Regulatory evolution of the Hox1 gene

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double_mutant_mouse.jpg

I've been getting swamped with links to this hot article, "Evolution reversed in mice," including one from my brother (hi, Mike!). It really is excellent and provocative and interesting work from Tvrdik and Capecchi, but the news slant is simply weird—they didn't take "a mouse back in time," nor did they "reverse evolution." They restored the regulatory state of one of the Hox genes to a condition like that found half a billion years ago, and got a viable mouse; it gives us information about the specializations that occurred in these genes after their duplication early in chordate history. I am rather amused at the photos the news stories are all running of a mutant mouse, as if it has become a primeval creature. It's two similar genes out of a few tens of thousands, operating in a modern mammal! The ancestral state the authors are studying would have been present in a fish in the Cambrian.

I can see where what they've actually accomplished is difficult to explain to a readership that doesn't even know what the Hox genes are. I've written an overview of Hox genes previously, so if you want to bone up real quick, go ahead; otherwise, though, I'll summarize the basics and tell you what the experiment really did.

Continue reading "Regulatory evolution of the Hox1 gene" (on Pharyngula)

15 Comments

It is interesting to me because the Intelligent Design “theorist” Mike Behe once demanded that:

Professor Bottaro, perhaps sensing that the paper he cites won’t be persuasive to people who are skeptical of Darwinian claims, laments that “Behe and other ID advocates will retreat further and further into impossible demands, such as asking for mutation-by-mutation accounts of specific evolutionary pathways…” Well, yes, of course that’s exactly what I ask of Darwinian claims — a mutation-by-mutation account of critical steps (which will likely be very, very many), at the amino acid level.” Behe later adds, “And not only a list of mutations, but also a detailed account of the selective pressures that would be operating, the difficulties such changes would cause for the organism, the expected time scale over which the changes would be expected to occur, the likely population sizes available in the relevant ancestral species at each step, other potential ways to solve the problem which might interfere, and much more. “ “Calvin and Hobbs are Alive and Well in Darwinland”

Behe assumed incorrectly it seems that this data could never be examined at this degree of detail.

This is a little off-topic, but as a non-biologist who in particular never really learned anything about vertebrates except important extinction dates, I was fascinated to hear that giraffes have the same number of cervical vertebrae as humans about a month after my mother’s x-ray tech pointed out to her that she’s got an extra… I guess repetition of “segments” in a particular number can be a neutral mutation? Are these bone numbers standard to all mammals? All vertebrates? What about ribs?

Here’s a table of vertebral number. Cervical vertebrae are relatively fixed, others show variation.

Behe assumed incorrectly it seems that this data could never be examined at this degree of detail.

That assumes good faith on his part. I don’t think he assumes such things; I think he’s well aware that any of his objections can be met over time, but he can always come up with new ones – or simply ignore or wave away the work that has been done.

Imagine discounting Galileo’s experiments rolling balls down ramps because he couldn’t provide moment-by-moment details of the forces acting on the ramp and ball down to the Planck level. Or discounting his telescope observations because he couldn’t give a detailed explanation of how light arrived from distant objects and then interacted with the material of the telescope, or how it then made impressions upon the eye and the mind. The epistemology of science is based on inference to the best explanation, not upon absolute proof, or divine revelation. When Behe says “Darwinists’ fantastic claims are very difficult to support in a convincing fashion”, he’s no different than those who failed to be convinced of Saturn’s rings by refusing to peer into the telescope.

What about ribs?

I hear that women have one more than men. :-) A double whammy resulting from biblical literalism joined to Lamarckianism.

I know that when we have ribs for dinner my wife usually gets one more than me.

Is that what you mean?

PZ Myers Wrote:

It really is excellent and provocative and interesting work from Tvrdik and Capecchi, but the news slant is simply weird—they didn’t take “a mouse back in time,” nor did they “reverse evolution.”

By insisting on caricaturizing evolution as such, the media helps anti-evolution activists even when it claims to be pro-science.

Gary Hurd Wrote:

Behe assumed incorrectly it seems that this data could never be examined at this degree of detail.

As long as the public is blissfully unaware of the double standard (not that many wouldn’t defend it anyway), Behe et al will continue to get away with simply demanding more detail from “Darwinian claims” while not providing any of their own.

PZ Myers wrote:

It really is excellent and provocative and interesting work from Tvrdik and Capecchi, but the news slant is simply weird—they didn’t take “a mouse back in time,” nor did they “reverse evolution.”

By insisting on caricaturizing evolution as such, the media helps anti-evolution activists even when it claims to be pro-science.

Right, the IDists/creos like to attack the media mistakes and to pretend (though it’s true that many don’t know the difference at all) that these are mistakes that the scientists made. And because their audience doesn’t know science beyond what they receive from the media (if that much), it all seems legitimate to them.

Indeed, wait for UD, AIG, and/or ICR to “make the point” that no mouse was brought back in time, no evolution reversed. At which point they’ll be completely done with it, without learning about or dealing properly with the evolutionary implications of this work.

Glen D http://tinyurl.com/b8ykm

Your brother is Mike Meyers?

Michael Myers, yes. We got such a kick out of him every Halloween.

It is interesting to note that it took 1/2 billion (or 1/4 of a billion if you want to average the time out) years for one gene to split into two genes, together with the age of the earliest life form, which is about 3.5 billion years. To put it very crudely, at such a rate of gene mutation evolution seems very unlikely.

Jerry

To put it very crudely, at such a rate of gene mutation evolution seems very unlikely.

Says you. (shrug)

It is interesting to note that it took 1/2 billion (or 1/4 of a billion if you want to average the time out) years for one gene to split into two genes, together with the age of the earliest life form, which is about 3.5 billion years. To put it very crudely, at such a rate of gene mutation evolution seems very unlikely.

If you’re really serious about learning (which I seriously doubt), you may want to read the stuff about how evolutionary processes do not proceed at fixed rates.

Re “It is interesting to note that it took 1/2 billion (or 1/4 of a billion if you want to average the time out) years for one gene to split into two genes, […] at such a rate of gene mutation evolution seems very unlikely.”

I suppose if that rate applied across the board, maybe. But if the gene referred to here was an isolated case rather than this rate being an average, then the “conclusion” doesn’t follow.

Henry

And if evolution did not occur in parallel, and if this were the only mutation event in the history of this gene (about half the amino acids differ between the two proteins).

Actually, Jerry, that was a pretty dumb comment.

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This page contains a single entry by PZ Myers published on August 8, 2006 1:02 PM.

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