The exaggerated similarities of Haeckel's vertebrate embryos thus better demonstrate the truth of common descent through gradual modification than does the reality, and therefore can be considered a boon to education, since students can be finally showed the real deal after "mountains of evidence" have cowed them into ideological commitment. (Maybe in upper division courses.)
P.Z. Myers denounces Dr. Jonathan Wells for (among many other things) the low grade he awards Campell's Biology for its treatment of the vertebrate embryo. Campbell dispenses altogether (in my 4th edition) with visual comparisons, Haeckelian or realistic, and simply displays a human embryo and points out the "post-anal tail" and the "gill pouches" as though they were vestiges of our evolutionary history. However much Haeckel's particular version of recapitulation is said to be outmoded and repudiated, it sounds awfully like these features pointed out by Campbell are vestigial developmental characters left over from our evolutionary past.
When Randy Olson in his Flock of Dodos documentary displays the bones of the pentadactyl limb as prima facie evidence (an obvious example of the "mountains" of self-evident proofs of evolution) what he is implicitly arguing is: These are all alike, and they'd have no good reason for being alike if it weren't for common descent (one major hypothesis of the neo-Darwinian Synthesis) as well as undirected selection (the other major hypothesis). Since Olson's film is about "anti-science" vs. Evolution, for Olson the pentadactyl limb speaks truth to power about Evolution. The pentadactyl limb is highly conserved among non-fish vertebrates, like the ideal vertebrate embryo is more or less conserved among vertebrates.
If there is a design, an intelligent plan, or formal cause for these patterns, then these are examples of basic developmental patterns being used (or adapted) to different needs or niches. But these patterns are the explananda of narrative biology, not the explanans.
If the extensive re-use of common developmental designs are not evidence of unintentional briccolage in "greedy search" reaction to historical contingencies then they are evidence of some sort of re-appropriation of programming solutions. The rule of Frann's The Shape of Life for embryological similarity is like that of molecular homology: They are similar except where they are not. Among the vertebrates in general and mammals in particular, diverse non-homologous genes are responsible for "homologous" features and forms, apparently conserved or derived genes are used for analogous features, and embryologically, very different morphologies in early embryology will converge to a variation of a common archetype. The only evolutionary idea being demonstrated is what is termed homoplasy or convergent evolution. Thus ontogeny recapitulates phylogeny about as much as molecular cladistics closely follows morphology; very generally, the more animals are alike the more likely they will make use of similar genes and similar developmental processes. Specifically, there are too many exceptions to the rules to have useful rules.
But in the mental landscape inhabited by P.Z. Myers, Campbell, and Randy Olson, human embryos don't have a "post-anal tail" and "gill pouches" because we have vertebrate bodies that share a common developmental program with other vertebrates. Rather, we have these (according to them) because we descended from creatures with tails and gills. The tail and gill pouches are vestiges of our phylogenic history, and in this sense pieces of our ancient evolutionary origins are being recapitulated. Vertebrates have (eponymous) vertebrae that themselves are formed through a segmentation development pattern (one that is so highly conserved, or resistant to briccolage, that giraffes have the same number of cervical vertebrae as other vertebrates). One variation of the segmentation is the segmented structure of the vertebrate ribcage. Another more versatile variation is the cluster of pharyngeal pouches. In fish, this cluster develops into the breathing apparatus known as "gills" and keeps a recognizably segmented architecture. In mammals, this segmented structure is appropriated for structures related to the jaw and ear. The versatility of the pharyngeal segments is proof of evolution much as the relative conservatism of the rib segments are proof of evolution. So the existence of a "post-anal tail" and "gill pouches" is supposed to make historical pronouncements without any paradigmatic interpretation.
Now to talk specifically about Intelligent Design is to coax from biologists various theological arguments, implicit or explicit, since to most of them an Intelligent Designer can't be divorced from various theological preconceptions. So implicit in these arguments is that a Designer adapting the human body would remove the "post-anal tail" and the obvious segmentation in those "gill pouches"-- after all, don't these things just confuse us creationists as much as million-year-old bones in the dirt? (Does anyone seriously believe that Randy Olson isn't thinking this as he talks about pellet-eating and failing hearts?)
Truly, an omnipotent, omniscient Zeus figure would have made the human form unlike anything in the animal kingdom, with a unique nucleotide code (or something different from DNA), non-pentadactyl limbs and surely not created any animal as similar as the apes. In a way, they are arguing that God should not have formed humankind "from the dust of the earth." This situation would not be much ameliorated if vertebrate embryos were tailless (only growing tails later), or if human embryos specifically tailless. Evolution (as ideology and enterprise) would weather that contingency as easily as it has weathered the loss of Haeckelian recapitulation-as-law or the return of neo-Lamarckian effects or the potential loss of junk DNA.
If humankind were intelligently designed, the animal kingdom would seem designed to maximize our ability to understand how the body develops and how it operates. The kingdoms together constitute a Rosetta Stone for the mystery of biological life. It is rather like the good fortune of our astronomical living arrangements: unusual number of visible planets to reveal the nature of the solar system, a moon that perfectly eclipses the sun to reveal its nature, a position on the edge of the galaxy to reveal the structure of the universe, etc.
Since the neo-Darwinian has dispensed with Haeckel's failed ideas--if not with the images that were fudged to support them--attacking the use of Haeckel's images is allegedly a straw-man attack. Yet, even where the images are not used, I find notions of recapitulation (however non-Haeckelian) in the idea that the von Baerian developmental trajectory is a picture of our deep evolutionary past. It is this notion which Eugenie Scott considered "basically correct" that is supported neatly by the manufactured simplicity of Haeckel's illustrations. The illustrations survive as Dawkins-esque memes; they proliferate because they are well adapted to the Darwinist mind, and they allow the Darwinist mind to make more Darwinist minds. Like the shark, it's so well adapted to its environment it doesn't need to evolve.
The common theme of Wells' Icons of Evolution (a book that is one of the least central to the ideas of ID of all the books from Discovery's CSC) is how the commonly presented evidence for neo-Darwinism is a lot less compelling when looked at objectively and critically. P.Z. Myers and others might complain that there is much better evidence, but that begs the question why it hasn't been taught.
In what Dr. Wells has called the "cracked kettle" approach to the problem, the biology community has known for many decades that the illustrations are wrong, which is why they stopped using them a long time ago, and the only reason why the illustrations are still being used is because they are basically right and only wrong in some "trivial" sense. At what point can an entrenched paradigm like neo-Darwinism be expected to trade exaggeration for accuracy? When it is no longer threatened by the existence of detractors?
In his "Pulled Punches" extra, Olson refers the viewer to P.Z. Myers' criticism of Dr. Wells. P.Z. Myers is an ardent atheist and anti-creationist and regularly mean writer of screeds. Among the criticisms of Wells is that Dr. Futuyma's book actually goes into a long discussion of exactly how Haeckel was wrong. If you look at the Haeckel drawings that appear with his discussion, you'll see every indication that the embryo pictures convey inexorable truth.
Similar issues have haunted many of Kenneth Miller's editions of Biology: The Living Science, a textbook that only later corrected its treatment of recapitulation and the embryos (see here and here for how Miller has fudged the evolutionary history of his textbooks). Read the caption to Figure 8.15 below.
It might take an expert to tell Haeckel's embryos apart. Again, the outdated illustrations are useful to highlight that our developmental history (ontogeny) demonstrates our evolutionary history (phylogeny) through "remnants of structures needed by our aquatic ancestors."
If anything, Haeckel's theory is chastised (in some sense) for not being quite right and is then revised to express a recapitulation theory more consistent with the facts. For instance, in the Futuyma text:
From Rudolf Raff's Shape of Life (1996, p. 255):
One of the few scientific concepts to resonate well in popular culture [i.e. long after 1914] is the idea that the evolutionary history of ancestors is recapitulated in the development of their descendants. There is a wonderful mystery in the idea that the anatomy of our remote ancestors, gill arches, tail buds, and all unfolds in our own development. No matter how we deride the naivete of Haeckelian recapitulation, and however we redefine [e.g. Garstang] the mechanisms that connect evolution and development, there is a shadow of truth in the idea. Nineteenth-century concepts of evolutionary changes in development hinged upon recapitulation of ancestral events by the addition of new stages to the adult end of the developmental sequence. However, this is too constraining. Evolution is not limited to terminal addition. . . . Change could proceed by terminal addition to produce classic [i.e. Haeckelian] recapitulation, but it might also occur by [neoteny]. [emphasis mine]Certainly the Haeckelian imagery has helped this concept to "resonate well in popular culture," which in Darwinian terms, is all that is necessary to explain this selfish meme's long survival in textbooks despite the "naivete" that it was obviously designed to support. If Haeckel indeed came so close to the mark, why is his naivete derided so much more than the naivete of Charles Darwin's original mechanism of variation? Maybe precisely so that biologists can hate their Haeckel cake and eat it too.