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Evolutionary Biologists Are Unaware of Their Own Arguments: Reappraising Nature‘s Prized “Gem,” Tiktaalik (Updated)

Links to our 9-Part Series Responding to Nature‘s Evolution Evangelism Packet:

Part 1: Evaluating Nature’s 2009 “15 Evolutionary Gems” Darwin-Evangelism Kit
Part 2: Microevolutionary Gems: Lizards, Fish, Snakes, and Clams
Part 3: Microevolutionary Gems: Bird-Sized Evolutionary Change
Part 4: Microevolutionary Gems: Flea and Guppy-Sized Evolutionary Change
Part 5: Microevolution Meets Microevolution
Part 6: Evolutionary “Gems” or “Narrative Gloss”?
Part 7: Muscling Past Homology Problems in Nature’s Vertebrate Skeleton “Evolutionary Gem”
Part 8: Of Whale and Feather Evolution: Two Macroevolutionary Lumps of Coal
Part 9 (This Article): Evolutionary Biologists Are Unaware of Their Own Arguments: Reappraising Nature‘s Prized “Gem,” Tiktaalik

Download Our Full Response to the Packet as a PDF.

The final “gem” from Nature‘s evolution-evangelism packet which remains to be assessed in this series deals with the origin of tetrapods, focusing on the alleged transitional form Tiktaalik roseae. The packet states: “The discovery and painstaking analysis of Tiktaalik illuminates the stage before tetrapods evolved.” That was printed in 2009. But how defensible is that statement in 2010? As I discussed in January 2010 at Tiktaalik Blown “Out of the Water” by Earlier Tetrapod Fossil Footprints, new evidence of tracks of full tetrapods before Tiktaalik refute claims that known specimens of Tiktaalik directly document, as the packet implies, “the stage before tetrapods evolved.”

To understand the implications of these tracks, here’s exactly how Nature reported it in January, 2010:

The fish-tetrapod transition was thus seemingly quite well documented. There was a consensus that the divergence between some elpistostegalians (such as Tiktaalik or Panderichthys) and tetrapods might have occurred during the Givetian, 391-385 Myr ago. Coeval with the earliest fossil tetrapods, trackways dating to the Late Devonian were evidence for their ability to walk or crawl on shores.

Now, however, Nied?wiedzki et al. lob a grenade into that picture. They report the stunning discovery of tetrapod trackways with distinct digit imprints from Zache?mie, Poland, that are unambiguously dated to the lowermost Eifelian (397 Myr ago). This site (an old quarry) has yielded a dozen trackways made by several individuals that ranged from about 0.5 to 2.5 metres in total length, and numerous isolated footprints found on fragments of scree. The tracks predate the oldest tetrapod skeletal remains by 18 Myr and, more surprisingly, the earliest elpistostegalian fishes by about 10 Myr.

(Philippe Janvier & Gaël Clément, “Muddy tetrapod origins,” Nature 463:40-41 (January 7, 2010).)

Or as a Nature news article put it:

The oldest known tracks of a four-limbed land animal could rewrite part of vertebrate evolution.
Some prints, showing individual digits, were found in limestone slabs unearthed in a quarry near Zache?mie, Poland, dated to about 395 million years ago — more than 18 million years before tetrapods were thought to have evolved.

The tracks suggest that the animals that made them were up to 2.5 metres long and had a footpad up to 26 centimetres wide, although most prints were about 15 centimetres wide, reports a team of Polish and Swedish scientists in Nature this week. This would mean that large, land-roaming tetrapods would have coexisted for 10 million years with the elpistostegids — including Tiktaalik roseae, which lived 375 million years ago — a group thought to mark the transition from fish to land-roaming animals.

(“Discovery pushes back date of first four-legged animal“)

Simply put, these tracks suggest that tetrapods predated Tiktaalik and thus Tiktaalik is not, as Nature put it elsewhere, a “direct transitional form” between fish and tetrapods.

What Does It Mean to be “Transitional”?
Before going further, I must note that the term “transitional form” is generally used in two different ways. The soft definition of “transitional” implies that an organism merely needs to bear features that are representative of a potential intermediate–even if the fossil itself could not have been a direct transitional form. Under the hard definition of “transitional form,” a stronger claim is made that this organism actually was a real-life lineal intermediate between two taxa, a direct transitional form.

As evidence that this soft/hard distinction is used, when the early tetrapod tracks were first reported in early 2010, Nature’s Editor’s Summary said that “The finds suggests that the elpistostegids that we know were late-surviving relics rather than direct transitional forms, and they highlight just how little we know of the earliest history of land vertebrates.” (emphasis added) Usage of the qualified term “direct transitional form” shows that such a hard meaning of transitional form exists, and that these tetrapod tracks suggest that Tiktaalik does not meet that hard definition.

With Tiktaalik we don’t just see arguments for its transitional nature based upon the soft definition of transitional forms. What has made Darwin’s promoters so excited about Tiktaalik is the claim that its placement in the fossil record directly before the first known tetrapods, and after certain fish groups allegedly ancestral to tetrapods, makes it a direct transitional form, in the hard sense.

A Barrage of Examples from Highly Credible Authorities
Evolutionists have boasted greatly about the purported claim that Tiktaalik is an example of a fossil that meets the hard definition of a transitional form. Badly needing examples of hard transitional forms, many evolutionists have placed great rhetorical weight upon the stratigraphic location of Tiktaalik in the fossil record, even claiming it was a “prediction” of neo-Darwinian evolution. Here are some noteworthy examples:

1. Tiktaalik‘s official website (that’s right — it’s called “tiktaalik.uchicago.edu“) at the University of Chicago claims that Tiktaalik‘s placement in the fossil record was “predicted” by “common sense” leading to “another affirmation of our theory”:

[A]ll four groups of lobe-finned fish we looked at first appear in the fossil record around 390-380 million years ago. The first tetrapods appear around 363 million years ago. Common sense tells us that the transitional form between fish and land animals must have arisen between 380 and 363 million years ago. In order to find our transitional fossil, we’ll need to find rocks that are between 380 and 363 million years old … Ultimately, the site produced Tiktaalik in 2004! Not only was it exciting to find a new species, but it was made all the better by the fact that scientists had predicted the existence of a creature like this all along. We only needed to do some detective work to find it. Another affirmation of our theory! (The Search for Tiktaalik, emphasis added)

2. In his book Why Evolution is True, University of Chicago evolutionary biologist Jerry Coyne hails the discovery of Tiktaalik and its placement in the fossil record in similarly triumphant terms. Coyne couldn’t have laid out the hard “fulfilled prediction of evolutionary biology” any clearer:

One of the greatest fulfilled predictions of evolutionary biology is the discovery, in 2004, of a transitional form between fish and amphibians. This is the fossil species Tiktaalik roseae, which tells us a lot about how vertebrates came to live on the land. Its discovery is a stunning vindication of the theory of evolution. … This is where the prediction comes in. If there were lobe-finned fishes but no terrestrial vertebrates 390 million years ago, and clearly terrestrial vertebrates 360 million years ago, where would you expect to find the transitional forms? Somewhere in between. Following this logic, Shubin predicted that if transitional forms existed, their fossils would be found in strata around 375 million years old. … equally marvelous is that [Tiktaalik‘s] discovery was not only anticipated, but predicted to occur in rocks of a certain age and in a certain place. (Why Evolution is True, pp. 35-38, emphases added)

3. During the rhetorical climax of PBS / NOVA’s “Judgment Day: Intelligent Design on Trial,” Tiktaalik co-discoverer Neil Shubin likewise claimed that the stratigraphic placement of Tiktaalik fulfilled “specific predictions” of neo-Darwinian theory:

What evolution enables us to do is to make specific predictions about what we should find in the fossil record. The prediction in this case is clear-cut. That is, if we go to rocks of the right age, and the rocks of the right type, we should find transitions between two great forms of life, between fish and amphibian. … What we see when we look at the fossil record, at rocks of just the right age, is a creature like Tiktaalik.

(Neil Shubin in “Judgment Day: Intelligent Design on Trial,” emphasis added)

This forceful argument has of course been broadcasted and rebroadcasted on PBS stations around the country.

4. Likewise, the U.S. National Academy of Sciences’ (NAS) 2008 booklet Science, Evolution and Creationism focused on Tiktaalik‘s placement in the fossil record as one of its primary arguments for evolution:

The team that discovered the new fossil decided to focus on far northern Canada when they noticed in a textbook that the region contained sedimentary rock deposited about 375 million years ago, just when shallow-water fishes were predicted by evolutionary science to be making the transition to land. … A prediction from more than a century of findings from evolutionary biology suggests that one of the early species that emerged from the Earth’s oceans about 375 million years ago was the ancestor of amphibians, reptiles, dinosaurs, birds, and mammals. The discovery of Tiktaalik strongly supports that prediction.

(Science, Evolution, and Creationism, pp. 1-3, emphasis added)

The NAS feels so strongly that the “just when” of Tiktaalik confirmed a “prediction” of “evolutionary science” that it presents this material on the very first pages of its seventy-page booklet promoting evolution. Later, the NAS booklet again reiterates this “confirmed … prediction” in a section explaining why evolutionary theory is both theory and ‘fact”:

The evolutionary biologists who discovered Tiktaalik (see page 2) predicted that they would find fossils intermediate between fish and limbed terrestrial animals in sediments that were about 375 million years old. Their discovery confirmed the prediction made on the basis of evolutionary theory. In turn, confirmation of a prediction increases confidence in that theory.

(Science, Evolution, and Creationism, p. 11)

With rhetorical guns blazing, the NAS made Tiktaalik‘s placement in the fossil record one of its central arguments for evolution. No wonder that Time Magazine stated that Tiktaalik has become the Darwin lobby’s “Exhibit A in their long-running debate with creationists and other antievolutionists,” or that the New York Times quoted paleontologists saying Tiktaalik “‘might in time become as much an evolutionary icon as the proto-bird Archaeopteryx‘ bridged the gap between reptiles (probably dinosaurs) and today’s birds.”

But did Tiktaalik really “bridge the gap”?

5. Neurologist Steve Novella thinks it did. He got Shubin’s message from the PBS / NOVA documentary and recommunicated that message, touting Tiktaalik‘s location in the fossil record as a confirmed “prediction” of evolutionary biology:

“What is especially cool about Tiktaalik is that the researchers, Edward B. Daeschler, Neil H. Shubin and Farish A. Jenkins, predicted that they would discover something like Tiktaalik. These paleontologists made the prediction that such a transitional form must exist in order to bridge the gap between fish and amphibians. Even more, they predicted that such a species should exist in the late Devonian period, about 375 million years ago.”

6. As a final example, in his book on Tiktaalik, Your Inner Fish, University of Chicago paleontologist and lead Tiktaalik researcher Neil Shubin praises its placement in the rock record as having “confirmed a prediction of paleontology”:

It took us six years to find [Tiktaalik], but this fossil confirmed a prediction of paleontology: not only was the new fish an intermediate between two different kinds of animal, but we had found it also in the right time period in earth’s history and in the right ancient environment. The answer came from 375-million-year-old rocks, formed in ancient streams. (Your Inner Fish, p. 24, all emphases in original)

It appears evident that leading evolutionary scientists have invested heavily in Tiktaalik‘s stratigraphic and temporal placement in the fossil record as an argument for their cause. They have claimed it fulfills a “specific prediction” of evolution. But if new evidence arises that challenges the view that 375 million years ago is “the right time period in earth’s history” to find organisms making the transition from water to land, what should we expect? Should we expect Darwin’s loudest defenders to admit their “specific prediction” was wrong? Or will emotions run high and keep us from constructive conversation?

The Collapse of the “Prediction” of Tiktaalik‘s Stratigraphic Placement
Darwin-critics who follow this debate closely were well-aware of the importance of Tiktaalik‘s stratigraphic placement for the Darwin lobby’s public case for evolution. David Tyler at the pro-ID Access Research Network (ARN) wrote an excellent blog post explaining why newly discovered tetrapod tracks from about 395 million years ago refute the prediction of Tiktaalik‘s placement in the fossil record:

Just when everyone thought that a consensus had emerged, a new fossil find is reported — throwing everything into the melting pot (again!). Trackways of an unknown tetrapod have been recovered from rocks dated 10 million years earlier than Tiktaalik. The authors say that the trackways occur in rocks that “can be securely assigned to the lower-middle Eifelian, corresponding to an age of approximately 395 million years.” At a stroke, this rules out not only Tiktaalik as a tetrapod ancestor, but also all known representatives of the elpistostegids. The arrival of tetrapods is now considered to be 20 million years earlier than previously thought and these tetrapods must now be regarded as coexisting with the elpistostegids. Once again, the fossil record has thrown up a big surprise, but this one is not “entirely compatible with evolutionary thinking.” It is a find that was not predicted and it does not fit at all into the emerging consensus.

(David Tyler, “Lobbing a grenade into the Tetrapod Evolution picture“)

A few–though only a few–evolutionists also acknowledged the collapse of this prediction. Nature editor Henry Gee acknowledged on his Nature blog that the early tetrapod tracks “means that the neatly gift-wrapped correlation between stratigraphy and phylogeny, in which elpistostegids represent a transitional form in the swift evolution of tetrapods in the mid-Frasnian, is a cruel illusion. If — as the Polish footprints show — tetrapods already existed in the Eifelian, then an enormous evolutionary void has opened beneath our feet…”

Gee’s comments, which were buried in an obscure blog at Nature, understood the great rhetorical weight his camp had placed on Tiktaalik‘s stratigraphic placement in the fossil record. He tried to deflect the collapse of the “neatly gift-wrapped correlation between stratigraphy and phylogeny” by stating “Note: the first person to find any part of this post quote-mined in support of creationism will receive the highly prestigious and coveted Order of the Unicycling Girrafe [sic].”

The Critical Response
New scientific discoveries are exciting because they force us to revise, rethink, and improve our scientific explanations. In fact, neo-Darwinian evolution is certainly not refuted by these newly discovered tetrapod tracks. However, it’s clear that evolutionary thinking led some researchers to make a prediction here. They claimed this prediction was a great confirmation of evolutionary theory. But this prediction is now known to be false. Neo-Darwinism lost an important argument. Thus, I wrote around the same time:

But this week Tiktaalik‘s status as an actual transitional fossil between fish and tetrapods has been called into question by the discovery of unambiguous footprints (with digits) of a full-tetrapod that were made about 20 million years before Tiktaalik.

My original post provoked some spirited responses from Darwin-defenders like P.Z. Myers, Darrel Falk, and Josh Rosenau. Their rebuttals made the usual charges of ignorance and incompetence.

Namely, they charged that I don’t understand that being a “transitional” fossil doesn’t require that the fossil actually be found temporally between that fossil’s alleged ancestors and descendants. In other words, a transitional form need not be a “direct transitional form.” Accompanying this was the charge that I am ignorant of the fact that known fossils may not necessarily mark the actual stratigraphic range of a fossil.

I get it, I really do. If one defines “transitional form” soft enough such that its temporal placement no longer matters, then it becomes very difficult to disprove claims that a fossil was “transitional.” And new fossil discoveries are constantly extending the known ranges of taxa. I took plenty of evolutionary biology and earth sciences at one of the top secular science universities in the country and this is basic stuff everyone learns in evolution / paleontology courses. This is all old news to me. So what’s really going on here?

It is my sense that some Darwin-defenders were unaware of the great rhetorical weight placed by others on Tiktaalik‘s placement in the fossil record. This plausible deniability allowed them to bash Darwin-critics who observed that claimed predictions about Tiktaalik‘s stratigraphic location were wrong. These evolutionary biologists were unaware of their own side’s arguments.

The problem for my critics is that other Darwin-defenders were attempting to make a different, much stronger argument for evolution based on Tiktaalik. As documented above, they were arguing that Tiktaalik‘s temporal location in the fossil record places it in a position where it could be a direct ancestor of tetrapods, and this was a confirmed “prediction” of evolution. They were making an argument for Tiktaalik‘s transitional nature based upon the hard definition.

For example, BioLogos president Darrel Falk confessed to having an intense response to my original post, stating that he “almost hollered in frustration” because he felt I’d misunderstood the science. He promised to show restraint, but then he said my post “is not fair to the Church and it dishonors the discipline,” further writing that the ID movement’s, “leaders owe it to members of the Church who are not scientists to make sure that this kind of writing ceases for good.”

As for the scientific implications of the track discovery, Falk tried to dismiss any negative repercussions for evolutionary thinking, nonchalantly saying that this new find doesn’t change anything since “Finding a new piece that doesn’t quite fit into the picture and then revising it accordingly is what brings great joy to being a scientist” and “it will simply involve a revision in the timing of the origin of land vertebrates.”

Of course that’s right and it’s all fine and good. There’s nothing wrong with evolutionists revising and improving their ideas in light of new data. That’s what science is supposed to do. But what about the fact that so much rhetorical weight was placed on Tiktaalik‘s “predicted” stratigraphic place in the fossil record? Are we supposed to just ignore all of those forceful arguments that Darwin promoters made, and then attack Darwin-critics (like me) who remind the world of those arguments, noting that they were wrong? My sense is that Dr. Falk was not aware of what his fellow neo-Darwinism advocates were arguing.

P.Z. Myers didn’t promise to show any restraint, and restraint he didn’t show. Calling me the “Baghdad Bob of creationism,” he wrote:

Errm, no. Shubin and Daeschler are smart guys who understand what fossils tell us, and they never, ever argued that Tiktaalik’s status as a transitional form depended on slotting it in precisely in a specific chronological time period as a “link” between two stages in the evolution of a lineage. A fossil is representative of a range of individuals that existed over a window of time; a window that might be quite wide. They would never express the kind of simplistic, naive view of the relationship of a fossil that the DI clowns seem to have.

P.Z. also makes a good point that scientists shouldn’t assume that known fossils necessarily mark the exact stratigraphic range of that species. Except that we’ve seen that smart guys like Neil Shubin and Jerry Coyne, or groups like the NAS and PBS / NOVA did in fact argue that evolution is confirmed by the purported “rocks of just the right age” (Shubin’s words) which yielded Tiktaalik. This, of course, was all based upon a prediction coming from the supposedly true stratigraphic ranges of tetrapods and lobe-finned fishes. So whether or not P.Z. is right, it seems that P.Z. isn’t aware of what his fellow evolutionary biologists have been arguing.

Again, I get it. I really do. In fact I’ve gotten this point since I studied paleontology, evolutionary biology, and earth sciences in my undergrad and graduate studies; none of this is new to me. Here’s my take:

If you use a sufficiently loose, or soft definition of “transitional form,” then you can better avoid the possibility that future discoveries will overturn your claim that it was “transitional.” Under soft transitional thinking, the imperfections and ambiguities of the fossil record never require that a “transitional” must be ancestral to its alleged descendants — it merely needs to bear features that are representative of a potential intermediate, even if the fossil itself is not a direct ancestor. In other words, under the soft definition, “transitional” fossils merely serve as proof-of-concept of a transitional form even if they aren’t actually fossils from the right place in the fossil record to document that evolutionary transition. As long as it kind of looks like something that could have been a transitional form, then you can say it’s a transitional form, even if it was not, as Nature put it, a “direct transitional form.” The potential for imperfections in the fossil record can absorb any lingering doubts.

Thus, in a mistitled post “Creationists don’t understand fossils,” Josh Rosenau does a good job of explaining this soft definition:

This doesn’t mean that Tiktaalik is your great-great-great-…-great-grandparent, but it is a close descendant of that ancestor. Even if that ancestor lived 18 million years earlier than Tiktaalik, the transitional state of that ancestor is preserved in its descendants. Casey cites various news articles which mess up this distinction, but never points to the scientific literature where these points are clarified.

The problem for Mr. Rosenau is that it’s not “various news articles” that pushed Tiktaalik based upon its precise placement in the fossil record, but the scientific literature from top scientists and top scientific groups. These leading Darwin lobbyists have been arguing that Tiktaalik, as Coyne put it, was “predicted to occur in rocks of a certain age.” Whether or not Shubin or Coyne “mess up” evolutionary thinking is not for me to say; they are leaders in their fields. What is clear is that they are reliable authorities whose credibility is leaps and bounds above “news articles.”

Thus, when Professor Falk writes, “Science works through constant revision of the individual little hypotheses that make up the entire body of the theory. Luskin and Donald M don’t seem to understand this,” that’s a pretty inaccurate characterization of my views. Of course I understand that scientific hypotheses are constantly revised. That’s fine. The problem for Dr. Falk is that he apparently does not realize the immense rhetorical weight placed on Tiktaalik‘s stratigraphic location in the fossil record.

Evolutionists are welcome to revise their theory. But they are not welcome to revise the history of their theory. They should acknowledge that some widely and forcefully promulgated arguments for evolution based upon Tiktaalik turned out to be wrong.

In Sum
When a widely touted prediction of evolution falls apart, evolutionists often rewrite history, soften the “prediction,” and claim that the harder prediction was never made in the first place. They also attack those who talk about the failure of this prediction as being ignorant of the true claims of evolution. This is known as moving the goalposts.

In this case, my critics cannot escape history. We’re left with the following points:

  • This post has provided clear documentation that leading evolutionary biologists argued that the known ranges of tetrapods and lobe-finned fishes led them to “predict” that a fossil like Tiktaalik would be found in a particular stratigraphic location in the fossil record. When that alleged transitional form was found in that location, they touted it as a confirmed prediction of evolutionary science.
  • Some evolutionary scientists apparently didn’t realize that many leading Darwin lobbyists had argued that Tiktaalik was found in “rocks of just the right age” and thus claimed it confirmed a “specific prediction” of neo-Darwinism, purportedly making Tiktaalik a “direct transitional” form.
  • Tetrapod tracks have now been discovered millions of years before Tiktaalik, meaning Tiktaalik is not a “direct transitional” form leading to tetrapods, and that the supposed “prediction” of neo-Darwinian theory has collapsed.
  • When a Darwin-critic (like me) who realizes the rhetorical importance Darwin-lobbyists have placed on Tiktaalik‘s place in the fossil record points out that this prediction is challenged by new data, Darwin’s defenders respond by (1) claiming no one made that prediction in the first place, and (2) levying various amounts of name-calling and allegations of ignorance against the critic.
  • The reality is that just like I do, evolutionary biologists understand evolutionary theory perfectly well. But they often use slippery definitions of terms to push their theory harder than the evidence allows, and then fall back to weaker arguments when the data contradicts their “prediction.” This is a rhetorical strategy. Sadly, those who are willing to call them on it are subjected to ridicule and name-calling.
  • My approach is to not respond in kind, to not return name-calling with name-calling, and to continue to just talk about the evidence.

Note: Edited on 9/20/10 to fix a quote accidentally misattributed to David Wisker

Casey Luskin

Associate Director and Senior Fellow, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.