Friday, April 07, 2006

Missing links

I'm pretty excited by the discovery of Tiktaalik roseae skeletons, and not just because if the models are correct, this fish looked awesome. From the times article:
In the fishes' forward fins, the scientists found evidence of limbs in the making. There are the beginnings of digits, proto-wrists, elbows and shoulders. The fish also had a flat skull resembling a crocodile's, a neck, ribs and other parts that were similar to four-legged land animals known as tetrapods.
So the fossils appear to be one of the best examples of a transitional form discovered to date. This should be bad news for creationists, and to a lesser extent, proponents of intelligent design.

The bad news for us is that the discovery won't really do that much. For a long time, the missing link argument has been a bad argument bolstered by a lie. The obvious points are that we have no strong a priori reason to expect a complete fossil record, and much less of a reason to expect a discovery of the complete fossil record. But while the anti-evolution argument requires that we have a complete fossil record, with missing links, claims about common ancestry can be established in spite of huge gaps in the fossil record. Given some large number of species with gaps present, we may be unsure of certain details of descent, we can identify evolved traits and get a course-grained image of the phylogentic tree sufficient to confirm the hypothesis of common descent. There's more wiggle-room for intelligent design here, as they don't question common descent, but even they would lack any strong argument from missing links.

The lie concerns the status of the missing links. While it is true that we don't have many transitional fossils similar to Tiktaalik roseae, creationists are fond of asserting missing links that are not missing. To take an example, some estimates show as many as 20 early hominid species, not all of whom are our ancestors, and quite a number of species who are not obviously either hominids or other apes (this isn't to say we could use a few more fossils). And yet creationists are fond of asserting that there is a problem of missing links between early apes and man. The argumentative strategy goes something like this: if you say there's a missing link between A and C, once a scientist finds B, you just proclaim one missing link between A and B and another missing link between B and C. That this rhetorical strategy has some force relies on neatly forgetting all previous claims about unbridgable missing links and completely ignoring the issue of what a problematic missing link would be, as in the last paragraph.

So I think it's safe to say that while this discovery might help convince some people who are sitting on the fence in this whole discussion, it won't have a serious effect on creationists and even less of one on the ID folks.

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