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

Percy, I'll respond to this one specifically: Should I then adopt this definition of NS? Does this mean that humans have to go out into the wild to be naturally selected? Can't they get selected at home in the comfort and privacy of their own bedrooms? Does this mean that every reproducing organism is naturally selected? I have children. Does this mean that I have been naturally selected? And what about gay individuals who put their sperm into the mouths and rectums of other gay individuals? Does this mean they are being naturally selected against?I certainly do agree that unless individuals mate and have offspring there is no role for natural selection to play in the course of biological evolution. I'm just having trouble seeing how the individual gets naturally selected. By your definition, then, if the individual has offspring it has been "selected," in the Darwinian sense, to undergo biological evolution (since selection = evolution). This seems to concur with what AZPaul3 who wrote in Message 46: I do not agree that sexual selection is an "element" of natural selection, but I'll defer on that issue. I suppose, then, that everything that reproduces is evolving. Makes me wonder how there are any species at all.But wait, doesn't natural selection, in Darwinian terms, amount to evolution? And is there something other than individuals, per se, that get "selected for," rather than individuals being merely "selected" by nature to evolve? Maybe "selected for"”as in "selected for traits"”is a better perspective. JustinC wrote in Message 37: But of course we know that individuals die in relatively short order, so maybe we need to look at the extant genes, traits, or lineages as those biological thingies that get naturally selected and evolve, since they don't die with the ephemeral individuals. I suppose you could say they live on in their homologies, but that seems self-evident.”HM

Percy, I simply don't agree with you, and furthermore I don't write "nonsensical ramblings." (Your attitude causes me to think that you have not read very much of S. J. Gould.) You have not yet convinced me that, even with cartoon characterization for a colorful spin, all reproducing individuals experience natural selction.Thus far, we have established three schools of thought on the operational definition of natural selection:1. Natural selection selects or selects for groups. For example, crashfrog wrote in Message 3: 2. Natural selection selects or selects for individuals. For example, Quetzal wrote in Message 67: And Percy wrote in Message 66: 3. Natural selection selects or selects for for genes (or kin). For example, Modolous wrote in Message 63I happen to agree with Modolous, mostly, if more emphasis is placed in allele frequencies. Individuals don’t get naturally selected, or selected for, not in the Darwinian sense.But there is another issue here: Does natural selection, in and of itself, amount to evolution? Or does natural selection only lead to eventual evolution?I’ll think Darwin saw natural selection as the actual evolutionary event, or as its cause, because he explained it (standing on Malthus’s shoulders) as an active mechanism or agency of evolution. While I agree that evolution can happen without natural selection”via random genetic drift, for example, as crashfrog points out”I don’t agree that natural selection and evolution are NOT the same thing. Indeed they are, if one views NS in an active context. Why would Darwin even bring up the idea of natural selection if it didn’t explain how biological evolution works in the active sense?To me, the Darwinian meaning of natural selection is best seen in the active context. You however prefer to view natural selection is the passive context. Which one of us is right?”HM

All right, thank you, everyone. My education is coming along nicely. You teachers have been so kind and polite about my corrective surgery. Just to be sure I have things right, though, maybe you could critique these two statements about the agencies of evolution:1. The allele frequencies of population A over time t remain unchanged, owing to the absence of selective pressure and/or random genetic drift.2. The allele frequencies of population B over time t change, owning to the presence of selective pressure and/or random genetic drift.More nonsense?”HM

I'm going with #5, then, because allele frequencies must have nothing to do with selection pressure and/or random genetic drift. Hmm, I wonder what accounts for them. Morphogenic fields? Parallel convergences?”HM

Thank you. It is a good one, but a wet one here in the Puget Sound region.I take it, then, that you disagree with Modulous, who wrote in Message 136: To explain NS and other agencies of evolution, I think you have to focus on the replicators, which are the genes and their alleles. Replicators are the biological entities that get selected and evolve. Individual organisms are not replicators. They do not replicate themselves, not as unique individuals. They only reproduce more unique individuals. And what about the worker ant individuals (re: Modulous's discussion) that don't reproduce at all? Would you say they get naturally selected against? (Are eunuchs and homosexuals naturally selected against?)”HM

Just curious: Do you think that 'individuals selected to reproduce' is different from 'replicators selected to replicate'?I do agree that Darwinian evolution by "natural selection" is Malthusian in principle, and
I think I understand it: A population may grow faster than its supply of food and resources, possibly causing differential reproduction success amongst it members. And I do understand that individuals succeeding in reproduction may be seen as “being selected”” in the sense of “selected to reproduce.” But I still don’t see this as Darwinian "natural selection."I agree that natural selection can be correctly defined as differential reproductive success of individuals across a population. But you confuse me when you imply in Message 143 that natural selection occurs even in populations whose members enjoy effectively equal reproductive success: Selective pressure with no change in allele frequecies? How could that be? If there is no change in alllele frequencies how else would you measure selection pressure? And just because an organism successfully reproduces doesn’t mean it has been “naturally selected." (I think natural selection operates on the relative favorability of genetic traits inherited generationally”I'll call them "allele frequencies"”not on the ephemeral individuals who bear them temporarily.)”HM

But, Chiro, you haven't yet explained how natural selection occurs in a population with unchanging allele frequencies, owing to effectively equal reproductive success amongst its individuals. You're just saying that any individual that reproduces successfuly is naturally selected. I'm still confused. I thought Darwinian natural selection happens, or can happen, when the individuals of a populations have differential reproductive success.”HM

crashfrog, just what do you mean by "the Hardy-Weinberg population [that] moves towards equilibrium"? And why would mutations cause changes in allele frequencies? Wouldn't a population have to assimilate those changes homologically? And wouldn't a population have to experience selection pressure of random genetic drift to alter those allele frequencies?”HM

I suppose you can go hang upside down in your cave, Chiroptera, if you want to. Does this mean, then, that you have abandoned your position that natural selection happens even in populations experiencing no differential reproductive success amongst its individuals?”HM

No, I wasn't trying to be rude. I was only trying to understand how natural selection happens when there is no natural selection. If natural selection happens even when there is no differential reproductive success, as you claim, then how do you explain it?”HM

I could not possibly put it any better than Modulous has done here in Message 166. His view of NS is precisely consistent with my view of it.”HM

The way you explain Darwinian natural selection serves as a nice differentiation from the way Modulous's explains it in Message 166. These two POVs are quite different. Effective understanding of Darwinian evolution by natural selection is at stake here. From my understanding of it, Modolous is entirely correct about how to observe and interpret NS. But I'am always interesting seeing how the other side explains itself. And for that reason, at least, this discussion has served a good purpose.”HM

Quetzal, I am pretty clear about the way you differentiate natural selection from evolution. I'll have to agree with you, mostly, but I have a few more questions. Are you saying that evolution cannot happen at other levels besides the population? Do you mean only speciation? Why can't traits (even a single phenotype/genotype) evolve, as is claimed to be the case in microevolution? Ah, but you will probably say that it takes a population to do that. I wouldn't disagree, but there is still a rumple on my bed of understanding.Maybe it's the idea that natural selection can occur without evolution, even microevolution, taking place. So, is it correct to say that natural selection is something that manifests in a population having differential reproductive success amongst its individuals, causing evolutionary effects ranging from zero to speciation? Are you saying that the action of NS may have no effect on the evolution of a population? Are you saying that natural selection sort of lurks in almost every population, causing evolution to occur only on occasion when the selection pressure gets too high? I guess I'd have to agree.I agree that evolution can happen without natural selection. There are other agencies, such as random genetic drift. But I will have to adjust my perspective a little, as you convince me that differential reproductive success does not necessarily make evolution happen every time. Of course it does not. So your point is well taken.Two things still bother me:1. Doesn't your view of natural selection obviate the "selected for" aspect of the concept? That is, nothing could be "selected for" when natural selection is merely the occasion of differential reproductive success (with its evolutionary effects ranging from zero to speciation).2. This absurd idea, not yours but Chiro's, that natural selection happens even when there is no differential reproductive success. What? This one is hard for me to swallow.”HM

Kinda fickle, aren’t we? Actually. I see it mostly your way: And Modulous’s way, too. But I still have a quibble with this: This is troublesome for me, because the agreed-upon definition of natural selection is: ”differential reproductive success amongst individuals across a population’. This definition does NOT take into account: individual survival, sexual selection, “ . or whatever impacts the individual’s fitness in the current environment.” If natural selection is, by definition, ”differential reproductive success across a population’ then natural selection can only impact a relatively even distribution of reproductive success across of population.
But I still get a confusing response from your when I mention: I think you are using the sieve metaphor incorrectly. If natural selection can be seen as a sieve, then its filtering action works ONLY by disturbing a condition we understand to be ”evenly distributed reproductive success across a population’, n'est-ce pas? Understand the difference? If there is no disturbance of evenly distributed reproductive success across a population there is no natural selection. Period. Your sieve is turned off. Do you wish to change the definition of natural selection to suit your needs? You need to explain how natural selection works as a sieve even when there is no natural selection.”HMEdited by Hoot Mon, : No reason given.

Percy, Quetzal, Chiroptera, et al, I think I understand your problem with the specific meaning of natural selection. You think natural selection is anything that affects the survivability and general wellbeing of individuals or genes in a population, while not necessarily affecting the evenness of reproductive success amongst its individuals. If, for example, a mutation occurs that affects certain individuals by making them shorter, then that, in and of itself, by your reasoning, would be a form of natural selection”nevermind if it helps or hurts their reproductive success. But it's good to remember that natural selection it is not the only mechanism of evolution.Let me point out, as I did earlier, the five known causes, drivers, or mechanisms of evolution:1. Random genetic drift”change in allele frequencies owing to decrease in population size (non-selective)2. Gene flow”genes/alleles entering or leaving a gene pool (non-selective)3. Mutation”heritable nucleotide sequence alteration (non-selective)4. Sexual selection”differential mating success (non-selective)5. Natural selection”differential reproductive success (selective)Evolution can happen without natural selection. There are four other “drivers.” Sure, any one or more of them may affect the evenness of reproductive success in a population (i.e., natural selection), but any one or more of these mechanisms may bypass natural selection altogether en route to an evolutionary event.You seem to be saying, if I understand you correctly, that natural selection is all five of the above, whether or not they cause differential reproductive success in a population. You might be saying that mutation, for example, serves the cause of natural selection. I would not necessarily agree, because evolution can happen apart from natural selection. Random genetic drift is as valid a mechanism of evolution as natural selection is.”HM