On the Evolution, News & Views Web site, Casey Luskin’s piece critiques the new Smithsonian exhibit "What Does It Mean To Be Human?". In his post, he addresses what has become a standard creationist argument: that gaps in the fossil record disprove evolution. In support of this perspective, he quotes from a section of the Smithsonian educator's guide, written by David Koch, which reads:
Misconception: Gaps in the fossil record disprove evolution.
Response: Science actually predicts gaps in the fossil record. Many species leave no fossils at all, and the environmental conditions for forming good fossils are not common. The chance of any individual organism becoming fossilized is incredibly small. Nevertheless, new fossils are constantly being discovered. These include many transitional fossils—e.g., intermediary fossils between birds and dinosaurs, and between humans and our primate ancestors. Our lack of knowledge about certain parts of the fossil record does not disprove evolution.
Did you get that? Ignoring the fact that transitional fossils are often missing even among taxa whose records are very complete, now Darwin’s defenders argue that their theory “predicts gaps in the fossil record.” How convenient!
This is a semantic trick. It is the same as saying black holes don't exist because we cannot see them. Such a statement completely overlooks the fact that there is a very large amount of evidence, based on how astronomical bodies behave under the influence of strong gravimetric forces, that, yes indeed, black holes do exist. I would venture to guess that very few professional astronomers doubt the existence of black holes.
Because we are missing sections of the fossil record, even large sections of the fossil record overtrivializes the fact that we do have very good fossils to work with and almost unbroken sequences of fossils of many different orders. Luskin, in fact, ignores the second part of the paragraph that he quotes.
That we have gaps is unavoidable. Evolutionary theory doesn't predict gaps. Geology predicts gaps. There is simply no way short of a miracle that we would have completely fossil rich preservation sites for every conceivable depositional environment. Such an expectation misunderstands how geological processes work. Expecting such a fossilized environment misunderstands how taphonomy works. Luskin continues:
What's ironic, however, is that if you ask the question How Do We Know Humans Evolved? the answer you’re given is, “Fossils like the ones shown in our Human Fossils Gallery provide evidence that modern humans evolved from earlier humans.” So whether you find fossils or you don’t, that’s evidence for evolution.
Here's irony for you. The human fossil record, in fact, is replete with transitional forms. In a future post here, I will demonstrate just exactly how rich the human fossil record really is. The recent controversy surrounding the new hominin discovery in South Africa has revealed not just that different researchers have different ideas about how to best view the succession of forms in south and east Africa but also that there is a very wide diversity of forms present. No one working in the field doubts that there was an evolutionary progression fromAustralopithecus to Homo, even if they cannot quite figure out how it happened.
The point is that, despite the fact that we have gaps in the fossil record, what we do have is good enough to make some solid assessments of what happened in the past. The human fossil record is a wealth of information about our history as a species. To dismiss it entirely because there are gaps is simplistic at best and ignorant at worst.
Luskin ends by quoting the great evolutionary biologist Ernst Mayr, who passed away a few years ago:
But the exhibit gives no evidence of dissent from the official party line, such as an admission from Ernst Mayr in 2004 that "[t]he earliest fossils of Homo, Homo rudolfensis and Homo erectus, are separated from Australopithecus by a large, unbridged gap,” and therefore we’re in a position of “[n]ot having any fossils that can serve as missing links."
Mayr was a brilliant evolutionary biologist but he did not work in the human fossil record. He is incorrect about his assessment. There are fossils of all shapes and sizes between the late australopithecines and Homo erectus. The problem is that there is no agreement about what they represent. It is, nonetheless, not an unbridged gap. Finds like Australopithecus sediba help to bridge that gap. Maybe it is not a direct ancestor to early Homo. It still shows the progression toward the Homo line in one of these late australopithecines.
The fact that there are gaps in the fossil record has nothing to do with the fact that evolution has or has not taken place. How does Mr. Luskin explain the areas where there aren't gaps?