Evolution Requires Reduction in Genetic Diversity

Why can't you just see how it works from my descriptions? I've given enough of the reasoning for that many times.

This needs more of a response. You apparently didn't notice where I said these same traits can emerge from time to time in the original larger population as well but would be buried by the dominant traits. Or overshadowed. Or suppressed. Or whatever the higher frequency alleles do to the lower frequency alleles.The traits that dominate in the population are those with the highest frequency of alleles along with other factors such as dominance of course, so if they're low frequency they'll only show up here and there once in a while, but where they are high frequency, over generations of inbreeding they should combine with other high-frequency traits that may be low frequency in the original population. So it won't just be the emergence here and there of a single trait but new combinations that start showing up, which eventually give the daughter population a new set of traits for a new "look" ifrom that of the original population. Perhaps new striping pattern plus new coloration plus new ear shape etc. Just think about the implications of new allele frequencies as I just tried to describe the effect. The alleles that are high frequency in the new population don't have to have been "impossible" in the original population, just very rare, BUT the COMBINATIONS of a number of alleles that are now high frequency but in the old population lower frequency, could have been impossible there though now favored. Repeat: Combinations of high frequency alleles that were low frequency before should definitely create new combinations of traits from those of the original population. Not if they refuse to think it through it won't. I haven't seen an attempt to make a point with hypothetical alleles that works and I haven't been able to come up with one of my own either. What?Even if a mutation contributes something to the new traits it has to be high frequency to come to prominence in the new population and that involves a very strong selection factor BEFORE the population split. One mutation isn't going to change anything. You aren't following the argument. Mutations also have to be selected and isolated and that's what brings about the decreased genetic diversity. The mutation is just another allele that has to be selected or mixed in new frequencies.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.

Not necessarily. The point is that the founding population is small enough that the original distribution of alleles will be significantly under-represented. It is not really about the number of individuals, but it does usually involve a small number of individuals. For example, would 1,000 individuals be considered a small, founding population? Probably not. But what if the parent population had a billion individuals? In that case 1,000 would be a very small number and would definitely under-represent the allelic distribution of the parent population.It seems to me this is the situation you are describing. The allelic diversity of the parental population is significantly under-represented in the daughter population. That is the whole point of the founder effect, not how many individuals established a new population. Migration has a specific meaning in population genetics - it means gene flow. You are simply describing formation of a daughter population separated from the parent population by a physical/geographical barrier. Allopatric speciation. It is fine to focus on only allopatric speciation, since not only is it the easiest to discuss, but also is the most common situation. In fact, the other modes of speciation are quite controversial, so better to stay away from them for now. I don't deny that. The daughter population would probably have a different allele frequency that the parent population, but it is not inevitable. Yes, a small founding population would significantly change allele frequency; no one denys that. I am not sure what this means, but I think you are saying that you would need to count all alleles at all loci. ??msg 670 This... is the same as "change the genotype frequency"msg 673 Inbreeding means something specific in population genetics, which is what we are discussing. If you are using it to mean a population that breeds with itself, that is just silly. All populations breed with themselves. Inbreeding is a form of non-random mating and it means that individuals are more likely to mate with a close relative than would be expected by chance. Yes, you would expect inbreeding with a small population (again this is part of the consequences of the founder effect). However, once the population reaches a certain size, you would expect random mating to resume and inbreeding to diminish. Well, if that's your position then there is no inbreeding at all. There is just breeding. Ok, fine. I don't want to go back and find where you said what. If you never said it and you agree that inbreeding does not change allele frequency, then there was no point in you arguing about it.msg 674 Where did I say anything about loci being fixed? Loci being homozygous is not the same as being fixed. Homozygous is on an individual level, fixed is on a population level. How you create a recombinant inbreed line (RIL) is to mate two parents that have complimentary character states of a trait of interest. For example, if you are interested in what genes control flower color you might cross a white flowered individual with a pink flowered individual. You would then grow an F₁ progeny and would cross it with itself to produce the F₂ generation. This F₂ generation will have a random distribution of genes from both parental lines. Next you will grow out the F₂ and self-fertilize again. Then you will take one seed from each F₂ plant and grow it out and repeat this cycle for 6 - 10 generations.The size of the RIL population varies, but usually between 100 and 5000 individuals. The point of these lines is to produce as many combinations of homozygous genotypes as possible - each individual will have its own unique combination of alleles. The phenotype of each individual can then be mapped onto genetic markers so that an association can be made such as when a trait is present so is a particular molecular marker. This is known as QTL mappingBut this actually goes against what you are claiming, which is... Why do we not have 500 new species in a RIL? Because new allele combinations are just not enough. In the case of an RIL, you haven't decreased the genetic diversity of the metapopulation, just of individuals. If you allowed the RILs to begin randomly mating again, the population would return to equilibrium genotype frequencies.HBD

Although the case of a much smaller number of individuals forming the daughter population gets the point across more clearly, I do not limit the possibilities that way. Eventually any population that continues to develop new traits is doing it with decreasing genetic diversity and is going to end up in the same place. Perhaps founder effect is always a stage in what I'm describing.I found this statement on the "Founder Effect" Wikipedia page very interesting: Yes. YES! Seems to be saying that the new allele combinations ALONE are sufficient to lead to speciation, contrary to some pretty aggressive assertions on this subject in this thread.Certainly not to the "subsequent evolution of new species" of course, because that is impossible with the decreased genetic diversity that brought about the new species, as I've been arguing.Now I have to stop for a while and come back later.By the way, I will use whatever terminology gets my point across. I hate to give up "migration" because it's such a natural term for the use I put it to, and unnatural for what you mean by it but I care more that you can understand me.Edited by Faith, : No reason given.

There is always some chance that any combination present in the original population will produce the result shown in the smaller population. 'Whatever' is you saying that you don't know what you are talking about. No, mutations do not have to be selected for. They can stay in the population if they are neutral and can do so for long periods of time.Yes I do follow your argument. Can you follow mine?A dominant new mutation will show up regardless of anything else. That means that it can even migrate through the entire population without decreasing diversity. It is instead added diversity. There are an unlimited number of variations on dog with a curly ear. The only thing you cannot have is dog with an uncurled curly ear. We already have lots of different dogs with curl ears.Then we might get another mutation producing dog with a curly tail.Rinse lather repeat with more mutations over time. Yes, all of those things are still dogs, but they are population with increased diversity.Now when we finally get effect that causes an isolation, it is on a population that is more diverse than before the rinse lather repeat which leaves open the possibility that the sub population is also more diverse than before the rinse lather repeat.Is it clear now what is being argued?Here is another example. Imagine a trait for tiny wings appears in the collie breed. What prevents that trait from getting into other dog breeds absent human intervention.Nothing at all. Dogs don't care all that much about preserving their breed. Even if there are some dogs that collies don't particular feel inclined to breed with, the new mutts likely won't show the same dis-inclination. So let's assume that a great deal of mixing happens.Now dogs as a whole are more diverse. If at some later date, tiny wings turns out to be beneficial for some reason, there might be huge variations in the dogs with wings. There is no guarantee that the new smaller population will be less diverse than before the winged stuff started.Your silly one-way isolation scenarios doesn't disprove those kinds of scenarios and for at least that reason is unpersuasive.We believe that human evolution includes separations and re-mixes with interfertile groups of homo somethings. It is not clear how far back we must go before we hit an ancestor with whom we are inter fertile with. I don't know if has been demonstrated that different apes cannot interbreed.So making up silly dog breeding isolation scenarios in which all variation among does must be wiped out does not begin to address all of the possibilities.Consider this question: Do humans become more diverse or less diverse when a group of us survives on a new isolated place?Let's say 10000 Russians move to a station on the moon. The loss of a small group has essentially no effect on the diversity of the original population which still has plenty of Russians. As long as the two groups remain interfertile, if the lunar Russsian group acquires any new alleles at all, then no matter what else they lose, humanity gains diversity overall. Now imagine that the lunar group returns to earth. Is it your claim that the re-merged humanity is less diverse than before? Then your claim is wrong. Clearly.Edited by NoNukes, : No reason given.Edited by NoNukes, : No reason given.

Yes, a small chance that ONE individual will have that combination but who cares? To matter it would have to be selected. It COULD happen but the odds are very small. I'm talking about traits that come to CHARACTERIZE a population by being possessed by many individuals, and if the alleles that make up that combination are high frequency in the daughter population whereas low enough frequency in the mother population to show up only once in a while or never, the point is the new allele frequency has brought about a new subspecies. The occasional appearance in individuals in the original population of the same traits or even combination of traits is completely beside the point and I don't know why you think it matters. It's me saying the low frequency alleles don't show up in the original population due to the domination of the high frequency alleles, but how that occurs, perhaps by a combination of factors but at least by sheer numbers, the different frequency of alleles, is totally irrelevant to this discussion. Oh brother. You are NOT following the argument. The POINT was that they HAVE to be selected to come to any kind of expression in the new subpopulation, or in genetic drift where they are for that matter. You are NOT following the argument. To figure in the situation I've been describing forever here THEY HAVE TO BE SELECTED. Sheesh. If they stay in the population for a long period of time then they will be getting duplicated and passed on, but until they become high frequency they are not contributing to the new subspecies. Oh my aching head.I have to go back to HBD's post first, but it may not be until tomorrow.

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Oh brother. You are NOT following the argument. The POINT was that they HAVE to be selected to come to any kind of expression in the new subpopulation, or in genetic drift where they are for that matter. ou are NOT following the argument. To figure in the situation I've been describing forever here THEY HAVE TO BE SELECTED

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Disagreeing with claims that are obviously wrong does not indicate a lack of understanding. A dominant allele will obviously make it's presence in the population known, whether it is selected or not. Genetic drift is changes in allele frequency without selection.And, the extreme case of the founder effect is the best case for alleles become fixed through drift alone....

PaulK has addressed this. Following your argument does not mean nodding agreement when you make statements that are wrong. Drift occurs without selection. If a dominant, neutral mutation shows up, it gets expressed regardless of selection. And genetic drift is NOT selection. It is the propagation of traits without selection.I see now that when we catch you in errors, you simply say we are not following the argument. That was a rather timely head ache. I take it you have no response to examples of new variation created without a loss of diversity. Why did you even bother with my post?Edited by NoNukes, : No reason given.

I've been trying to discourage inventing new terminology when existing terminology already exists, and in any case, I don't think you have to give up using the term "migration." When HBD says that in population genetics migration only means gene flow he only means that not only can a subpopulation migrate away, they can migrate back. I think your scenario is not just migration but migration followed by isolation. In your scenario a subpopulation migrates far enough away or encounters a significant enough barrier to become isolated from the original population, causing a cessation of gene flow between the subpopulation and the main population. Do I have that right?

I was thinking about this issue this morning and was already going to comment on it. It is unfortunate that science often uses terms that already have common meanings but are used in a specific way - like the word theory. Clarity depends on how the word is used. For example, if I were to say "My theory is..." it would indicate that I am going to speculate about a specific topic and make my best guess about it. However, if I say "Well, that's only a theory..." that instantly gives the impression that I don't understand what the word theory means as used in a scientific context.Migration IS appropriate to use when referring to populations moving from one area to another. But when it is used to refer to an evolutionary process, it refers specifically to gene flow - not movement of individuals. If an individual moves from one population to another but does not breed in the new population, migration has not occurred. Without going back and quoting Faith exactly, I got the impression she was using the word migration in the context of an evolutionary process which is why I asked questions such as "Why would gene flow only occur in one direction?"In the context of population genetics, movement of individuals is sort of irrelevant. I mean, of course individuals need to move in order for genes to move, but we are not really concerned about the individuals per say. Furthermore, if a population can move into an area there is no reason it cannot move back. What would prevent gene flow back and forth is the generation of a barrier - which is really the concern - isolation. And what if there is no movement of populations but a barrier develops that simply separate them - such as a road, that would also produce the same effect without "migration" at all.So my advice is rather than talking about a "subpopulation migrating to a new area" just say "when a daughter population is isolated from the parent population." Yes, no need to invent new terminology.HBD

No. The founder effect is the platform on which following populations are build. In order for speciation to occur there must be a genetic difference that inhibits interbreeding when populations reconnect. That difference is shown to be due to different fixed mutations.A small population is more likely to fix more new mutations to be shared as they need every reproductive individual to grow. Here's that "V" diagram discussed above: We can imagine that the left branch is a small founding population and the right branch is the parent population.Even with these mutations becoming fixed in each population, genetic incompatibility is not guaranteed, but without them you don't have any possibility of genetic incompatibiliity, as then all possible combinations are tested. If some combinations of alleles is lethal then it will continue to be lethal. If some combination of alleles is infertile then it will continue to be infertile. Any other combinations get distributed within the population.Enjoy

Yes, exactly. But HBD's use is going to make it impossible to continue to use it this way although that's how I've used it for years. And I thought I got it from websites about population genetics.

That is the ONLY way I've EVER used the word. I've NEVER used it to mean that and I don't understand why context doesn't make that clear. I'm ALWAYS talking about a daughter population becoming REPRODUCTIVELY ISOLATED from the parent population as a result of MOVING AWAY FROM IT. It's simply that noving away is a more certain way of ending gene flow than any of the partial splits from the parent population, and ending gene flow is the main point I'm trying to get established because gene flow makes things too complicated. You keep reintroducing gene flow but that's been explicitly eliminated by my wording: REPRODUCTIVE ISOLATION alone ought to get that across. By that definition I never use. But in ALL my descriptions I'm talking about a number of individuals leaving the parent population and becoming reproductively isolated from it at some distance. There they constitute their own subpopulation and their new allele frequencies get worked through that subpopulation over some number of generations of inbreeding within that population. This brings out the traits in new combinations because of the new allele frequencies and over time produces a new subspecies out of that daughter population. That's unfortunate because I NEVER use the term "migration" as an evolutionary process. I wish there was another term for that process as a matter of fact. It's a pretty simple idea: gene flow resumes between formerly isolated populations. I don't see why since in many cases the number of those individuals is specifically relevant to the level of genetic diversity in the population. Founder effect is a dramatic loss of genetic diversity, but most population splits are not that drastic by a long shot and reduction of genetic diversity is hardly noticeable. This is one reason I like ring species for an example: a series of population splits, again the numbers of individuals determining the degree of reduction of genetic diversity, each split decreasing the genetic diversity from the previous but not necessarily dramatically until the end of the series. True, which is why I try to be very clear that I'm talking about its establishing reproductive isolation in its new location and explicitly eliminating gene flow from the picture altogether, such as eliminating hybrid zones between it and the former population and so on, although in reality these are common occurrences. Gene flow doesn't stop the pattern I'm describing: there would still be overall reduced genetic diversity, but it makes it much harder to describe so that's why I like to avoid it, as in Two Steps Forward, One Step Back etc. Yes, the most certain barrier but not the only; but the way reproductive isolation is brought about is incidental so I don't make an issue of it. I would think simply stating that the new subpopulation inbreeds in reproductive isolation from all other populations gets across the condition I have in mind. BUT IF IT DOESN'T AND YOU REALLY NEED IT SPELLED OUT FOR THE SAKE OF IMPROVED COMMUNICATION I'LL TRY. Yes, but all this is incidental or circumstantial. I say migration because to my mind it seems the clearest way of picturing enough distance to make reproductive isolation most likely. Besides, chickens DO sometimes cross roads to get to the other side. BUT I CAN TRY TO GET ALL THE INCIDENTALS INTO THE PICTURE IF IT WOULD REALLY HELP COMMUNICATION. Edited by Faith, : No reason given.

The quote on Wikipedia seemed to say that speciation can occur from the normal combinations of alleles present from founder effect so you appear to be arguing with that quote.Besides, you are assuming mutations without showing that there are any mutations there. It's often said that mutations simply do not appear frequently enough to have any kind of beneficial effect so how can you assume they're occurring here?ABE: Why do they have to be fixed "mutations" anyway? The idea seems to be that fixed RARE alleles is the point, why do they have to be mutations?Edited by Faith, : No reason given.Edited by Faith, : No reason given.

No need to accuse me of avoiding your post; I simply had to stop for the night and HBD's was on my list. I still haven't got back to his, but oh well. BUT WHEN IT IS SELECTED THEN GENETIC DIVERSITY BEGINS TO DECREASE. By now this really ought to be clear. AT THAT STAGE, YES. You really are not following the argument and continuing to insist you are just gives me a headache. You aren't making any sense. Yes, mutations add diversity. So what? Any form of gene flow can add genetic diversity. So what? The point is that when you are getting a new subspecies you have a new subset of allele frequencies that bring out new combinations of traits and that's in a sense a form of selection, random selection but selection because you are getting NEW traits (a single trait like a curled ear isn't a subspecies, or if you are going to call it that we need some new definitions). Yes, at this stage it is more genetically diverse. It's never been unclear, and it still completely misses MY argument. You are absolutely totally missing my point. Once the wings are selected and becoming high frequency in the new population, THE OTHER ALLELE for some other characteristic that the wing mutation originally replaced is either no longer present at all or at least starts out low frequency and eventually dropsd out altogether if the selection is very strong. THAT'S where you get the reduced genetic diversity. This is why all the mutations you can think of adding will never prevent this eventual effect of loss of genetic diversity. Whenever a trait comes to dominate a population other traits drop out. Doesn't matter if the dominating trait is mutated wings or the ordinary result of some new combination of the original alleles. Totally disproves them. You are not persuaded simply because you cannot follow the argument. ? Sigh. You can't follow the argument but the problem is your insistence that you are following it. As with any inbreeding population people will develop new traits if some number of individuals is isolated somewhere, and eventually down some number of generations probably a completely new look that could constitute a recognizable subspecies or race. Pick a tribe, any tribe, the Inuit, Mongolians, Pygmies, Icelanders, whatever, they got their own "look" or recognizable set of traits by being reproductively isolated among themselves over many generations. Meanwhile their genetic diversity will have started out low with respect to the total human population because of course the number of individuals in such a scenario is necessarily quite limited, and over time some alleles for some traits that were low frequency at the population split may drop out altogether, making the genetic diversity lower yet. Of course. In such a case it's the new population that will vary, not the original population. I'm only always talking about loss of genetic diversity within the NEW subpopulation, and I would have thought that very very clear. If new traits are coming to characterize this new smaller subpopulation THAT's where we'll see the reduction in genetic diversity as the new traits replace the former traits, it does not matter how many mutations may have occurred (though the possibility of even one beneficial mutation is remote).As for humanity at large, it would only be relevant if the two populations were reunited. Then if the supposed new traits become high frequency in the reunitedpopulation then the traits they replace will become low frequency or drop out if selection is strong. And again, this is the reduction in genetic diversity I'm always talking about that always occurs with the development of a new look to a population or if by genetic drift a recognizable segment of a population. You don't get "evolution" except where the genetic diversity is being reduced and it doesn't matter if the new traits came by mutation or by new combinations of old alleles, though the latter is really most likely what is happening. Already discussed this above. You focus on a new trait, the phenotype, which is always more diverse wherever evolution is occurring, (the most common way what I'm saying is misunderstood); but (micro)evolution, or the development of a new POPULATION or subspecies (not just scattered new traits in individuals), REQURES loss of GENETIC diversity, so even if new mutations underlie a new set of traits, for those traits to become characteristic of a population requires the loss of the others the new ones replace.This has been explained so many times I am quite sure you'll still not get it but oh well.