8/16/2007

VOX DEI BAIT #3

First of all, I added some stuff to the prior post.

Second of all, if you were expecting me to reply to any comments on Vox's site today, that's not going to happen during business hours. Don't have the time, and even if I did, I'd have to run an end-around the district's firewall to leave comments from my computer at school. Leave comments for me on my site, and I'll make a good-faith effort to always provide the appropriate context to which my response is based, as well as a link to Vox's latest offering.

Vox writes:

A change in the frequency of alleles within a population is the genetic definition of evolution. What is the genetic definition of speciation?

I'm not really sure we could define speciation in genetic terms without it being very awkward and disjointed. Speciation is usually defined in functional terms, according to the reproductive (or biological) species concept popularized by Mayr. That is, a species is defined as a population or populations which are only able to bear fertile offspring with one another in nature. You could, if you wanted to, express that genetically but why go to all that trouble? We know that there is a genetic basis for whom we are able to have fertile offspring with, and that should be enough for our purposes.

Note that species concepts are just that, concepts. If you're really interested in learning about some of the other ways of conceptualizing the elusive notion of 'species' you should really check out Wilkins's archive, especially this.

Are nucleotide substitutions to be regarded as the genetic equivalent to darwins?

Definitely not. Darwins are scalar quantities that represent measurable changes in traits, in the phenotype. Many nucleotide substitutions have absolutely no effect on the phenotype. Evolution as defined genetically can occur without speciation, without any sort of observable phenotypic trend in the population.

If not, what would be a reasonable definition of a "mendel" that would allow us to track the average rate of genetic evolution as one species transforms into another?

Nucleotide substitutions allow us to estimate rates in which new mutations become fixed in the population, but this has no direct correspondence with speciation. In fact, the higher the rate, the less likely the locus in question is under direct selection, and (as far as I know) the less likely it would contribute to any speciation event---based on what we know today. I add that caveat because the regulatory role of non-coding DNA is an active area of research, and it is always possible that we may find that certain introns might have a role in, say, stabilizing the genome if it is undergoing an episode of reorganization.

3 comments:

Kseniya said...

Hi Scott,

I think maybe Nicole is my long-lost twin sister, because she says things like this.

(Plus, we're both fans of our Pharyngulan buddy Blake Stacey. More than coincidence?)

You're a rare creature on the 'net, Scott: erudite, eloquent, good-natured, unfailingly polite, and... a baseball fan! (You're kinda cute, too.) :-p

I had no intentions (or illusions) of adding to the intellectual discourse here, I just wanted to say "Hi" in a way that I hope doesn't embarrass you too much. Feel free to delete me if it does. ~K.

Scott Hatfield . . . said...

I'm sure I'm flattered, rather than embarrassed. I can't even believe that brains like Blake Stacey or Torjborn Larsson even exchange notions with the likes of me.

Kseniya said...

Pfft. You? Surely not. I, on the other hand, sometimes feel more like a mascot than a peer. *grin*

Anyways, it's a pleasure to read you, either here, or there. Cheers!