Over on The Panda’s Thumb blog, Darwinian apologist P.Z. Myers recently posted a pejorative laden critique of a review article by Casey Luskin. Luskin was responding to a recent New York Times article on a study purporting to show how certain genes in fish might hold an important clue on how fins turned to feet.
I won’t rehearse the articles here, you can read them in the links. Rather, I want to look a bit more closely at Myer’s critique of Luskin’s article and the supposedly “scientific” problems he has with Luskin. He begins by highlighting a quote from Luskin’s article where Luskin writes, “Hox genes are known to be widely conserved among vertebrates, so the fact that homology was found between Hox-gene-associated DNA across these organisms isn’t very surprising.”
Myers goes right after this simple observation:
Stop, Casey, and think. Here’s this fascinating observation, that we keep finding conserved genes and conserved regulatory regions between mice and fish, which ought to tell you something, and your argument against a specific example is that it isn’t rare? It really tells you something when your critics’ rebuttal to a piece of evidence is that you’ve got so much evidence for your position that they’re tuning out whenever you talk about the detais.
This is Luskin’s approach to every example given in the NY Times article: ‘Yeah? So? There are homologous genes all over the place!’ I think Luskin might just live forever, which thrills me to pieces. He could get into a running gun battle with a mob from Answers in Genesis, be riddled with bullets, and he’ll just point to a nick in his ear and say, “Yeah, so? This one didn’t kill me!” and then dismiss all the other wounds because they’re so common that no one should care any more. It is truly the logic of immortals.
The specific example he’s addressing in his dismissal of Hox conservation, though, is a region of DNA that may play a role in mammals in the formation of the placenta. Luskin pooh-poohs the relevance of this observation by highlighting what we don’t know, rather than the evidence at hand.
Pejoratives aside, the crux of Myers comment is that he thinks the explanation for all these homologous Hox genes ought to be plainly obvious to Luskin (or anyone else for that matter), “Stop, Casey, and think. Here’s this fascinating observation, that we keep finding conserved genes and conserved regulatory regions between mice and fish, which ought to tell you something…” Well, it did tell Luskin something…just not the something Myers thinks it should have. Here’s what Luskin actually wrote in his article (which Myers refers to as a “tirade” – so brace yourself!)
The real story isn’t quite that interesting. According to the Nature paper, a particular region of DNA associated with a Hox gene cluster in the coelocanth genome showed sequence homology with a stretch of Hox gene-related DNA in tetrapods. Hox genes are known to be widely conserved among vertebrates, so the fact that homology was found between Hox-gene-associated DNA across these organisms isn’t very surprising. The authors aren’t sure exactly what this particular segment of DNA does, though it’s probably a promoter region. In mice the corresponding homologous region is associated with Hox genes that are important for forming the placenta. Ergo, we’ve solved the mystery of how the placenta evolved. Right?
Not really. Again, all that was found was a little homologous promoter region in Hox-gene related DNA in these two types of organisms. Given that we don’t even understand exactly what these genes do or how they work, obviously the study offered no discussion of what mutations might have provided an evolutionary advantage. No evolutionary pathway was proposed, or even discussed. So there’s not much meat to this story, other than a nice little region of homology between two shared, functional pieces of Hox-gene-related DNA. But of course, such shared functional DNA could be the result of common design and need not indicate common descent or Darwinian evolution.
Luskin’s point is quite simple. The evidence cited in the original study in Nature, which was the focus of the New York Times story, is as easily explained by common design as common descent. Later in his article, Luskin reiterates the point:
Again, it’s well known that Hox genes are conserved throughout most vertebrates, including fish (like the coelacanth) and tetrapods (like mice). In this case, the genetically homologous enhancer in the two organisms seems to have had a similar, homologous function as well: in coelacanth it enhanced a Hox gene for building fins, and in mice it enhanced a Hox gene for building limbs. This similarity of function and genetic role makes it unsurprising that that these enhancers had a similar DNA sequence. The similarity of function, genetic role, and DNA sequence is thus interesting, but it’s not overly surprising to find that it sort of worked when inserted in a mouse.
But what’s evolution got to do with any of this? The experiment worked because of functional and genetic similarities between the coelacanth enchancer and the mouse enchancer. Once again, such similarities of sequence and function could be explained by common design and don’t necessarily tell us much about common descent.
Of course, Luskin’s point is well taken, as there is no real scientific reason to reject common design in favor of common descent. But that is exactly what P.Z. Myers thinks is the case. Here’s the crux of Myer’s argument and critique of Luskin:
The key point is the known information: this snippet of DNA is highly conserved across all vertebrates, but the gene it is associated with has decayed in sharks and disappeared entirely in tetrapods. The question is how the switch has persisted: Luskin’s preferred explanation is that God spliced this particular piece of DNA into every vertebrate species; the scientific explanation is that it shows a pattern of shared history, and that its role is conserved in tetrapods because it has found a novel function in regulating a different gene.
Notice how Myers compares the two explanations: Luskin’s “common design” comment is translated as “God did it that way” (even though Luskin doesn’t mention God a single time in his article) while Myer’s explanation is the “scientific explanation”….the pattern of “shared history”.
And lest we miss the point, Myers concludes with:
The evolutionary explanation requires three mundane events, the simple loss of a gene in an ancestral population.
The Intelligent Design creationist explanation requires that every extant species was specifically and intentionally stocked with a set of genes hand-chosen by a designer. God magically inserted IgM into each vertebrate species, except that he missed the coelacanths, and he magically inserted IgW into each and every shark, ray, coelacanth, and lungfish, but he intentionally left them out of every tetrapod and teleost.
Myers can’t resist throwing in the word “creationist”, likely for its emotive, pejorative value and uses “Intelligent Design” as a modifier. Then mentions God again, and magic. It is clear that Myers will accept only the common ancestry explanation. But is he making an actual scientific case against Luskin’s position?
Well, no, not really. Remove the ad hominems, which are colorful and plentiful in Myers post, and Myers actual argument boils down to something like this: 1 – we observe numerous homologies of highly conserved genes across widely divergent species 2 – God or an intelligent designer really wouldn’t have done it that way (magically or otherwise), ERGO, it can only be attributed to common ancestry. Game over…Darwinism triumphant. Except, there’s a problem for Myers here. That second premise doesn’t seem all that scientific to me. Its a theological (or at least metaphysical) premise. What’s a theological premise doing in what is supposed to be a purely scientific argument?
Perhaps Myers could enlighten us as to how or where or by whom it has been determined that if God had in fact created all the various species, He most certainly would not have done so using all these homologous genes. He would have designed everything uniquely, starting from scratch with each species. If that particular hypothesis has been tested and confirmed scientifically somewhere, I would really like to read the peer reviewed research study in the relevant science journal. If there is no such study (hint: there isn’t!), then on what scientific basis does Myers reject the concept of common design as a viable explanation?
Here’s a challenge to P.Z. Myers, and its a purely scientific one, so well within his wheelhouse. How do we know scientifically (not philosophically, metaphysically or theologically) that the properties of biological systems are such that the observed homologies across divergent species can only be the result common ancestry and can not be attributed to common design, even in principle? When Myers or anyone else publishes the purely scientific research study that confirms that hypothesis, I would love to read it. Until that happens, what we have here is yet another example of philosophical prejudice masquerading as “scientific explanation”.
While it is not surprising in the least to read this sort of post over at The Panda’s Thumb, it is worth noting that there is nothing new in this of critique. The late Stephen J. Gould wrote in his book The Panda’s Thumb (the namesake for the blog site),
Our text books like to illustrate evolution with examples of optimal design–nearly perfect mimicry of a dead leaf by a butterfly or of a poisonous species by a palatable relative: But ideal design is a lousy argument for evolution, for it mimics the postulated action of an omnipotent creator. Odd arrangements and funny solutions are the proof of evolution–paths that a sensible God would never tread but that a natural process, constrained by history, follows perforce.
Gould is making the “God wouldn’t have done it that way” argument as “proof” of evolution. God, it seems, according to Gould, would do “perfect” design – whatever that is supposed to look like! This is exactly the path taken by Myers and is the main focus of his beef with Luskin’s article. “Common design? Pah! Are you kidding me!?! No God would have done it that way!” Maybe not, but where’s the scientific basis for that premise? Gould never provided one, and Myers for sure hasn’t. The only critique Myers has about Luskin is a theological one, and its not a very good one at that.