edition has any important differences please let me know (assuming you have the book and didn’t just cut and past the quote from a creationist and/or anti-abortion website).

Here is the the section which seem to contain Brad’s quote with the part Brad quoted in red:

Recapitulation, the So-Called Biogenetic Law.

The theory that successive stages of individual development (ontogeny) correspond with (“recapitulate”) successive adult ancestors in the line of evolutionary descent (phylogeny) became popular in the nineteenth century as the so-called biogenetic law. This theory of recapitulation, however, has had a “regrettable influence on the progress of embryology” (G. de Beer). The work of Carl Ernst von Baer in 1828 was much closer to the mark. According to the “laws” of von Baer, general characters (e.g., brain, notochord) appear in development earlier than special characters (e.g., limbs, hair). Furthermore, during its development an animal departs more and more from the form of other animals. Indeed, the early stages in the development of an animal are not like the adult stages of other forms but resemble only the early stages of those animals. The pharyngeal clefts of vertebrate embryos, for example, are neither gills nor slits. Although a fish elaborates this region into gill slits, in reptiles, birds, and mammals it is converted into such structures as the tonsils and the thymus. According to the hourglass model of evolutionary development, a conserved pattern of developmental gene expression is linked with considerable resemblance among embryos of different species at a constricted phase, whereas divergence is found earlier and later. Morphological evidence for such a phase, however, is unconvincing (Richardson et al., 1997). (O’Rahilly & Müller 2001, p. 16)

Although there are issues I could take with their description of recapitulation as necessarily being about a strict correspondence between embryos and the adult forms of ancestors or with the short shrift they give the concept of the phylotypic stage (at least in this paragraph), however those are really nuanced points that are not necessary to get into here.

One point I will quibble with regards the presence of slits in certain amniote embryos.

Everything I have seen on the subject indicates that the pharyngeal clefts of some “reptiles” and birds do normally perforate during development and are therefore technically “slits” for a short time before they re-close. This also sometimes occurs in mammals, including humans, though it is not a normal condition. (see my earlier article for links). Also they’ve left out any reference to the larvae of amphibians some of which do develop functional gill slits.

Beyond that, they are absolutely correct, the pharyngeal apparatus of amniotes never function as gills and as I said in one of my earlier posts, I don’t know of any biologist who has ever claimed that they do, save one, the creationist Louis Agassiz.

The Great Satan, Ernst Haeckel, stated in no uncertain terms in his writings that these structures never function as respiratory organs in amniote embryos.

It is not required that the pharyngeal apparatus of amniote embryo function as gills for them to be evidence—not absolute, stand alone proof, but evidence—of their ancestors aquatic nature any more than it is necessary for the hind limb buds of whale embryos to function as working legs for them to be evidence that their ancestors once walked on land.

Brad: Blechschmidt is more forceful, concluding that ‘the so-called basic law of biogenetics is wrong.

The late Erich Blechschmidt (1904-1992) was a scientific outlier (as are some of his followers, i.e. Brian Freeman). That is his views were not representative of developmental biologists as a whole. Creationists love to quote Blechschmidt and other outliers such as Alan Feduccia (who denies that birds are descended from dinosaurs) and Charles Oxnard (who denies that australopithecines are human ancestors) in an attempt to make it seem as if they are tapping into some real controversy amongst scientists. In reality they are just quoting people who are only slightly less on the fringe of science than themselves.

You can find someone with an advanced degree that will say just about anything. For example there is PhD astronomer (and creationist) Gerardus Bouw who argues that the Earth is the center of the solar system.

In this case Blechschmidt (and Freeman) seem to be the source for creationists absurd argument that pharyngeal clefts are merely “flexion folds” caused by the bending of the embryonic neck (Freeman 2001).

As for the biogenetic law, no one is arguing for that. If you read the article you were commenting under you would have seen that I quoted Michael Richardson (a critic of Haeckel) as saying that there are studies which support the recapitulation of individual character transformations, just not whole ancestral stages (Richardson & Keuck 2002, p. 522)

Brad: ” ‘No buts or ifs can mitigate this fact.’ He adds that the gill stage myth is ‘not even a tiny bit correct or correct in a different form…It is totally wrong’. 2 This view is shared by many mainstream embryologists.

No, it is not.

Although among the strongest opponents to Haeckel in recent years, and favourably differing from him by a paramount respect for detail, Blechschmidt resembled Haeckel in several respects: they both were intrepid and very persuasive defenders of their views, they were both artists at heart – witness Haeckel’s illustrations and Blechschmidt’s giantsized models of human embryos – and, most importantly in the present context, they both stuck to some outdated ideas not shared by the majority of contemporaneous biologists: Haeckel remained Lamarckist, defending the inheritance of acquired characters throughout his life, and Blechschmidt strove to maintain the special status of Man by condemning any embryological interpretation or terminology suggesting his descent from other vertebrates. (Sander 2002, p. 531, emphasis mine)

So Blechschmidt apparently had issues with accepting the evolutionary development of humans from other animals. As I said an outlier with an extreme minority view.

Brad: in the end, this is probably an argument evolutionists should give up on.

You’ll understand, I hope, that this evolutionist will not be taking advice on what is or is not valid evidence from a creationist.

Brad: But keep right on with it if you insist, it just makes dogmatic evolutionists sound nuts.

Only to those too ignorant to know better and/or too intellectually lazy to look up the evidence for themselves.

*Note: I am thinking primarily of the first stage shown in the comparative embryo illustration in the 3rd edition of his Anthropogenie (1874)

References

Freeman, Brian (2001) “The Myth of the “Biogenetic Law””, The American Biology Teacher 63(2):84

Gould, Stephen Jay (1991) “The Case of the Creeping Fox Terrier Clone”, in: Bully for Brontosaurus: Reflections in Natural History,  W.W. Norton & Co., pp. 155-167

O’Rahilly, Ronan & Müller, Fabiola (2001) Human Embryology & Teratology, 3rd Edition, Wiley-Liss

Richardson, Michael & Keuck, Gerhard (2002) “Haeckel’s ABC of evolution and development“, Biological Reviews, 77: 495-528

Sander, Klaus (2002) “Ernst Haeckel’s ontogenetic recapitulation: irritation and incentive from 1866 to our time”, Annals of Anatomy 184:523-533