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.

10 comments:

Bjørn Østman said...

I'm with you, totally, of course. For example, see this little video I made a while ago of a population of 100 which shifts from pone peaks through a valley to another higher peak, and then again to an even higher peak. Stochastic effects (drift) prevents selection from ruling the game on it's own.

However, I would say that selection only favors the fitter variants - it's just that other factors than selection matter as well, like the mutation-supply rate, to be precise. What do you think?

Bjørn Østman said...

And the link...: http://pleiotropy.fieldofscience.com/2010/04/bad-mutations-are-good-for-you.html

SteveMatheson said...

I would say that selection favors fitter variants, all things being equal. But selection can be relaxed or even negated by drift. And the process can involve trade-offs such as the one that leads to hitchhiking of deleterious mutations. In cases like that, selection acted, strongly, but not every variant that was affected was a "fitter" variant. In this context, "variant" refers to alleles or SNPs affected by a selective sweep. And in that scenario, selection acted as we all would expect, but "favored" some "variants" that are not the most "advantageous" or are even deleterious.

Does that clarify? I was trying to lessen the confusion caused by simplistic focus on natural selection, as you noted.BTW, I'm a bystander in the adaptation wars but do find Lynch to be very persuasive. You?

SteveMatheson said...

COOL!!

Bjørn Østman said...

I'm not sure where I stand, really. I probably lean somewhat towards the side that says selection has the upper hand, though I am tainted by the focus of my own work, which is on adaptation. I am aware of models of speciation, for example, that has no fitness differential, and where the population still fragments. de Aguiar et al. (Nature, 2009) and Hoelzer et al. (PloS Comp Bio, 2008) are good examples.

R. E. Aguirre said...

The most distressing thing about misleading attacks such as those that are sometimes conducted by so called religious minded folk is the claim that they are led by morals of a higher standard than the rest of us...
_________________

R. E. Aguirre
Content Editor.,
readingsfrommodernity.tk

SteveMatheson said...

Good point, and thanks for the comment.

reneemjones said...

It is not even truly possible to define "fitter." Variations are good for some things and bad for others.  What is good or bad for the organism can change day to day!  The whole idea of "fitter" seems to imply that evolution is striving towards something specific.  It is not.

Dan Eastwood said...

>"ID thinkers need to do better."

ID thinkers ought to give it up.

Larry Gilman said...

The problem with insisting that the complications which biologists have been adding to the idea of natural selection are fundamental to any discussion is that so many people don't get the idea of natural selection to begin with.  The claim that there can be no such thing -- that natural selection is tautological ("Who survive? The fit.  Who are the fit?  The survivors.  A mere circle of words!") is very widespread.  It feels like an insight to people, a mind-blowing Gotcha.  I've found that it is difficult enough to get many people to understand selection at all, even in its most basic form, without introducing drift, genetic hitchhiking, etc.  The eyes would really glaze over . . .