Readers of this blog will have to indulge me from time to time so that I can respond to personal attacks from creationists. I write about science, and I strive to do so accurately. I also point out misinformation about science and explain why it’s wrong. So when someone claims I can’t admit a mistake when I make one, or that I suffer from an overactive imagination, I have to respond.
The Discovery Institute, which promotes Intelligent Design, tried to cast doubt a couple weeks ago on a transitional fish-tetrapod called Tiktaalik. The author of the post, Casey Luskin, wanted to convince us that despite the claims of scientists that it had a wrist, it didn’t seem to have one.
His argument turned on a passage from the original paper:
The intermedium and ulnare of Tiktaalik have homologues to eponymous wrist bones of tetrapods with which they share similar positions and articular relations.
Luskin then wrote:
Translation: OK, then exactly which “wrist bones of tetrapods” are Tiktaalik’s bones homologous to? Shubin doesn’t say. This is a technical scientific paper, so a few corresponding “wrist bone”-names from tetrapods would seem appropriate. But Shubin never gives any.
Along with other bloggers, I pointed out that Shubin had given the wrist bone names–the intermedium and ulnare. Hence the word eponymous. These sorts of basic errors wouldn’t be worth pointing out unless there were bills being introduced to promote “critical thinking” about evolution. Critical thinking is not an excuse for these kinds of mistakes.
Well, the Discovery Institute is at it again, with a new post from Luskin: “An Ulnare and an Intermedium a Wrist Do Not Make: A Response to Carl Zimmer.” Now I make the headlines over there, I guess. Wahoo!
This post is also loaded with errors and non sequiturs that the old fact-checker in me cannot resist. I would have left a response as a comment to the post but–interestingly–the Discovery Institute doesn’t let people leave comments. (Comments are welcome here–just be nice and don’t beat the same drum 100 times.) So you’ll have to indulge me.
Error #1 is this: “Dr. Zimmer.”
No Ph.D. here, folks. They call me Mister Zimmer. I was an English major who liked to take physics classes for the hell of it.
Error #2: I can’t admit mistakes.
Luskin writes, “I can admit my mistake” about the wrist bones, something “Zimmer is not known for doing.”
Those links will take you to four posts that Luskin wrote in 2006 about a National Geographic article I wrote about complex traits. As far as I can tell, the reasoning here is that Luskin pointed out my mistakes in these posts, which I then refused to admit.
Actually, I responded back then, (and again) explaining why he was wrong. If you haven’t seen those posts, they’re worth a visit. This was when Luskin crafted the Ford Pinto argument for intelligent design: “Was the Ford Pinto, with all its imperfections revealed in crash tests, not designed?”
Error#3: Structures can’t be homologous if they’re not precisely identical
Okay, this is not entirely a personal attack, but it’s a mistake that’s worth correcting, because it concerns some basic biology. Luskin admits that Shubin actually made an argument for two wrist bones in Tiktaalik, but then says they can’t be wrist bones because they don’t make contact with metacarpals (the long bones of the foot hand). The only way to accept this is to have an overactive imagination. (That’s where I come in, apparently.)
Luskin seems to be arguing that unless the complete tetrapod limb is already in place, including long bones, wrist bones, and toes, then a wrist cannot exist. But evolution works in steps, and so a limb without only some of the bones of living tetrapods is exactly what you’d expect from a transitional species. Is it a fully derived wrist as seen in living tetrapods? Of course not, and no one claimed it was. That’s the whole point.
More distant relatives of tetrapods only had long bones and no wrist bones. By Luskin’s logic, those long bones couldn’t have anything to do with a tetrapod limb. And, if you stretch it further, I guess a horse’s leg isn’t really a leg, because it has lost a lot of bones (including most metacarpals) as it evolved a hoof.
I could list more errors, but you get the idea. Thank you for your patience. Now I’ll return to our regularly scheduled blogcast of real science.
Originally published August 1, 2008. Copyright 2008 Carl Zimmer.