Monday, April 12, 2010

Casey Luskin on The Smithsonian Human Origins Exhibit

Casey Luskin has an article on Evolution, News & Views on the Smithsonian exhibit called "What Does It Mean To Be Human?" Luskin addresses the standard creationist argument that gaps in the fossil record disprove evolution. He quotes from the educator's guide, 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
Luskin responds:
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. Here are a few:
  • The recently discovered and described Ardipithecus shows the transition to from a quadupedal gait to bipedalism.
  • The material from Hadar and Laetoli show more advanced bipedalism relative to Ardipithecus in A. afarensis, which still possesses slightly curved fingers to grasp limbs, indicating that some time was still spent in the trees.
  • A. afarensis also shows remarkable features in the face that are exactly intermediate between apes and later humans.
  • There is a flurry of different australopithecine forms between 3.5 and 2.0 million years ago, some robust, some gracile. All are related and yet are different, showing regional variation and change through time.
  • The remains attributable Homo habilis, whether they be one species or many, show brain expansion on a basically australopithecine face (this is especially true with KNM-ER1470).
  • There is a remarkable series of gradations from what is considered Homo habilis to what is considered Homo erectus or Homo ergaster. There is disagreement about how many species are represented because the material is quite variable—and shows considerable change over time. This is also why we are having trouble figuring out which group early Homo came from.
  • There is considerable disagreement about when Homo erectus ends and archaic Homo sapiens begins due to the transitional nature of much of this material. This has led some, such as Milford Wolpoff, to suggest sinking H. erectus into the Homo sapiens line, arguing that it represents one long lineage.
  • It is also clear that some traits persist in some populations longer than others. Homo antecessor, from Spain, shows incipient archaic Homo sapiens characteristics at 800 000 years ago, while over in Germany, the Mauer mandible from Heidelberg, still shows H. erectus traits.
  • Over in China, Homo erectus (Zhoukoudian, Hexian) persists until around 250 000 years ago, while at 200 000, obvious changes have occurred in the face (Dali, Maba) in the Homo sapiens direction.
  • Modern human traits do not appear all at once, but rather over a period of 60 to 80 000 years in Africa (Herto, Klasies River Mouth, Border Cave) and the Near East (Mugharet-es Skhul, Jebel Qafzeh). Early "modern" specimens still show a mix of archaic and modern features
I could go on for pages and pages. 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 pretty dang good 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 out of hand because there are gaps is simplistic at best and ignorant at worst. He 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 show 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?

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  1. Jim,
    Thanks so much for putting the time and effort into this issue. I rely heavily upon your, and others, scientific knowledge to help me in my own understanding. I'm a science aficionado but not a scientist, so these efforts do more good than you can imagine. Keep up the good work!

  2. Tried to throw you a trackback from Panda's Thumb but got an error message. So this comment will have to do. :)

  3. Thanks for passing that on. "A nice takedown." Pithy.

  4. The major gap is in Casey's understanding of science. Science is inherently incomplete. If it were complete there'd be nothing left for us to do.

  5. "How does Mr. Luskin explain the areas where there aren't gaps?"

    Exactly. He never seems to address that. Or offer any alternative ideas that explain the evidence. It's almost as though he doesn't know what he's talking about.

  6. That's putting it nicely.

  7. Anonymous1:13 AM

    One could infer from Luskin's rant that Yahweh miracled one genus into another, leaving the gaps? But where is his evidence for that? Where does it say so in the Bible. He can;t articulate a theory except by innuendo because it would violate the beliefs of his own consistence if her spelled it out.

    The fact that one can leave comments here, but not at Luskin's post, speaks volumes.

  8. This is the position over at Reason to Believe as well: that God systematically went in an micromanaged the appearance of species, warts and all over time. Aside from being untestable, there is no theological justification for it.

    About the other: the thing I find amazing is that every time I have corresponded with someone at the Discovery Institute, it is always "through Casey Luskin" as though the people that write articles cannot be bothered to respond to critiques of their articles and want to "screen" the responses. This is not how ANY legitimate scientific institution behaves.

  9. Of course, Luskin is also assuming that the only alternative to evolution is Christian creationism. Who's to say it ain't turtles all the way down? This has always been the basic logical fallacy of Pascal's Wager. Humans have come up with a lot of creation stories - why would Luskin's have to be the right one? I'm partisan to Norse theology, myself. All hail Muspelheim and Niflheim!