In several posts I am currently responding to Eugenie Scott’s newly posted 2007 lecture, “What Do Creationists Believe about Human Evolution?” The lecture provides an opportunity to measure how far the case for Darwinian evolution has come — or hasn’t come — in the intervening 15 years. Yesterday, in the first installment, I noted that the former National Center for Science Education executive director conflates intelligent design with creationism.
That’s a familiar fallacy, as anyone who’s read some ID literature should know. For example, one of the leading ID theorists, Michael Behe, explains clearly in his books that he never was a creationist. He’s a Roman Catholic who has no particular theological objections to evolution and fully accepted it prior to being persuaded of intelligent design by the evidence. To this day Behe finds the evidence for common descent persuasive, but he objects to the thesis that natural selection (or other unguided mechanisms) can account for all of the complexity of life. As he wrote in Darwin’s Black Box (published some 11 years prior to Scott’s talk):
I find the idea of common descent (that all organisms share a common ancestor) fairly convincing, and have no particular reason to doubt it. I greatly respect the work of my colleagues who study the development and behavior of organisms within an evolutionary framework, and I think that evolutionary biologists have contributed enormously to our understanding of the world. Although Darwin’s mechanism — natural selection working on variation — might explain many things, however, I do not believe it explains molecular life.p. 5
Different Definitions of “Evolution”
Scott never mentions these facts about Behe’s views. Yet his acceptance of common descent, combined with skepticism about the creative power of natural selection, has an ironic consistency with Scott’s own framing of “evolution” in her lecture. She notes that the “pattern” of common ancestry and descent with modification is just one part of evolutionary biology. The other part is the “mechanism” which generates that pattern. That, she says, is driven by natural selection but also includes other forces like genetic drift, etc.
Presumably, therefore, one may accept one part of evolutionary biology (or at least not necessarily challenge it) but be skeptical of the other. This is precisely what ID does, except Scott gets ID’s approach exactly backwards.
Lumping ID with “creationism,” she claims ID only objects to descent with modification but accepts selection so long as it operates within “created kinds.” That may be what classic young earth creationists do, but it is the opposite of ID theory’s approach. As Behe, myself, and many others have noted, intelligent design is compatible with common ancestry. Where ID is skeptical of evolution is the claim that unguided mechanisms — driven by selection and random mutation but also including drift and other blind forces — can explain life’s whole show.
Having mischaracterized ID as only a challenge to common ancestry, Scott then gives three examples where she thinks the evidence supports “evolution” so defined: hominid skulls, pseudogenes, and chromosomal fusion, in that order. I’ll evaluate her arguments in this and two subsequent posts. But what’s most ironic is that she cites pseudogenes as evidence against intelligent design even though Michael Behe agrees with Scott that pseudogenes provide evidence for common ancestry!
Hominid Skulls and Human Origins
In her lecture, Scott gives a non-rigorous argument for human evolution based upon the diversity of hominid skulls. There’s no question that when it comes to skulls there are a large variety of shapes and sizes with various mosaics of traits that have been discovered in the hominid fossil record. As I noted in my 2005 paper on human origins and in the 2012 book Science and Human Origins, we’ve long known there are hominid skulls of “intermediate” size known from the fossil record. Indeed, in the latter source I explained that a major review of the origin of the genus Homo found that skull size was the only feature to show “intermediate” traits in the hominid fossil record:
Wood and Collard’s review in Science the following year found that only one single trait of one individual hominin fossil species qualified as “intermediate” between Australopithecus and Homo: the brain size of Homo erectus. However, even this one intermediate trait does not necessarily offer any evidence that Homo evolved from less intelligent hominids. As they explain: “Relative brain size does not group the fossil hominins in the same way as the other variables. This pattern suggests that the link between relative brain size and adaptive zone is a complex one.”
Likewise, others have shown that intelligence is determined largely by internal brain organization, and is far more complex than the sole variable of brain size. As one paper in the International Journal of Primatologywrites, “brain size may be secondary to the selective advantages of allometric reorganization within the brain.” Thus, finding a few skulls of intermediate size does little to bolster the case that humans evolved from more primitive ancestors.Science and Human Origins, p. 67
The Abrupt Appearance of Homo
What’s far more interesting than a few skulls of intermediate size is that when our genus Homo does appear with its large brain, it does so abruptly in a pattern that challenges unguided Darwinian explanations. Stephen Jay Gould and Niles Eldredge — both proponents of evolution who strongly oppose ID — acknowledge the non-gradual evolution of hominid skulls and even of entire hominid species. In a paper arguing for punctuated equilibrium and abrupt appearance in the hominid record, they wrote:
Recent discoveries have discredited the naïve notion of a single lineage, Australopithecus africanus–Homo erectus–Homo sapiens, with gradual increase in brain size within each taxon. All new evidence points to a branching bush with rapid origination and subsequent stasis within taxa. On mechanical and biometric grounds, Oxnard (1975) has argued that the australopithecines, although a sister group to us, were not directly ancestral to any subsequent hominid. (Several paleoanthropologists who generally support our model do not accept Oxnard’s specific conclusion — E. Delson and A. Walker, for example). In any case, there is no direct evidence for gradualism within any hominid taxon — A. africanus, A. robustus, A. boisei, H. habilis, H. erectus, and even H. sapiens. Each species disappears looking much as it did at its origin; admittedly “progressive” trends result from the differential survival of discrete taxa.
Richard Leakey’s discovery of hominid E.R. 1470 has shattered the conventional view that Homo evolved gradually from A. africanus; for this member of our genus, with its cranial capacity of nearly 800 cc, lived in sympatry with australopithecines, perhaps as long as 3 m.y. ago. The more recent discovery of a remarkable H. erectus from the Koobi Fora Formation, east of Lake Turkana in East Africa has discredited the strongest traditional tale of hominid gradualism — a progressive increase in brain size from primitive demes in Java to the advanced population at Choukoutien (Peking Man). This specimen, older than any non-African H. erectus, has a cranial capacity “well within the range of the Peking specimens”.
This punctuated, even saltational increase in hominid skull sizes over time continues to be recognized in the literature. That’s a point I made when responding to critics of Science and Human Origins:
There’s a reason why [Paul] McBride focuses his response so heavily on skull sizes — it’s a rare characteristic for which there’s some consistent kind of a trajectory over time. But as we’ll see, the technical literature finds there is a “rapid change in hominin brain size,” with “punctuated changes” and a “saltation” [increase] in skull size that occurred with the appearance of the genus Homo. Believe it or not, that language came from a paper McBride cited in response to me. As one might surmise, that paper supports my thesis rather than his.
Scott in her lecture cites me on other matters, but not on hominid skulls. Such skulls don’t seem to provide the kind of unqualified support for a Darwinian model of human origins that she’d undoubtedly like to claim they do. This abrupt appearance of our genus Homo in the fossil record is widely recognized in the literature, and it poses a problem not just for common ancestry but for standard unguided evolutionary explanations of human origins.
Next, “Blast from the Past: Eugenie Scott’s Failed Prediction on Pseudogenes.”