What exactly is natural selection and precisely where does it occur?

Oh, well, I suppose you could say that just about everything worth discussing here is a stretched metaphor of one kind or another. My point is that some people here would argue that the basic act of the marbles falling through the holes is, by way of metaphor, natural selection, whether or not any selection actually goes on. I don't think so, unless I can be convinced that natural selection occurs even where there is no differential reprodcutive succcess amongst individuals of a population.”HM

Irrelevant, you say? Merely theoretical mathematics? I wish Daniel Hartl were around here to explain why he thinks "The Hardy-Weinberg principle has important implications for population genetics." (Essential Genetics/A Genomics Perspective, pp. 507-10).”HM

Quetzal, would you suppose a “real-world, sexually reproducing population” would ever evolve without something disturbing is established allele frequencies”its HW equilibrium? If that actually happens in nature, and I think it does more than just abstractly, then that population’s HW equilibrium will have been affected in the real-world context.You know, I suppose one could always argue that Newtonian gravitation is only an abstraction, and maybe the Second Law, too. My point is that models of evolution and its causes will necessarily require some abstraction. Otherwise, we’ll be forced into talking only about the exact moment and location when the amphibians evolved into reptiles, for example, or when the Cambrian exploded.”HM

Thank you, Modulous. That was a very well-reasoned post (even though I can find quibbles). It makes me realize even more that the gene's-eye view of evolution is important in understanding what natural selection is and how evolution works. It helps a biologist take a more rigorous look at what Darwin was unable to see.”HM

Please do. I don't use smiley faces, but my hoot owl is winking.”HM

No. It's much simpler than that. Natural selection is, by agreed-upon definition, the differential reproductive success amongst individuals of a population. That's all.”HM

You can awlays tell when a guy's shorts are on fire when he resorts to name calling and Wikipedia for establishing his credibility.”HM

Regarding the exchange between Percy and Mod: No, I'm only struggling a little here in the deep end, because I'm really snorkeling with my water wings and flippers. I seriously doubt if anyone here is entirely free of struggles to apprehend the true meaning of natural selection. There are plenty of good reasons to be confused about what it is, exactly, and precisely where it occurs. Please consider this example.Richard Dawkins, in his The Ancestor’s Tale (2005, pp. 424-330), singles out the class Bdelloidea of the phylum Rotifera for an examination of how it may have evolved and may continue to evolve. The bdelloid rotifer has adapted to a parthenogenetic form of asexual reproduction, instead of the usual sexual reproduction that mixes male and female alleles together. In the case of bdelloid rotifers, all the genes passed on generationally come from females only, because there are no males in the population. So Dawkins wonders:

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Think of how different evolution must be for the bdelloid rotifer. Far from being swamped into normalcy but the gene pool, they don’t even have a gene pool. The very idea of a gene pool has no meaning if there is no sex.

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Certainly. And so the only way a bdelloid rotifer population could have evenly distributed reproductive success amongst its individuals, or a disturbance therein, is for all females to reproduce equally, which probably doesn’t always happen. And even then there is no gene pool to be the object of natural selection, if that's what really goes on with these all-girl rotifers. And so Dawkins wonders:

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Natural selection presumably takes place among the bdelloids, but it must be a very different kind of natural selection from the one the rest of the animal kingdom is accustomed to.

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Indeed, since the rule of differential reproductive success is matriarchal to the extreme. And it presents a nice exception to the concept, one that casts doubt on the firmness of our understanding of natural selection.While Dawkins finds the bdelloids an interesting study of evolution, possibly by way of natural selection but without a gene pool, he goes on to say:

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Where there is sexual mixing of genes, the entity that is carved into shape by natural selection is the gene pool. Good genes tend statistically to help the individual bodies in which they find themselves to survive. Bad genes tend to make them die. In sexually reproducing animals, its is the deaths and reproduction of individual animals that constitute the immediate selective event, but the long-term consequence is a change in the statistical profile of genes in the gene pool. So, it is the gene pool, as I say, that is the object of the Darwinian sculptor’s attention.

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Maybe both sides are right on the question of where natural selection occurs: indiviual vs. gene. But are these "immediate" and "long-term" stipulations always enough to place natural selection at the scene of an evolutionary crime?”HM

You can tell the ones with the chicken genes”they're all clucking down at the shallow end of the pool.I simply do not understand why Percy et al. are so angry with you, Mod. Aren't we just having a rigorous scientific debate? I like debating with most of thse guys. A few of them would like to insult me. But who needs to get angry over it? I've been held up for ridicule, called names like "schnook," flamed and abused, but I ain't angry; I'm happy to see more clearly what I am dealing with. And I don't mind a little dirty fighting in the alleys.”HM

If I am a 'Neville Chamberlain' then who is a 'Hitler'? Wait, wait, let me guess.But more to the point: I mostly have to agree with your argument.”HM

Those 288 posts were not wasted on me. Many good points were made on either side of the natural-selection argument. In general, the Quetzal v. Mod arguments were for us a fair representation of Gould v. Dawkins. Gould saw natural selection operating on the individual/group level of biological organization. Dawkins sees it instead as working at the gene/kin level. I think a great deal of clarity comes out of arguing these opposing views.As a scientist, I feel committed to viewing everything natural in terms of principles. If natural selection means anything at all, it must work according to biological principles, either known or unknown. So, as we argue the finer points of NS, we must necessarily attack each other’s principles, or lack thereof, to find the more durable explanation. Both Quetzal and Modulous express themselves so well that it is clear to me we have only one conclusion: Natural selection still shows disputed evidence of being at the scene of an evolutionary crime, because we can't agree on the scene.I think our only hope for agreeing on the meaning of natural selection, and agreeing on how evolution via natural selection works, is to focus on the specific definition of NS: Differential reproductive success amongst individuals of a population. Natural selection, in and of itself, does not mean sexual selection, random genetic drift, gene flows, or mutations; it means only that differential reproductive success amongst individuals of a population has taken place.Looking at NS as an effect, one might argue that sexual selection, random genetic drift, gene flows, and mutations could play their causal roles in NS. Or they might work independently to cause a microevolutionary event; NS may not always play a role. I would agree. But the bottom line, in my best estimation, is that NS associates causally with the redistribution of allele frequencies, because differential reproductive success will statistically do that, but it is only one of five known causes of allele-frequency redistribution. Therefore NS may also be an effect, suggesting a causal linkage to a microevolutionary event would need to be understood. To focus on the deeper meaning of NS, deeper than just “individual organisms being selected,” we have to focus on the evolution of allele frequencies. Genes, then, are where the NS action is. This seems to be obvious, at least to me, now in the modern times of molecular biology.”HM

And congratulations, froggie. That's the most substance I've seen in one of your posts since you reported finding E. Coli on your lawn.”HM

Non-random mating certaily would affect natural selection under most conditions, but not all of them. Why would every case of nonrandom mating necessarily cause differential reproductive success in a population if all individuals happen reproduced equally? Nonrandom mating does NOT automatically mean natural selection.”HM

Maybe some of us are most interested in a deeper meaning of natural selection than Wikipedia can provide.”HM

Are you a microbiologist? I suspect you are not, since you didn't even know about E. coli conjugation.”HM