In several posts, I am currently responding to Eugenie Scott’s recently published 2007 lecture, “What do creationists think of human evolution?The conference offers an opportunity to measure how far the case for Darwinian evolution has come – or hasn’t come – over the next 15 years. Yesterday in the first episode, I noted that the former executive director of the National Center for Science Education confused intelligent design with creationism.
It’s a familiar mistake, as anyone who’s read literature on identity knows. For example, one of the main ID theorists, Michael Behe, makes it clear in his books that he was never a creationist. He is a Roman Catholic who has no particular theological objection to evolution and fully embraced it before being persuaded of intelligent design by the evidence. To date, Behe finds the evidence for common ancestry compelling, but he argues against the thesis that natural selection (or other unguided mechanisms) can explain all of life’s complexity. As he wrote in Darwin’s black box (published about 11 years before Scott’s speech):
I find the idea of common descent (that all organisms share a common ancestor) quite compelling and have no particular reason to doubt it. I greatly respect the work of my colleagues who study the development and behavior of organisms in an evolutionary framework, and I believe that evolutionary biologists have contributed enormously to our understanding of the world. Although Darwin’s mechanism – natural selection working on variation – can explain a lot, I don’t believe it explains molecular life.
Different definitions of “evolution”
Scott never mentions these facts about Behe’s opinions. Yet his acceptance of common ancestry, combined with skepticism about the creative power of natural selection, is ironically consistent with Scott’s own framing of “evolution” in his lecture. She notes that the “pattern” of common ancestry and descent with modification is only part of evolutionary biology. The other part is the “mechanism” that generates this pattern. This, she says, is driven by natural selection, but also includes other forces like genetic drift, etc.
Therefore, one can presumably accept one part of evolutionary biology (or at least not necessarily dispute it) but be skeptical of the other. This is precisely what ID does, except Scott gets ID’s approach exactly backwards.
Grouping identity with ‘creationism’, it claims that identity only opposes descent with modification, but accepts selection as long as it operates in ‘created species’. This may be what classical young earth creationists do, but it is the opposite of the identity theory approach. As Behe, myself, and many others have noted, intelligent design is consistent with common ancestry. Where ID is skeptical of evolution is the claim that unguided mechanisms – driven by selection and random mutation, but also drift and other blind forces – can explain the whole spectacle of the life.
Having misinterpreted the identification as simply a challenge to common ancestry, Scott then gives three examples where she thinks the evidence supports “evolution” thus defined: hominid skulls, pseudogenes, and chromosome fusion, in this order. I will assess his arguments in this post and in the next two. But what’s most ironic is that she cites pseudogenes as evidence against intelligent design, even though Michael Behe accepted with Scott that the pseudogenes provide evidence of a common ancestry!
Hominid skulls and human origins
In his lecture, Scott gives a non-rigorous argument for human evolution based on the diversity of hominid skulls. There is no doubt that when it comes to skulls, there is a wide variety of shapes and sizes with various mosaics of features that have been discovered in the hominid fossil record. As I noted in my paper 2005 on human origins and in the 2012 book Sciences and human origins, we have long known that there are known “intermediate” sized hominid skulls from the fossil record. Indeed, in this last source, I explained that a major examination of the origin of the genus Homo found that the size of the skull was the single feature to show “intermediate” traits in the hominid fossil record:
Wood and Collard’s criticism in Science the following year revealed that a single trait of an individual fossil hominin species was called “intermediate” between Australopithecus and Homo: the size of the brain of Homo erectus. However, even this intermediate trait does not necessarily offer any evidence that Homo evolved from less intelligent hominids. As they explain: “The relative size of the brain does not cluster fossil hominins in the same way as other variables. This model suggests that the link between relative brain size and adaptive zone is complex.
Similarly, others have shown that intelligence is largely determined by the internal organization of the brain and is far more complex than the single variable of brain size. Like an article in the International Journal of Primatologywrites, “Brain size may be secondary to the selective advantages of allometric reorganization in the brain.” So finding a few intermediate-sized skulls does little to confirm that humans evolved from more primitive ancestors.
Sciences and human origins, p. 67
The sudden appearance of Homo
What is far more interesting than a few average sized skulls is that when our genus Homo appears with his big brain, he does so abruptly in a pattern that defies unguided Darwinian explanations. Stephen Jay Gould and Niles Eldredge—both proponents of evolution who strongly oppose identification—acknowledge the non-gradual evolution of hominid skulls and even entire hominid species. In a paper arguing for a punctuated balance and abrupt appearance in the hominid record, they wrote:
Recent discoveries have discredited the naive notion of a single lineage, African Australopithecus–homo erectus–Homo sapiens, with a gradual increase in brain size within each taxon. All new evidence points to a branching bush with rapid origin and later stasis within taxa. For mechanical and biometric reasons, Oxnard (1975) argued that Australopithecines, although a sister group to us, were not directly ancestral to any later hominids. (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 progressiveness in any hominid taxa – A. africanus, A. robustus, A. boisei, H.habilis, H. erectus, and even H. sapiens. Each species disappears much resembling its origin; admittedly “progressive” trends result from the differential survival of distinct taxa.
Richard Leakey’s discovery of the hominid ER 1470 upset the conventional view that Homo gradually evolved from A. africanus; for this member of our genus, with its cranial capacity of nearly 800 cc, lived in sympatry with Australopithecines, perhaps 3 my ago. The most recent discovery of a remarkable H. erectus from the Koobi Fora Formation, east of Lake Turkana in East Africa, has discredited the strongest traditional account of hominid gradualism – a gradual increase in brain size from the primitive demes of Java to the advanced population of Choukoutien. (Peking Man). This specimen, older than any non-African H. erectus, has a cranial capacity “well within the range of Beijing specimens”.
This punctuated, even saltational, increase in the size of hominid skulls over time continues to be recognized in the literature. This is a point that I underlined when responding to the criticisms of Sciences and human origins:
There’s a reason why [Paul] McBride focuses his answer so much on the size of the skull – it’s a rare feature for which there is some sort of consistent trajectory over time. But as we will see, the technical literature finds that there is a “rapid change in hominid brain size”, with “punctuated changes” and “saltation”. [increase] in the size of the skull which occurred with the appearance of the genus Homo. Believe it or not, this language comes from an article McBride quoted in response to me. As one might assume, this article supports my thesis rather than his.
Scott in his lecture quotes me on other topics, but not on hominid skulls. Such skulls don’t seem to provide the kind of unquestioning support for a Darwinian model of human origins that she would no doubt like to claim they provide. This sudden appearance of our kind Homo in the fossil record is widely recognized in the literature, and it poses a problem not only for common ancestry, but also for standard unguided evolutionary explanations of human origins.
Following, “Blast from the Past: Eugenie Scott’s Failed Prediction on Pseudogenes.”