Evolution Requires Reduction in Genetic Diversity

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. This is really YOUR misunderstanding. Selection and drift both act like population splits, which I've argued before. Yes they both change allele frequencies. 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.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. Yes,and that is an important part of the scenario I create for that reason. The differences are much clearer without gene flow. 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 many individuals back 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.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

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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.

Bizarrely wrong. What is left in the founding population is the allele frequencies carried by the founding individuals, which in the absence of selection pressure against them should continue, and result in new members being similar to the founding population. Unless you introduce new alleles by mutation and unless selection on the population is different than it was on the parent population, you will tend to get similar individuals in the following generations, because they were part of the selected population before.With new alleles via mutation (without gene flow to the parent population) you will get new variations/traits that cannot appear in the parent population because they don't have access (gene flow) to the mutation.Different selection pressure will cause different selection of the current alleles in the population and change the frequencies based on which provide better success in survival and breeding. The founding individuals define the gene frequencies of the founding population, the genome and the phenome. Magic fantasy is not genetics Faith.No, they will tend to continue to reproduce the founding phenotypes absent any cause to change (mutations, selection pressure).If the selection conditions are the same as in the original population then those phenotypes will continue to be selected for, including the tendency for deselection of new mutations that alter the fitness of the individual to the ecology away from the original successful types. More magic fantasy genetics ... lol. More like they contribute everything. ie more like everything. A bizarre fantasy of yours.Only if there is different selection pressure will gradual new combinations become prevalent. The available alleles do not provide enough variation for significant changes on their own, if they did they would have occurred in the original population and if they did occur and were selected against, that selection would continue unless selection changes. Just like it's meaningless to talk about the foundation of the building when you are building a new story ... The founding phenome sets the allele frequency for that population, the next generation will tend to be similar -- or do you not believe in populations reproducing after their own kind?New mutations will introduce new variations, different selection will tend to shift allele frequencies, as will additional drift, and all three over time will result in differences from the founding phenome to occur.The split alone does not cause any allele shift within the founding population.Enjoy.

When I first read this (and the rest of the paragraph, which I address below) I couldn't make sense of it, so I made a note to myself to come back to it and inquire what you meant. I then read forward to PaulK's response, and he couldn't make sense of it either.One can imagine a population with a large geographic range being subjected to different selection pressures in different geographic regions, and in such cases selection and drift could cause splits, but these genetics discussions have so far been operating under the simplifying assumption of uniform selection pressures across a population. Any shift away from this assumption should be explicitly noted. Since you didn't do that we have to assume you're not talking about populations with large geographic ranges and varying selection pressures.So perhaps you meant to say something else? Maybe that selection and drift act to differentiate isolated subpopulations?Whether I've guessed right or not, please let the discussion know what you meant. I think you misunderstood PaulK's meaning. He was only saying that selection pressures can maintain allele frequencies in a population. This is what happens to populations that are already well adapted to their environments. Individuals who by the luck of the genetic lottery receive an allele mix that deviates too greatly from the population's will be selected against and produce fewer or no offspring, so these different allele mixes tend to be removed from the population. Those who receive an allele mix that matches the population's pretty well will be selected for and produce more offspring, contributing more individuals with comparable allele mixes to the population.Or maybe I misunderstood what you're trying to say, in which case please clarify for the discussion. You again appear to be saying that selection within a population reproductively isolates individual members of the population from one another. This makes no sense. I would guess that you're instead referring to isolated subpopulations, and that you're saying that the different selection pressures will encourage changes in the direction of reproductive isolation, but you're reference to population splits seems to rule out this interpretation.So I'm unable to figure out a meaning that makes sense. Could you please clarify for the discussion?

So I step back from the details of the arguments and look at the broad argument ... Or in other words transformed into a totally new creature in just a few generation, with no cause other than splitting away from the parent population.But don't call it a new species or a new genus or a new family, because it is just allele variation that magics the new creatures from the parent population ... with an "entirely new phenom" ... ie entirely different physical traits.And this process can continue to produce new types as long as the genetics hold out. Perhaps causing phenotype changes like:

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The following discussion is taken from "29 Evidences for Macroevolution; Part 1: The Unique Universal Phylogenetic Tree" Copyright 1999-2002 by Douglas Theobald, Ph.D.
Reptile-mammal transition, with emphasis on the evolution of the interdependent mammalian middle ear ossicles.

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Figure 1.4.3. A comparison of the jawbones and ear-bones of several transitional forms in the evolution of mammals. Approximate stratigraphic ranges of the various taxa are indicated at the far left (more recent on top). The left column of jawbones shows the view of the left jawbone from the inside of the mouth. The right column is the view of the right jawbone from the right side (outside of the skull). As in Figure 1.4.1, the quadrate (mammalian anvil or incus) is in turquoise, the articular (mammalian hammer or malleus) is in yellow, and the angular (mammalian tympanic annulus) is in pink. For clarity, the teeth are not shown, and the squamosal upper jawbone is omitted (it replaces the quadrate in the mammalian jaw joint, and forms part of the jaw joint in advanced cynodonts and Morganucodon). Q = quadrate, Ar = articular, An = angular, I = incus (anvil), Ma = malleus (hammer), Ty = tympanic annulus, D = dentary. (Reproduced from Kardong 2002, pp. 274, with permission from the publisher, Copyright 2002 McGraw-Hill)

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Since Figure 1.4.3 was made, several important intermediate fossils have been discovered that fit between Morganucodon and the earliest mammals. These new discoveries include a complete skull of Hadrocodium wui (Luo et al. 2001) and cranial and jaw material from Repenomamus and Gobiconodon (Wang et al. 2001). These new fossil finds clarify exactly when and how the malleus, incus, and angular completely detached from the lower jaw and became solely auditory ear ossicles.

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Because they're just different phenotypes that appeared from a smaller set of alleles in new arrangements. Right?Enjoy

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.I hope I can make it clear.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. So you could say the Pod Mrcaru lizards were "selected" in that sense. This isn't natural selection because there is no selection pressure, it's random, but my point has always been that the genetic effect is the same because the same mechanisms are involved, only with different causes. Genetic drift too can be described as a form of random selection.Both selection and genetic drift occur within the population, but they nevertheless become reproductively isolated from that population and possess their own different gene/allele frequencies. Individuals that are selected for reproductive advantage, or just the random isolation of individuals in genetic drift both become isolated and that's THE mechanism that brings out new phenotypes and ultimately creates a new variety or race. Negative selection, selection against a group of individuals, would have the same effect, whichever group is reproductively favored creating a new subpopulation within the main population. (Reproductive isolation in any of these cases may not be absolute, even in population splits, but for the purposes of the discussion it helps to think in terms of absolute isolation.)Like population splits, selection and genetic drift have their own gene/allele frequencies (because they are a reproductively isolated smaller number of individuals) that are set apart from those of the parent population, and if that isolation is maintained, as they recombine through many generations they all bring out new phenotypes as a result of the new gene/allele frequencies. If the isolation continues for enough generations a distinctive new population within the parent population can form, just as it will for a geographically isolated subpopulation. In other words the only real difference between these three populations is the reason for the isolation. All the different ways these subpopulations form follow the same pattern: changed gene frequencies, new phenotypes, reduced genetic diversity from the original population (which, incidentally, could also undergo a similar sequence unless it is a very large population.Your following question should be answered by what I just said. I hope so.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

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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.

You're drifting toward creating your own definitions again, which only creates confusion. Yes, population splits and genetic drifts can be viewed as performing a form of selection, but not natural selection, which is what is meant in this discussion by the shortened "selection." Natural selection operates on the phenotype and influences the degree to which individuals pass their genes on to the next generation. Population splits and genetic drifts are not operating on the phenotype. You're envisioning a scenario where new breeds emerge as a subpopulation within a population without some form physical separation or isolation. While some kind of non-physical impediment or isolation is not impossible, it must be by far the less common case. Is there some reason you want to focus on this uncommon circumstance? If it's not central to your point then it seems best avoided. If the new population is "within the parent population," could you make clear for the discussion what you are imagining is the barrier that creates isolation? By "three populations" that have become isolated you evidently mean a population created via split, another created via selection, and another created via drift. Isolation through physical splits is easy to understand, but could you please make clear for the discussion how natural selection and drift can cause a subpopulation to break off from a parent population while still within that parent population?

I know that and my point was that it makes no difference to the basic pattern. The mechanisms and results are the same no matter what the cause of the reproductive isolation. 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. So a subpopulation is produced with the selected trait or traits dominant and those alleles highest frequency. Other traits will also be affected by the new allele frequencies due to the reproductive isolation of the individuals that possess the selected trait or traits. Functionally there is no difference between the effects of natural selection and those of the random selection of genetic drift and population split. 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."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.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

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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.

Wrong. The effects of the different evolutionary forces are different and leave a different "signature" in the population. Unless you are saying that each individual is a separate subpopulation, this makes no sense. Organisms with a favored trait can still mate with organisms without the favorable trait. There is no isolation involved. There is a phenomenon that describes an effect like this, it is called linkage, but I don't think that is what you are describing or that you have in mind. We discussed this issue in this very thread, Faith. If you want to go against what is currently known about population genetics you should present some experimental results that support your understanding. You are simply imagining a scenario that supports your conclusions. Not the current understanding of genetic drift. See Message 985 for a better explanation. Not the current understanding. See Message 983 for a better explanation.Present some research on these subjects and show how your interpretation fits the evidence better.HBD

This is just self-evidently wrong. You're declaring that the mechanisms of physical population splits, natural selection and genetic drift are the same, despite that they're completely different mechanisms. And you're also declaring the results the same, despite that the results of these mechanisms differ, particularly natural selection which produces adaptation, something the other mechanisms do not.I was hoping that by noting those portions of your messages that seemed hard to interpret that I might bring greater clarity to the discussion, but your clarifications seem to be marching off in directions of greater error. I don't want the thread to begin spending all its time trying to figure out what you mean, or trying to convince you that what you're saying makes no sense.You don't have to agree with anything anyone else says. You can have a different opinion on everything. But there *are* a few rules. You can't change existing terminology. And you have to say things that most other people can understand.I'll comment on a few more things. You need to make clear to the discussion how isolation occurs while still in the parent population, i.e., explain what prevents a creature (one that is only very modestly changed in phenotype) from breeding with any other member of the population that it still resides within. As PaulK notes, a favorable allele will spread through a population, not create an isolated subpopulation co-resident within the parent population. I just want to note that traits can also emerge or be emphasized by diminished allele frequency, or by new allele combinations. Allele frequency is just a measurement across a population. It doesn't tell you the allele makeup of individuals. As PaulK notes, if natural selection is unlikely to produce isolation within a population, then genetic drift is even more unlikely. Except that it doesn't isolate the selected individuals. A creature with a new and advantageous allele can only breed with other members of its population. Its offspring can also only breed with other members of its population. The process you're describing is how favorable alleles spread through a population, not how isolated subpopulations form right in the middle of their parent populations.These claims that natural selection and genetic drift can cause isolation within a parent population seem like a digression from the main topic. I think it would help the discussion if you could either drop these claims, or make clear how they bear on the main topic. Please help the discussion along by doing one or the other.

Your utter lack of comprehension is beyond depressing. I suppose I'll eventually recover and then may come back to give an answer later.ABE: Which I did in #1020Edited by Faith, : No reason given.Edited by Faith, : No reason given.

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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.

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. Yes the results in terms of new gene frequencies bringing out new phenotypes along with reduced genetic diversity occur in all these cases. These are the cases I'm calling "active evolution" where the evolutionary changes are clearly happening, which is not clearly the case in large stable populations or situations where gene flow persists or resumes.Also, population splits do lead to adaptations, as I've often argued here. I don't accept Darwin's understanding of the adaptations of the different finch beaks for instance, I believe the beak came first, through new gene frequencies brought about by a population split, probably a migration of a subpopulation to a new territory, and the beak found a food suited to it and that's how the adaptation occurred. While some adaptations may occur through natural selection working on the creature, that's the expensive way for it to happen and my argument is that most adaptations occur as just described. The lizards of Pod Mrcaru I believe are a similar case: they gravitated to food their larger jaws and tougher digestive systems could handle AFTER those traits developed simply through the new gene frequencies brought about by the small number of founders. What you are calling error is my dogged attempt to get an original view of these things on the table. There is nothing wrong with the view, you are simply not familiar with it.(ABE: The more I think about it the more I think this is a classic paradigm clash myself) /ABE Neither do I, to put it mildly. The only solution I see is for me to get off the thread. This is not a threat, as usual it may not happen, depends on what comes next I suppose, but at the moment it seems the reasonable thing to do. You persist in not getting what I'm saying, calling it an error, and I persist in pursuing it as an essential part of my argument, and neither of us wants to go through another round of this.(ABE: But what if this IS a paradigm clash? I'm naturally using terminology in new ways because I have a different way of organizing the information. I can't change that because it's intrinsic to my argument.) /ABE I've done my best and if it isn't enough I should leave, don't you think? ABE: You must be talking about physical isolation, I'm talking about reproductive isolation. /ABEMost 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. You are right there is no clear reason why natural selection should work the same way -- unless it's by sexual selection and that could be the explanation. If the unadapted don't just die off then there has to be reproductive advantage for the adapted without leaving the population. I can drop this speculation for the moment, but the principle still stands: IF selection occurs it isolates a subpopulation of the selected, it has to, and a reproductively isolated subpopulation acts like other reproductively isolated subpopulations: it has new gene frequencies, in this case the higher frequency of the adaptive trait, the adaptive phenotype grows in numbers (along with some others that happen to be in the genotypes of those individuals), and a reduction in genetic diversity necessarily also develops in this subpopulation.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. How does it spread? It has to be reproductively favored somehow over the unfavorable alleles and that means the unfavored ones simply don't reproduce, either as much or at all, doesn't it? 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.Again I think you have some kind of physical isolation in mind rather than reproductive isolation. (This isn't about the paradigm clash, of course, just a typical error). NOTHING "emerges" or gets "emphasized" by diminished allele frequency except maybe as their last gasp before being eclipsed by the higher allele frequencies, and I'm well aware that new allele combinations bring out new phenotypes, that's THE main process that occurs in the first few generations of new gene frequencies playing out in a new population, as I've described MANY times; it's what new gene frequencies DO, they set the stage for a lot of new allele combinations, and those are the source of the new phenotypes in the new population. Of course. This is all about populations, not individuals. Again you seem to be thinking of some kind of physical isolation rather than reproductive isolation.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. If random selection can do it then natural adaptive selection ought to do the same thing or there isn't any selection going on at all. Selection means the reproductive favoring of a trait or traits over others and if that's actually happening then a subpopulation IS forming out of those selected traits and growing in numbers within the greater population, just as the unadaptive traits are not being reproductively favored and become a smaller percentage of the population. Again, otherwise you don't have selection. HOW it happens? Sexual selection could be a part of it, depends on the particular adaptation we're talking about I suppose, but how it comes about is a different subject, the point is selection isn't happening unless we're getting a new subpopulation. 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. 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.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.