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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
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Author | Topic: Evolution Requires Reduction in Genetic Diversity | |||||||||||||||||||||||||||||||||||
Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
You're right, all HBD said was they are "removed from the population" But that isn't what HBD disagreed with since I didn't say that. You don't read very well.
You read a different source about the light anddark mice. I
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
All those mutations are like a ticking time bomb, it seems to me, nothing likely to contribute to anyone's health.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
If I use my own words I think I get it better, but you can tell me:
MUTATION:Adds an allele, so adds diversity to pop B = INCREASE WITHIN B Population A doesn't change, so there is now more of a difference between A and B than there was before = INCREASE IN DIFFERENCE BETWEEN the two populations Does not affect all loci MIGRATION: (corrected by Admin and PaulK below)Adds to one by subtracting from the other = INCREASE WITHIN B, One gains, Yes affects all Loci DRIFT:Subtracts from B, A doesn't change= DECREASE WITHIN B B is now more different from A than before = INCREASE IN DIFFERENCE BETWEEN A and B Yes affects all Loci SELECTION: My first take:Selection replaces one trait with another or its allele with another, so it subtracts diversity from B = DECREASE IN DIVERSITY WITHIN B A doesn't change so there is an INCREASE IN THE DIFFERENCE BETWEEN A and B But it's apparently more complicated than that, as you say, which I'll copy here and come back to it later:
Fourth, Selection: ... selection would bring about both INCREASE AND DECREASE in genetic diversity Increase OR decrease. Selection is kind of a difficult one. It will probably take more explaining that I have time for now, but I will at least explain the chart.Some alleles would tend to be favored and would increase in frequency, some alleles would be less favorable and would tend to decrease in frequency. As selection continues to act on the population the tendency would be that diversity within that population will DECREASE as the population moves towards an optimum fitness. However, there are situations where diversity can INCREASE such as with heterozygote advantage (where the heterozygote is more fit that either homozygote). If different selection pressures are operating on each population we would expect diversity between the two populations to INCREASE as in each population different alleles or combinations are being favored. However, if two populations are already slightly diverse and the same selection pressure begins to act on both populations, then they will become more similar, or diversity will DECREASE. It does not affect all loci because, in general, only loci that are being selected for or against will be affected. Like I said, selection is not quite as straight forward as the others and is a bit more difficult to grasp Edited by Faith, : No reason given. Edited by Faith, : No reason given. Edited by Faith, : No reason given.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
OK I get it, thanks.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
For drift, I will just point out that in reality drift will affect A For some reason the effect on only one population is considered on the chart. I think HBD mentioned this but I'll wait until he responds to all this.
Selection can be positive or negative. Alleles that add to fitness will become more common, those that subtract from it will become less common. In either case it will tend to eliminate alleles. That's how selection reduces diversity within a population. Which I take into account whenever selection comes up in my argument. But HBD's chart has Increase/Decrease and Increase/Decrease so he's going to have to explain some more.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
HBD got it right: alleles for two traits already available, one replaces the other. Trust you to misread me as usual.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
You've put up a lot of information to digest but for a while I'm not going to have the time for it. And most of it looks to be peripheral at best to the argument I've been pursuing. The Fitness Map is just going to drive me crazy though.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
So as I was pondering (and praying about) that example I realized that for such an event to have occurred would require many stages of population genetics, and that led me to recognize that population genetics doesn't work that way: first it doesn't make incremental changes from generation to generation: in a condition of reproductive isolation it makes clear DIFFERENT phenotypic variations in many individuals that over many further recombinations can become part of a new look for the entire new population.
The first error is that population genetics does not describe phenotypic changes. It describes how alleles change in frequency. Yes, and the phenotypes that emerge come from the greater frequencies.
The second error is that population genetics DOS work incrementally over generations. (Indeed, a generation would be a 'round of population genetics') Sticking with the one and only example I focus on, that of a reproductively isolated daughter population formed from a relatively small number of individuals, what happens in the first few generations is the emergence of a number of different phenotypes in different individuals due to the new gene frequencies, and after whatever number of generations of inbreeding it takes to mix all the genetic types, the population as a whole acquires a new phenotypic look. Where's the incremental development?
The third error is - as usual - to exclude the role of mutation That's because, as I've explained so many times, the source of alleles has nothing to do with the processes that reduce genetic diversity. I found this interesting discussion from a dog-breeding site / They discuss many problems connected with breeding programs, and refer to natural populations for comparison from time to time. The only mention of mutations is in the paragraph about Hardy-Weinberg stability of large populations in which mutations are specifically excluded from the discussion. They discuss all sorts of genetic processes without mutation entering in at all.
...in limited, genetically isolated populations such as CKC breeds a certain amount of genetic diversity is lost with each reproductive event, through the action of genetic drift, inbreeding and artificial selection, The article is concerned with the problems of breeders and the only real description of natural populations is that very large stable sort of population. They don't discuss the examples I keep focusing on, where active evolution is going on and genetic diversity is consequently being lost from subspecies to subspecies or race to race. But what they say about breeding makes it clear that what they are battling is the same tendency: the reduction in genetic diversity due to the development of a particular phenotypic expression. That really ought to be pretty good support for what I've been arguing. Might as well answer JAR here too:
But yet again, Faith has NEVER provided the evidence to support "genetic depletion" (whatever that actually means) or explain why genetics shows that folk living at the same time as Adam and even thousands of years before Adam show pretty much the same genetic signature as folk living today or why there is no evidence of the genetic depletion that had to have occurred if either of the Biblical Floods had actually happened and not been just fantasy. I've many times given the evidence of the effect of the One Flood bottleneck which is the 7% homozygosity in the human genome. It's a reduction in genetic diversity from what had to have been the former more heterozygous condition, though not yet genetic depletion, which comes with extreme homozygosity. The dog breeding article mentions the problems connected with homozygosity.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
No, the change in allele frequency is due to the different phenotypes having different levels of success in surviving and breeding. Those phenotypes are already in the population. Change in allele frequency most obviously occurs with the formation of a new isolated population by a relatively small number of individuals. This is the classic view. I don't know where you are getting yours. Other things may contribute to the same effect of course, but population splits are THE known cause of changes in gene/allele frequencies. It is that change that gives rise to new phenotypes in the new population that didn't exist in the parent population, that eventually over generations of inbreeding create a new phenotypic appearance in the new population that differentiates it from the parent population. Evolution, in a word. Of the micro sort of course.
Sticking with the one and only example I focus on, ...
Arbitrarily chosen because it is the only one that fits your concept? It's the example that demonstrates evolution in action. A large stable population that isn't evolving (see breeder article if you doubt there is such a thing) doesn't demonstrate what happens during active evolution. Active evolution that produces new phenotypes doesn't happen without reduced genetic diversity. Reduced genetic diversity is the inevitable TREND of evolution. At the extremes it becomes genetic depletion. The extremes define the boundary of a species beyond which evolution is impossible for lack of genetic fuel. The extremes can be avoided in breeding by careful attention to maintaining heterozygosity, as the dog breeding article points out. The same article says that nature seems to work to maintain heterozygosity as well, it being the most healthy state of a population. But when new populations arise from splits you start to see the effect I'm talking about: active evolution, the production of new varieties, is always accompanied by reduced genetic diversity. Mutation merely supplies alleles (according to current ToE anyway), but alleles are what get reduced by the evolutionary processes. Mutation therefore does nothing to prevent reduced genetic diversity. Cheers.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
Curiously, I was pointing out that what you said in Message 995 ("Yes, and the phenotypes that emerge come from the greater frequencies.") was somewhat backwards. The founding phenotypes were those already in the founding population at the time of the founding event, and it is the phenome formed by all those founding individual phenotypes that formed the pool of alleles\genes\traits for that founding populations next generation, the founding phenotypes did not emerge from those alleles. The founding phenotypes soon disappear as the new population reproduces because they were founded on the allele frequencies of the original population. Those individuals of course do collectively contain the new gene frequencies, but the new gene frequencies bring out new phenotypes that eventually eclipse the originals. The originals don't contribute anything to the ultimate phenome (if that is really the word) that will ultimately characterize the new population. Their alleles will but in entirely new combinations. It's meaningless to talk about the original phenome; what emerges eventually from the new allele frequencies is the entirely new phenome of the new population over generations of reproductive mixing. Edited by Faith, : No reason given.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
Change in allele frequency goes on all the time. It's just faster in small populations. 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 the classic view. I don't know where you are getting yours. Other things may contribute to the same effect of course, but population splits are THE known cause of changes in gene/allele frequencie
NO. This is another of your misunderstandings. Selection and drift cause changes in allele frequencies (although selection can also maintain them). 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.
Population splits can increase the rate of drift (because the sub-populations are smaller than the whole). But the real reason they are important is that they eliminate gene flow between the sub-populations allowing them to change relative to each other. 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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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
Faith writes: This is really YOUR misunderstanding. Selection and drift both act like population splits, which I've argued before. Yes they both change allele frequencies. Admin writes: 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. 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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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
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. 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.
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? 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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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
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 #1020 Edited by Faith, : No reason given. Edited by Faith, : No reason given.
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Faith  Suspended Member (Idle past 1475 days) Posts: 35298 From: Nevada, USA Joined: |
Faith writes: 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. 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. 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.
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. 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.
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. 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
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. 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
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've done my best and if it isn't enough I should leave, don't you think?
I'll comment on a few more things.
Natural selection in operating on the phenotype reproductively isolates that phenotype from the other phenotypes in the population,... 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. ABE: You must be talking about physical isolation, I'm talking about reproductive isolation. /ABE 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. 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.
As PaulK notes, a favorable allele will spread through a population, not create an isolated subpopulation co-resident within the parent population. 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).
...the highest frequency alleles in this case being those for those traits that are selected for.
I just want to note that traits can also emerge or be emphasized by diminished allele frequency, or by new allele combinations. 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.
Allele frequency is just a measurement across a population. It doesn't tell you the allele makeup of individuals. Of course. This is all about populations, not individuals.
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."
As PaulK notes, if natural selection is unlikely to produce isolation within a population, then genetic drift is even more unlikely. 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.
Natural selection isolates the individuals it selects by selecting them,...
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. 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.
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. 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.
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