What is the mechanism that prevents microevolution to become macroevolution?

I don't have the time right now to walk you though the experiment, but let me just jump to the end: I'm talking about experiments that are designed to prove that mutations are a source of genetic diversity in populations. The experiments accomplish this by eliminating all sources of diversity except mutation, and then monitoring the population's subesquent rise in genetic diversity. Yes. If, later in the population, we find bacteria with alleles that are different than the original one, we know those arose through mutation, because we've designed the experiment to eliminate all other sources of alleles. Further proof is the fact that we can add chemicals that promote mutations - mutagens - and watch the diversity climb even faster.If this isn't enough I'd be happy to try to explain again, or answer any other questions. We can even go to a specific experiment if you like, but I warn you that it will be quite detailed and technical.

It seems to me that we have a fairly simple and elegant way to test Faith's hypothesis.If the world is young, and if there was some Fall, and if Genetic diversity has been decreasing, then we should be able to see remarkable changes over even short periods of time.Considering humans initially.If we look at the DNA from a human from say 5000 years ago, and one from say 4000 years ago, we should see an enormous difference. If we look then at one from 3000 years ago, and 2000 years ago and 1000 years ago and today we should see an enormous difference at each step, a decrease in the size of the genome.This should hold true across all species sampled.If we look back a little further, say before the Fall or before Creation, we should see even bigger differences.

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Aslan is not a Tame Lion

A question to Quetzal, crash, Faith, anybody who knows enough to answer: If an allele exists in a population, isn't it expressed in some individuals? Would it even be possible for a split like this to occur and have different phenotypes expressed? Since the pool of genotypes is exactly the same.The only thing I could think of is that if the environments were different, different chemical reactions might be altered (for example, if I remember correctly, some fur will only become white in cold environments, and is brown if the animal with the fur develops in a warmer environment) and the same pool of alleles might produce different phenotypes. Do we have any examples of such environment / genotype interaction being so severe that organisms with identical genotypes would be considered different species?I'm at the edge of my understanding, but I hope this makes sense. I know that, given mutations exist, such an experiment might not be possible.I'm just surprised nobody addressed this point, as it was beyond anything I've read. As far as I knew, given similar developmental environments, the changes in the phenotypes between the two separated groups could not be due to different frequencies of alleles, since those very alleles must be present (and expressed) in the original population.Thanks!Edited by Ben, : Changed subtitle and message icon

Well, a lot of that's been done. The Ensatina article shows quite clearly increasing divergeance between the two populations. If there's some kind of decrease in the genetics as the "strong claim" version of Faith and MJ's idea holds true (that genomes are reduced during speciation), then the genetics of the two salamander populations should show it. They don't. In fact, increased diversity is the case as different alleles exist in both populations with no apparent loss in genome size (MJ's claim), and insufficient gene flow/mixing for recombination to account for the novelty (Faith's claim).This isn't the only example, either. See, for instance, Jiggins CD, Mallet J, 2000, "Bimodal Hybrid Zones and Evolution", Trends in Ecology and Evolution, 15:250-255 (available cached here. Also see Via S, 2002, "The Ecological Genetics of Speciation", Am Nat 159:51-57 (I don't know if it's on-line somewhere). Anyway, there's a bunch of research out there. The entire line of argument is bogus.

The increase in diversity is observable at the level of the population in that it consists of a much greater range of genotypes than would be observed if it was all one gene pool.Diversity at the level of the population can arise in many ways other than simply an increase in the number of alleles occurring at specific loci.
For example, the linkage disequilibrium Quetzal refered to refers to a multi-locus effect.Lets assume 2 loci, A and B, with two alternative alleles at each, A/a and B/b. Assuming diploid sexual reproduction, meiosis yields four types of possible gametes:AB
ab
Ab
abThe first two are referred to as 'coupling' gametes and the second two as 'repulsion' gametes.Now, if there is no linklage between these alleles (or meiotic drive of any kind), we expect these gametes to be formed at equal rates and be present in equal proportions (.25) in the population.When there are statistical deviations from the .25 frequency (when coupling gametes outnumber repulsion gametes or vice versa), this can be considered evidence for selection favoring one type of gene combination over another. Thus AB and ab may be the most advantageous gametes to produce in one particular population, and aB and Ab the most advantageous in another population. These populations are then different, i.e. they are genetically 'diverse' relative to one another even though there is no increase in the number of alleles, or even any difference in the actual alleles possessed by them.Hope this helps,EZEdited by EZscience, : to change title...

At the initial stage of separation (i.e., first generation), no. When one population becomes two, the selection of alleles in the new population is probably a statistical match with that of the parent population. Any phenotype in the daughter population has to have existed in the parent. However, the frequency (distribution) of a given allele or set of alleles in the daughter population may be quite different than the frequency of the same alleles in the parent. That's what that orange sock represents in the analogy I gave Faith. It's entirely possible that purely by chance a rare allele might be over-represented in the new population. I can't think of any example where an immediate new phenotype pops up following some kind of isolation, however. Doesn't mean it couldn't, I've just never heard of such a thing. Subsequent generations, however, with both recombination and mutation acting to develop novelty, coupled with different selection pressures in the new habitat, remove all bets. Correct. However, such drastic differences in phenotype imply drastically different environments (hence different selection pressures). When we're talking about adjacent populations moving toward speciation, on the other hand, even though the microhabitat each population/subpopulation lives in may have different pressures, it's generally not going to be a radical change from one to the other. If the species dispersal capability or some other aspect decreases the gene flow between the populations, there will be a gradual (or rapid, for that matter - depends on many factors), increase in the genetic divergeance between parent/daughter. In other words, the phenotypic difference between them is going to be indistinguishable in the first generation, and only later does the accumulation of genetic changes from whatever source coupled with differences in selection pressure lead to substantial phenotypical change. Yes and no. The different allelic frequencies between the two populations may cause them to not really resemble each other very much if the daughter has a vastly different distribution of alleles. It's only when there's some isolating mechanism that limits or prevents gene flow between the two that we start to see the two populations really genetically diverging (evolving) on separate trajectories, as each starts accumulating unique alleles in response to their own particular selection pressures. Even if the pressures are mostly the same, as long as there is sufficient isolation, we'll start seeing novel alleles (and hence divergeant phenotypes) appearing.Hope that made sense.Edited by Quetzal, : fixed weirdness in the UBB

While speciation and bottlenecks are quite interesting topics, can anybody explain me how does that relate to the mechanism that prevents microevolution to become macroevolution?
I don't even know what the heck is Macroevolution.
can anybody explain me that?

Sure. In a nutshell, MJ and Faith together and separately are using misunderstandings of speciation and bottlenecks (etc) to indicate that "here there be mechanisms". Explaining what really happens in those two cases is necessary to show the putative mechanism, while at least theoretically existing (and I'm being generous), doesn't lie in either of the two. Neither does anyone else. The term, while used in paleontology, "doesn't mean what [they] think it means" (with apologies to a rather fun movie line). Some creationists claim it relates to speciation, others claim it has to do with "changes between kinds", others relate it to their claim of the non-existence of transitionals, still others try and link it to somekind of saltationism between classes, orders or whatever. It's all very confusing.

The terms aren't used all that often in biology but I have seen them used. They are defined as:microevolution: any changes to the population genetics that does not produce a speciation event.macroevolution: changes producing speciation and from then on.Then nature of the changes may be exactly the same; that is, any one of the number of different kinds of mutations may occur and not be sufficiently different to produce speciation but exactly the same kind of mutation (simple substitution etc) might happen to force a speciation.In actual practice, of course, single genetic changes do NOT produce successful speciation. Even if they produce a successful individual a "real", total speciation would (as in the oft given creo strawmen) an individual with no one to breed with.This has, however, still be observed in plants that don't kneed a breeding partner.It isn't, for the most part, the genetic changes that allow speciation to happen. This is way it really is of value to discuss micro and macro evolution. It actually does, most of the time, require some other mechanisms to allow speciation to occur.The most obvious is geographic separation. With a population split into two between which there is no (or very little) gene flow the ongoing genetic changes which have to happen are not "smoothed" out but rather can accumulate in each of the populations.Over time the accumlated differences gradually reduce the likelyhood of the success of any pairings from the two populations. The time frames can be very short for some organisms (generations) and, more often, very long (millions of years) for others. Eg tigers and lions have not yet completed the total separation.The accumulated differences are, just like the changes of microevolution, the same set of kinds of mutations that always occur.There is no difference in the nature of the changes on either side of the line. The only difference is that gene flow is not (for some reason) available to keep the populations more or less homogeneous.This is what the "kind" folk don't seem to grasp or deal with. They look at the over all phenotypes but don't see that the genetic changes between even rather widely separated branches of the tree of life just more and more of the same thing.I'm not totally sure but I think there has been a few decade old history of the creationist idea of "kind". Once upon a time it was a species just as it is clear the bible means. As speciation events became demonstratable they backed "up" the taxonomic chart and have also gotten very fuzzy. They've been forced high enough up that humans and the other primates become one kind so they start to waffle. It is most amusing to watch.Kind must be defined in terms of genetics but there isn't anything there to point at.

I think Faith is proposing that speciation that we see is part of microevolution and is explained by allele frequency changes of isolated populations. She's denying that mutation necessarily have a role in this "microevolution", i.e. adaptation to new environments and species-specific changes due to isolation.By doing so, she's trying to cut the bridge between such adaptation and large-scale "macroevolution". The bridge in evolutionary theory is mutation; Faith is saying microevolution won't accumulate and lead to macroevolution because microevolution can be explained by allele frequency changes ONLY and thus cuts out the bridge to macroevolution--mutation.Well, whether I can explain it or not, I think the discussion is on-topic.

OK, I guess something in what you said wasn't clear to me. Anyway, I'm going with the sexual recombination view of it as the most common way this happens. Mutation remains a big question mark, not that it doesn't happen, but that it very seldom does anything desirable from the point of view of the species. I know there are different kinds of mutations and I'm still open to the possibility that maybe some of it is beneficial, but given the facts that sexual recombination produces all the necessary changes to speciation without it, and that most of its effects are either null or deleterious, and that so far only about a dozen putatively beneficial examples have been given, it's still very much in doubt in my mind. I did not see that anything said about that example showed that mutation had to be involved. You said it was involved but haven't proved it. From what I read, reshuffling existing alleles can explain it just fine. This is what one would expect from the ways alleles get shuffled in the normal course of things. Gene flow between the two would keep supplying diversity, {edit: that is, resupplying it, recombining formerly lost alleles, but over time this tends to homogenization rather than divergence} but otherwise, without the gene flow, the separated populations would develop differing phenotypes based on their different allele frequencies, which might include the absence of some alleles as well. Since I think the {EDIT: following above }paragraph is where our views most sharply diverge I'm going to respond to pieces of it as I go: Yes, clear. OK OK. Perhaps I should adopt the term, since this is the very situation my argument has specifically focused on all along. That is, while the divergence between the populations MAY be simply a reflection of new allele frequencies without any actual loss of alleles, and speciation can occur even with this situation, or at least be approached by it (since a change in the frequencies will produce new phenotypes), the actual loss of alleles means a loss of genetic diversity; that is, there are fewer allelic possibilities in at least one population -- and possibly in both as they may both have lost alleles to the other in the exchange at the population split. Fewer alleles means reduced genetic diversity and it may also possibly mean a more rapid path to speciation. Exactly, as I've been arguing. And this is most likely to have been brought about by the migration of a small population, which is less likely to contain all the alleles in the original combined population. Well, many things may bring about this disequilibrium, as I've been arguing for months. Migration of a small portion of the population as I mention above may eliminate quite a few alleles from the new population; bottleneck certainly does it, and founder effect -- those are the most drastic routes to allele elimination = reduced genetic diversity = dramatic phenotypic divergence = speciation. Natural selection may sometimes exert just as drastic an effect by favoring one allelic set while all the others in the population die. In fact all the "evolutionary processes" that split populations can bring about this condition of allele loss. So does geographic separation all by itself in some cases though, as well as all the other processes I just listed. But OK so does this more complex scenario involving the hybrid zone. Yes. However, this raises an interesting side question about what degree of allelic overlap may continue to exist between two populations that have clearly speciated away from each other. Oh but I do not see why not. This has been asserted many times but only asserted. Mutation seems to be assumed in this scenario but it has not been proved to have a part in it at all. Since mutations occur frequently I can't deny that they've occurred, but their role in this scenario of divergence has not been shown.I think you are confusing diversity of phenotypes with diversity of genotypes. {EDIT: Should not have used the term "genotypes." This confuses the issue. I mean diversity of allelic possibilities or many allelic possibilites.} Great divergence in the phenotype may be brought about by a change in allele frequencies, but an even greater one by a complete loss of alleles formerly present in the formerly combined population. It is the reduction of alleles that leads to diversity of phenotypes. Less genetic diversity = greater phenotypic divergence from the original population. Reduced number of alleles = reduced genetic diversity = still the main route to speciation. Gene flow would never account for divergence at all, it tends to homogenize rather than diversify. Yes, I believe you have confused divergence of phenotypes with genetic diversity. It is the loss of genetic diversity that produces the divergence of phenotypes in the ordinary course of sexual recombination.===
Sorry if you did indeed abstract the technical paper. I thought you'd said you weren't going to but simply cite it for others, and then went on to mention one aspect of it. My mistake. No, I'm not asking for the detailed technical information, just a clear discussion of the content of the paper. Apparently this has been covered so no problem. But this is precisely the situation I've been addressing from the getgo in my own arguments, this different set of alleles in each source population. This is indeed what makes them distinct subspecies, and, as I've been arguing, this is most likely brought about by the loss of alleles between the two of them. This means decreased genetic diversity. This is what brings about new phenotypes and, at greater degrees of divergence, even new species. Mutation is not needed in this scenario at all. I'm not arguing that you haven't provided evidence. You've provided a great deal of evidence. But you haven't grasped that the evidence you've provided does not support the idea that mutation is necessary at any point in all the situations you've described. It actually supports what I've been arguing for, that speciation is the result of reduced genetic diversity, which is the opposite of what is needed for evolution. Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

You got a lot of it, Ben. Thanks. But I'm saying more than this. I'm saying that the very processes of microevolution lead to what is called speciation, but that speciation is bought at the price of reduced genetic diversity through the reduction of alleles in the population, so that you end up with the scenario that directly contradicts evolution and provides the defining limits of a Kind. The actual processes that are happening toward speciation, or phenotypic divergence, are brought about by, or characterized by, a loss of genetic diversity: Speciation = reduced genetic diversity. No way you are going to get evolution out of that formula, which reflects the actual reality. The degree and quality of mutation needed to overcome this inexorable trend is incalculable.Yes, this is very on-topic. This has been my argument from my first thread at EvC, Natural Limitation to Evolutionary Processes or however it was titled.{Edit: I have to keep repeating the formula in various forms:Phenotypic Divergence (first step to speciation) is the result of Decreased Genetic Diversity.Speciation and Evolution are at odds with each other. The more speciation the less possibility of evolution.Again: Barring of course a prodigiously huge amount of beneficial mutations, and this would take some thinking about anyway.Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : No reason given.

interesting strikeouts. The question is whether it must always result in this. I don't think so. What I'm arguing is that this is one case where they are related, there are others I give where they aren't. It may make no selection of alleles at all. Think of a population of 10,000 individuals and 1 in 10 survive a random catastrophe by luck not genetics\selection -- they just happened to be in the right place.The distribution of alleles in both populations is the same, both in kinds of alleles involved and in their relative number -- say a bell curve distribution -- so that the shape of the distribution is the same, just the total population is reduced. The result is the same degree of diversity (the same bell curve) just fewer individuals.The species will still have the same distribution of alleles. Speciation without bottleneck, bottleneck without speciation, therefore not necessarily related. It's like a grid: Any population can fall into any one of those four quadrants at different times. No, mutation has no bearing on whether population fall into one quadrant or another -- there are other factors that affect which quadrant they are in that can override any relation between speciation and bottlenecks. The only way that a strict relationship could exist is if two corners of the grid could not be populated with different species at different times. It does NOT reduce the diversity in the total population of life on the planet, and it allows the now separated populations to expand their population diversity with subsequent mutation, thus ending up with more diversity than the total population of life on the planet started with: that is the issue. That is the other problem with the supposed relationship - in some cases {A} can happen before {B} and in some cases {B} can happen before {A}. That makes it hard to show that {A} causes {B} eh?

some speciations cause bottlenecks in daughter populations

some speciations don't cause bottlenecks in daughter populations

some bottlenecks cause speciation

some bottlenecks don't cause speciation

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Conclusion: bottlenecks and speciation are not necessarily related events.

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Enjoy.

Thanks for the detailed reply. In the interests of time, I'm going to focus on those bits of your post where the divergeance ( ) is greatest. If you think there's another piece that I should also address, please let me know. And: In some cases you'd be right. However, in the specific example provided, the effect of natural selection working against the hybrids in the contact zone means that the two subspecies have limited gene flow across their range. If the populations contain alleles different from each other, then recombination cannot explain their existence. This isn't a founder effect we're looking at here. This is a fairly straight-forward example of two populations diverging over time. I can't "prove" it to your satisfaction without reference to the technical literature, which contains the data you are asking for. Just the way the thing works.Beyond the article I cited previously, I'd like to reference another that contains even more data that "proves" that mutation is a significant cause of the divergeance between Ensatina populations: Wake DB, 1997, "Incipient species formation in salamanders of the Ensatina complex", PNAS 94:7761-7767 (full article online here). To give you a synopsis, the researchers used genetic markers not only to show divergeance in the different subspecies, but also used population genetics to show that some of the subspecies had been isolated from each other for a long time, and that several of the subspecies show multiple recontacts. They can literally trace the number of times gene flow was interrupted, regained, and then interrupted again. The article goes a very long way toward showing the new alleles that appeared when the populations were isolated could not have been simple recombination of existing alleles. The separated populations didn't just have different frequencies - they developed different alleles for the same loci (called allozymes). The only possible way this could have occurred is through mutation. Again, if you're unwilling or unable to read the article, then you're just going to have to take my word for the fact that the science is solid. If you don't believe me, you'll have to ask someone else to look at the article and verify (or disconfirm), my explanation of what the article contains. Except there is no loss of alleles, at least without subsequent replacement by other, novel alleles. When two populations are separated, we see new alleles appear. That's the piece you keep missing. The technical literature is quite explicit and clear once you look into it. You are correct that in some cases a small population may not contain all of the alleles that are present in the parent population. That doesn't translate to "loss" of alleles, however. The original alleles are still present in the parent population, and a subset of these - especially in founder situations - are present in a smaller population. The distribution, however, will tend to homogenize if there is sufficient gene flow between parent and daughter populations as you know. Only when gene flow is interrupted or lessened, as in the first article I cited, will the two populations start diverging. Over the generations, these populations will start showing up different alleles that weren't originally present. Recombination can explain some of the new stuff, but not all. One piece of evidence that allows us to conclude this is that the older the split, the more divergeance exists, and the more likely it is that the two populations will have very different alleles (at least at certain loci), whereas populations that have only recently separated will have fewer differences. It's not just frequency, it's novelty - stuff in one population that doesn't exist in the other. The point is speciation doesn't "eliminate alleles". They all still exist. Some may disappear from a small population due to drift, but we're not talking about daughter populations losing alleles - we're talking about daughter populations with different alleles than the parent. Big difference. Biologists have answered the "where did the new alleles come from" by postulating mutation. Experiments such as crash has been talking about show that mutation can generate novelty. In the absence of any other explanation, mutation remains the most likely candidate for what we observe in "wild" populations. Depends on what species, what selection pressures are present, how long since the isolation/speciation, etc. It hasn't been asserted - it's been observed. The data is in the references (as well as many others) I've cited for you. I've given you the $0.10 version of the articles. If you want more, you'll need to wade through the data and discussion yourself. However, until you do (or until you find someone who'll show me I'm grossly misinterpreting the articles), I'd appreciate it if you'd stop claiming you haven't been given the information you've requested. I'm confusing things? Too funny. Some phenotypical divergeance can be expected to occur if frequency distribution is skewed between two populations of the same species. Hell, phenotypical divergeance existed within a given population. We can identify geographical races within species, varieties, subspecies, etc, usually by phenotype but demonstrated genetically. You're the one that seems to be confused here.You need to provide some kind of example or documentation on your continued claim about "less genetic diversity". I've demonstrated the opposite with the articles I've cited. Reduction of diversity ONLY happens in founder cases where a tiny (often a single organism) forms the basis of a new population. Moreover, your argument isn't even self-consistent: you keep claiming that recombination creates the novelty we see between diverging populations, but here you are claiming that, in addition, creation of novelty actually reduces diversity????? New alleles created through recombination - which means greater genetic diversity - is the same as elimination of alleles removing genetic diversity. Very strange. Thank you for at long last admitting that I've provided you evidence. The downside is you apparently haven't grasped that the discussion of the role of mutations is in fact contained the articles you won't read. I've stated that the allelic differences among the subspecies of the Ensatina complex are due to mutation, and cited the references from which I derive the information - you don't believe me. We are, apparently, at an impasse. Any suggestions?

Does the 96% similarity between us and chimps suggest that a very high degree of overlap can remain for a long time?