What is the mechanism that prevents microevolution to become macroevolution?

Actually, your description of what happens during speciation is very wrong. So much so, in fact, that I'm surprised none of the biologists on EvC Forum have pointed it out yet.You stated: This is a very misleading way of putting it. The "genetic information" (whatever that is) in the population doesn't get "divided up". Rather, a statistical sampling of the available alleles in the population are sorted into the "new" population.Here's an analogy: say you have ten pairs of socks, nine brown and black pairs, and one bright orange pair (that your Aunt Gertrude gave you for Christmas). You take off on a business trip, leaving at 3 am. Since you are a true procrastinator, you didn't pack beforehand. Not wanting to wake your spouse/best friend/significant other up, you don't turn the light on as you throw stuff into your bag. You grab four pairs of socks at random. What are the odds you'll grab all brown or black pairs? Pretty good. Is it still possible you might have accidently picked up the orange pair? Absolutely. (With apologies to Richard Dawkins).Same thing happens when a population splits prior to speciation. A subset of all the alleles available in the pool will "sort" into the new population. This DOES NOT "remove" anything from the source population (except very possibly in extremely rare instances where a "unique" allele was the only one of its kind - like the orange socks). The same alleles are still available in the source population - and most of them are going to be present in the "new" population as well. This makes no sense whatsoever. Could you please expand on what you are attempting to convey, here? Thanks. This entire last bit is utterly wrong. In the first place, the population that splits off (to use laymen's terms) doesn't remove genes from the gene pool. It might - in absolutely exceptional circumstances - remove an extremely rare allele, but it most definitely doesn't remove genes.Beyond that, if the parent and daughter populations remain separated, they will both continue to generate new alleles. Mutation and recombination provide new variations/alleles, and differences in selection pressures or drift between the parent and daughter populations may emphasize or filter out these different alleles. Ultimately, the two populations - unless whatever barrier is removed - may differentiate enough that they can be identified as new varieties, subspecies, or even species. Even if there is some gene flow between the populations, it may be so reduced that the two populations follow separate or separating evolutionary trajectories. We see this in the existence of hybrid zones between different populations with limited gene flow (sort of "pre-speciation").Anyway, I doubt strongly whether any biologist worthy of the name would accept what you described. Primarily because that's not even close to what really happens.

Analogies are often unfortunately pushed beyond the limits of what they are intended to illustrate. In this case, my socks example was simply intended to demonstrate how a random selection of alleles statistically could end up in a new population. It's quite probable that you wouldn't end up with your orange socks in your bag - leaving that particular allele in the initial "sock population" - meaning no loss of "sock diversity".Yes, most populations can have a whole bunch of different alleles for particular traits (depends on what the selection pressures might be). Much of the diversity in alleles is likely due to recombination - although there's more than sufficient evidence to indicate that many novel alleles arise through mutation - the Frog's bacteria examples show empirical proof of this. If there's no particular advantage or disadvantage provided by a particular allele or suite of alleles ('cause you really can't consider one allele in isolation as most genes have multiple, often synergistic effects), the frequency of the particular alleles varies mostly via drift. In fact, even disadvantageous alleles may be retained in a population if they are linked to other normal or even advantageous alleles. It's kind of a trade-off. An allele or suite of alleles may be retained in a population in what is called ecological polymorphism (a discussion of which will take us beyond this thread).Anyway, when a population splits, an assortment of the existing alleles is contained in the new population. This could be a really skewed distribution (like the orange socks), or simply (like the brown/black socks) a representative sample of the existing alleles. If there's a normal representative sample in the new population, then the amount of divergeance between the two parent and daughter populations over time will depend on the relative level of gene flow between the two populations which is in turn based on several factors (which I don't think we need to get into unless you want). Well, there may not be any need for mutation to create new alleles, but nonetheless that's what happens. We see this in the existence of hybrid zones between two related populations. You mentioned ring species, and this is a critical issue in the formation of those rings. Adjacent populations - which start out with the same assortment of alleles prior to the split - diverge from each other, but generally remain "in contact". The hybrid zone between these populations gives an indicator of how much gene flow there is between them. Selection can cause linkage disequilibrium, but doesn't have to.One of the really good examples of ring species that has been extensively studied in this context is the Ensatina salamander complex. Since you've consistently complained that technical references are a bit much, I'll just cite one for others who might be interested: Alexandrino J, Baird SJ, Lawson L, Macey JR, Moritz C, Wake DB, 2005, Strong selection against hybrids at a hybrid zone in the Ensatina ring species complex and its evolutionary implications, Evolution, 59:1334-1347. The interesting thing about this article, although the overall research was not directly related to my point, is that they were able to go back through 20 years of genetic data (as well as performing their own analyses), that showed divergeance between two subspecies populations (E. eschscholtzii xanthoptica and E. eschscholtzii platensis). The further apart geographically the populations of these two subspecies were, the greater the genetic divergeance. However, there was a well-defined hybrid zone between the closest populations. The researchers were able to show linkage disequilibrium due to differential selection pressures on either side of the zone. The selection pressures against the hybrids permitted the researchers to demonstrate a gradual increase in incompatibility between the two subspecies at the ends of the species' range. In other words, we're looking at incipient speciation between E. eschscholtzii xanthoptica and E. eschscholtzii platensis - and where we draw the line is kind of arbitrary. A taxonomic "splitter" could conceivably declare the populations at the extreme ends of the range separate species.Making a long story short, there is sufficient genetic divergeance between the two "ends" of the E. eschscholtzii chain to indicate that a) the most distant populations do not simply represent a statistical assortment of existing alleles, and b) genetic diversity has not only not decreased, but has actually increased over the range of the species.Hope this clarifies why you might be mistaken concerning both what happens in speciation and why mutation - in the case of the example provided - is the only realistic option for how the genetic incompatibility arose at the ends of a chain of populations leading to speciation.

Okay, as long as we're clear on what the original analogy was intended to illustrate. Yeah, but this wasn't the main point of the paragraph. As I noted, if we see a bunch of novel alleles appearing in separated populations, there's only two possibilities: recombination in sexually reproducing organisms, or one or another form of mutation. The discussion Froggie has had on bacteria shows pretty unequivocally that mutation can produce novelty. I suppose you can still argue that recombination is a more important factor, but the salamander article I linked to shows that the differences in the most divergeant populations is NOT due to simply reshuffling existing alleles, and therefore MUST (unless there's some other mechanism you haven't revealed yet) be due to mutation. Precisely. The hybrid zone is the area where the gene pools of the populations are mixing. As far as it goes, you're correct on the combining of alleles bit. That's what a hybrid zone is, after all. However, "linkage disequilibrium" is a fancy term that basically means alleles in one population are not necessarily found in the second population. The greater the degree of disequilibrium, the more divergeant the two populations are genetically. When you have differential selection pressures operating on the two populations - and especially when you have selection pressures more greatly effecting the hybrids between them than either of the two source populations - you get disequilibrium. It's kind of like a "tightening of the gene flow pipe" to use another analogy. It reduces the gene flow between source populations. Since neither of the two populations in my example have reached the stage of true "species" yet, we would expect the two populations to have quite a bit of allelic overlap between them. However, the choking off of gene flow caused by selection disfavoring the hybrids means that the two populations are becoming more and more divergeant over time. From where did this diversity arise? Recombination can't explain it entirely. Gene flow from one to another can't explain it entirely, because the gene flow is being choked off. What's left? For biologists, what's left is mutation giving rise to novel alleles. I thought I did that. I'm at a loss as to how to address this. The mutation data including the specific loci the research addressed is contained in the article. For whatever reason, you have consistently stated that the articles we generally cite as reference for our claims are too technical, and you want a sort of "reader's digest condensed version". I have no problem with that request - and in fact discussed the relevant portions of the article in layman's terms. However, given that, I can't see how you can demand a simplified version that covers the relevance and at the same time demand the detailed technical evidence. It's there, in the article. I've simplified things about as much as I can. If you want the hard data, feel free to peruse the article itself. Otherwise, you're just going to have to take my word for it . Demonstrated, as noted in the article, by the fact that there is a somewhat different set of alleles in each source population. That's what makes them distinct subspecies in the first place. Make up your mind, Faith. Either you want the technical details, or you want a simplified version. Maybe Percy can make sense of this - he's generally very good at that - much better than I am. The mutation evidence is contained in the article. If you don't want to get technical, I'm not sure how you can accuse me of failing to provide evidence. In point of fact, I DID provide the evidence. My discussion was - at your request - simplified and as non-technical as I can make it. I'm really not sure how you think you can have it both ways. The evidence is there. I've provided the layman's explanation. I guess it's up to you to make the connection.

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.

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

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.

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?

Hi Nosy. Don't get confused here. I was talking about overlap in the sense of shared alleles between populations, not genetic similarity between species. I'm not sure there's much if any correlation between the two concepts.

I'm aware that this is your contention, but MJ was quite clear that he believes entire genes are lost during speciation. I pointed out the differences between your stance and his in the post to which you are responding. Of course, you have yet to provide any example which indicates that what you are suggesting actually occurs. Now would be a good time. Find me an example in a living population where this has ocurred. And you have an example of the genes dying or whatever? I have given you examples of increasing genetic diversity in sister populations, which would tend to disconfirm your hypothesis. You need at this point to provide an actual counter-example. Otherwise, your argument stands refuted.

Almost certainly true in some cases. On the other hand, as the second article I referenced quite clearly explains, there are ways of determining the relative amount of time that different populations have been separated. In these cases, it's not a matter of frequency distribution, but rather novel alleles that are quite distinct between the two populations - and thus had to "appear" after the split. Sure, and that's one of the things that the researcher's look for. They're examining the genetics of both populations. If it were simply a matter of unexpressed alleles, that would be obvious from the molecular data. Since that isn't the case, then the new alleles must have appeared de novo in the two populations. It's not a question of expression, it's a question of novelty. Recombination simply doesn't account for the divergeance. I probably wasn't clear. Isolation - from whatever cause, but in the specific example of the Ensatina complex it's natural selection operating against the hybrids in the contact zone - is what prevents gene flow from mixing the genetic material between populations. It is indeed what is required for speciation, but is not sufficient to explain novelty in and of itself. If you believe otherwise, you need to explain, preferably with actual living examples, how this can occur.

Actually, I have been demonstrating specifically what's wrong with your arguments. I've even used specific examples from actual populations that show you are very wrong in what you are stating. I am not making up stuff - I'm giving you what has actually been observed. Now it's your turn - show your examples and stop claiming you haven't been provided with the information you requested. You are certainly free to show where I'm wrong in my interpretation, but to simply hand-wave away the discussion by claiming I haven't responded is not going to be conducive to a productive discussion. Time to respond substantively, Faith: What data from the Ensatina studies actually supports your contention? No, you haven't actually shown it, merely asserted it over and over. You are at least trying (with the idea about allelic and - in MJ's case, genomic - reduction), which is why I'm willing to continue this discussion in spite of your demeaning rhetoric. Your task now is to show this reduction actually occurs, using specific real-world populations.

Don't bother on my account unless you are prepared to offer substantive rebuttal to the observations I've outlined, or alternatively a valid counter-example.

It doesn't usually work that way. It CAN so happen that an exceptionally rare allele is either retained in the parent population or makes it's way exclusively to the daughter population. However, what normally happens is a distribution of existing alleles to both populations. In other words, unless we're talking about a unique individual organism with a unique set of alleles that becomes a founder all by itself, both populations are going to have a random sampling of all the existing alleles. Statistically, there could be a skewed frequency distribution simply by sampling error. It depends on how big the source population is, how big the daughter population is, how much gene flow exists between the two, and how many rare alleles there are in the source population. Among other things. Bottom line: speciation does NOT NECESSARILY lead to loss of genetic or allelic diversity, all other things being equal.Added by edit: Nor would anyone else. On the other hand, Faith's argument doesn't refer to comparing elephant and human genetic diversity. It revolves around her claim that two adjacent populations of the same species will ALWAYS lose genetic diversity as they differentiate to the point they become separate species. This is where her argument falls flat. Doesn't happen that way. If anything, genetic diversity INCREASES due to speciation and the processes leading up to it. Edited by Quetzal, : No reason given.

Because they are discussing divergeance in genotype. We're not talking here about phenotypical differences - they're using 16s and mtDNA sequence differences between the populations to show that genetically these populations are diverging. Some of them, indeed, as in the second article I linked to, are very different from each other. Not just 'cause one population has different stripe patterns, or whatever. Well, for one thing, the greater the geographic distance between the populations, the less gene flow there is - which calls into question your contention that the differences seen are due only to recombination or some kind of skewed frequency distribution. In addition, the most distant populations (from each other) contain novel alleles not found in the populations closer to each other, which leads to the question: "Where did these sequences come from?". How about the very first line of the abstract?:

quote:

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The analysis of interactions between lineages at varying levels of genetic divergence can provide insights into the process of speciation through the accumulation of incompatible mutations.

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AND...

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We compared the genetic structure across two transects (southern and northern Calaveras Co.), one of which was resampled over 20 years, and examined diagnostic molecular markers (eight allozyme loci and mitochondrial DNA) and a diagnostic quantitative trait (color pattern).

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The full article goes on to discuss - in some detail - the reasoning behind this. Since the full article isn't on-line (unless you have a subscription), you can see a similar set of research in the PNAS article I provided (which is available free). I can also provide other, similar, references if it makes you feel any better. The point is molecular/genetic level studies of diverging populations (incipient speciation) show genotype differences that simply cannot be accounted for by changes in frequency distribution of pre-existing alleles. These are not hypothetical examples, but examinations of real-world populations. You stated things along these lines several times, so I'll ask you again: how does "reduced genetic diversity" create "new phenotypes"? This contention is so completely counterintuitive that I'm half convinced I'm missing something in what you're trying to say. So, actually reading the research is probably out of the question? But you won't take my word for what the articles say when I try and use simpler terms to explain it? That being the case, I ask you again "Where do we go from here?"

If you think he's right, perhaps you can pick up his dropped gauntlet and provide one, single, solitary real-world example where this has occurred? If this is the case, perhaps it would be better for you to hold off on critiquing research you seem to be admitting you don't understand? Or even forebearing to argue against the conclusions of the folks who are actually researching the subject - at least until the putative "scientifically knowledgeable creationist" appears?You've put your finger on one of the most frustrating parts of the EvC debate. Someone who admits they don't understand the science and can't be bothered to learn it feels free to utterly dismiss its findings, and in the same breath refuses to accept someone else's simplified explanation. Very strange, and something I've never understood. Perhaps you can explain why this makes sense to you. Perhaps, but if so it's "theory" (in the common-usage sense) based on absolutely nothing except imagination. No, I provided a simplified explanation of what the article contained, as you requested. The specific molecular data that led the researchers to their conclusions is contained in the article. This is kind of a corollary to the problem I mentioned above. It's perhaps a failing on my part that I can't see how to communicate the conclusions in terms you'll accept without providing the technical details you have stated repeatedly you don't understand. When you accuse me of failing to provide the technical details, in spite of the fact that they are contained in the reference, but when any kind of technical detail is provided you state you don't understand them, I'm afraid we have a terminal case of (as so eloquently expressed in the movie "Cool Hand Luke"), "a failure to communicate".I'm open to suggestions. The studies aren't dealing with phenotype - they deal with the molecular and genetic data (i.e., genotype). When I speak of diversity, I'm talking genetic diversity based on molecular data - not phenotype. I'm not the one making the claim. Ask MJ - it's his assertion. You tell me...