What Exactly Does Genetic Similarity Demonstrate?

Francix X. Clines, an excellent writer for The City Life and Editorial Observer sections of The New York Times, today (April 23, 2007) repeats what may be the most common mistake in trying to sell Darwinism to the public. In “Evolution, on Broadway and Off,” Clines writes of the American Museum of Natural History’s exhibition on evolution:

The DNA exhibit shows how the chimpanzee’s DNA has been conclusively shown to be 98.8 percent the same as the visitor’s DNA. Hey, that’s no show stopper for the monkey-song chorus — it still allows a one in 100 chance they’re right.

In other words, you are silly for not believing in Darwinism because you have very similar genes which make the proteins in your body as the chimps do to make their proteins. Game over, right? Not so fast.

The Main Issue: Unintelligent vs. Intelligent Mechanism
My hope is that one day thinking about Darwinian Theory will become clearer in the public square. Recall that Darwin made two claims: (1) all living beings descend from one or a few original ancestors, and (2) the mechanism driving the changes among species is the blind, unguided mechanism of natural selection.
The controversial claim, of course, is the second one–the idea that a purely material mechanism, without any intelligence involved, is responsible for all of the genetic information necessary for life (DNA) and hence for all of life’s diversity.
Clines and others seem to think that evidence for claim one establishes claim two. This is poor thinking. Sequence similarity may indeed be evidence for a common origin–but it does nothing to show that the common origin stems from a material cause rather than an intelligent cause.
Sequence Similarity Alone Does NOT Prove Common Ancestry
Second, the 98.8% DNA sequence similarity between chimps and humans that Clines references does not even establish claim one (common ancestry). And “you don’t have to take my word for it,” as LeVar Burton always used to say on Reading Rainbow.
As Francis Collins, head of the project which mapped the human genome, has written of DNA sequence similarities, “This evidence alone does not, of course, prove a common ancestor” because an intelligent cause can reuse successful design principles. We know this because we are intelligent agents ourselves, and we do this all the time. We take instructions we have written for one thing and use them for another. The similarity is not the result of a blind mechanism but rather the result of our intelligent activity.
Some design proponents think the evidence for common ancestry is good (e.g., Michael Behe), while others–citing the fossil record, especially The Cambrian Explosion–do not. But neither group thinks that sequence similarity alone proves either common ancestry or the Darwinian mechanism, as so many science writers of our day seem eager to assume.

Logan Paul Gage

Logan Paul Gage is Assistant Professor of Philosophy at Franciscan University of Steubenville. Dr. Gage received his B.A. in history, philosophy, and American studies from Whitworth College (2004) and his M.A. (2011) and Ph.D. (2014) in philosophy from Baylor University. His dissertation, written under the supervision of Trent Dougherty, was a defense of the phenomenal conception of evidence and conservative principles in epistemology.



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