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

The difference is that I believe that the replicator is what is being selected for. Obviously individuals can be said to be selected - but that is not necessarily anything to do with evolution by means of natural selection. If I lived in a culture whereby I was born into a rich family, and only rich families got medical care I could be said to have been selected to be more likely to breed based on that. I have inhereted a cultural benefit - not a genetic one (assuming for illustration's sake that getting rich is unrelated to genes). This is not natural selection, but cultural selection.It can be evolution, in a sense. It is not biological evolution. Thus individual selection is not really what we should be looking at when we consider biological evolution. Some indivuals will never reproduce - but their gene's frequency increases in the next generation.Likewise - it is possible for an individual to be selected to breed -but the individual's gene's frequency decreases in the next generation.Thus: what is really being selected for (in biological evolution terms) is a gene's ability (in aggregate) to be part of a team of genes that creates succesful phenotypes. A succesful phenotype is a phenotype that succesfully causes its genes frequency to increase. A succesful phenotype does not have to reproduce to accomplish this goal.A genetically caused genius who is faced with the options of raising a family or developing a cure for some infertility in the human race and who chooses the latter may actually increase the frequency of many of his own genes. However- if he was caused to be a genius by the presence of a novel gene that novel gene will be selected out. If the gene was not novel - but more often than not caused its phenotype to not reproduce would also be selected out eventually (or perhaps it will be selected down to some equilibrium level (as in ESS)). That's natural selection in biological evolution terms. Individuals are not of import at all.So in my view - the phenotypes themselves are what decides if a gene or its alleles get selected or not. Thus - genes are selected for by virtue of the phenotypes they on average help create. Genes that increase fecundity can still be selected against despite the fact that from an individual point of view it looks like they are being selected for. Genes that decrease fecundity can be selected for, even though it looks like the individual is being selected against.Thus: it is often useful to discuss these things in terms of individuals, to really get a grip on what is happening, the genecentric model is vastly superior.It is much like Bohr's simple model of the atom that gets taught to novice chemists. It is a useful model, but it isn't the most accurate model.Edited by Modulous, : No reason given.

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

No, they are not quite different. They both describe the exact same process, but from different perspectives. That you think the different ways of describing natural selection represents some sort of disagreement about what it involves means you still don't understand it. Only for you. I assume that you still think genetic change is part of natural selection, so the view you say you prefer is not actually Modulous's view, but some misinterpretation of it.--Percy

Mod,I'm going to skip the cultural evolution piece, because that's not what we've been talking about in this thread, and I really think that the topic will derail things too much. I have my own views of cultural evolution, but they would be better discussed on another thread. Suffice, for the moment, that we are primarily in agreement there - but I feel there is little relevance for natural selection. We are not in disagreement. However, the reason I keep coming back to the phenotype (the individual sum of genotype and environment), is that selection can operate on non-inheritable characteristics. Although these characteristics may have no bearing on evolution, they DO prevent or enhance the reproduction of the individual. Which is how genes get transmitted. Since the selection part of natural selection refers to the filter created by the totality of the biotic and abiotic factors affecting the organism in its particular environment, this would, perforce, have to include things that operate only at the individual level - regardless of genotype. For example, an organism that is damaged but not killed by a predator may have difficulty reproducing, no matter what its genotype may be. An epiphyte overburden may exceed the structural tolerance of a forest emergent, causing it to fall and bring down multiple neighbors - in spite of their genotype. The problem I have with the gene's-eye-view is that it ignores the stochastic events that may change the allele frequency of a population - by eliminating those individuals who carry them - it is an inherently deterministic view of natural selection.Now, before you go ballistic, please remember that I am NOT talking about evolution, only natural selection. Since we both agree that evolution occurs at the level of population, then I assume we have no disagreement that talking of the change in allele frequencies - the result of natural selection (among other things) - in a population is evolution. In this sense, it is absolutely imperative to use the gene's-eye-view, because that's what evolution is all about - adaptation of populations to changes in the environment (again, among other things). Yes, when discussing evolution.

Okay, Mod. I'm clearly not explaining myself well. That being the case, let me post a few quotes from people who are MUCH smarter and better at explaining things than I am.

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What is exposed to natural selection is not the individual gene or the genotype, but rather the phenotype, the product of the interactions of all genes with each other and with the environment. (Ernst Mayr, Evolution and the Diversity of Life, Belknap Harvard, 1997, pg 318)

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Natural selection acts on phenotypes, regardless of their genetic basis, and produces immediate phenotypical effects within a generation that can be measured without recourse to principles of heredity or evolution. In contrast, evolutionary response to selection, the genetic change that occurs from one generation to the next, does depend on genetic variation. (Lande R, Arnold SJ, 1983, "The measurement of selection on correlated characters", Evolution, 37:1210-1226)

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Evolutionary biologists differ on whether or not the definition of selection should require that the classes differ genetically. Some authors...define selection as a consistent difference in fitness among phenotypes, acting within a single generation. Whether or not it alters the frequencies of phenotypes in the next generation depends on whether and how the phenotypical differences are inherited. The change in the population from one generation to another is termed the response to selection. Authors who advocate this phenotypical definition distinguish the response, which is solely a matter of inheritance, from differences in survival and reproduction, which constitute selection itself. (Futyma DJ, Evolutionary Biology, Sinauer, 1998, pg 349. Emphasis in original)

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I'm one of those who advocate the distinction between selection - which is against phenotypes - and the evolutionary response to selection - which is based on genotypes. I hope that makes my position a bit clearer. Edited by Quetzal, : Kuz I kant spel

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We could even combine our two definitions and arrive at, "Natural selection operates on individuals, and their different fitnesses result in differential reproductive success."

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Two cheers for this definition (only two because I think the concept "fitness" can be confusing and needs to be thoroughly qualified, i.e, never introduce NS as "survival of the fittest")[edit] After reading Quetzel's quote, I believe I can understand your position better. The quote being I didn't realize some biologists made the distinction between selection and the change in frequency of traits in the population that results from it. Edited by JustinC, : No reason given.

I am not so sure.I do not see that Moduluous would be thinking against Gould's simple idea that the "skin" of vertebrates is something that "protects" (I can find the quote if you prefer) their evolutionary individuality.You series of talking points would turn a nictating membrane into a whole body kinesis, not something impossible physiologically, across verts (when put into a rotating room of black and white bars painted on the wall some verts move eyes, some turn heads and some turn the whole body), but psychologically of a different order than Modulous' strident orbit.If one refuses to grant the skin the interactors' organon of first defense it will be hard to realize the suffiency of superfludity that your position remains redactable for/to. I think only when polyploidy(vs haploid or diploid forms) and DNA copying are better remanded can we shake out the copyists from the replicators through interaction.One way to get there is to clearly cognize the levels and then to discuss the relative frequency of them in nature. If biology really was at its analytic best I think thinking that replicators are WHAT is being selected may be the razor but because syntheses are proceeding with parsimony without being far enough analyzed this gulf exists where instead a "transition" was and that suits the creationist as it is opposite to ground truths to some extent.Gould's anti-creationist rehtoric only holds so much logos. The disjunction may exist and not be digital. This is not where Modulous's phrases and phases go.Edited by Brad McFall, : for/to

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

I thought you said Mod was "right" and the rest of us were full of it (or words to that effect). Fickle, aren't you? Before I go any further, I want to emphasize that neither Mod nor I are "right" in the sense that the other perspective is "wrong". As Percy pointed out, these are just two different ways of looking at the facts. Indeed, both perspectives are "right". It all depends on what you're trying to measure (or describe). For me, conceptually, isolating selection as in the phenotypical definition of selection is more useful when discussing what happens in a given generation. However, when describing the effects of selection as it pertains to evolution, the gene's-eye-view is the more relevant - because it describes the result of selection over evolutionary timescales. This is, in essence (and Mod can correct me if I mis-state), the only difference between the two. It's really a fairly esoteric disagreement. No. The population is the fundamental element of evolution. It makes no sense to talk about evolving individuals, or for that matter the arbitrary groupings we call species, genera, etc, except in the abstract. However, it is quite useful to talk about gene lineages evolving. In this, Mod and I are in 100% agreement, and the genecentric view provides a clearer picture of what is happening. The argument on this thread is about selection, not evolution. In what sense? I'm not sure I understand the question. Please clarify what it is you are asking. Traits DO evolve. Single characteristics, suites of genes, etc, all evolve in response to long-term selection pressures. I'm not sure where this question comes from. That is the definition of evolutionary response to selection. I even quoted it above. As long as the differences are inheritable, then phenotypes, genotypes, single genes, polygenes, etc, all can evolve. And by the way, I absolutely loathe the term "microevolution". It's all evolution. The arbitrary distinction serves no useful function outside of paleontology, in my opinion.I think for some reason you are still conflating "natural selection" with "evolution". As just about everybody participating in this thread has stated about a million times, they are two distinct, separate concepts. Natural selection is one of the engines that drives evolution. It is NOT evolution. It is a mechanism of evolution. The motor is NOT the car. Let's let ol' Douglas Futuyma (yeah, I know I mis-spelled his name in the citation above, it's too late to go back and re-edit that post. Sue me.) state it (from further down the page I cited previously):

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For our purposes, we will define natural selection as any consistent difference in fitness (i.e., survival and reproduction) among phenotypically different biological entities. The entities may be individual genes (which must have some phenotypically variable property if the differe consistently in fintess), groups of genes, individual organisms, populations, or taxa such as species. (Although we have adopted a phenotypic definition, we will almost always discuss the fitness of phenotypes that are inherited to at least some degree, because selection has no evolutionary effect unless there is inheritance.) (Futuyma 1998, op cit. Emphasis in original).

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What? I think you're still confusing selection with response to selection. Natural selection is basically just a seive that "sorts" individual organisms based on some trait or characteristic (or suites of traits or characteristics). This sorting may affect the individual's survival, reproduction, reproductive rate, etc. In other words, the trait or whatever impacts the individual's fitness in its current environment. That's all.The response to this sorting, whether we look at it from a populational standpoint OR from a genecentric standpoint, is evolution. Speciation is one form of evolution - one of the directions evolution can take. Yes. No. The seive is always operating. The "sorting machine" of natural selection is always "on". The key thing to remember is that in reference to evolution, it is only when the phenotypical effects of NS are inheritable that NS drives evolution. This latter point, by the way, is the basis for the "loophole" that allows NS to promote traits that are actually less fit that Mod mentioned. No. "Selected for" (i.e., selected because) is precisely what the seive does. It sorts organisms based on (a) particular trait(s). There may be selection of some other trait that the organism also posesses - but simply because that other trait also passed through the seive at the same time - not because the seive was "set up" to filter that other trait. Natural selection ISN'T the "occasion of differential reproductive sucess". That's the response to selection (sort of - although that's a rather poor way of describing it). What do you mean, "absurd"? Chiro said precisely the same thing I said. You can't agree with me and disagree with Chiro, since we merely used different words to say the same thing. Maybe you need to re-read Chiro's post in light of what I've said? Again, it seems to boil down to "selection" vs. "response to selection", n'est-ce pas? Understand the difference?

I understand better your position, now.However, all selection is natural - potentially making natural selection is a hopeless term. The only other option is for supernatural selection, which is beyond our scope. When natural selection is usually discussed, the general implication is that it is being discussed in the context of biological evolution. Sometimes it is being discussed in the context of non-biological evolution. Evolution is usually the subject matter.However we can consider natural selection in other terms - but then 'pick a card, any card' becomes natural selection. Indeed, why bother with the 'natural' part at all? My counterpoint is that essentially, the phrase natural selection is more than the sum of the meanings of its words. In my opinion, that is the problem I have with the individualistic view. The genecentric view shows us that 'bad luck' (being selected out in spite of the gene's good points) averages out over time. The genecentric view insists on a stochastic view: the genes which, on the whole (on average etc), help create sucessful phenotypes, are the genes which have a tendency towards increasing in frequency.It doesn't ignore bad luck - it just says that bad luck isn't evolution by natural selection (other than in the sense that genes which can defend best against bad luck tend to increase, but we're defining bad luck as being events which hamper reproductive success despite the genes. If the bad luck happens to affect an entire environment, then we have natural selection since only those genes which on average were able to create succesful phenotypes that can survive that piece of bad luck will survive. Hence why we aren't particularly good at surviving deadly asteroid impacts...that bad luck is part of our history but natural selection is geared more toward the immediate past rather than the far past or the future. Naturally, this bad luck is dependent somewhat on genetic effects and isn't the kind of bad luck that genecentric natural selection ignores.If getting injured a certain way is a constant risk - then natural seleciton in a genecentric view applies. It it is purely random bad luck, then the genecentric view does not regard it as natural selection (as far as I can tell anyway). I'm not sure if purely random selection happens in the real world, until meddlers such as ourselves come into being - we can set up experiments that simulate pure bad luck, but the change in allele frequencies here is not caused by natural selection, it is the selection equivalent of random drift.In this experiment a gene could be selected against purely by accident. A gene which generally is involved in creating succesful phenotypes might still become extinct (the more copies of that gene exist in the population the less likely this becomes). The genecentric view takes care of this though with the magic word 'tendency'. These genes have a tendency towards increasing their frequency, but it doesn't have to happen - freak and rare occurances do happen. Much like thermodynamics - the gas molecules that escape from a bottle of coke have a tendency to evenly distribute themselves around the room - however it is possible for them all to redistribute temporarily back into the bottle.It is possible that a succesful and common gene will be made extinct - but on the whole, we'd expect that gene to increase in frequency until it reaches some kind of ESS (at which point it will stay there with minor pertubations until the ESS changes). The 'stable state' of gas molecules is to be all over the place, until we introduce a selective mechanism ala Maxwell's demon.

I believe Darwin chose the term natural selection by way of contrast with artificial selection, i.e., what breeders do.--Percy

Indeed, but his treatise was on the origin of species by means of natural selection. If farmers randomly selected animals to breed, we'd hardly call it artificial selection - even though it is, but we wouldn't call it that because artificial selection commonly refers to the selection carried out by breeders.I agree that natural selection is a useful phrase.. Artificial selection is where breeders decide what genes remain and what don't carried over based on what is best for the 'artificial' environment that is agriculture. Artificial selection is anything but artificial. It is very real, and it is very natural. If we limit ourselves to saying that any selection that occurs is natural selection...we render the phrase meaningless.My point was that natural selection doesn't just mean an individual is selected out for whatever reason. That is just selection. It could be chance, it could be artificial selection or it could be natural selection.Lions select which gazelle to kill (and thus which ones get to live to breed), and it turns out to be the one that is the slowest, least attentive, or what have you. Thus, any genes that contributed to this, will be lowered in frequency. However, if all the gazelles are equal in speed and attention, the lion will simply end up killing a random one (bad luck). Gene frequencies will change, but that isn't natural selection. The next generation the gene frequencies will tend towards the original result. So the gene frequencies will simply go slighlty up and down, hovering around a certain value until something changes (a better gene starts to spread or a natural disaster...). At this point things like drift might begin to happen and terrible strokes of luck can render some genes extinct. However, this is just the stochastic background of chance that natural selection works against.

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.

Hi Modulous,I think you're trying to resolve a confusion that doesn't exist. When Darwin distinguished between artificial and natural selection, it was to distinguish between man-caused selection and in-nature selection. But in a very short sentence you've used "artificial" in two different senses: By which you mean, "Man-caused selection does not involve any processes that violate the laws of nature." Your first use of "artificial" uses the definition "man-caused", while your second uses the definition "processes that violate the laws of nature." No one could disagree with your meaning, but no one interprets "artificial selection" as "selection that involves processes that violate the laws of nature" - they interpret it as selection done by people.Darwin emphasized fitness to a great degree in Origins, and he explained natural selection in terms of the fittest producing the most progeny. This makes his reasons for distinguishing between artificial selection and natural selection even more clear, because breeders select not on the basis of fitness, but upon the basis of arbitrary human preferences often not related to fitness.Natural selection is the term people use when speaking of evolution. Evolution according to Darwin is natural selection and descent with modification, and natural selection does not seem a particularly confusing term. If you prefer to say just "selection", though, I don't think anyone would have a problem with it, and I think they'd assume you're talking about natural selection.While I think the discussion you're having with Quetzal is very useful and informative, I think it is also confusing the heck out of Hoot Mon.--Percy