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Are Fitness Valleys Too Deep?

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Over at PhysOrg.com, there’s a new news item about a computer program that was run simulating evolutionary characteristics. What’s interesting about it are two things: (1) who the people are that are running this program, and (2) one of the results—which is being downplayed, it would seem.

First, one of the people associated with this new program is Christoph Adami, who, with others, gave us the touted “Avida” evolutionary algorithm. So, this isn’t just anybody doing this simulation.

Second, here’s what the lead author had to say:
“These fitness landscapes simply could not be traversed with mutations that did not interact.”

This wasn’t a ‘main conclusion’ of the study; however, I don’t know about you, but this sounds to me like any ‘single’ mutation cannot get you across any fitness valley, and, therefore, seems to rule out having a single mutation ‘sweep’ across a population to fixation.

IOW, without epistatic effects, evolution cannot move forward. This is unexpected. It makes simple neo-Darwinian evolution that more complex with more hurdles to get over. And, it is another nail in the coffin of neo-Darwinism. That is: “Another day, another bad day for Darwinism.”

Comments
Hi. Just want to clear up a few things. If anyone feels like discussing evolutionary theory, I invite you to take it to my own post about my paper. I will not be posting on this thread again. #5 For the record, that is indeed my article quoted. #46 If the fitness landscape (really, fitness function) has a steep slope, it means that a small change in genotype (or phenotype) can change fitness a lot. I.e., your 1) is correct, while 2) is not. #50 and #54 One can talk about both individual and population fitness. In simulations (as the one the OP is about), fitness is known, and it determines the probability that the individual will have offspring. In biological organisms individual fitness can be measured in different ways; for bacteria it is often done by measuring the growth rate (yes, of an individual). Other proxies for fitness are used, such as the number of offspring. #60 Neutral mutations do not "drift across the fitness landscape," as you seem to correctly imply. Drift refers only to fixation or loss of mutations or alleles. however, part of the fitness landscape (really, think of it just as a function) may be flat, so that a population in a flat part of the fitness landscape can experience mutations that are neutral: changes in genotype/phenotype results in organisms with the same fitness, and so those changes are equal in fitness, and can thus drift. P.S. I submitted this comment on 7/2, but it didn't make moderation.bjornostman
July 4, 2011
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Elizabeth, Well, that does make sense as regards graduality. Thanks for this. Anyway, this graduality must terminate at the point of the new species emerging. So the main claim remains that speciation has NOT been observed. The effect of RM+NS is really there BUT it is marginal as has been shown experimentally (see "The Edge of Evolution" by Behe). And that I find very convincing. It is there to enable a certain degree of adaptation of species to make them survivable. Unfortunately, what evolutionists keep saying extrapolating the results too far to include speciation or formation of higher taxonomic entities, I find implausible. In theory it may look nice (but even that is questionable and the theory becomes clumsier as new data comes in). Unfortunately, as soon as the talk is down to business, Darwinists fail to present convincing evidence.Eugene S
July 4, 2011
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oops messed up the tags. Penultimate and antepenultimate paragraphs above are Eugene S's words, not mine! Sorry!Elizabeth Liddle
July 4, 2011
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Eugene:
Elizabeth, I just remembered a friendly argument between two biologists (both of University of Manchester, UK), of which I was a witness. One of them insisted that the definition of “species” should include not only the aspect of just being able to produce offspring but that the offsping should be big enough in size. We can have a mule but does it mean that horses and asses are one species?
I don't think the category is a binary one, Eugene! i.e. I don't pairs of populations are cleanly "either" the same species or "not the same species". Speciation is a gradual process, and even many generations after speciation began, and the two populations no longer interbreed in the wild (lions and tigers, for instance) hybridisation (even with fertile offspring) remains possible. So I'd say it was true to say that speciation processes have been observed, but that "complete" speciation processes (if that requires that hybridisation with fertile offspring is impossible) hasn't, because, clearly, as the existence of ligers and tigons shows, hybridisation can still occur many generations later. By the way, as far as I remember both agreed that speciation has NOT been observed. I am afraid that, as is unfortunately usual with Darwinism, actual observations are in this case interpreted in its favour. But I may be wrong. BTW, interesting paper here, not sure if it's open access or not: http://www.sciencedirect.com/science/article/pii/S0169534707002868Elizabeth Liddle
July 4, 2011
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Regarding #65, I meant to say "in numbers", of course.Eugene S
July 4, 2011
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Bornagain77, Many Thanks for this. I would have thought so.Eugene S
July 4, 2011
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Elizabeth, I just remembered a friendly argument between two biologists (both of University of Manchester, UK), of which I was a witness. One of them insisted that the definition of "species" should include not only the aspect of just being able to produce offspring but that the offsping should be big enough in size. We can have a mule but does it mean that horses and asses are one species? By the way, as far as I remember both agreed that speciation has NOT been observed. I am afraid that, as is unfortunately usual with Darwinism, actual observations are in this case interpreted in its favour. But I may be wrong.Eugene S
July 4, 2011
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Eugene this recent summary paper on fruit flies may be of interest: Experimental Evolution in Fruit Flies (35 years of trying to force fruit flies to evolve in the laboratory fails, spectacularly) - October 2010 Excerpt: "Despite decades of sustained selection in relatively small, sexually reproducing laboratory populations, selection did not lead to the fixation of newly arising unconditionally advantageous alleles.,,, "This research really upends the dominant paradigm about how species evolve," said ecology and evolutionary biology professor Anthony Long, the primary investigator. http://www.arn.org/blogs/index.php/literature/2010/10/07/experimental_evolution_in_fruit_flies ============== f/n Darwin's Theory - Fruit Flies and Morphology - video http://www.youtube.com/watch?v=hZJTIwRY0bs ...Advantageous anatomical mutations are never observed. The four-winged fruit fly is a case in point: The second set of wings lacks flight muscles, so the useless appendages interfere with flying and mating, and the mutant fly cannot survive long outside the laboratory. Similar mutations in other genes also produce various anatomical deformations, but they are harmful, too. In 1963, Harvard evolutionary biologist Ernst Mayr wrote that the resulting mutants “are such evident freaks that these monsters can be designated only as ‘hopeless.’ They are so utterly unbalanced that they would not have the slightest chance of escaping elimination through natural selection." - Jonathan Wells http://www.evolutionnews.org/2008/08/inherit_the_spin_the_ncse_answ.html#footnote19bornagain77
July 4, 2011
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Elizabeth, In addition to #62. I mean by speciation the emergence of populations unable to interbreed. According to my very limited knowledge, experiments on fruitflies end up in (a) dead flies, (b) severely mutilated flies unable to produce any offspring, (c) healthy flies with minor differences from ancestry where the scale of these differences does not lead to reproductive isolation. Maybe I am missing something...Eugene S
July 4, 2011
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Elizabeth, 1. Could you point to papers showing speciation of fruitflies please. What I read as of 2004 strongly suggested that poor fruitflies remained fruitflies: healthy, mutants or dead. Even a fruitfly with its legs sticking out of the eyes is a fuitfly. So no speciation was observed. Maybe I read the wrong papers. When I said "in earnest", I meant the fuzziness of taxonomy in bacteria. What is also important when we speak about speciation, is how these experiments were conducted and whether what is done in the lab can happen in nature. 2. I do find time a mightily limiting factor for evolution. You tacitly acknowledge this as well when you say it is hard to traverse a plateau when a lot of things are involved (the curse of dimensionality as I put it :) Overall, Darwinism does not stand practice. Even IF we accept speciation, I hazard a guess that 13 billion years are nowhere near to allow for what we can see flourishing around.Eugene S
July 4, 2011
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Elizabeth Liddle:
That’s where drift comes in. Drift allows mutations to wander across plains until they come to something they can climb. Although the more dimensions in which that plain exists, the tougher it is to cross.
I don't have time now to give a full answer. If I did, I would look at what individual genomes might look like after 100's of thousands of generations. But to the point here: to invoke "drift" is to invoke stochastic/chance mechanisms. The argument that Dawkins makes is that, indeed, the 'stuff' of evolution is of chance origins, but that NS is what makes the random ultimately non-random. So here we are, as critics of Darwinism, being told that NS is indispensable; and then that it only comes in at the end (when the fitness peak needs to be climbed). How does one falsify a theory that wants it both ways?PaV
July 2, 2011
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Hi. Just want to clear up a few things. If anyone feels like discussing evolutionary theory, I invite you to take it to my own post about my paper. I will not be posting on this thread again. #5 For the record, that is indeed my article quoted. #46 If the fitness landscape (really, fitness function) has a steep slope, it means that a small change in genotype (or phenotype) can change fitness a lot. I.e., your 1) is correct, while 2) is not. #50 and #54 One can talk about both individual and population fitness. In simulations (as the one the OP is about), fitness is known, and it determines the probability that the individual will have offspring. In biological organisms individual fitness can be measured in different ways; for bacteria it is often done by measuring the growth rate (yes, of an individual). Other proxies for fitness are used, such as the number of offspring. #60 Neutral mutations do not "drift across the fitness landscape," as you seem to correctly imply. Drift refers only to fixation or loss of mutations or alleles. however, part of the fitness landscape (really, think of it just as a function) may be flat, so that a population in a flat part of the fitness landscape can experience mutations that are neutral: changes in genotype/phenotype results in organisms with the same fitness, and so those changes are equal in fitness, and can thus drift.bjornostman
July 2, 2011
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Elizabeth Liddle: How do neutral mutations "drift" across the fitness landscape? Don't they stay at the same location, since the x-y plane presumably represents genetic configuration. The occurrence of a new mutation would move the organismmagnan
July 1, 2011
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Elizabeth Liddle:
That’s where drift comes in. Drift allows mutations to wander across plains until they come to something they can climb.
Following the analogy, how does one ascend from the valley or descend from the peak in order to reach the plain such that the neutral mutation can wander across it? Without selection how does one either descend or ascend? And if selection is taking place, it's either towards the depth of the valley or towards the peak of the mountain. It's never towards the plain. I'm sorry, but the theory you present just isn't believable.Mung
July 1, 2011
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uoflcard: (how do you pronounce that thing?!)
U of L CardsMung
July 1, 2011
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uoflcard: (how do you pronounce that thing?!) You wrote:
Elizabeth, I have been carefully reading your comment #7 about fitness landscapes. Let me first ask a question about fitness landscapes. What does a steep cliff imply? Reading different resources, I seem to see two very different possibilities: 1.) If seen as a 3-D graph, with the z-direction being vertical, the x-y plane can be seen as genetic mutations and the z-axis is the fitness. So if you’re standing at the base of a steep cliff, a slight change in the x-y plane (i.e. a slight change to a genome) can result in you now being on top of the cliff (i.e. a huge increase in fitness). 2.) Translation within the 3-D system is accomplished with step-by-step changes, like hiking in a mountain range. You cannot “walk” up a cliff, therefore you need to find the gentle slopes to reach the higher elevations. I’ve always been under the impression that it is #2, but I wanted to confirm that you agreed with that before I went further. Thanks for the response, if you have the opportunity.
Well, there are different ways of representing a fitness landscape, but actually, 1 is the most common, and tbh I've always found it easier to envisage with high fitness as the low points,rather than the high points! Simply because I find it easier to walk down hill than up. However that's just me. The idea is that populations move readily upwards and tend to "climb" towards "fitness peaks". However, moving horizontally, in straightforward Darwinian terms doesn't work, because there is no "selection" to move the population along. This is essentially the problem identified by Behe - however enticing the Bacterial Flagellum looks at the top of that far cliff, it can't get to it because it has to traverse a vast plain to get there. That's where drift comes in. Drift allows mutations to wander across plains until they come to something they can climb. Although the more dimensions in which that plain exists, the tougher it is to cross. But things get even worse, at least in theory, when a potentially advantageous peak is not just across a plain, but across a deep valley from the peak the population is on, and the only way it can get to the higher peak is by going downhill first (and it doesn't like going downhill). There are two ways it can reach the higher peak. One is, again, by drift - even deleterious mutations need not be fatal, and can still be replicated often enough that there enough survivors to reach the foot of the advantageous summit (although remember this is "blind search" - populations can only "feel" the next step, as it were). The other is via another dimension, and we know that evolutionary search space is multi-dimensional. That's where the ramp comes in. What seems like a butte in a flat plane seen from a neighbouring smaller butte, may, in another dimension or three, have a gentle ramp from one summit to the next. But thinking in more than 3D makes my head hurt :)Elizabeth Liddle
July 1, 2011
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Elizabeth, I know you're having 3 or 4 different conversations in this thread alone, but please see my comment #46uoflcard
July 1, 2011
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PaV:
Elizabeth Liddle:
Yes, eventually some mutations do become fixed (as, interestingly, do some neutral mutations as well as slightly deleterious ones, but beneficial ones are more likely to go to fixation).
So, in addition to “beneficial” mutations sweeping through the population I should have said that “deleterious” and “neutral” mutations sweep through the population (but at lesser rates)?
Well, as long as those rates can have a negative value! The "sweep" is a "drunkard's walk", but it's a biased drunkard's walk. All mutations drunkards start at the Tavern at the South end of Main Street. the street runs north-south. There is a police station just south of the Tavern. If the drunkard is a neutral mutation, each step he takes has a .5 probability of being in a Northern or Southern direction. So half of the neutral drunkards will end in the police station after one step. In fact, a lot of them will end up in the police station after just one step. But a few of them, just by chance, will make it a fair distance up Main Street, and some of them may even make the far end (fixation). This is called drift. If a mutation is deleterious, the city is built on a south facing slope, so the drunkard is far more likely to end up in the police station, than not, but if the slope is only very slight, some will "drift" up main street, and a few will actually make it to fixation, despite being deleterious. If mutation is beneficial, the city is built on a north-facing slope, and although some will still end up in the police station, these guys have a much better chances of making it to the end of main street, or at least to another tavern. So "sweep" might not be the best term! "Stagger" seems more appropriate, but if a mutation is extremely beneficial (very steep North-facing slope) yes, the drunkard may simply roll down Main street without stopping and hit the Fixation buffers at the end :)
So, per this logic, Darwinian evolution depends on neutral (no selective value) and deleterious (negative selection factor) mutations. How does this help?
Well, no, it doesn't. I hope I've clarified with my silly story :)
Here’s what the lead author wrote per William Roache: The process of acquiring beneficial mutations, many of which will add up in effect to cause a population of organisms to evolve, depends on a second factor – the process of natural selection.
Well, my analogy needs a bit adaptation here :) But essentially, what this means is that for some mutations, the phenotypic effect (which is what matters - the effect on the actual organism) may be enhanced by the presence of another. For instance an allele for glorious main of golden hair might not improve your chances of snagging a mate unless it was also coupled with an allele that ensured that you don't go bald shortly after puberty! So my drunkard's story ignores the complications of different slopes for different genes, and different slopes for different combinations of genes.
A better mental picture of the neo-Darwinist (if I must use that term! Not sure I like it because I’m not anti-Margulis for instance) is of lots of nearly-neutral mutations occurring all the time i.e. new alleles appearing all the time, some of which result in a slightly fitter genotype, some a slightly less fit genotype, but, as I tried to convey in my response to Joseph above, the concept of fitness is always in relation to a single generation, and what is slightly beneficial in one generation may be slightly deleterious in another.
I suspected you would come up with Kimura’s “Neutral Theory”. But, Lizzie, the neutral theory is not Darwinian. Kimura invented the neutral theory because of the radical inadequacy of Darwinian (Modern Synthesis) theory to explain newly discovered rates of polymorphism, rates which were staggeringly higher than ‘theory’ predicted. Yes indeed. Darwin did not envisage the role of drift. But we now know it is extremely important.
So the kind of “sweep” that occurs is not that a single mutation “sweeps” through the population, but that there are lots of different alleles, and that the frequency distribution of each allele changes from generation to generation, the ones that tended to be associated with more progeny increasing in frequency, and the ones that tended to be associated with fewer, reducing. And so the mean fitness of the population tends to optimise with the alleles that contribute to the most successful gene cocktails (aka genotypes) in that environment, at that time, becoming the most frequently. Over time, the least successful alleles may drop out of the gene pool altogether, and, if they are ever needed again, will have to mutate ab initio (which occasionally happens). But that isn’t “speciation” – that’s simply adaptation. Speciation happens when a population diverges for some reason, into two populations that don’t, or rarely interbreed, for example if they become separated by a mountain range, or a stretch of water. When that happens, adaptation continues, but the environmental history of the two populations will change – one side of the mountain may be drier than the other, or there may be different predators. And, because the two populations are now adapting independently to environmental changes, they will not only tend to differ from their ancestral populations, but also from each other, to the point where they could not interbreed even if the barrier between them was removed. And it is this divergent adaptation that we call “speciation”. Adaptation is what happens down a single lineage; speciation is the process by which one population lineage diverges into two.
So, based on this argument, FIRST,there are no differences between adaptation and speciation. SECOND, it is purely qualitative and, so, speculative. And, THIRD, where is Natural Selection mentioned in any of this?
FIRST: adaptation and speciation are terms that refer to two different, but related aspects of evolution. "Speciation" is the term used for a process in which a single population diverges into two independentally adapting sub-population. "Adaptation" is the term used to describe the evolution down a single lineage. Speciation, if you like, is about cousins; Adaptation is about ancestry! You and your second cousins have (not literally) speciated - your two sets of descendents (unless they interbreed) will be less closely related in each generation. However, both you and your second cousin (and both your descendents and your cousin's descendents) can both trace your ancestry as a single line (if we take, say maternal ancestry) to your shared great-great...great grandmother. That line is the line we are talking about when we talk about "adaptaton". The distancing relationship between your own progeny and your second cousins is what we are talking about when we talk about "speciation". SECOND:, no it's not "purely qualitative" (and even it it were, that wouldn't render it "speculative" necessarily!). Phylogenetics is a heavily quantitive field, even if the result come with confidence estimates and question marks. And what is measured can be anatomical features or DNA sequences. THIRD: Natural selection aka differential reproduction is the drunkard's walk. North is more progeny, South is fewer. Mutations that tend to move the phenotype "north" become more prevalent, by definition. Those that tend to move it south become less prevalent, by definition. Adaptation is the process by which alleles, or combinations of alleles, that tend to maximise successful progeny in a given environment become most prevalent. Speciation is when the adaptation (or even neutral drift) occurs independently in two subpopulations that have diverged from an ancestral single population. (Sorry for the delay - missed your post even though it was white! H/T to Mung for the reminder.)Elizabeth Liddle
July 1, 2011
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Mung:
Fitness is understood as the degree of adaptation to the environment. I do not see any problem with this. The degree of adaptation by the individual? The degree of adaptation by the population? Both?
Population. Fitness, in the population genetics sense, is a population-level concept.
How would one ever measure or calculate such a thing?
You can't measure the fitness (in the population genetics sense) of an individual. It's a meaningless concept, like the mean and standard deviation of a population of one. You can only measure it in the sense that your Personal Trainer might measure it in the gym :)
Elizabeth Liddle
July 1, 2011
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Yes, there are. As I've said a few times :)Elizabeth Liddle
July 1, 2011
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That’s why dogs will never evolve into cats.
So there ARE limits!Mung
July 1, 2011
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What resources do you consider limit these dimensions?
How do you define any limits on the undefinable? In your theory you've simply replaced God with another ineffable. That makes it science?Mung
July 1, 2011
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Fitness is understood as the degree of adaptation to the environment. I do not see any problem with this.
The degree of adaptation by the individual? The degree of adaptation by the population? Both? How would one ever measure or calculate such a thing?Mung
July 1, 2011
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You mean explain what polymorphisms are? Or explain how they arise?
See PaV's post @36.Mung
July 1, 2011
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Elizabeth #45 I still don't see the significance of the distinction because, as you said, "Obviously, a population cannot interbreed with its long-dead ancestors". Do you say "obviously" because frog 1.2 can't travel back in time to mate with frog 1.1, or because even if you did put them together, they are now so different that they would not be able to breed? I'm talking about the 2nd disambiguation, and in that case, I fail to see how the two are not different species. Also, I understand speciation to be horizontal (the "moment" one species becomes two different ones), but I thought species was horizontal and vertical. But this is not a major quibble for me, so I'll let it be. Regarding alleles dropping out of the population being "far more important"... I guess my main reason for bringing this up is because most ID advocates would tend to agree that natural selection is good at eliminating useless (or, at least, less useful) information. But the entire debate is about the generation of new material. Okay, an animal with night vision that now sleeps at night will probably lose its night vision; I understand that. .. How did the mutations add up to allow night vision in the first place? That is the type of question we are interested inuoflcard
July 1, 2011
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Eugene S:
Elizabeth, “Why is there a practical limit to the number of mutations of paralogous genes?” Possibly because various mutations do not go together well. Broadly speaking, I don’t know why such and other limits to macroevolution should exist. It just so happens.
Well, that's what I'm asking you about - how do you know it "so happens"? Because I don't see any reason why it should NOR evidence that it does! What are you basing your claim on?
Practice is a good measure of the validity of any theory. E.g. speciation has not been observed in earnest at all: either in real time in bacteria or in retrospect in fossils.
Well, I notice you put "in earnest" in there :) Yes, speciation has been observed, both in the field and in the lab i.e. populations have been observed to diverge so far as to no longer be able to interbreed. That's fairly "earnest". And while speciation is difficult to observe in the inevitably gappy fossil record, we can still derive phylogenies that trace out a clear branching tree, even if data from around the actual branch point are going to be, necessarily, sparse (necessarily, because fossilisation is a rare event, and so small populations have an even lower probability of leaving fossils than large ones). As far as bacteria go, bacteria, are not, strictly speaking, divided into "species", at least not in the sense that sexually reproducing organisms are. So although they are a wonderful resource for watching evolution in action, seeing as they reproduce so rapidly. we won't see "speciation" in bacteria. What you need is fruitflies! And yes, speciation has been observed in fruitflies.
Of course, we can hypothesise to our hearts’ content but practical science must be realistic
Yes indeed. But where speciation and evolution can be observed on a human time scale (as in fruitflies and bacteria) both have been observed. Where it can't be (because it happens too slowly) we have phylogenetic analysis, both of anatomical characters and genetic characters. So to make the case that evolution has limits and you can't get macroevolution from microevolution we need an actual argument that it can't happen. Behe has attempted to supply one of course, but it has serious problems. There are limits to evolution of course, but not in the direction of macroevolution over long periods of time. The big limits are imposed by common descent - once an allele is lost, as I said above, it's gone, unless it coincidentally reappears, or an allele that does the equivalent appears in a different gene. So you don't get transfer of adaptive "solutions" from one lineage to another. I find it one of the most persuasive arguments against Design, actually :)Elizabeth Liddle
July 1, 2011
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Elizabeth, I have been carefully reading your comment #7 about fitness landscapes. Let me first ask a question about fitness landscapes. What does a steep cliff imply? Reading different resources, I seem to see two very different possibilities: 1.) If seen as a 3-D graph, with the z-direction being vertical, the x-y plane can be seen as genetic mutations and the z-axis is the fitness. So if you're standing at the base of a steep cliff, a slight change in the x-y plane (i.e. a slight change to a genome) can result in you now being on top of the cliff (i.e. a huge increase in fitness). 2.) Translation within the 3-D system is accomplished with step-by-step changes, like hiking in a mountain range. You cannot "walk" up a cliff, therefore you need to find the gentle slopes to reach the higher elevations. I've always been under the impression that it is #2, but I wanted to confirm that you agreed with that before I went further. Thanks for the response, if you have the opportunity.uoflcard
July 1, 2011
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uoflcard: Well, it's an important distinction, I think - "species" is a horizontal concept, not a vertical one. The simplest definition of a species is an "interbreeding population", and "two different species" are "species that do not interbreed". Obviously a population cannot interbreed with its long-dead ancestors! But that doesn't mean it is a different species to them. It's just not a concept relevant to longitidinal differences. So a population of frogs that evolves into a rather different looking/behaving population of froggy things hasn't "evolved into a new species of frog". It has simply evolved. It has even evolved if it stays the same! (Evolutionary processes can also act to conserve optimal adaptive traits). That's why dogs will never evolve into cats. In fact, dogs will never evolve into not-dogs, if "dog" is regarded as taxonomic category.
What do you mean by “far more important” in this context?
Good question. What I meant was that once an allele has vanished from a population (the last bearer has died) that allele has gone for good. And if it once conferred an advantage - perhaps it assisted night vision) - but stopped being beneficial because the population underwent an adaptation that involved sleeping through the night hours. So the allele is now not beneficial and so drifted out to extinction i.e. it is lost for good. That matters, because now, if the population finds itself in a environment where good night vision would have helped, it will either face extinction, or have to adapt in some other way. But there may be many other alleles of once-night-vision-conferring allele, and none of these may go to fixation because they are neutral, or even slightly beneficial for some other purpose. Or may simply be non-functional. So what matters is that the potentially useful allele was lost, not that some other allele of the same gene went to fixation (which it may or may not have done). Once an allele is gone, it is not "selectable" obviously. So the population then is ratcheted out of the zone in which that allele was potentially advantageous. The poster child of course is the Vitamin C gene - the good allele dropped out of the great ape gene pool, so if we ever find ourselves in an edible fruit-poor environment we may face extinction, unless another allele appears that does the same job, or we find a work-around. But so far, apes (which include us!) are stuck with fruit-dependency!Elizabeth Liddle
July 1, 2011
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Elizabeth (29)
One species is never “changed into another species”. You are confusing speciation with adaptation.
I thought he meant something like a frog evolving into the next version (species) of that frog, not a frog evolving into a different frog that already exists.
Certainly some alleles do become fixed. But many (most?) genes have polymorphisms. What is far more important is the other end – that some alleles drop right out of the gene pool.
What do you mean by "far more important" in this context?uoflcard
July 1, 2011
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Elizabeth, "Why is there a practical limit to the number of mutations of paralogous genes?" Possibly because various mutations do not go together well. Broadly speaking, I don't know why such and other limits to macroevolution should exist. It just so happens. Practice is a good measure of the validity of any theory. E.g. speciation has not been observed in earnest at all: either in real time in bacteria or in retrospect in fossils. Of course, we can hypothesise to our hearts' content but practical science must be realistic :)Eugene S
July 1, 2011
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