Hard and soft transitional forms in the fossil record

Casey Luskin writes about it at Evolution News. (I removed all his links from the excerpts)

Excerpt:

Another good example is what the principal blogger covering human origins at BioLogos, Dr. James Kidder, did last year did in a series on human origins. His series is a good read and quite a competent presentation of the standard Darwinian evolutionary view of human origins — which no doubt reflects Dr. Kidder’s extensive training and experience with this issue. But it accedes 100% to the standard Darwinian story of human origins with essentially no critical analysis whatsoever. But how solid is the evidence behind Dr. Kidder’s view, and are there credible paleoanthropologists who doubt key parts of the orthodox story?

Here’s ONE of the problems that Luskin writes about:

Dr. Kidder’s BioLogos post tried to argue that I misunderstand the meaning of “transitional fossil.” This is a common and characteristically unfounded charge from Darwinian evolutionary biologists. They make the accusation because it takes the focus off the problems the fossil evidence poses for Darwinian evolution, and puts it on Darwin-critics. Advocates of Darwinian evolution also redefine what counts as “transitional,” so that the term becomes nearly meaningless. Here’s what’s going on:

We see that the phrase “transitional form” is 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 was not 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, for example, when some early tetrapod tracks were first reported in early 2010, Nature‘s Editor’s Summary said: “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). The qualified term “direct transitional form” is a nod to the writer’s understanding that there is in fact a “hard” definition of a transitional form, and a “soft” definition, and that some fossils don’t meet the hard definition. What some people call a “transitional form” isn’t necessarily a “direct transitional form.”

So are there direct transitional forms in the hominid fossil record?

If you define “transitional form” in a soft enough way, so that neither temporal placement nor phylogenetic relationship matters any more, then it becomes very difficult to disprove claims that a fossil was “transitional.” It’s a wily rhetorical tactic, designed to make Darwin-skeptics look ignorant while simultaneously taking the focus off the lack of actual (e.g. hard) transitional forms in the fossil record. Dr. Kidder complains that ID proponents define such forms “in such a way that none could ever be found,” when in reality it’s Darwinian evolutionists who define transitional fossils so that they must, by definition, be found in abundance–even if they weren’t necessarily part of an evolutionary transition. Thus we see the Nature blogger quoted above saying absurd things like “every newly discovered fossil of a creature we didn’t know of before IS a missing link.” Or, we see Dr. Kidder making the less-absurd (though similarly inspired) claim that “[t]he human fossil record, in fact, is replete with transitional forms” as well as:

Transitional fossils in the human fossil record are distinguished at both the genus and species level. This group includes the extinct genera Ardipithecus andAustralopithecus and the current genus Homo.

Kidder would have no troubling finding some authorities who agree with him. But there are also credible authorities who disagree — especially with regard to those specific fossils. For example, in my series we’ve seen there are credible authorities who believe that “one of the most critical” areas of the human fossil record lacks transitional forms–specifically, “the transition fromAustralopithecus to Homo.”

Likewise, my series has also cited authorities who would disagree with Dr. Kidder’s claim that Ardi “was advanced in the human direction,” in the sense of developing bipedal locomotion, and who would sharply dispute his assertion that Ardi represents “a phenomenal example of a transitional form in the human fossil record.” Other experts would dispute the claim advanced by Kidder that the australopithecines show clearly “transitional characteristics.” In particular, many doubt theclaim that Lucy’s morphology was “perfectly intermediate between the ape position and the human position.”

Indeed, even Kidder admits: “Unfortunately, the path from Australopithecus to early Homo is shrouded in mystery, with no clear hominin form considered decisively to be the progenitor.” True! But then why does Kidder feel the need to so completely capitulate to the view that humans evolved from Australopithecus? He claims that ID proponents take it as an “article of faith” that transitional forms don’t exist, but it seems that some Darwinian evolutionary scientists take it as an “article of faith” that they do exist, and that the standard Darwinian story of human origins is true.

My point is not that Dr. Kidder is unequivocally wrong or that he’s uninformed. Hardly. He’s welcome to hold and express his opinion, and his series is a highly competent presentation of the standard Darwinian evolutionary account of human origins. Rather, I want to note that the standard story of human evolution — to which BioLogos’s principle blogger on this topic fully capitulates — is not the only scientifically credible position out there. When you dig into the technical literature, many parts of the standard story turn out to be based upon very weak evidence. In short, there are strong scientific reasons to dispute the claim that humans evolved from ape-like precursors. Is it acceptable to point this out?

It seems to me that whoever makes a claim about how we got here has the burden of proof. Both sides are making claims, so both sides have to shoulder the burden of proof. Our side had made claims about what would be found in the human genome for years, and we were vindicated recently with research published in Nature. Can the other side do that?

I recommend reading the whole article. There are good links in there to other things that Luskin has written on this topic, and links to the research he uses in his arguments as well. There’s also a new book out now on human origins that presents more evidence on both sides of this debate.

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