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

I agree with you that mutation is non-selective, but this is a rubbish description of mutation. For a start there is not need for a change in amino acid sequence to produce a potentially adaptive mutation and for another 'rearrangement' simply suggests the sort of recombinatorial shuffling you get with sexual reproduciton and totally fails to encompass the wide spectrum of potential genetic mutations.Your cases 2 and 4 I would argue are, or at least can be, selective. Assortative mating and other forms of sexual selection certainly are. It should be obvious from your own definition of Natural selection that this is the case since sexual selection will clearly lead to differential reproductive success of the sexually favoured traits. The gene flow one is more arguable since there is a clear overlap with the issue of mate selection as to the degree of gene flow between populations.So really drift and mutation are the only solid candidates I see here for clearly non-selective mechanisms of allele frequency change.With only the non-selective factors you may get evolution in the trivial sense of changes in allele frequency but never the sort of adaptive evolution that is what makes evolutionary biology so interesting.TTFN,WK

Hi Hoot Mon,I was only trying to explain that natural selection operates on individuals and that there's really no disagreement about this among creationists and evolutionists. Your reply mentions all kinds of other things, and sounds like you may have made the mistake of delving into the details of evolution before obtaining an overview.Darwin said it best. Evolution combines two things: descent with modification is one, and natural selection is the other. Descent with modification means that offspring are not exact copies of the parents. Natural selection means that individuals best suited for their environment have the best chance of surviving to produce offspring. Any organism that produces offspring in the wild has been naturally selected. It's as simple as that.Of course, as you've noted elsewhere, the real differentiator often isn't merely surviving to reproduce or not. A more accurate term is differential reproductive success. Some organisms are better at producing offspring than others, and this can happen in any number of ways. Some organisms live longer than others of their species, and so live through more reproductive seasons, thereby producing more offspring. Some organisms simply produce more offspring during each reproductive season. Some organisms mate more often, etc.Darwin drew an analogy between human breeders (artificial selection) and breeding in the wild (natural selection). A human breeder brings together two specific individuals to mate based upon what he judges to be favorable characteristics. In an analogous way, the environment brings individuals together to mate based upon their ability to survive to that point in time and upon their ability to persuade the other they are worth mating with (asexual species do not have this latter problem, of course).If it helps, Wikipedia has a good definition: Natural selection - Wikipedia. Pay particular attention to this sentence in the opening paragraph: Some of the detailed items you mentioned, genetic drift, gene flow, and random mutation, really have nothing to do conceptually with natural selection. A definition of natural selection doesn't require these concepts. Darwin certainly never knew anything about these things, and he had no trouble at all defining natural selection.But with your last two items, differential mating and differential reproductive success, the former is just one type of the latter.--Percy

All of those individuals will eventually get 'selected' by natural selection. No individual will survive. The only thing that survives are the genes (until universal extinction of course). Natural selection does not affect the frequencies of individuals, it selects which genes survive in the population...it affects gene frequencies.Granted - all genes die so all genes eventually get selected too. The difference is there are more than one copy of a gene, and any given unique gene make copies of itself. Individuals cannot copy themselves, they are unique and...individual.Selection is about selecting for things that make more copies of themselves that can surive to make more copies of themselves, not about selecting individuals that die since they all will. The things that make copies are genes. All individuals get removed from the gene pool, but its the genes that stay and those that don't stay that are the subject matter of selection.

Actually, where selection can or cannot occur is one of those real controversies that biology has had. Here is Richard Dawkins:

On the contrary, large numbers of "small furry mouse" taxa DIDN'T in fact survive the KT event. Whereas there is a lot of evidence that indicates various dinosaur taxa were in decline prior to the KT event, and the hypothesis that the asteroid finished them off seems pretty conclusive, there were too many vastly different taxa that survived the event to conclude that phenotype had any play in it. There is no identifiable thread that runs through the survivors - no particular phenotype gave any special advantages. This is one reason I like the "field of bullets" analogy. It derives from carnage of WWI battlefields. Picture 10,000 infantry charging across open fields in the face of entrenched machine guns. Individual ability, training, etc, has absolutely NOTHING to do with which ones of those infantry survive. It's pure luck of the draw. There's no selection; it really is random chance. The same goes for a bloody great rock falling on someone's head. Random events are NOT selective because the genotype/phenotype of the individual organism has no bearing on whether the organism survives or perishes - as PaulK noted, luck is not a component of natural selection. Right. The frog thing was probably unclear in my post. I was visualizing a sudden drying of the stream - and probably stretched the analogy further than it should have gone. Yep, them's the questions. Those are ALL examples of natural selection - the filter that "weeds out" the less successful organisms.My butterfly example was another poor analogy, I guess. What I was trying to illustrate is that regardless of all the wonderous adaptations and neat genes the now-eaten butterfly may possess, the random event of a bird managing to snack on it had nothing to do with them. It got eaten regardless of the adaptations. This probably wasn't a good analogy of a random event - unless it was simply the fact that the bird got lucky... As PaulK noted, I'm not sure but what you are confusing natural selection - the sum total of the biotic and abiotic factors that affect individual reproductive success - and the results of this selective filter (e.g., evolution). The two are not synonymous. A bloody great rock may eliminate enough taxa to provide the wide-open spaces necessary for ecological release, but it isn't selection in action. Hope this helps rather than obfuscates.

The gene is the unit of heredity, not the unit of selection. Genes can only be selected in entire collective bunches because natural selection operates on individuals.--Percy

Of course not. Evolution (what you describe here), operates at the level of population, not individuals. Natural selection, on the other hand, is an individual selective filter. Evolution operates ONLY over generations. Selection operates during the individual's lifetime. Individuals have nothing to do with evolution, because individuals don't evolve. Additionally, your second statement is also incorrect: individuals ARE the victims of natural selection, which factors serve to either promote individuals who have some selective advantage in the current environment by increasing their chance of reproduction and hence passing on this advantage to their progeny, or select against individuals who are "less fit" in the particular environment. Although it isn't an "all or nothing" affair, and leaving aside the gene-centric or organism-centric viewpoints, this is the basic definition of natural selection.

I haven't the foggiest notion what your remarks have to do with my example. Natural selection isn't death; it's when environment promotes differential reproduction of individuals because of traits they possess that make them better or worse adapted to conditions in that environment.The fact that all organisms die doesn't represent selection - simply because of how universal that is.As I said, selection for antibiotic resistance is the classic example of natural selection. Individuals with a resistant phenotype are selected for; individuals without that phenotype are selected against. A gene that has no effect on phenotype experiences no selection, by definition, because selection can only occur based on phenotype.

Yes, I agree, Dawkins, Williams, Hamilton et al. have offered the most convincing models for NS and non-selective evolution. Thinking that NS works on individuals doesn't makes any sense. How would I know if it ever worked on me?”HM

Do you have kids?

I wasn't discussing what selection is so much as I was discussing what is being selected. The genes are the ones getting selected, the individuals don't...not in the sense of natural selection. Yes - but not all phenotypical characteristics are hereditry. The only things that gets passed on are the genes. Because the genes getting passed on decide a large part of the phenotype, the phenotype - to some extent survives. It might be useful to think of phenotypes as being selected like this - but it is not individuals getting selected. I see what you are saying. However, a gene that has no effect on phenotype does experience selection. Pointless genes of longer length, are more likely to be damaged during sexual recombination or through random mutations. Thus, shorter pointless genes stick around longer. Of course, since they don't do anything they aren't actually genes - they are pseudogenes. Since many eminent biologists agree that the gene is the unit of selection (whether you agree with them or not) - by their definition the things you are describing are not actually genes. What are they selected for? To pass on their genes. Why did they survive? If we are talking about natural selection, their genes helped them survive. Their phenotype only helped as much as the genes were responsible. If their phenotype had been damaged somehow giving them resistance, then its offspring may well be passed on with 'inferior' survival genes.Sure, all those aberrant phenotypes that somehow survived despite their genes were selected. I don't think its useful to consider it as natural selection in the same sense the phrase normally refers to.It is the genes that get selected. They get selected based on how well they cooperate with other genes in the pool to create succesful phenotypes. Those alleles that do not cooperate to create succesful phenotypes get selected out (their frequency decreases), those that do cooperate well with the other genes in the pool, get selected in.

I think you and crash are essentially saying the same thing in different ways. I'm pretty sure he acknowledges that genes determine phenotype to a large extent, and that they are the units of inheritance, and thus the part that is of evolutionary significance. On the other hand, individuals most certainly do "get selected". Without the ability to pass on their genes - which has everything to do with phenotype - genotype is immaterial. The filter of natural selection doesn't pick out a particular gene or suite of genes on which to have an effect. It selects the totality of the phenotype - i.e., the individual organism - to operate on. An organism might have several excellent genes, but if the overall phenotype is less fit than another set of genes (individual), then they may not get passed on to subsequent generations. This is one of the reasons I don't fully agree with Dawkins' concepts. Yes, in some ways (especially when you're talking generational timescales) to talk about how suites of genes get passed down. However, unless you can demonstrate any selection pressure that operates at the level of the gene in "real time", then I'm not sure the concept holds. You just stated it: successful phenotypes are what get passed down the generations. Why? Because natural selection operates on the phenotype, not the genotype. This is where people tend, I think, to misunderstand what Dawkins is talking about. He's using the "cooperative gene" and "selfish gene" concepts to show - not how, which is what natural selection is all about - but why.

Percy - I'll repeat what I said to crash, in quote form. From HereDo you disagree with this position?

No, the genes are being inherited. The individuals are being selected based on phenotype. Genes that have no effect on phenotype experience no selection; this fact is sufficient to dispel notions that genes are selected. Right. Genes are inherited. Right. Through genes, which are the units of heredity. I'm not sure what the relevance of any biologist's "eminence" is, exactly. Individuals are selected; then their genes are inherited. The attributes they had that rendered them more or less adapted to their environment. Only because of their expression in the phenotype. If the genes were not expressed, they had no effect on selection.You can have the Super Mutant X gene, that gives you powers over metal or mental powers, or whatever; but if you also have the gene for, say, progeria, you're going to be selected against. Genes are not the units of selection because it's impossible for gene to be selected except as part and parcel of an organism's complete genetic content. An organism is only as "evolutionarily strong" as it's "weakest" gene, regardless of how great other genes might be - since an organism either passes on half or more of it's genes, or none at all.

The phenotype and genotype can be destroyed, and often are. However, genes are hardier and there are many copies of them. They are the ones that get selected to be passed on. We don't care about the frequency of the individuals. The success of the genes to create successful phenotypes is what is being tested. If a suite of genes or one gene gets in the way of reproductive success of the genotype, the genotype as a whole suffers. The 'good' genes, those that did well with cooperating will be passed on through their other hosts. Those genes that hamper reproduction will reduce in frequency. The cooperative genes get selected for, uncooperative ones get selected against reproduction.The individuals all get selected against in a short time period, they are all unique and there is thus no 'frequency'. That isn't evolution, and it isn't natural selection.Sure, phenotype is what decides whether the genes get to reproduce, but natural selection is only concerned with the parts of the phenotype that are connected with the genotype. The genotype won't survive, but many of its genes will. If not in this phenotype, then in others...until extinction. I understand why some people don't agree with Dawkins, but everytime I hear the 'other side', I hear no compelling reason to change my mind on the position. I'm not sure I know what 'real time' has to do with it. Perhaps we sould think of the selection pressure being demonstrated with the rate of change of the frequencies of various alleles? But only the parts of the phenotype that is deteremined by the genotype (discounting epigenitics for the moment), and not all of that gets selected. The phenotype would only be selected for if it were perfect clone of its parent, but this rarely happens. It is only the phenotype in the broad strokes that can be viewed as being selected, but that might be just an emergent observation. We could say that white bunnies are selected for in snowy climate, but that's not really what is happening. It is the genes that cooperate towards creating white bunnies that are being selected for.