3/28/2008

RAPPING EVOLUTION, WITH STAN

Stan sums up his feelings regarding the theory of evolution by natural selection (TENS, for short):

First, evolution resulting in speciation requires mutation; possibly introgression; and sexual selection. I am now able quote sources on this.

I'd like to see them. As far as I can see, there's absolutely no requirement for sexual selection. Asexual populations evolve as well. And, I think Stan's too hung up on mutations, especially in terms of their randomness. Mutations happen constantly, whether the populations in question speciate, or no. You might say it is a built-in feature of living things. One could just as well say that 'evolution resulting in speciation requires reproduction.'

Second, I am still unaware of real examples of true speciation, with the single possible exception of ring species, which I still have under study. I am not convinced that the species ever really were the same identical creature; that is not empirically provable. It appears to be another extrapolation of fortuitous circumstances, ie, circumstantial evidence.

The classic unlooked-for case of incipient speciation was stumbled upon, quite by accident, by Dobzhansky's group in the late 1950's and spawned a fascinating series of articles, many of which are available at the PNAS archives. The Drosophila literature is filled with this stuff, but what makes the Llanos B strain of D. paulistorium so intriguing is that it appears to be sympatric with other populations. It's been suggested that somewhere between the Orinoco basin and the lab that some of the flies got 'jet lag', and habitually bred later than other varieties whose internal clocks were less brittle. These flies were effectively separated from other flies with which they might have interbred in the wild.

Whether or not a mutation was instrumental was not actually determined in the initial research, though I should confess for Stan's benefit that I am certain that mutations occurred both before and after the speciation event. For me, bottom line, there are other mechanisms besides point mutations which, when coupled with some form of isolation, c
an lead to speciation. Stan, I would encourage you to go to the PNAS site and just search under 'Drosophila paulistorium' or 'Dobzhansky' and enjoy the reads. They are surprisingly accessible, tokens of an earlier time in biology before the molecular revolution had hit its stride.

And, for a very specific and recent instance of Drosophila sp. undergoing speciation in the wild,
check out this article. It's part of a burgeoning literature on in situ evolution in various taxa from a model site in Israel that's been christened 'Evolution Canyon', whose usefulness can be seen in this graphic, from Johannes Sikorski's home page:



If the usefulness of this location doesn't immediately suggest itself, Sikorski has a very thorough explanation on his site which I commend to everyone.



3 comments:

Stan said...

Scott, thanks for the references. I can't comment on them right now, not enough time to study them for a day or two.

As for my references, I did give them before, and here they are again:

"Evolutionary Dynamics of a Natural Population"; Grant & Grant, pg 282:

"The main generating processes are mutation, which we cannot study, and introgression of genes."


The second reference:

"The Origins of Order"; S.A.Kauffman, pg 11, under the heading, "Four Conceptual Correlates of the Neo-Darwinian Synthesis":

"Since Darwin we have come to view selection as the overwhelming, even the sole, source of order in organisms. Natural selection operating on gratuitous random mutations is the sieve that retains order and lets chaos pass into oblivion. This phrase is no understatement of our worldview; it is its heart. No idea derivative from Darwin lies deeper in our minds than this: myriad mutations, selection sifting. Here rebels the 'creation scientist', here cavil many, but here is the core." [emphasis added]

This almost poetic vision of selection and mutations being "the sieve that retains order and lets chaos pass into oblivion" ... is a statement of selection and mutation as the Darwinian and neo Darwinian position on evolution, according to Kauffman.

Third reference:

"Biology of Plants"; Raven, Evert, Eichhorn; 1987, page 566:

"Selection does not actually cause the changes that occur. By continually eliminating alleles from a population under a given set of conditions, selection channels the pattern of variation in characteristics that is caused by mutation and recombination."
[emphasis in original]

And,

"Mutations are, of course, the basis for variability in individuals, but changes in populations occur as a result ofselection acting on the variability provided by mutations."

As I said sometime back, I think for some reason there is a hesitancy to use the word "mutation", and certainly a rebellion against the word "random", even when many evolutionists accept these things. Could this perhaps be due to the assault on these concepts by creationists? For what ever reason, it seems to exist.

"Mutation:
1. The act or process of changing.
2. Change; alteration, either in form or qualities.
3. In biology, (a) a sudden variation in some inheritable characteristic of an individual animal or plant, as distinguished from a gradual change; (b)an individual resulting from such variation: a mutant."
Webster's New Twentieth Century Dictionary, 2nd Ed, 1979.



That's all for now, gotta git.

Scott Hatfield . . . . said...

No idea derivative from Darwin lies deeper in our minds than this: myriad mutations, selection sifting.

Hey, Stan! Great quote! And, you know what? I'm tickled to say that I am 100 percent confident that Kauffman misspoke with respect to the emphasis (mine) in the above quote.

Here's why:

Darwin and his contemporaries didn't even know what genes were, much less mutations. Darwin's theory does not reference mutation. Virtually no evolutionary accounts do until the early 1930's, when Fisher, Wright, Haldane etc. invented the math that demonstrated the consilience of the genetic evidence with the power of natural selection.

If Darwin never mentions 'mutations', then where does Kaufmann get his idea, you might ask? Simple: as a non-geneticist, he's conflating mutation, which is but one means of generating genetic diversity, with phenotypic variation, which term is all over Darwin's book. Kaufmann's gloss is poetic, but inaccurate. If he was going to represent Darwin's thought, he should've written something like 'voluminous variation, selection sifting.'

I agree with the 'Biology of Plants' quote entirely. I probably should get a copy of the Grant's book, but I suspect that they are generalizing from their finch populations, not speaking authoritatively about all taxa.

In any case, they have the dreaded qualifiers in there: "MAIN generating processes" for the Grants, and "mutation AND recombination" for the botany text.

As I said sometime back, I think for some reason there is a hesitancy to use the word "mutation", and certainly a rebellion against the word "random", even when many evolutionists accept these things. Could this perhaps be due to the assault on these concepts by creationists? For what ever reason, it seems to exist.

Frankly, I hope that your perception is correct, because if so that means the correct formulation of TENS is gaining ground in the popular culture. Indeed, you are correct: many of us feel that earlier accounts give far too much credit to mutation (which is almost entirely random), and short-shrift to selection. This isn't just a problem with popularizations, either. Time and again, researchers have been stunned to realize that they have been underselling the power of NS. It seems that, no matter how logical Darwin's 'long argument' is, some of its predictions or conclusions are always going to seem counter-intuitive to a lot of people, religious or no. As you have surmised, creationists have been quick to seize upon this conceptual gap by misrepresenting TENS as sheer randomness, which is then claimed to move from 'goo to you'.

BTW, the rancor that I received from some evangelical Christians today over an allusion to an incident in the Gospels depresses me, as did what happened next. I had 50+ comments on that thread, which leap-frogged from denouncing my heresy to an interminable squabble over the tactics of PZ Myers. I regret treating the whole affair so light-heartedly. I like a good argument as much as the next guy, but I prefer it to be substantive. If someone doesn't like PZ's tactics, they can say so, but I have no interest in going on and on about it, especially with all these people completely uninterested in actually listening to the other.

I guess that experience makes me appreciate our correspondence all the more.

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