28 September 2011

If it's not natural selection, then it must be...

The folks at the Discovery Institute (DI) are engaged in an extensive attempt to rebut my friend Dennis Venema's critiques of Stephen Meyer's surprisingly lame ID manifesto, Signature in the Cell. There are several aspects of this conversation that I hope to address in the coming days and weeks, but one jumped out at me today: the consistent confusion about natural selection in depictions of evolutionary theory by design advocates.

Consider this excerpt from a recent blog post by a writer at the Discovery Institute:

...we need a brief primer in fundamental evolutionary theory. Natural selection preserves randomly arising variations only if those variations cause functional differences affecting reproductive output.
A few sentences later, the same claim is repeated:
Indeed, given that natural selection favors only functionally advantageous variations, ...
Those claims were first made in a piece written by unnamed DI "fellows" mocking the work and conclusions of Joe Thornton, an evolutionary biologist at the University of Oregon and the University of Chicago. And the claims are badly misleading.

For one thing, in my view the DI commentators imply that Thornton and colleagues relied exclusively on natural selection in their analysis of the evolutionary trajectory in question. That's false. (Read Joe Thornton addressing these criticisms himself at Carl Zimmer's blog.)

But more importantly, the DI commentators falsely claim "that natural selection favors only functionally advantageous variations," referring to this as "fundamental evolutionary theory." As I regularly emphasize, that simplistic summary looks reasonable at first blush, but it morphs into a seriously misleading error when it is presented the way that design advocates persistently do. These are very, very basic concepts, but they're worth emphasizing. Here's why the DI's portrayal of "fundamental evolutionary theory" above is badly wrong.

1. Natural selection is not the only force that can yield evolutionary change. In some situations, it is not even the most prominent force yielding evolutionary change: random genetic drift is known to strongly influence evolution. And the relative contributions of natural selection versus genetic drift are constantly debated among biologists, both in general terms and on a case-by-case basis.

Friends, you should be suspicious anytime you read a depiction of evolution that focuses solely on natural selection, especially if the writer is addressing function or design. It's hard to overstate the seriousness of that error.

2. Even when natural selection is acting strongly, it most certainly can favor variations that are not "functionally advantageous." This is one major motivation for the new "Harmful mutations" series here at Quintessence of Dust. Not only can natural selection fail to remove variants that we may judge to be disadvantageous, it can actually favor them in some situations. It's simply not true that "natural selection favors only functionally advantageous variations," and again I urge you to be suspicious of writers who disparage the work of professional scientists like Joe Thornton with slogans like that one.

Questions and theories of design and purpose need not rely on such careless errors. ID thinkers need to do better.

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