Posted by PZ Myers on February 17, 2007 01:41 PM
Lately, the Discovery Institute has stuck its neck out in response to the popularity of showings of Randy Olson's movie, Flock of Dodos, which I reviewed a while back. They slapped together some lame critiques packaged on the web as Hoax of Dodos (a clunker of a name; it's especially ironic since the film tries to portray the Institute as good at PR), which mainly seem to be driven by the sloppy delusions of that poor excuse for a developmental biologist, Jonathan Wells. In the past week, I've also put up my responses to the Wells deceptions—as a developmental biologist myself, I get a little cranky when a creationist clown abuses my discipline.
Discovery Institute fires its first salvo in the War Against Dodos: in which I point out that the two 'big' objections the DI levies against the movie are complete duds.
Wells’ false accusation against Randy Olson: in which I show that Olson actually described the representation of Haeckel in textbooks accurately.
Exorcising the spectre of Haeckel again: in which a commenter lists how Haeckel's figure was actually used in 15 textbooks.
Wells and Haeckel's Embryos: in which I go on at some length about Wells' misrepresentations of developmental biology in his Icons of Evolution.
In case you are completely baffled by this whole episode, here's a shorter summary.
In the early 19th century, a very famous embryologist, Karl Ernst von Baer, made the observation that vertebrate embryos go through a stage in which all are surprisingly similar to one another — so similar that he, probably the greatest embryologist of his day, couldn't tell bird and reptile embryos apart. This observation has been repeatedly confirmed; no rational person argues against the general statement, although there have also been good, detailed studies (by Richardson in particular) that show that there are differences in specifics that need to be appreciated. In addition, modern observations of patterns of gene expression show that there is also a deeper similarity in the molecules involved in this particular period.
I emphasized the observations above because these are the data, and they aren't in question. One could argue that interpretations are open to questioning, however. So what are the interpretations?
Karl Ernst von Baer was a creationist. He lived long enough to know of Darwin's work, and was critical of it; he never accepted evolutionary explanations. His interpretation of his own observations was that as a general principle, development proceeded from a general foundation and then the specific details emerged progressively. Because we also classified organisms into phyla on the basis of universal, general characters, it isn't surprising that we would then see that phylum-wide, general features develop at an early stage, and that all embryos in a phylum would briefly resemble one another. He did not infer any other relationship between species, especially not an ancestral relationship.
Ernst Haeckel was an enthusiastic promoter of evolutionary theory in the late 19th century. His interpretation was wishful—he wanted to study processes that occurred in the past by studying processes that occur now, so he postulated that development was a process that replayed evolutionary history, and that we could review an organism's evolution by working out the details of its developmental history. This was an appealing idea, especially since at that time we lacked any knowledge of the actual mechanisms of inheritance. The interpretation didn't work, since as observations of development accumulated, it became clear that they weren't simple records of evolutionary change—developmental changes could occur at any step in the process, muddying the history. It was discarded because of a lack of utility, conflict with the growing data, and later, because genetics revealed a deeper mechanism that wasn't tied in any way to the sequence of development.
Almost incidentally, Haeckel also faked a couple of figures, which earned him some academic censure. This is not why his theory was discarded, though; the observations of similarity at an early stage were secured by independent confirmation. One bit of sloppiness and his backing of a fruitless theory made him increasingly irrelevant (which is actually unfortunate—he was otherwise an interesting, if bombastic and overzealous, thinker who contributed to many disciplines) but his theory, called recapitulation or the biogenetic law, was abandoned because his theory didn't fit the facts.
The modern interpretation is still a work in progress. What we see is conserved genetic circuitry involved in patterning the whole of the organism, and the idea is that this is particularly refractory to change. We agree with von Baer, that we're looking at very general properties of the organism—which end is the front, how is it partitioned into regions, how the heart is specified to form in the chest/throat area rather than the tail, for instance—but we're also finding that the molecular mechanisms driving these processes are so similar that homology, or similarity by shared ancestry, is the best explanation.
The explanation by the Intelligent Design creationists is…uh, it seems to be…well, actually, they don't offer an explanation. Instead, under the leadership of Jonathan Wells, they've chosen to attack the veracity of the observations rather than producing a better interpretation.
This is the level of intellectual bankruptcy the Discovery Institute has reached. They choose to deny the facts, an observation made by a fellow creationist almost 180 years ago and repeated over and over again, to the point that Wells in his book Icons of Evolution condemns textbooks that show photos of embryos at this particularly interesting stage. This Intelligent Design 'theory' they promote is so toothless that they have no alternative explanations, so they choose try to to bury the data.
What I also find interesting is that these proponents of 'teaching the controversy' are so anxious to hide the fact that legitimate biologists wrestled over an alternative theory that had, for a brief (but still too many decades) time had engaged a significant number of members of the scientific community. Haeckel's theory was popular among scientists and the public, had some intuitive appeal, and also promised to explain many phenomena…but it fizzled precisely because it failed to accumulate scientific evidence in its favor. The textbooks that still mention it do so because it was our example of phlogiston—an interesting historical curiosity that tried to explain real observations, but failed under growing experimental tests. Wells' denial of the similarity of vertebrate embryos as a tactic for disputing evolutionary theory is comparable to trying to refute modern chemistry by attacking phlogiston theory on the grounds that substances don't burn. Not only does the absurdity of the target label them a kook, but even if they were successful, no one is defending phlogiston or the biogenetic law anymore.