Luskin's Tiktaalik Nonsense

In addition to AIG, Reasons to Believe and all the other DI folks falling all over themselves to say nonsensical things about Tiktaalik roseae, Casey Luskin has now jumped into the fray with this silly post at the DI's blog. His argument can be summed up thusly: even though this find fills in a gap in the fossil record documenting the fish to amphibian transition, the fact that there was a gap to fill in in the first place means evolution isn't backed up by evidence. Yes, I presume he made that argument with something resembling a straight face. he starts by making a big deal out of the fact that scientists actually admit that there was a gap there to be filled:

I love it when new "missing links" are discovered, because it's then--and only then--that Darwinists admit how precious little evidence had previously existed for the evolutionary transition in question. When reports came out this week of an alleged example of a fossil representative of the stock that might have led from fish to tetrapods -- Tiktaalik roseae -- evolutionists finally came clean about the previous lack of fossil evidence for such a transition.

As usual with Casey, it's difficult to tell whether he's being dishonest or just being dense. He quotes two articles in nature in which the scientists "admit" - as though this was some startling fact hitherto unknown - that we didn't have a perfect series of fossils showing every single adaptation in the series leading from fish to amphibians. Here's the first:

"The relationship of limbed vertebrates (tetrapods) to lobe-finned fish (sarcopterygians) is well established, but the origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes."

(Edward B. Daeschler, Neil H. Shubin, and Farish A. Jenkins, "A Devonian tetrapod-like fish and the evolution of the tetrapod body plan," Nature Vol 440: 757-763 (April 6, 2006))

And here's the second:

"It has long been clear that limbed vertebrates (tetrapods) evolved from osteolepiform lobefinned fishes3, but until recently the morphological gap between the two groups remained frustratingly wide. The gap was bounded at the top by primitive Devonian tetrapods such as Ichthyostega and Acanthostega from Greenland, and at the bottom by Panderichthys, a tetrapod-like predatory fish from the latest Middle Devonian of Latvia (Fig. 1)."

(Jennifer A. Clack & Per Erik Ahlberg, "A firm step from water to land," Nature 440:747-749 (April 6, 2006); emphasis added)

Now recall Luskin's characterization of what those two sources said. He said that they "came clean" about the "lack of fossil evidence for such a transition" - the fish to amphibian transition. But that isn't what they said at all. In fact, they both said that we have long known that amphibians did in fact evolve from lobe-finned fish, and there are many reasons, all backed up with plenty of evidence, for why we could infer that ancestral relationship. The level of specificity about which Luskin is talking simply isn't the same as the level of specificity about which those two articles are talking. Both articles that he cites are discussing the lack of fossil evidence that would answer very specific questions about how that transition took place, not about whether that transition took place.

The first quote is does not say there was a lack of evidence "for the transition" from fish to amphibian, but a lack of direct evidence of the sequence of evolutionary changes. That's why it specifically refers to both levels of specificity - the first clause refers to the solid evidence of the ancestral relationship in general, the second clause refers to the much more specific question of the sequence in which the morphological changes took place.

The second quote likewise is talking not about the general question of whether there was a transition, an ancestral relationship between lobe-finned fish and amphibians, but about the specific questions of how those changes in morphology took place. And it even defines exactly where the biggest gap was to be found, between the primarily fish-like Panderichthys and the later Devonian tetrapods like Ichthyostega and Acanthostega. But bear in mind that this transition began much earlier.

The gradual evolution of several traits that allowed for terrestrial adaptation did not begin with Tiktaalik. The skull had already begun to flatten as far back as Eusthenopteron and it got flatter with every species that appears in the lineage. The dorsal fins had already disappeared. The pectoral girdle and the fins that attached to them had already begun to grow more robust and better adapted to being able to sustain the weight of the fish as it moved around in shallow water.

What Luskin conveniently ignores is that the existence of this intermediate form was predicted by scientists based upon the evidence we already had showing the early and later stages of the transition. That prediction was, in essence, a test of the theory that amphibians evolved from lobe-finned fish. If that theory is true, given the fossil evidence we already had, then there should exist at least one species and probably more than one that showed a morphology intermediate between Panderichthys and the true tetrapods. Furthermore, it had to exist in rocks of a certain age (370 million years, give or take) and in a certain environment (shallow marine, particularly rivers). So they began to search where they predicted such a species would be found and, lo and behold, they found one.

And incidentally, the same thing happened in documenting the transition from land mammals to whales. Predictions were made on the nature, age and circumstances in which that transition took place - again, based on the evidence from the beginning and later stages of the transition that we already had - that narrowed it down to a specific type of sediments (shallow marine) in a specific geographic location (Pakistan and India) and of a specific age (50 million years old). And once again, the prediction was borne out. Both predictions are brilliantly documented in Carl Zimmer's book At the Water's Edge.

Luskin then goes to note something that is obvious to anyone not trying to present a cartoonish caricature of the evidence, the fact that there are still gaps. He quotes the Clack and Ahlberg paper:

"There remains a large morphological gap between them and digits as seen in, for example, Acanthostega: if the digits evolved from these distal bones, the process must have involved considerable developmental repatterning. The implication is that function changed in advance of morphology." (Clack & Ahlberg, Nature 440:748; emphasis added).

But wait, Casey. Your entire thesis up until this point is that scientists won't "come clean" that any gaps exist until they've filled in the gap, and now you're quoting scientists today pointing to gaps that still exist and need to be filled in with future finds. Contradiction? You bet it is. The fact is that scientists have been honest from the start that there are gaps in our knowledge of how this transition took place, not whether it took place. And even after Tiktaalik there are still details to be filled in.

But you see, this is where we come to a key difference between how actual scientists deal with the data and how ID advocates deal with the data: actual scientists will now continue to look for the evidence that fills in the details. And when they find another specimen that allows us to verify those details with greater specificity than we can now, the ID crowd will react to that one the same way they reacted to this one, by pretending that since we didn't have answers for every single specific question of how the transition took place before that point, we couldn't possibly have been able to understand that any transition took place at all.

Again I go back to the puzzle analogy - you can tell what the big picture is long before you've fit in all the pieces, and only a fool or a fraud would say that you can't tell that it's a flower until the last piece is in place. And this is especially true when the person who thinks it's a flower is able to make accurate predictions based upon that inference. Once they've figured out that it's a flower, they can predict that there must be a piece or two that shows the bloom, and when that turns out to be the case, it's rather silly for an observer to continue to deny that the picture is what it is.

He then reprints this picture:

And makes the following arguments:

This figure, which Nature graciously has granted permission to reprint, reveals the massive difference in the ray-finned fish-fin of Tiktaalik and the true tetrapod limbs of Acanthostega and Tulerpeton.

No Casey, Tiktaalik is a lobe-finned fish, not a ray-finned fish. The distinction is very important because the vast, vast majority of all species of fish, about 25,000 of them, are ray-finned - which means their fins are thin and have spines in them that run "vertically" through the fin from the body to the tip of the fin. Amphibians did not evolve from ray-finned fish but from lobe-finned fish, members of the class known as Sarcopterygian. Lobe-finned fish do not have flat fins with spines in them, but as the name suggests, rounded, lobe-shaped fins with a central bone and muscle structure in them.

This new fish fossil doesn't seem to add much--if anything--to bridge the gap between fish fins and tetrapod limbs. In fact, if anything, the fin of Panderichthys appears closer to a true tetrapod limb than does the fin of Tiktaalik.

This is an absolutely baffling statement. Did he actually look at the picture he put in his post? Look at the picture. Panderichthys has no "fingers" (distal bones at the tips of the fin), while Tiktaalik does. That fact alone places the latter much closer to the tetrapod form than the former. If anything, Panderichthys appears to be the anamoly in the series and may well be a sideline that died out rather than ancestral. The importance of Panderichthys is in other traits, such as the pectoral girdle and skull structure, which were already beginning to move toward the later form at that early date.

In conclusion, this is a fascinating fossil which I'm sure will stir up much debate. But the next time we dig up some fossil of a fin-bound fish (possibly with a few tetrapod-ish characteristics), we'll hear again all about the previously existing big gaps and how Tiktaalik didn't really teach us much after all--but how the new fossil solves all the problems. That's how it usually works, and that makes me wonder where we're really left today. Anyone who thinks that we've found the "missing link" or clear evidence of an evolutionary transition has either forgotten history, or isn't looking very carefully at the evidence.

I've got a different take on it: any time you see someone talking about a new find being "the missing link", you're almost certainly dealing with someone who is vastly oversmiplifying the data and presenting a crude caricature of evolution. Tiktaalik is just one in a long series of fossil forms. It allows us to understand the transition in more detail than we could before and at a higher level of specificity. But it was not "the missing link". There are lots of gaps in the fossil record, but the overall patterns of appearance can only be explained by common descent. Each new find like this only allows us to get more detailed in our understanding, but it isn't necessary for us to be certain that common descent is a reality, nor is it the end of the search for more detailed understanding. And anyone who tells you otherwise is either an ignoramus or a liar.