Thursday, February 19, 2009

Blunt Talk from Four Evolutionists

 
Do you remember this cover? It caused a minor uproar a few weeks ago [see Explaining the New Scientist Cover].

Today's issue of New Scientist has a letter signed by four people who criticize the journal for its choice of cover design. It may be just about the only important thing those four have in common. There are; Daniel Dennett, Jerry Coyne, Richard Dawkins, and PZ Myers. What a motley crew! [Darwin Was Right].
What on earth were you thinking when you produced a garish cover proclaiming that "Darwin was wrong" (24 January)?

First, it's false, and second, it's inflammatory. And, as you surely know, many readers will interpret the cover not as being about Darwin, the historical figure, but about evolution.

Nothing in the article showed that the concept of the tree of life is unsound; only that it is more complicated than was realised before the advent of molecular genetics. It is still true that all of life arose from "a few forms or... one", as Darwin concluded in The Origin of Species. It is still true that it diversified by descent with modification via natural selection and other factors.

Of course there's a tree; it's just more of a banyan than an oak at its single-celled-organism base. The problem of horizontal gene-transfer in most non-bacterial species is not serious enough to obscure the branches we find by sequencing their DNA.
Darwin was wrong about a lot of things but the tree of life wasn't one of them. It's still an accurate metaphor for most of the history of life—certainly the parts Darwin wrote about.

That's not to deny the fundamentally accurate part of the inside story. At its base the tree of life looks an awful lot like a web. That's correct. It's just that it has nothing to do with Darwin. The magazine's attempt to connect modern molecular evolution with Charles Darwin was just cheap opportunism.

I can't resist noting an irony in the letter. The authors say that, "It is still true that [life] diversified by descent with modification via natural selection and other factors." The irony is that the article inside the magazine discusses molecular evolution ("molecular genetics" in their terminology). The trees derived from those studies are based almost exclusively on neutral mutations that have become fixed in species by random genetic drift. What these studies show is that life diversified by descent with modification via random genetic drift.

Even when they are writing about changes at the molecular level, some adaptationists just can't bring themselves to utter the words "random genetic drift" in public.


5 comments :

  1. I can't help feeling this letter is going to be counterproductive. Meaning, instead of 'the usual suspects' it might have been better had PZ et al encouraged some lesser known colleagues to write and sign the letter. Just for a little diversity.

    Now I fear creationists will point to it as further evidence of closed minded "Darwinist Groupthink" or something like that.

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  2. ... it might have been better had PZ et al encouraged some lesser known colleagues to write and sign the letter.

    Well, he didn't ask me, but I wouldn't have signed it if he had. :-)

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  3. The trees derived from those studies are based almost exclusively on neutral mutations that have become fixed in species by random genetic drift.


    That claim is false, regardless of your stance on the cause of protein polymorphism and variation. Modern phylogenies, especially those discussed in the article in question, are determined by maximum likelihood and Bayesian methods. In model-based probabilistic methods such as these, 'lack of change' (molecular stasis, if you will) is just as important as 'change' for inference. This is, of course, one of the great advantages of model-based methods over other competitors (e.g. parsimony). Model-based methods use all of the data; parsimony ignores invariant sites. The majority of molecular evolution is due to natural selection -- negative selection, which results in slow rates, or in the extreme, invariance. Hence, negative selection is as important as positive selection and/or neutral fixation (i.e., genetic drift) for determining accurate trees.

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  4. LOL. Okay, 'lesser known' was a poor choice of words!

    Mea culpa.

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  5. One thing I took issue with in the Letter by Dawkins, Dennet, Coyne, and PZ (as well as your own coverage Larry) is the consistent framing of rampant LGT occuring at "the base" of the tree. By that I am supposing that the authors (and Larry) are talking strictly about very early evolution. But the point made in the referenced inside article of that issue of New Scientist discusses both "the base" and modern extant organisms, particularly bacteria.

    Modern single-celled organisms should not be refered to as "the base" of the tree of life. After all, multi-cellular eukaryotes comprise only a small fraction of the diversity of life on this planet. Bacteria, Archea, and Single-celled Eukaryotic Protists make up the bulk of life on Earth.

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