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Planet Earth

Once More Into the Flaming Pinto, My Friends!

The LoomBy Carl ZimmerMay 22, 2007 10:03 AM


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For those who don't know what I'm talking about, let me quickly recap (and then, at your leisure, read this post.) Last November, my article on the evolution of complex features came out in National Geographic. A few weeks later the article inspired a long but baseless attack from the Discovery Institute, an outfit that promotes intelligent design (a k a "the progeny of creationism"). The attack, authored by one Casey Luskin, came in three parts, climaxing in an argument for intelligent design that required me to wire my jaw back shut: "Was the Ford Pinto, with all its imperfections revealed in crash tests, not designed?" I took a lot of time to refute Luskin's various claims, pointing out how he contradicts himself, doesn't bother to consider the actual scientific evidence I wrote about in the article, and accuses me of deceptions I did not commit. And that, I thought, was that. I went back to reporting on new scientific research, including plenty of new work on evolution. But today I was stunned to discover that six months later, Luskin still can't stop stewing about that National Geographic article. Luskin is now attacking my blog post. In particular, he focuses on what I have to say about the evolution of vertebrate development. Again, to recap: in my article there was an illustration showing three vertebrate embryos, with a caption pointing out their similarities and discussing how the evolution of the genes that control development gave rise to different structures, such as fins, limbs, and wings. In response, Luskin posted an illustration showing vertebrate embryos developing from egg to adult, starting out looking more different, then passing through a very similar stage, and then diverging again. This concept is widely known as a developmental hourglass. He claimed that "transitions from fishlike development ultimately into other forms of development would require radical restructuring (not 'tinkering') from the earliest stages of development." I explained how the differences between early vertebrate embryos are less than meets the eye, and how developmental biologists see the variation as just the sort of descent with modification you'd expect during evolution. Now, in Luskin's lightning response, he claims that I'm arguing the hourglass is imaginary. He shows us two illustrations of the hourglass, and then writes, in plaintive italics, "Clearly I am not inventing the evolutionary hourglass." No one said he did. The actual question at hand is what accounts for the variations before and after the stage when embryos are so similar. I have yet to see a paper published in a peer-reviewed biology journal making the case that an intelligent designer was responsible for the hourglass. I have, on the other hand, read scads of papers on how, as vertebrates descended from an ancestral fish, their development diverged in some ways, while still retaining traces of their common heritage. Instead of dealing with this scientific literature, Luskin quotes an anonymous "pro-ID embryologist friend" who points out differences between the early embryos of various vertebrates. Let me stop here for a moment to point out a glaring contradiction. Luskin's post appears on a site called Evolution News & Views, which declares that "The misreporting of the evolution issue is one key reason for this site. Unfortunately, much of the news coverage has been sloppy, inaccurate, and in some cases, overtly biased. Evolution News & Views presents analysis of that coverage, as well as original reporting that accurately delivers information about the current state of the debate over Darwinian evolution." [Bold emphasis mine] Quoting your anonymous friends rather than reviewing the newest published research in a field is...oh, what's the word I'm looking for...sloppy? Along with Luskin's friend who dare not speak his or her name, he also quotes a 1987 paper by Duquesne University biologist Richard Elinson on the differences between the early development of vertebrates. What he does not bother to mention is that Elinson does not find these differences so vast that they could only be the result of intelligent design. Far from it. He has actually spent the past forty years studying the evolution of these different kinds of development. He has looked at how the transition from water to land drove the evolution of new kinds of embryos, for example, and also how frogs later underwent significant changes as well. (See Elinson's web site or a Google Search of some of his papers.) Rather than quoting anonymous buddies, or conveniently distorting the work of scientists, perhaps Luskin might have looked for himself at some recent scientific journals to see the current thinking about early embryos. Once again, he would find research illuminating how embryos diverged from a common ancestor. Here's a paper entitled "Building Divergent Body Plans With Similar Genetic Pathways tracing the evolution of early development among vertebrates and their closest invertebrate relatives. And another paper published in the Journal of Experimental Zoology on the evolution of fish embryos. But perhaps we should not expect that sort of original reporting from a site that claims to offer original reporting. These studies demonstrate anew a common pattern that I described in my National Geographic article: new structures in animal embryos have often evolved through the modification of old genetic circuitry. (I'll have much more to say about this very soon.) Luskin, on the other hand, uses this shuffling to claim--or at least vaguely gesture towards--evidence of a designer. "Perhaps the 'variations on a theme' implies exactly what we might expect from a creative designer," he writes. Did you notice how smoothly we just slid from intelligent design to creative design? We didn't even stop for Luskin to tell us what creative design is. Of course, Luskin is breaking his own rules about how one is supposed to talk about intelligent design, as I pointed out in my earlier post. He doesn't want anyone to talk about the sort of "good design" you'd expect from an intelligent designer, instead of the many examples of "bad design" that surround us. All we are supposed to do, Luskin informs us, is simply recognize intelligent design through a mysterious quality known as "specified complexity." Except, of course, when Luskin decides that co-opting old genes seems to him exactly what he's expect a creative designer to do. Or an intelligent designer. Same difference. Later Luskin adds, "Why couldn't an intelligent cause re-use the same module to produce these different types of limbs?" To which, of course, one can respond, "Why couldn't an intelligent cause have created the world five seconds ago, placing in it millions of clues that would fool us into thinking life evolved?" Luskin ends his post with a final paragraph loaded with basic errors. He refers to me as a biologist, which I'm not. He claims that my article "focuses on vertebrate development," when in fact I also wrote about bacterial flagella, flowers, insect larvae, and the origin of multicellarity. And then he closes by trying to deliver a coup de grace, pointing out that the regulatory genes used to control the growth of vertebrate limbs also control the growth of appendages in other animals. "Can Zimmer's hypothesis account for such extreme convergence? Does Zimmer knows something most other biologists don't know?" The answer to that last question is no. I am hiding no secret knowledge. That knowledge is out in the open, published in scientific journals. Consider, for example, the latest issue of the journal Nature Reviews Genetics. There the biologist Gunter Wagner presents a new synthesis of evolution and development that address exactly the point that Luskin claims is so difficult for evolution to account for. Wagner makes the case that genetic networks specify the identity of characters such as wings, and while other genes can then specify the state (a hindwing may be a flying wing, as in butterflies, or balance organs in flies). These networks have evolved over time, and can now be found controlling many different structures. But the gene networks responsible for determining the states of characters tend, for various reasons, to hang together over evolutionary time, even as they come to control many different kinds of anatomy. Wagner ends with a series of predictions that can be tested by manipulating the genes in developing embryos. We get nothing so wonderful as a flaming Pinto this time around, I'm afraid. Just more misinformation, six months late.

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