Natural Limitation to Evolutionary Processes (2/14/05)

When I posted here briefly a few years ago we creationists seemed to have the main problem of not being able to show the clear end point we claim must exist for the processes of evolution. Evolutionists claim these processes are open ended, creationists claim they are limited to the Kind or Species itself, these "processes of evolution" including natural selection, migration, genetic drift and mutation with some subcategories such as bottleneck and founder effect.I was playing with the idea that the fact that some examples of speciation (such as the cheetah) demonstrate a severely limited genetic variability suggests that evolution reaches a built-in ending point. Since then I haven't thought about these questions much but when they came up again recently in another forum I became even more convinced that this is the case.Originally that discussion came up around the PBS series on Evolution in the Fall of 2001. I just reviewed it. http://EvC Forum: Review: PBS's Evolution -->EvC Forum: Review: PBS's Evolution I got a couple of nice responses from Mark24 to my contribution but since I never came back I didn't know they were there until now. I hope I will answer them in this.In that discussion I complained about the PBS program's defining as evolution what a creationist would regard as simple variation within a species, which in the two cases given were brought about by natural selection. 1) Genetically variable bacteria are attacked by an antibiotic which kills off all but one gene type which is resistant to it. This type then proliferates and becomes a new headache for the human race who have been trying to get rid of the whole species for some time now. What happens? The program calls this an example of evolution. What it is, and Mark24 acknowledged this, is merely natural selection working in pre-existing genetic types. 2) A type of newt is threatened by a snake in a certain locale and as the snake wipes out much of the population of the newt the newt develops a poison that kills the snake or causes it to avoid the poisonous newts. This was also called evolution in the PBS series but again all it is is the natural selection of a more adaptable type of newt by the predator snake. In turn the snake had to evolve immunity to the poison. All this is not evolution, merely natural selection from among given genetic possibilities. The genetic capacity for a poison type was already present in the species, but natural selection brought it out in response to environmental threat.Now, in every case of natural selection the genetic variability of the species is reduced. The new adapted population has less capacity to change. In some cases there may still be quite a bit of variability left, but it is nevertheless less than the previous population's ability to adapt, and if the process continues to yet another adaptation in this poisonous newt its ability to change or "evolve" will be reduced even further. Ultimately it is conceivable that a branch of the newt population could become like the cheetah with such fixed alleles that no change in any direction is possible. The same can be said of the bacteria population. It may have reached the limit of its adaptability.It seems to me that this can be said about all the "processes of evolution," with the exception of migration into a population and mutation. Migration out of a population leaves both the remaining populations genetically reduced. This is what happened with Darwin's Galapagos turtles. They are both likely to develop traits peculiar to themselves from their reduced allotment of alleles, and unless the process continues may remain able to crossbreed, but the point is that the process of migration reduces the variability of the group, or to put it another way, reduces the frequencies of alleles in the population.The same with genetic drift, bottleneck and founder's effect, in fact in this case the effect is particularly dramatic. In migration a population splits into two or more, but both populations may live on, as in the case of the Galapagos turtles. In genetic drift some portion of the population dies and the resultant loss of genetic variability in the surviving portion cannot be reclaimed by remixing as could conceivably occur in migration. In bottleneck and founder effect the population reduction is even more drastic. The new populations develop new traits but their genetic adaptability has been sharply reduced.Now all these processes are called evolution and are said to lead to speciation. In fact the Hardy-Weinberg principle was formulated to explain why the processes of reduced genetic diversity don't occur faster. Populations may remain relatively static, NOT evolving. When any of the "processes of evolution" occur they are no longer in "Hardy-Weinberg equilibrium" but are "evolving."However, all these "processes of evolution" lead to reduced genetic variability. In fact, I believe this is a rule: the processes of speciation ALWAYS result in reduced genetic variability, at the extremes to the point of absolute inability to vary in any direction at all. This effect is acknowledged in many things I've read on the subject, because the extremes often lead to concern about extinctions, but its theoretical implications seem to have been overlooked: How can evolution proceed via processes that inevitably lead to the inability to evolve?I left out two of the processes of evolution, migration into the population and mutation. Migration into the population from a previously split-off group does increase genetic variability and thus the overall health of the group, but I don't see how you can get conditions for evolution out of this situation. If anything the population tends to homogenize over time and remain relatively stable. But THEN if any of the OTHER processes occur, killing off a portion of the group either by natural selection or genetic drift, or separating the group into smaller groups again, the same processes of "evolution" and "speciation" will occur as above -- and always with reduced genetic variability at each change.As for mutation, Mark24 suggested that mutation increases evolution potential, balancing out the effect of the loss of genetic variability through these processes, and claimed that mutation occurs at an amazingly rapid rate. I need to look into that, but for the moment I would just consider the possibility that beneficial mutations are occurring in all populations. What happens then? Either the population absorbs the new characteristics, homogenizes and remains relatively stable over time as in the case of immigration of new genetic material, or it is subjected to "processes of evolution" that reduce its genetic variability as in all the above cases.I suppose you could postulate that enormous numbers of mutations over time could transform a species into another species without any of the other "processes of evolution" occurring, but this isn't how the theory goes: all the emphasis is on the processes that reduce variability as THE processes by which evolution, that is, speciation, occurs.I believe that these facts show that evolution simply does not occur past certain given limits that are built into the genome of the species, and that this constitutes the "barrier" to further evolution into new species that creationists have believed must be there. It seems that every process that produces change, evolution, speciation, while doing so also produces less and less ability to change or evolve or speciate, and there's no way you can get evolution past the far fringes of a given species out of such processes.According to creationism, there is abundant variability and adaptability built into each species that gradually plays out over time. This is not evolution. It is often called "microevolution" but since that term implies a "macroevolution" I tend to avoid it. But that is what it refers to, intraspecies variability which can be quite enormous. Unfortunately in our fallen world these processes lead to death and ultimately even species extinction, the opposite of open-ended evolution. In the original world of Eden they would simply go on to produce wonderful varieties.This message has been edited by Faith, 02-14-2005 09:58 AMEdited by Faith, : To add date of thread to titleEdited by Faith, : No reason given.Edited by Faith, : Changed the title back; the creationist angle is clear in the posts.

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As for mutation, Mark24 suggested that mutation increases evolution potential, balancing out the effect of the loss of genetic variability through these processes, and claimed that mutation occurs at an amazingly rapid rate. I need to look into that, but for the moment I would just consider the possibility that beneficial mutations are occurring in all populations. What happens then? Either the population absorbs the new characteristics, homogenizes and remains relatively stable over time as in the case of immigration of new genetic material, or it is subjected to "processes of evolution" that reduce its genetic variability as in all the above cases.

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I think you need to check your reasoning on this point.

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If you accept for the sake of argument that new variation is entering the population through mutation then what happens depends on the rate at which new variations appear against the rate at which variation is lost through selection. Only if the rate at which variation is lost is greater than the rate at which new variation enters the population will there be a net decrease in variation.

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First, are you accepting the rest of what I said, that is, that except for mutation and immigration all the "evolutionary processes" produce decreased variability, or less ability to change, which would seem highly incompatible with the theory of evolution?As for a very high rate of beneficial variations changing the picture here, assuming that such occur for the sake of argument as you propose, which I believe is highly doubtful, even if huge quantities of new adaptive alleles were to enter the population [at least as problematic a possibility as the idea of God's intervention I would think], natural selection and the other evolutionary processes are going inexorably to operate in the direction of decreasing variability among them. There would be more adaptability possible but with each new selection of a survival-enhancing or adapted trait comes decreased variability. Even if the process continues, and more variability enters into each new reduced population it is still subject to the same processes of reduction of variability -- and if that were in reality the case and an abundance of adaptive possibilities were constantly occurring in all populations then why would anybody worry about extinctions? So given the scenario you propose I think the usual process of reduced variability will produce adaptive or neutral changes in the phenotype as usual, but it will simply take longer to play itself out than if a given complement of alleles belongs to the Species at the outset, which is the creationist view. In other words it doesn't ultimately matter whether you have twenty adaptive possibilities in a population or 20,000, as the processes of evolution are going to relentlessly reduce their variability over time in either case.Of course you may also imagine that among all these beneficial mutations are changes in the direction of something outside the characteristics of the Species if you are going to get "macroevolution" out of this formula, BUT at any point that you have a new population that has been created by all the processes that inexorably reduce variability you nevertheless have created a situation that has less ability to evolve beyond itself and again is self-limiting at SOME point WAY before any further evolution could possibly occur. Also this doesn't fit the time frame evolution posits, as macroevolution changes would have to be considered to be going on within populations at all times rather than accumulated in slow increments over unimaginable aeons of time.This message has been edited by Faith, 02-14-2005 17:38 AMThis message has been edited by Faith, 02-14-2005 17:49 AM

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1) Genetically variable bacteria are attacked by an antibiotic which kills off all but one gene type which is resistant to it. This type then proliferates and becomes a new headache for the human race who have been trying to get rid of the whole species for some time now. What happens? The program calls this an example of evolution. What it is, and Mark24 acknowledged this, is merely natural selection working in pre-existing genetic types.

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This may well be the case in the wild but it is possible to perform similar selection for antibiotic resistance artificially on a population grown from a single bacterium which is known not to have antibiotic resistance. Fora an example see...

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What you are doing is changing the subject. I presented the scenario of the "evolution" of a bacteria population in answer to the PBS "Evolution" program's claim that it represents evolution by mutation. The answer is no, it is merely natural selection from pre-existing genetic possibilities, "classical natural selection" as Mark24 put it three years ago. In fact the diagram given in the program even showed the existence of the adaptive type in the starting population, which was the only type left after the antibiotic killed off the rest. Yet they called this evolution, meaning mutation. It is not mutation. The same was said about the "evolution" of the newt, but again the potential for a poisonous kind was already in the population, merely selected by the snake. I find this confusion in many discussions of evolution. I have to assume the program had scientific consultants so how explain this kind of elementary confusion?As for your example of resistance to an antibiotic in a population grown from a single bacterium, I see no reason to suppose this was the result of any novel processes, but of changes that naturally occur, just as in the above examples, having to do with genetic variability built into a single bacterium, however that happens. Your point that "the antibiotic is added after the single progenitor has expanded over many generations, to introduce variation to the population before the antibiotic is introduced" shows the expectation of variation under such circumstances. Assuming such variations are beneficial or at least not lethal implies this is not mutation, but business as usual for bacterial genes. Novel beneficial mutation would imply something nearly mystical, like the introduction of changes by a beneficent power from outside wouldn't it? But I would assume that what is going on simply follows the pattern of what bacteria were patterned to do. Besides the pre-antibiotic variation that was established, the fact that four separate genes were ultimately affected in the acquisition of resistance to the antibiotic also suggests quite a bit of variability built into the original code.(By the way I'm not a scientist and it would help if you would keep the scientific jargon to a minimum. I don't know what MIC means, or the labels of the different kinds of genes, but I think I've grasped the general point in any case).

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It also depends upon what definition of evolution you are working under, if you are simply thinking in terms of changes in allelic frequency then selection on 'pre-existent'variation is a perfectly legitimate example of evolution. You are obviously thinking of evolution as something generating novelty, but even with that point of view the experimental evidence shows that antibiotic resistance can arise as a novel mutation in a non-resistant population.

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I'm using the definition of evolution you can find at most biology websites and at Talkorigins.com, "Changes in gene (allele) frequencies in a population over time." In fact I have been using this definition in a sense as an argument against the idea of novel mutations as having much if anything to do with evolution, as PBS misrepresented the situation. There are multiple allelic possibilities for many genes in many species, which provide for perfectly normal variation in the species without introducing anything novel. They obey Mendel's laws. I've discovered that you can get the most lucid understanding of these processes from animal breeders rather than scientists. They seem to know how many different genes are involved in the production of different colors and patterns of coats in dog breeds for instance, and how these can combine to produce desired results in offspring. This is all genetic business as usual, involving no novel mutations. Novel mutations would be unpredictable in any case, but the business of breeders is prediction.

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What is very important is not to make the mistaken assumption that this is neccessarily being put forward as a response to the antibiotic. Even in the experiment I referenced the antibiotic is added after the single progenitor has expanded over many generations, to introduce variation to the population, before the antibiotic is introduced. Depending on the type of antibiotic it is certainly not impossible for resistance to arise de-novo in the presence of the antibiotic, but such a demonstration is not required to show evolution in action.

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I would suggest that "for resistance to arise de-novo in the presence of the antibiotic" definitely flirts with mystical processes outside the normal workings of nature. If one could count on such happy interventions in any species whatever we could stop worrying about death and extinctions altogether it seems to me.

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The genetic capacity for a poison type was already present in the species, but natural selection brought it out in response to environmental threat.

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This is a tricksy statement, from an evolutionary perspective simply using DNA as its genetic material is sufficient to produce the 'genetic capacity' for poison no matter what the species.

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Again, the PBS program (probably a NOVA but I don't remember) presented the situation as if the adaptation were the result of novel mutation, while I see no reason to assume that it's any more than a genetic potential for a poisonous type being allowed to be expressed phenotypically when great numbers of the population have been killed.I don't know what you mean about DNA's own ability to produce poison, but this implies a completely other scenario than either PBS's or mine which I'd need you to explain. In any case, the poison type didn't occur in the population until it had been drastically reduced by natural selection, and apparently it is not a novel mutation but a built-in factor in any case.To get back to my own topic however, when you say that "if you are simply thinking in terms of changes in allelic frequency then selection on 'pre-existent' variation is a perfectly legitimate example of evolution" I agree as far as "microevolution" is concerned, as I go on to point out that all the "processes of evolution" that bring about these changes in fact lead to reduced genetic variability which is inconsistent with the idea of "macroevolution" over time.I wasn't "obviously thinking of evolution as something generating novelty" except to answer the implications in some statements that that is what some believe evolution is. In any case, as I answered Paulk, even on the remote possibility that such mutations do occur in great frequencies, the populations they occur in are nevertheless subject to the same "evolutionary processes" which inevitably lead only to decreased evolutionary potential, which defeats the whole theory of evolution. IMHO of course.

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The answer is no, it is merely natural selection from pre-existing genetic possibilities,

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But they design the experiment so that the population is decended, clonally, from one individual - what's called a "monoculture." Since bacteria are haploid, we know that one individual can have at most one allele for every gene.

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So if genetic variants are being selected for or against in the mature population, we know that those variants arose through mutation. So we know that mutation is occuring. Selection among mutated variants is, of course, evolution. Your analysis is quite inaccurate.

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Besides the pre-antibiotic variation that was established, the fact that four separate genes were ultimately affected in the acquisition of resistance to the antibiotic also suggests quite a bit of variability built into the original code.

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Yes. And that variability is expressed through the occurance of mutations.

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I get your point but it sounds awfully mystical that mutations simply show up out of the blue in order to provide resistance to the antibiotic. I don't understand the processes involved in single-cell reproduction but this kind of explanation just doesn't fit with scientific assumptions. Whatever it is that leads to resistance, or in fact to variation in the population at all from a single individual HAS to be pre-programmed, has to follow a Law of some sort, or we're out in la-la land. Perhaps this situation has to do with the definition of "mutation" -- I've certainly discovered that that is one malleable term. What about the fact that MOST mutations are acknowledged to be not beneficial in any way at all? How does resistance to the antibiotic develop in this population before something lethal to its existence develops given that mutations of all kinds are supposedly occurring apace?In any case, I don't want to lose sight of my original observation which I see the next poster is going to address: the very processes that select the adaptive trait involve the reduction of genetic variability in the population, which is inconsistent with the overall theory of evolution. That is, no matter how the new strain of bacteria arrived, increasing variability temporarily, its selection involves a reduction in variability, and even if the increase in variability is enormous, the processes that select from it spell an end to the variability eventually. OR -- following out the assumption of exuberant mutations in all populations, how come the cheetah can't evolve further? It would seem to follow from such ideas that it could.

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No, I don't agree with everything you said - I CERTAINLY don't agree that genetic drift reduces variation (quite the opposite).

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Sorry, this is absolutely known. ALL the processes that select out a portion of a population as a rule reduce the total allelic potential so that a reduced allelic potential, meaning reduced genetic variability, defines the smaller populations. Genetic drift is only one of the processes that does this, and it does it through the death of a part of a population which makes the reduction irreparable. Depending on the extent of the process the reduction may not be particularly noticeable, but the process nevertheless tends in the direction of reduction of allelic frequencies and therefore of genetic variability. NO WAY is it "quite the opposite" as you claim.

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Nor do I agree that the cheetah represents a normal outcome (the cheetah suffered a SEVERE genetic bottleneck - a population reduction so bad that extinction would be the normal outcome plus lesser bottlenecks trhough more recent hunting).

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I didn't say it was a normal outcome, I emphasized that it is at an extreme. Bottleneck is simply an extreme version of genetic drift. Nevertheless the cheetah is the normal expectable result of selection to that extreme. Selection processes always reduce allelic frequencies in a population, and at the extremes reduce them extremely.The point is that this extreme is one very possible -- though extreme it is not an anomaly -- outcome of processes described as "processes of evolution" that lead to "speciation." This is correct, these processes DO lead to "speciation" -- this is how new types emerge in a population, by isolation of a portion of a population which reduces the allelic frequencies so that new allelic combinations come to the fore as old ones are eliminated or suppressed. The cheetah is one example of speciation at an extreme. The fact that its extreme loss of genetic variability makes it particularly vulnerable to extinction is crucial to my point -- this extreme end product of the very processes that lead to speciation and are called "processes of evolution" in fact demonstrates the opposite effect -- not evolution but potential extinction, not higher genetic potentials but lower. This demonstrates that there is a built-in limit to the processes of evolution, and that limit may be defined as the Species itself beyond which evolution is impossible.That is, a Species starts out with a very great built-in potential for variation. (This variability is scattered throughout whole populations although I believe an assumption consistent with creationist theory is that at one time individual members of Species contained within themselves much more potential for variation, probably in the form of more gene loci for given traits -- the loss of such previous genetic richness could account for "junk DNA" which could simply reflect the death of previous genetic potentials in the genome, lost through many processes of selection).The processes of variation (called "speciation" by evolutionists) proceed by selecting out portions of the built-in potential for expression in the phenotype. The process ALWAYS involves reduction of the frequency of alleles and of genetic variability because for new traits to come to the fore new allelic combinations are required and you don't get these unless other allelic expressions are somehow suppressed -- or unfortunately in some cases actually killed. This process of "speciation" works beautifully within the creationist model of variation limited to a Species, but it contradicts the evolutionist model of open-ended change.

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I focussed on the one point I did since it was crucial to your argument and needed to be rethought.

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Let us also be clear that I am not necessarily proposing a high rate of beneficial mutations. The rate of mutation requied only needs to be igh enough to maintain variation and neutral mutations will do - so long as they have a phenotypic effect. In neutral mutations that remain neutral or neutral mutations that become deleterious - or even mildly deleterious mutations will do, since their removal still accounts for part of the loss.

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I may not be following you at this point, but my observation is that the processes that SELECT the variations REDUCE genetic variability and that this is the overall tendency in ALL processes of speciation or "evolution." I believe that much of what is called "mutation" is in fact merely pre-existing allelic potentials that come to the fore as combinations typical of the parent population are eliminated from the new population. That was clearly the case in the PBS example of the bacteria and the newt and I find the term used carelessly in similar contexts -- no new material is being added, it's that previously suppressed potentials are getting expressed. The resistant form of the bacteria were already present in the original population but did not express in the phenotype until the majority of that population was eliminated. Same with the poisonous newt.

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The real problem here however is that you are not addressing my point. Your whole argument depends on the assumption that the rate at which variation is lost must exceed th rate at which variation is introduced by mutation.

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I believe in actual reality this is simply factual. If variability were being introduced at any observable rate whatever, there would never be a genetically stable population. In any relatively stable population you simply do not see an increase in variability which is what would seem to be implied by your statement. Shouldn't observable changes just be occurring from generation to generation if phenotypically expressable mutations did in fact occur at any noticeable rate? They simply do not. (They do not in populations that reproduce sexually, at least. Your example of the bacterium introduces an element that is outside the context here, but does suggest a capacity for variation that is contained within the bacterium itself. Sexually reproducing populations (deer, bears, raccoons, kangaroos, marmots, mice) do not demonstrate this abundance of increasing variability which I would think should be expected according to your claim). (The only remotely similar process would be immigration in which new genetic potentials are added and through generations produce new phenotypes, even a totally new character to the whole population -- but this is nothing more than the REintroduction of allelic potentials, not anything truly new.)But very observable changes DO occur through the processes of selection which are what bring about new varieties, or "speciation" by concentrating certain allelic potentials at the expense of others in an overall reduction of genetic variability. This IS the process by which new "species" or types come about, in a word REDUCTION. This part of evolutionary theory is abolutely correct.

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You've offered no reason to beleive that the former rate is very high (although you claim that it is) or that the rates cannot balance. So I ask you again to reconsider your claim - and if you cannot support it accept that your argument lacks a foundation.

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I believe you are probably using the term "mutation" to describe what are really pre-existing potentials in a gene pool. The whole idea of an increase in variability is a fiction and the only source of such a misimpression that I can see is the misnaming of normal variations as mutations.This message has been edited by Faith, 02-15-2005 08:42 AMThis message has been edited by Faith, 02-15-2005 08:53 AM

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Genetic drift is NOT a selective process. So what is "absolutely known" about selective processes simply does not apply.

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Funny it's categorized on so many biology sites as a "process of evolution" then. I myself am pointing out that all those processes (with the exception of immigration and mutation) are processes of selection. For heaven's sake it's obvious. It selected out the cheetah. It selected out the northern elephant seals. All a bottleneck is is an extreme form of genetic drift. I've found THAT on umpteen biology websites too.

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And you're simply wrong that genetic bottlenecks represent a form of selection. A bottleneck is caused by a redution in the population to a low number - whether it is selective or not. The YEC view of Noah's Flood represents a massive bottleneck for all affected species.

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That is true, and it most certainly IS a form of selection. What on earth can you be thinking? Noah and his family were selected out of all human types to propagate and only their genetic potentials were preserved out of the entire previous human population. Their genetic potentials were obviously severely reduced from the previous. Darwin's Galapagos turtles were selected by isolation from the parent population on the mainland. Whatever isolates a portion of the gene pool is selection. What on earth is your definition of "selection" anyway?

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And it is absolutely daft to insist that species start out with a huge amount of potential for variation. More likely they start out with comparatively little variation and variation accumulates as the population expands.

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You have the evolutionist assumption. I am trying to introduce the creationist assumption. Your assumption is not borne out by the facts. Increasing variation is a fiction. All new types are formed from a reduction in genetic potentials.

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And this is also badly wrong:

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If variability were being introduced at any observable rate whatever, there would never be a genetically stable population.

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This essentially denies that genetic drift happens at all !

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Excuse me??? It sounds like YOU are denying that a genetically stable population happens at all!!

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Alternatively you could consider the alternative that stabilising selection generally removes new variations INSTEAD of existing variability.

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BTW perhaps you would like to clarify what you mean by "pre-existing potentials". It appears to refer to the variations already present - which would be a clear misrepresentation of my point since I expressly refer to mutation as adding new variations.

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I'm DISAGREEING with your view not representing it. What you call mutation I believe is really the expression of pre-existing allelic potentials, as exemplified in the discussion of the PBS example of the bacteria and the newt.I think my conversation with you has ended as you seem to be making no effort whatever to follow what I'm saying.

I have to take a break from this exciting discussion for a while, but I do eventually want to get back to posters I haven't yet answered.It seems that so far the general tendency has been to contradict my assertion that the processes of evolution all involve a reduction in genetic variability by insisting that there are balancing or even greater processes of increasing variability going on.I would really appreciate it if at least the fact that the processes I am talking about DO entail an inevitable reduction in genetic variability were acknowledged as this part is fundamental.I guess I'm repeating, but since it doesn't seem I've been understood I think I need to repeat: My general answer to the claim of increasing variability is that -- assuming that such processes exist, and I doubt that they do; most of them can be accounted for by the misnaming of pre-existing potentials as "mutations" -- the overall effect of speciation is a reduction in genetic potentials in any case whatever. That's what speciation/evolution IS -- a selection of specific characteristics from a larger roster of possibilities, and the genetic variability of the new "species" of NECESSITY is reduced in order for the new type to appear phenotypically. All the supposed processes of increasing variability would do is provide a larger roster of possibilities from which to select, but the selection process always produces reduced variability and theoretically at least always has an end point beyond which evolution/speciation simply cannot continue.I understand this to follow from what EVOLUTIONISTS say. Or do you all think it is brought about by mutations in the sense of NON-pre-existing accidents, or outside intervention as it were? If so, somebody should tell all the biology sites that say evolution is change in gene or allele frequencies over time (they fail to note, however, that the change in question is always a reduction except in the case of mutation and immigration. This is my own observation).This message has been edited by Faith, 02-15-2005 10:44 AM

A general reply again. The reason I took a time out was that I had work to do, and there's more of it to be done today; but I'm up in the middle of the night and did read through the answers, although I will no doubt need to read them again.It is apparently true that I don't understand genetic drift. I have found it presented with bottleneck and founder effect in discussions of evolution as if it were the same kind of process though not as extreme; that is, as if it involves the destruction of some number of a population, only fewer than are destroyed in bottleneck and founder effect. It seems to me that if it refers to a reduction in a population that it would lead to a reduction in genetic variability. I suppose if the reduction in population isn't dramatic there isn't necessarily a reduction in genetic variability, or at least not a noticeable one, but in any case there wouldn't be an increase.Now you are all introducing mutations into the mix, which, if they occur at the great rate you claim, would provide the great increases in variability you all seem to be assuming, to such an extent that they overcome the processes that reduce variability -- if the population is large enough to begin with, if I'm following correctly. If such mutations are always part of the picture in genetic drift (or any of the processes if the population is large enough to be affected by them), it seems to me mutations ought to be assumed in connection with ALL the "processes of evolution," but in fact mutation is only treated as ONE of the processes of evolution in the usual presentation of evolution. That is, from what you all seem to be saying, evolution should be defined as Mutation Plus all the other processes, and should be assumed prior to each of the others.In any case I'm still not sure what genetic drift is. Is it a reduction in population or an increase in variation through mutations or what?My point was always that overall the tendency of all these processes including genetic drift (as it seems to be defined but I perhaps have misunderstood it), is reduction in variability and that this seems to conflict with the assumptions of evolution which these processes define. Yes, it does seem odd that scientists wouldn't have noticed this, to answer the person who said scientists aren't stupid, but I figure scientists are assuming evolution to such an extent that they think evolution into all of it. One suggestion of such a bias is that I simply don't find these processes DEFINED as a decrease but merely as "change" as if they sometimes lead to increase. Hence the necessity, so it seemed to me, to point out that they all lead to decrease -- except mutation and immigration of course. Yes, again, it does seem odd to me that the scientists who inspire these lists define them as change in frequencies rather than decrease in frequencies. Somebody said pointing this out was pointless as it's obvious. If so, then why isn't it already pointed out on these lists? I can give some links but they aren't hard to find. I find versions of them whenever I google something related to evolution.Again, overall the answer to me from others here appears to be that mutations overcome all the processes that reduce population and therefore reduce genetic variability. Again, a redefinition of the "processes of evolution" seems to me to be in order: Mutations PLUS, as the entire edifice of evolution must rest entirely on mutations, as mutations are obviously the ONLY counterforce to all the forces of genetic reduction that I have been focusing on.If such tremendous numbers of mutations do indeed occur such that they contribute an overall adaptive or beneficial effect that overcomes all the processes that reduce genetic variability, then my argument certainly is defeated.==============
Somebody also said that I misuse the term "selection." I am aware that it is normally used in a specific sense, but I was applying it logically to all the processes that reduce genetic variability as it certainly seems to me to apply to all of them. Didn't Darwin apply it to the Galapagos turtles which were developed not from natural selection proper which involves the death of most of a population, but from migration, or possibly even a bottleneck? Any process which eliminates some alleles from a population while permitting the phenotypic expression of others previously latent seems to me is reasonably described as selection.As usual I'm leaving out the enormous input of mutations which seem to make the whole idea of the normal shuffling of given allelic variations obsolete, though this wouldn't affect the definition of selection. Or perhaps I should ask: Is there any room any more for the idea of normal allelic variation or is everything mutation? Actually somebody pretty much already answered that everything is mutation.Again, if so, my argument is certainly defeated.But I hope to have some time to think about this more later.This message has been edited by Faith, 02-16-2005 06:42 AMThis message has been edited by Faith, 02-16-2005 06:49 AM

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Yes, again, it does seem odd to me that the scientists who inspire these lists define them as change in frequencies rather than decrease in frequencies.

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I can't see the sense in this. Any decrease in frequency of one allele is going to be balanced by an increase in frequency of another allele.

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OK, that makes sense. As some alleles are eliminated from a population, or their frequencies reduced, others are increased. So I'm apparently arguing with the wrong thing. But when there is a population reduction that reduces or eliminates some alleles there is a reduction in the overall capacity for variation in the new population, simply because some allelic opportunities have been lost or reduced. That's what I'm trying to get at. Yes, frequencies of alleles is independent of this effect. In fact frequencies of some alleles will increase along with the decrease in variability. So I should keep my focus on the decrease in variability and not confuse it with the frequencies of alleles. Decreased NUMBERS of allelic possibilities is really what I'm getting at. For some to increase others have to be eliminated. When this is drastic, as in the degree of natural selection that brings an antibiotic-resistant bacterium to the fore, or a poisonous newt, or bottlenecked creatures, some allelic frequencies are increased enormously, but the overall effect is a drastic decrease in allelic variation.This message has been edited by Faith, 02-16-2005 07:08 AM

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Genetic drift is a general term for non-selective change in allele frequencies. It includes things like bottlenecks (where the cause is NOT selective) and the founder effect (which needn't be due to "destruction" at all - the classic example is colonising a new habitat, like an island).

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It is hard then to sort out the various processes, as "migration" would seem to define that circumstance just as well. And the example of Noah -- is that a bottleneck or a founder effect? But thanks for the clarification that the REASON for the change in allele frequencies (such as "non-selective") is intended by some terminology. I tend to focus only on the effect and ignore the cause. Actually I don't see the relevance or importance of the cause now that I think of it.

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But drift doesn't need a reduction in population - statistics guarantees that some degree of drift will happen whatever the populations does.

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So the causes of drift are, say, differences in breeding patterns within the population over time, or mutation?

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As for mutation let me stress the reason that it is referred to as only one of the mechanisms of evolution is because it acts only as a source of variation for selection (and drift). I find it odd that you weren't aware of that - or even aware that scientists recognised that there was a need for a source of new variation.

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Not sure I'm getting you. You mean scientists had noticed that the theory of evolution WOULD fail because of the overall tendency to reduction in variability from all the selective processes, and therefore had to suppose input from somewhere to balance out or overcome these processes?

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On the other hand I haven't noticed anyone claiming that there is an improbable "great rate" of mutation - just a rate high enough to compensate for losses (which as I have pointed out can be qute low, due to feedback effects). So it seems that your claim relies on an implicit assumption that there is a "great" rate of loss of variation - but I haven't seen any support for that claim.

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Because all the processes of evolution except immigration and mutation tend in that direction. Rate doesn't seem crucial if this is the overall tendency and these processes are operating as frequently as SEEMS to be understood to be the case. But I understand that the Hardy-Weinberg principle was formulated because of the observation of overall reduction in genetic diversity through all the processes of reduction, needing to account for the fact that in reality such drastic reduction in diversity doesn't occur as rapidly as would be expected if those were the only processes in operation.Any rate of mutation sufficient to be a counterforce to the processes of reduction of variability seems to me to be a great rate.

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As to your talk about "alleleic variation" the term as I understand it refers to variations already present. If that is what you meant you've already seen examples refuting that as an explanation of all variations.

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Yes, your bacterium. But still in my mind are the examples from the PBS program that called the process of selection of the poisonous newt and the antibiotic-resistant tuberculosis "mutation" while nevertheless ILLUSTRATING the process by diagrams showing that the adaptive trait was present in the beginning of the process. Surely that is not mutation, that is simply an already-present allelic variant. And such a case makes the whole question of mutation very iffy.

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THe fundamental problem of your argument is that it relies on comparing two rates but estimates neither. Rather it just assumes that one rate must be "great" without any support or without any estimation of the actual rate

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I have trouble with the whole idea of mutation, a random input that follows no law but somehow manages to be a beneficial effect in some cases. The probabilities against anything that would increase survivability would seem to have to outstrip any rate of such random changes whatever but yes, I'm no mathematician and would rather keep away from rates and estimates. I don't think they are really necessary. If you are right you are right that mutations provide enough variability to overcome all the processes that decrease variability, which seem to me to be happening all the time just because death happens all the time and allelic potentials must disappear from genomes at some noticeable rate simply because of death. It's slower than one might think, for various reasons including the Hardy-Weinberg principle, which says that the processes of reduction aren't always happening, but it seems to me inevitable. Rate isn't crucial to the idea.

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(or even a theoretical look at the issue of negative feedback leading to dynamic equilibrium which I raised). Yet this assumption is the core of the argument. At this stage your argument is not so much refuted rather, it is shown to be an unsupported assumption

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If I've missed the "core of the argument" I will have to go back and review.This message has been edited by Faith, 02-16-2005 07:48 AMThis message has been edited by Faith, 02-16-2005 07:50 AM

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But when there is a population reduction that reduces or eliminates some alleles there is a reduction in the overall capacity for variation in the new population, simply because some allelic opportunities have been lost or reduced. That's what I'm trying to get at.

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As I see it the problem here is your use of terms such as 'capacity' and 'possibilities'. In terms of extant allelic variation you are correct that much of the time selection leads to a restriction of variation even to the point of fixation. The problem is that in terms of capacity and possibility there is no restriction, the genes are still perfectly capable of producing any possible allelic variation as a result of mutation.

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And mutation is random input? Of what from where? In fact, please define mutation.

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In terms of producing novelty mutation, in a relatively broad sense, pretty much is everything.

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For some to increase others have to be eliminated. When this is drastic, as in the degree of natural selection that brings an antibiotic-resistant bacterium to the fore, or a poisonous newt, or bottlenecked creatures, some allelic frequencies are increased enormously, but the overall effect is a drastic decrease in allelic variation.

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This depends very much on the initial prevalence of the selected trait, if the selection is very strong and the trait at very low abundance then you may see a drastic reduction in population and genetic variability, if on the other hand the selected trait is already fairly evenly distributed then there is a good chance that much of the genetic variability of the population can be maintained, except for at the particular locus under selection

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OK, but the OVERALL tendency, leaving aside mutation and equilibrium when no selecting processes are operating, is a reduction in variability. Without the input of mutation over time the net effect of all the selection processes would be reduction in variability, often to the point of fixation. This may occur only in SOME traits but that may be enough to fix the "species" past the point where further variation is possible. In other words the processes may be quite slow, and I assume they are, but the accumulated overall effect is a loss of enough alleles in a population, or reduction in variability, to complete contradict any idea of evolution -- EXCEPT if mutation does increase variability in a beneficial way overall to such an extent that the processes of selection and reduction are overcome.

Deleting this because I accidentally repeated it below.This message has been edited by Faith, 02-16-2005 15:47 AM

I wish I had more time. I had no idea how much time this debate would take. I appreciate all the responses but it can be a lot to deal with. Anyway I'm answering your latest post just because I think I can do it briefly as I'm not going to be able to get back to this for most of the day or longer, to all the posts that are accumulating unanswered.

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When this is drastic, as in the degree of natural selection that brings an antibiotic-resistant bacterium to the fore, or a poisonous newt, or bottlenecked creatures, some allelic frequencies are increased enormously, but the overall effect is a drastic decrease in allelic variation.

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Perhaps ...

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Only "perhaps?" Isn't it understood that variability is lost through drastic events because many alleles are lost, and that, overall, creatures inbreeding at this point are especially vulnerable to genetic diseases and even extinction?

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, but evolution does NOT only proceed by such drastic events that kill off the majority of the population. I tried to explain this to you on page one of this thread with a frog example, but perhaps you missed it. I'll try again:

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Sorry, no doubt that first post of yours is one I overlooked in my first general answer. I do hope to get back to all of them eventually unless I keep getting overwhelmed with new answers.

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An individual animal is born with a mutation that makes it slightly better at catching prey, and thus slightly more fit than the rest of the population. This does not mean that the rest of the population will now die off en masse. Instead, the frequency of that mutated allele may increase over generations in the population, since individuals carrying that allele are more fit and thus more likely to have offspring. As the frequency of the mutated allele increases, the frequency of the original alleles for that gene decreases. The mutated allele becomes fixed in the population, replacing previous allelic diversity for that gene with a single allele (a state which I'll call "zero allelic diversity").

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But here is the important part, that I fear you are missing: Even though the success of the mutated allele drops "diversity" for its gene to zero, the organisms within the population have NOT reduced the allelic diversity for the other 20,000 genes in their genome. Thus, fixation of an allele for one gene generally has neglible effects on the allelic diversity for the other 99.99% of the genome. Genes coding for any other trait the population have retained their allelic diversity.

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Is that clear?

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Yes, and helpful, but 1) how do you know "mutation" is the cause of the improvement in ability to catch prey rather than just a normal variation that normal Mendelian genetics operating on pre-existing genetic potentials could predict, that is, maybe a low-frequency allele's just happening to get expressed or perhaps a new combination of normally-occurring alleles at different loci, and 2) is this entirely theoretical or has it been observed?In any case my point has been that loss of diversity accompanies selection processes however caused and to whatever degree and in how ever many genes. If a trait is selected to the point that it works its way through a population, as you say the allele for that trait may become fixed without drastic events isolating it or otherwise selecting it. It's a tiny thing among 20,000 genes but it represents the pattern I'm talking about. The "processes of evolution" do tend toward loss of diversity, and ANY loss of diversity suggests the opposite of what the theory of evolution predicts.Or put it another way, the continuing diversity in the other 20,000 genes isn't producing evolution. Selection is what produces evolution, and selection reduces diversity.Again, the very processes that produce the improvements all the way out to actual "speciation" are accompanied by one degree or another of loss of diversity. As you are pointing out this doesn't have to be drastic, it is simply the way it happens at all levels. It is only when it is drastic that it becomes really visible and that's when you get "new species," not just a small improvement that works its way through a population but a whole new population based on many such improvements in many genes, or a type that is either selected for its fitness to its peculiar circumstances while others are destroyed by those same circumstances, or is accidentally created by bottlenecks and other disasters. In all cases the improvements /changes involve a reduction in diversity. It is just striking, it seems to me, that the "speciation" which is supposed to be the biggest proof of evolution, is in fact the case where the least diversity, least ability to change, adapt, continue to speciate, is possible.Now, apparently mutations counteract the effects of this process to a degree I am incapable of judging at this point, and I'm still very skeptical about that whole line of thought in any case.

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Also - you seem hung up on the bacteria-mutation example, which is a good example because monoculture allows the experiment to begin with zero allelic diversity. However, that is not the only example of documented mutations (I gave you another one - the Baldwin mutation that appeared in a closed population several years ago and results in hairless (and I think darn cute) guinea pigs.)

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How do you know that this is a mutation rather than a normally occurring allelic variation, however rare in the guinea pig population? Do you know this from its DNA? As I understand it a mutation is an accident that happens in the ordering of the DNA, switching positions of segments or deleting them altogether and the like, which usually produces either something neutral that doesn't help the creature or something that hurts it. Does this question make sense? Already, knowing that what genes do is shuffle a few chemicals around, it boggles the mind to consider that such shufflings correspond to actual phenotypic traits anyway, but that being the case a mutation just sounds like another shuffling of chemicals, the question being whether it is a mistake or a normal possibility given whatever laws govern the whole process-- and it is usually defined as a mistake or an accident.

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I worked in mouse genetics for several years - mouse geneticists have established "inbred" mice that are homozygous for every gene, which means they have zero allelic diversity, not unlike bacterial monoculture. Mutations occur on a very regular basis in closed populations of these inbred, zero-allelic-diversity-mice. A simple example is an inbred mouse strain that happened to have black fur. One day white-furred mice began appearing in the population, and the mutation that caused this difference was identified. Examination of the DNA of the great-grandparents of the white-furred mice did not reveal the same mutation. There was no source of the white-furred gene except for mutation, since there was zero allelic diversity at that gene in the grandparents of the mice with the mutation.

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Fascinating. So even at the extremes of least genetic variability variation can occur. This and the bacterium example do raise questions about what variation is. The probabilities of anything nonlethal occurring through random "accidents" just "seem" astronomical to my untutored mind. I can't think they are accidents but are obeying some law. It just boggles the mind that an "accident" such as mutation is said to be, can have such a pinpoint nonlethal effect. Deleterious effects, of course, are easy to understand as the product of accidental changes.But in any case, again, if a particular mutation, or oddball normal allele, any change in a gene, is selected by any process whatever, from the gradual dispersion through the population you describe above, to allowing the naked guinea pigs or white mice to breed only with each other, again you have the reduction-in-diversity effect which always accompanies selection, and again the question for the sake of the theory of evolution is whether life-enhancing or at least nonthreatening mutations outstrip these effects or not.This message has been edited by Faith, 02-16-2005 15:42 AM

Just snatching a moment to answer this:

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Now, apparently mutations counteract the effects of this process to a degree I am incapable of judging at this point,

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Then you should stop making concrete statements like the following:

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The "processes of evolution" do tend toward loss of diversity, and ANY loss of diversity suggests the opposite of what the theory of evolution predicts.

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No, because this is an independent process that is always true whether mutation occurs at a rate that can overcome it or not. ALWAYS selection decreases diversity. I haven't yet seen anything that contradicts it. Whether it is one allele that is becoming dominant in a population due to sexual selection, or multiple alleles of multiple genes altering the character of a whole population even more noticeably, or the reductions in population that are caused by natural selection or events such as bottleneck, ALWAYS selection processes decrease genetic diversity.The only question is whether mutation increases genetic diversity enough to keep the theory of evolution afloat.

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The processes of variation (called "speciation" by evolutionists) proceed by selecting out portions of the built-in potential for expression in the phenotype. The process ALWAYS involves reduction of the frequency of alleles and of genetic variability because for new traits to come to the fore new allelic combinations are required and you don't get these unless other allelic expressions are somehow suppressed -- or unfortunately in some cases actually killed.

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The process of natural selection works on the phenotypes. This can cause a reduction in variation but you mustn't forget that there is still hidden variation within the genotype which can continue on in later generations and not be expressed.

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Not "can" cause a reduction, but natural selection ALWAYS causes a reduction in variation by selecting some types at the expense of others. The change may be small depending on the severity of the selecting factors. And I don't forget about hidden variation at all -- it seems to me it is often generally forgotten in fact by some who seem to think all variation is produced by mutations. It is hidden variation that is selected FOR in many situations of natural selection: Poison variety of newt hidden in nonpoisonous newt population gets expressed phenotypically as newt population is eaten by newt-loving snake; antibiotic-resistant bacterium hidden in nonresistant bacteria population gets expressed after nonresistant ones are killed. In both cases while there may still be some variability left in either population, the overall effect is a reduction in variability as there are simply fewer alleles (or resistant bacteria). Some alleles (or bacteria types) may no longer exist in the population at all. Some variation may certainly remain in the new selected population but my only point is that although there may be equilibrium or very small effects from any of the "processes of evolution" (except migration and mutation), the effect is always going to be in the direction of reduction of variability.None of these processes increase variability to say the least, but an increase in variability would seem to me to be THE engine to drive "macroevolution" if it is really possible. And for the processes that DO increase variability, mutation and migration, all migration does is add BACK alleles that were previously cut off or reduced in a previous population-reducing event in that Species, restoring a pre-selection condition, and that leaves mutation as the only possible mechanism for increasing variability, and mutation is still a very iffy thing in my mind.Hey if I'm wrong I'll admit it, but I haven't seen it yet. Most of the answers have been about OTHER processes acting in the opposite direction, which actually come down to one, Mutation, and I've admitted that it MAY counteract the reductive effect depending on what it really is, its rate, its life-enhancing versus life-compromising qualities etc. etc. etc. -- but that's to my mind another topic. I just keep coming back to this, that the overall TENDENCY of all the other "processes of evolution" is reduction of variability, reduction of allelic alternatives, even to the complete elimination of allelic alternatives at the extremes of these same processes. The point is that the direction is never toward increase, except possibly through mutation, and I don't yet know what to believe about mutation. ALL of these processes, while called processes of evolution, all work in the very direction that makes evolution past a certain point impossible. UNLESS mutation can save the day.