The Lessons of Tiktaalik

THE last time we mentioned Tiktaalik, the fossil of a transitional species midway between finned fish and four-footed land animals, was in this post: Creationism and Science, where we were pointing out the foolishness of the creationist claim that the past is scientifically unknowable because it can’t be observed or re-created in the lab.

We’re going to repeat some of what we said then, but we’re also going to elaborate a bit, because the discovery of Tiktaalik illustrates — and rebuts — many of the fallacies of creationism. In fact, we think the story of Tiktaalik should be told every time you find yourself in a conversation with a creationist.

When creationists address the subject of transitional fossils, they are in full denial mode. This is because of their dogmatic insistence that one species can’t evolve into another. They acknowledge what they call “micro-evolution” (observed changes due to mutation and selection, as with Darwin’s finches) but they insist that what they call “macro-evolution” (the result of cumulative changes over time) is impossible. Therefore they flatly assert that there are no transitional fossils, despite the abundant evidence to the contrary. See: list of transitional fossils.

They also claim that a transitional creature is impossible, because — and here they regurgitate comic-book creationism — such a creature would have one fin and one leg, or one lung and one gill, or half an eyeball, or some other ridiculous and impossible set of features. No creature like the creationists’ caricatures ever existed, and no biologist thinks otherwise. Gross genetic deformities sometimes occur, but are rarely viable. What we now recognize as transitional creatures were fully-functional and fully-formed members of a breeding population of similar creatures, entirely capable of surviving in their environment. Except for lines that suffered extinction, each ancient species was a link in the long chain of life between its ancestors and its descendants.

In one sense, every creature that produces offspring is transitional, but in a brief time-span there are no visible evolutionary effects. For example, your father is obviously transitional between you and your grandfather, but you’re all clearly the same species. However, if we find a fossil from the middle of a long evolutionary chain that stretches over millions of generations, changes that have occurred over that time span become evident.

The fossil will have some characteristics that were common to its early ancestors but which are absent in its modern descendants. It will possess other characteristics that its ancestors didn’t have, but which are common to its distant descendants. That’s the value of the fossil record — with enough specimens, each is like a single frame in time-lapse photography, or a page in a flip-book.

But still, how can we explain (or try to explain) to a creationist that the scientific approach to learning about the past has actual scientific value — the results of which are far more “true” (i.e., objectively verifiable) than some account that rests upon mere assumptions? There’s probably little to be gained from a philosophical lecture about the relative merits of natural versus supernatural explanations, because creationists are programmed to reject the former and prefer the latter. However, there is yet another method of explaining the merit of a scientific explanation of the past — cross-confirmation by independent lines of evidence.

A splendid instructional example is the discovery of Tiktaalik. Interestingly, Tiktaalik has its own website. One of the principal scientists involved in the discovery was Neil Shubin, author of Your Inner Fish (Amazon listing).

That fossil wasn’t an accidental discovery. It was found by predicting that a transition occurred approximately 360 to 380 million years ago, before which, according to the fossil record, there were no four-legged vertebrates living on land. Relying on geology, an appropriately aged and conveniently exposed rock stratum was located in the Canadian Arctic that had once been an ancient shoreline. That’s where the search commenced.

Bear in mind that the fossil search was based on two independent theories about the past — first, that the fossil record tells a reliable history of the development of life on earth, so the scientists knew when to search; and second, that geologists have developed reliable methods for determining the age of various rock strata, so the scientists knew where to search. The fossil hunt was a test of both theories.

This article in New Scientist, First fossil of fish that crawled onto land discovered, is from April of 2006, the time of the discovery. It says:

Palaeontologists didn’t previously have a decent fossil representing the intermediate between finned fish and four-footed land animals, or tetrapods. The new animal has been named Tiktaalik after suggestions from Inuit elders in the northern Canadian territory of Nunavut, where the fossil was found.

[…]

“We describe this as a ‘fishopod’: part fish, part tetrapod,” says Neil Shubin, a palaeontologist at the University of Chicago, and a member of the team that discovered Tiktaalik.

[…]

Tetrapods evolved from lobe-finned fishes between 380 and 365 million years ago.

[…]

Hoping to understand this key period better, Shubin and his colleague Ted Daeschler of the Academy of Natural Sciences in Philadelphia, together with Farish Jenkins of Harvard, began searching for fossil-bearing sediments of the right age. After five years of digging on Ellesmere Island, in the far north of Nunavut, they hit pay dirt …

There’s much more information in that article, and also at the Tiktaalik website to which we linked above. At that site, click on the “Discovery” tab. It’s worth the visit.

An additional point must be made: Creationists often claim that statements about the age of the earth and of fossils involve circular reasoning, because fossils — presumed to be old — are then used to claim that the rock strata in which they are found must also be old — which is all hogwash because the earth was created only 6,000 years ago. However, as the discovery of Tiktaalik so strikingly demonstrates, the fossil find isn’t what caused the rock stratum to be arbitrarily declared of the proper age, merely to suit the theory of evolution. The geological information was separately developed by geologists, using their own methods, and that information was relied upon as a guide to the proper location for the fossil hunt.

The point to be emphasized is this: Testing a specific prediction based on both evolution and geology, Shubin and his colleagues searched for the fossil of a transitional creature that — according to the theory of evolution — must have once existed in a place and time like the one geologists said they were searching. Their discovery, after five years of effort, spectacularly confirmed the validity of both geology and evolution theory. That is why the past is scientifically knowable, even if it can’t be observed or re-created in the lab.

Will the creationist to whom you explain this be convinced? Alas, probably not. But at least you’ll know you gave it a good try.

Copyright © 2009. The Sensuous Curmudgeon. All rights reserved.

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