Evolution Requires Reduction in Genetic Diversity

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That's what I would have thought but then that dog breeding article said you can have large populations where it doesn't change at all. It doesn't really matter. The change is always ultimately accompanied by some degree of loss of genetic diversity.

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Wrong. A change in allele frequency can increase diversity by any measure you choose. the dog breeding article isn't quite correct, either. Drift is just very slow to eliminate alleles in a large population.

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This is really YOUR misunderstanding. Selection and drift both act like population splits, which I've argued before.

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And now you're just spouting crazy nonsense. Sorry, but that's just too silly to be worth any other answer. Especially as I've already explained the reality.

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No, selection cannot possibly maintain them because, just as population splits and genetic drift do, it reproductively isolates some individuals from the rest of the population, which is THE way gene frequencies change, and THE way genetic diversity is reduced.

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Selection DOES maintain the frequency of the sickle-cell allele. Just as population genetics says that it should. And no, selection does not "isolate some individuals from the rest of the population". You're just stringing phrases together without any understanding at all.

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It's you who are mathematically challenged in the case of mutation as well. It doesn't matter where the alleles come from, when they are subjected to population splits, genetic drift, selection etc, any of the processes that bring about new allele frequencies, they are simply part of the pool of alleles that is getting redistributed in the new population, some increased, some reduced, some completely eliminated. Recent mutations are in fact more likely to be low-frequency and be suppressed or eliminated in the new population. If a mutation is high frequency it will merely become part of the new phenotype, or phenome as RAZD says it should be called

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Let us note that there is neither any mathematics or understanding of the issue in there. You will note that I never said that it matters where new alleles come from. What matters is that new alleles do appear, increasing genetic diversity.

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Eliminating gene flow helps to focus on the processes that lead to reduced genetic diversity. In reality gene flow is often maintained to some extent between parent and daughter populations, or two or more daughter populations. So in reality you get hybrid zones and may get the reintroduction of some individuals into the parent population etc etc etc. But keeping gene flow out of the picture streamlines the point I'm trying to make, that's all.

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At least that's not stupidly wrong. But the loss of gene flow is the reason why population splits have the effects that they do. If you want to understand what is going on you need to understand that.

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It is always risky for communication when I deviate from the simple example of population splits, but PaulK brought it up and I felt I had to say something. And it's true that many times I've mentioned selection and even drift in past threads on this same subject, as basically the same processes as geographical isolation, but I don't recall their ever getting discussed.

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It isn't a communicarion problem. You're just flat out wrong.

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One thing I used to do was identify population splits as a FORM of selection, random selection, because individuals are in a sense "selected" to be the founders of a new population when they are geographically (and therefore reproductively) isolated from the parent population.

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In this context "random selection" is an oxymoron. It's just a form of drift. And explicitly described as such, if you read up on the matter.

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Like population splits, selection and genetic drift have their own gene/allele frequencies (because they are a reproductively isolated smaller number of individuals)

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NO. That's just ridiculous. Selection and drift are the processes by which the allele frequencies of the population change (or don't change). They are not subgroups of the population (that's silly) and even if you looked at the individuals in the population containing a particular allele undergoing selection (positive or negative) there's no reason to think that they are unable or unwilling to breed with other members of the population. In fact that is almost always not the case.And it is even sillier when talking about drift. Drift is a random effect. Even if you look at those individuals have greater or lesser reproductive success by chance there's no reason to think that those offspring will be any different from the rest of the population. It is random. So you don't even have an identifiable subpopulation that could be considered reproductively isolated - which it wouldn't be anyway.So no. As is quite clear you don't understand what you are talking about.

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Natural selection in operating on the phenotype reproductively isolates that phenotype from the other phenotypes in the population, thereby creating a subpopulation with its own gene frequencies, the highest frequency alleles in this case being those for those traits that are selected for.

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In general selection does NOT produce reproductive isolation. Because not breeding or failing to produce fertile offspring is not often a good way to achieve reproductive success.More likely a selected allele will take over the population - so long as it continues to be selected for.

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Genetic drift for whatever reason is the random reproductive favoring of some individuals over others and their traits come to dominate the subpopulation simply randomly. The isolation is brought about simply by the random favoring of those individuals, random "selection."

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That is even more implausible. Because drift is random. While selection is likely to continue to favour an allele over the generations, drift is not.Reproductive isolation is not likely to appear within a population unless gene flow is already restricted. It will be selected against unless circumstances are favourable - and neither drift nor selection will automatically lead to that.

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Natural selection isolates the individuals it selects by selecting them, reproductively favoring them, increasing their numbers relative to the parent population. The unselected are less reproductively favored, don't proliferate, may even die out.

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You're putting the cart before the horse there. Reproductive advantage (or disadvantage) causes selection, not the other way around.

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Your utter lack of comprehension is beyond depressing. I suppose I'll eventually recover and then may come back to give an answer later.

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Faith, the lack of comprehension is clearly on your part. Youve made a ridiculous number of errors in this conversation, some of them quite mind-bogglingly silly.If you don't like people noticing your obvious errors, the only solution is to stop making obvious errors. You can't convince people who of your ideas just by spouting half-baked excuses you haven't bothered to think out, especially when you can't be bothered to understand the subject in the first place.

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Sorry, I've made my case that they are essentially the same in their operations and effects and that's all there is to say in the teeth of your incomprehension.

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The only thing we don't understand is why you expect us to agree with you when you are obviously wrong.

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Most discussions of genetic drift assume this sort of intrapopulation isolation is possible and occurs. It's strictly the result in that case of random selection of mates, without any particular explanation.

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No. They do not. They assume that reproductive isolation is possible but not that drift will cause it within a breeding population as you claim. If you want to assert otherwise, then give an example. Not a link to a Google search (a tactic which seems designed to obfuscate the issue) but a link to an actual mainstream discussion of genetic drift that actually supports the idea.

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BUT AFTER WRITING MOST OF THIS POST I REALIZED YOU AND PAULK MUST BE THINKING OF SOME KIND OF PHYSICAL ISOLATION SUCH AS GEOGRAPHIC ISOLATION, BUT I'M TALKING ABOUT REPRODUCTIVE ISOLATION. So I went back through the post and noted that where it seemed to be appropriate.

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That is not a realisation, it is a fantasy as is quite obvious. Asking after the cause of the isolation is not assuming a particular cause. And in the quote immediately following Percy makes it clear that he is not considering geographic isolation - he is asking about co-resident populations.

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So the upshot is that a subpopulation is being created of the favored alleles any way you look at it, the subpopulation of favored traits/alleles growing in number within the overall population, the unadapted traits/alleles diminishing in number.

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What's interesting is that this "upshot" is what I expect to happen - as I said. Agreeing with me - and omitting the point of disagreement - hardly demonstrates that I am wrong.And, as I pointed out while you can identify a subpopulation in the case of selection you can't even do that in the case of drift.

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Funny then that descriptions of genetic drift imply the development of a new subpopulation by random selection, meaning a collection of traits that sets it apart from the main population.

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The only funny thing about it is that you think that it supports your position. The fact that drift will cause reproductively isolated populations to diverge does not mean that drift will cause reproductive isolation within an interbreeding population.Again, if you disagree show us an actual discussion which says that drift is expected to produce reproductive isolation within a breeding population.

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Remember we're talking about REPRODUCTIVE ISOLATION, not geographic isolation or any other kind of isolation. Sexual selection can isolate individuals and create a subpopulation within a population. In fact the more I think about it the more it seems this must be how such an adaptive subpopulation would form.

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Again, we are not disputing that there are circumstances where you could get reproductive isolation within a breeding population. We're arguIng that that is not the normal or expected consequence of selection or drift. it needs particular circumstances, which are not going to be that common.

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PaulK brought up the subject of genetic drift and natural selection and I gave my view of it in response, I have no other reason to continue it. I haven't changed my view, I've had it for years so I'm not going to drop it beyond not pursuing it after this post unless somebody else keeps it alive.

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In fact I was responding to your claim that population genetics "doesn't do that". And if you can't see that selection and drift are the major mechanisms of change within population genetics then that is your problem. So, strictly speaking, you brought it up - I was pointing out your errors.And I have to say that I don't expect you to start caring about the truth any time soon. a pity. You aren't stupid. But you waste your intelligence by not bothering to employ it to understand what you are talking about or to produce good arguments.