Gaps

James Kidder is doing yeoman work. You see, Casey Luskin of the Disco. ‘Tute took a look at the new Smithsonian Institute exhibit on human origins, and wrote:

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!

Kidder then points out that this is a dumb argument by pointing to specific transitional fossils that we know about and that really do help us understand transitions in human evolution. Huzzah!

But that’s not enough. It’s never enough for the Disco. gang. It’s just like when you’re out at a club, and they’ve got one of those newfangled light-up dance floors at the discotheque with the differently colored squares on it that light up in sequence. You can’t jump over a square (no matter how small) that isn’t lit up or you have seven years of bad luck, or something. Fossils are just like that.

So to explain to Casey why “transitional fossils” is an erroneous metric, you have to go deeper. Pointing out a new transitional fossil just makes him drag out the old creationist standby: each new fossil just creates two new gaps in the fossil record. He doesn’t care about what new fossils do explain, he’s just interested in the questions that new fossils raise, which further research illuminates.

No, if you want to mess with a creationist, you can’t just cite beautiful fossils that perfectly illustrate the transitional state which they previously claimed was impossible. You have to show the full scale of the evolutionary trajectory:

i-422e343106695e26ce080e890862d5f9-hominid-crania.jpg
Toss that to the next creationist who insists that the hominid fossil record is full of gaps, and ask them to show where those gaps occur. This graph of cranial capacity over time through human evolution shows exactly why the concepts of a “missing link” or the transitional fossil can be so misleading. Which fossil from this dataset is the transition? Which, if removed from the graph, would be the missing link? Each is essential to the continuity of the dataset, but none is essential. This is exactly the sort of gradual transition that evolutionary processes tend to predict, and exactly what you would not expect if humans had been created specially and separately from all other life.

And before Casey tries to say that I just generated a prediction about his pet “orchard” model, let me emphasize: an omnipotent supernatural designer can, by assumption, do anything. There’s no reason to positively predict that a designer would work by making a new tree look as if it were grafted onto a single tree of life, but without saying something about the nature of the designer, it’s impossible to make any prediction at all about what such an entity would have done. Just because you wouldn’t expect God to do something doesn’t mean it wouldn’t happen. No one expected the Spanish Inquisition, either.

Interested parties would also do well to read Louise Mead’s excellent article on “Transforming our Thinking about Transitional Forms” in the issue of Evolution: Education and Outreach from almost exactly a year ago. To whet your appetite, the abstract reads:

A common misconception of evolutionary biology is that it involves a search for “missing links” in the history of life. Relying on this misconception, antievolutionists present the supposed absence of transitional forms from the fossil record as evidence against evolution. Students of biology need to understand that evolution is a branching process, paleontologists do not expect to find “missing links,” and evolutionary research uses independent lines of evidence to test hypotheses and make conclusions about the history of life. Teachers can facilitate such learning by incorporating cladistics and tree-thinking into the curriculum and using evograms to focus on important evolutionary transitions.

It’s a good summary, as if you needed another one, of why Casey Luskin is wrong.

Comments

  1. #1 csrster
    April 15, 2010

    “Each is essential to the continuity of the dataset, but none is essential. ”

    if you say so :-)

  2. #2 Jim Thomerson
    April 15, 2010

    I have converted to Cladism, and therefore no longer understand the concept of “missing link” and think ancestors can only be hypothetical.

  3. #3 Jimpithecus
    April 16, 2010

    Thank you for the kind words, Josh. I am still a tad leary of systematics, being raised in the best Simpsonian tradition. I am concerned that population variability is not adequately taken into account. Having said that, the concept of collateral evolution explains much.