Does Genetic Variance Cause Increased Fitness a la RA Fisher?

_{September 7, 2011

Intelligent Design}

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Here’s a quote from a paper I ran into a few months back. I’ve been meaning to post it. I certainly have Liz Liddle in mind as I do so.

I would ask that you resist your urge to ‘google’ the quote, and simply ask yourself the question: when was this paper published. Then have a gander. It’s a paper by Hampton L. Carson. From the abstract:

The experiments reported in this paper are designed to test the effect of raising
the genetic variance in experimental populations in a different way, namely, by
the use of large doses of X-rays delivered frequently to all the adults in the popu-
lation. The populations were thus closed ones in which the mutation rate was
artificially maintained at a very high level. Under these conditions, the experi-
mental populations represent a sensitive system for the detection of the effects of
newly induced genes that cause increase in fitness, whether these effects may be
manifested in the heterozygous condition, the homozygous condition, or both.
The results clearly show that there is no sustained increase in fitness despite an
increased genetic variance as indicated by an observed increase in genetic load.
There is thus no evidence for single-gene heterosis or for the induction of new
genes having a favorable effect on any of the fitness characters.

Liz Liddle seems convinced that neutral drift/draft is sufficient to provide all the genetic variance needed for evlution. And here’s an experiment where they raised the mutation rate to its limit, and, still, no overall gain in fitness (These were Drosophila populations). RM+NS just doesn’t have enough fire-power. Actually, it’s not even close to having enough fire-power to explain the progression of life-forms. Why wasn’t Darwinism dead a long time ago? Here’s the link.

Comments

Clearly, mutations do not accumulate at the same rate when they are forced by radiation. Are the mutations forced by radiation mostly neutral? There's probably data on that in the literature. We can't automatically assume that what applies to the background mutations applies equally to mutations forced by radiation.Neil Rickert_{September 9, 2011
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Neil@ 2.1.2.1.2: This is simply how neutral drift is characterized. From Wikipedia: According to the mathematics of drift, when comparing divergent populations, most of the single-nucleotide differences can be assumed to have accumulated at the same rate as individuals with mutations are born. According to the Neutral Theory, most mutations are neutral; hence, NS doesn't 'see' them.PaV_{September 9, 2011
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The mutation rate determines the ‘speed’ of neutral drift.
I doubt that. Mutations that are quickly filtered out by natural selection would not have any effect on drift. For that matter, they wouldn't be neutral, either.Neil Rickert_{September 9, 2011
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Liz: How do you "falsify" your hypothesis? How do you test that it's right or wrong? In the case this paper presents, from 1962, they artificially increased the genetic variance. They increased the mutation rate. The mutation rate determines the 'speed' of neutral drift. So they sped up 'neutral drift', and no fitness increase was detected. In fact, there was a fitness decrease. How do these facts fit into your hypothesis? Per your hypothesis, "neutral" alleles are at the ready. So, then, why is it that species become extinct? Further, why is the fossil record marked by stasis and extinctions? Per your hypothesis, there should be wholesale variation within species as time passes. But we see, instead, stasis. The coelocanth comes to mind. Some ancient fossil was found showing a species basically unchanged for hundreds of millions of years. Doesn't this falsify your hypothesis? (Surely, you're not going to say that the species "environment" was unchanged for 350 million years, are you? If you take this route, then please draw up a list of the 89 million different micro-environments needed to explain the presence of 89 million different species on earth.)PaV_{September 9, 2011
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The reported experimental results are what I would have predicted. However, I'm not a Darwinist, though I am often accused of being one in discussions here. Come to think of it, neutral drift is not really Darwinian either. In the particular experiment, we see forced increase in variation, so that isn't exactly the same as drift. I would expect the radiation to result in an overload of deleterious mutations. I actually doubt that strict Darwinians would be at all perturbed by the reported experiment. I didn't google it, but I assume that it is old and well known. But that's a guess. As for the Fisher claim, that increased variation results in increased fitness - that's probably true to a degree. But it would apply to natural variation that is maintained by the population and subject to natural selection which would weed out the more deleterious variants. The trouble with using radiation to force an increase in variation, is that the forcing does not allow natural selection to play its role.Neil Rickert_{September 8, 2011
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"You inclusion of Fisher’s “main” (I said “fundamental”) theorem, I take as a form of “know-it-all”-ism, typical of the Darwinist, who are so wise and learned. (Just ask them!)" Hence the use of the word "probably", if you were not talking about this one, please say so. "Of course an increased mutation rate will result in lots of deleterious mutations. Why? Because the vast majority of mutations is deleterious. This is why Darwinism doesn’t work" It doesn't work if the rate of mutation is too high. But for a lower rate, they will be discarded. From the article: "These increased loads, however, disappeared within a year." "[...] if the overall background of the population is one that is lower in fitness, then, surely, one of this large number of flies has received a “beneficial” mutation, raising its “fitness”; against such a large number of other flies carrying a, or many, deleterious mutation/s, the selection factor for this “beneficial” mutation is all the more higher. So why doesn’t it appear?" Take two individuals, one with one beneficial mutation and no deleterious mutation and one with the same beneficial mutation and 1000 deleterious mutations. In which case is the beneficial mutation more likely to get fixed in the population? What about 1 beneficial and 5 deleterious? Is there a clear cut line? What about a normal rate of mutation? What about an increased rate of mutation caused by UV? Finally you say: "Let’s further note that “heterosis” simply seems to be an expanded form of the Hardy-Weinberg Law, which, like NS, is conservative, not creative." If it is conservative, why do we see an increase in fitness?CharlesJ_{September 8, 2011
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I take your point, PaV, which was why I tried to clarify what I meant, to Eric. Clearly, the generation of variance is via specific reproductive mechanisms that introduce variance in various random (with respect to fitness) ways. My point is that because neutral variants (currently neutral) can and do drift across the population, then a substantial pool of variants will tend to be maintained, even when none are currently advantageous or deleterious. This means that when a change in environment occurs, there is already a pool of potential variants that may prove advantageous in the new conditions - the population doesn't have to wait for a brand new allele to come and rescue it in the nick of time! As for your comment about rhetoric, no it isn't :) Clearly, the relevant environmental properties are those that persist over the organism's reproductive cycle, so that a population that lives in an extreme climate, like the Arctic hare, may be best served by genetic traits that give it a white coat in winter and a brown in summer - that's an population-level adaptation that makes the organism itself adaptable! But we do observe "microevolution" happening year-by-year, for example in the Galapagos finches. That's often dismissed as "only" microevolution by those who say that it doesn't account for larger development and "only" selects traits that already exist in the population. But that's my point - I suggest that even substantial net evolutionary trajectories result from continuous selection of pre-existing traits, and that because so many variants are neutral, at any given time, there will be a large pool of variants of which some will turn out to be advantageous as the environment changes. I suppose I'm putting forward the picture of the gene pool as being constantly drip fed with neutral mutations, and constantly "leaking" once-neutral mutations that have become deleterious. So the mean moves with environmental demands, with no sudden novelty being required. Although clearly, the faster the environmental change, the more rapid will be the evolutionary change, up to a point when the supply of potentially advantageous variants is outstripped by the rate at which they are required.Elizabeth Liddle_{September 8, 2011
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Liz: You wrote:
“Neutral drift” does not provide variance in the first place, but it does serve to maintain variance in the population, even when the variants are not currently advantageous.
This is a bit of distinction without a difference. Neutral drift relies on neutral mutations, ipso facto. And these mutations are proportional to time. And with time, more neutral mutations build up over time, changing the genome, as it 'drifts' through time. But neutral drift "maintains" nothing. It simply gets rid of nothing, an action that NS is normally responsible for.
It must happen sometimes that a brand new allele is also currently advantageous, but we know that a lot of adaptation occurs as already-existing traits become more or less advantageous in a changed environment.
This has a ring to it. ;) But isn't it just empty rhetoric? For example, take the "changed environment". Outside my house, the environment changes all the time. In the morning it's cold. In the afternoon, it can be hot. In winter time, there's lots of rain; in the summertime, not much. The latest count on the number of species was, what, 89 million, or something like that. Can you please identify 89 million different "changed environments". This is just empty talk. No more. Or, put another way, wishful thinking.PaV_{September 8, 2011
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CharlesJ: You inclusion of Fisher's "main" (I said "fundamental") theorem, I take as a form of "know-it-all"-ism, typical of the Darwinist, who are so wise and learned. (Just ask them!) As to this remark:
If the mutation rate is too high, deleterious mutation will start accumulating, decreasing fitness.
Of course an increased mutation rate will result in lots of deleterious mutations. Why? Because the vast majority of mutations is deleterious. This is why Darwinism doesn't work. But what you fail to take into account is this: if the overall background of the population is one that is lower in fitness, then, surely, one of this large number of flies has received a "beneficial" mutation, raising its "fitness"; against such a large number of other flies carrying a, or many, deleterious mutation/s, the selection factor for this "beneficial" mutation is all the more higher. So why doesn't it appear? These are simple questions. Darwinism is powerless to answer them. Only "belief" in Darwinism, a belief that leads to all kinds of rationalizations, can overcome this powerlessness. As to:
n these experiments, genetic variance has been increased by the additions of smell amounts of foreign genetic material by outcrossing.”
Well, duh, this is called "heterosis", a phenomena still unexplained, and which led Darwin down the trail of his silly hypothesis. Darwin's "silly hypothesis" is the "origin of species"---an example of which is not to be found in the pages of the "Origins"---since "Origin of Adaptations" is both correct and logically sustainable. But, of course, this was already known and accepted by mainstream biologists at the time of the "Origins" publication. Let's further note that "heterosis" simply seems to be an expanded form of the Hardy-Weinberg Law, which, like NS, is conservative, not creative.PaV_{September 8, 2011
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"You can say that it was NS." That would be the why, but what I wanted to know is the how. Actually, I should have asked my question differently: Do you think every deleterious mutation reversed to wild type by point mutation or by other mechanism? By Fisher's main theorem, you probably mean: "The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time." I don't think it should be interpreted as higher mutation rate is better. Selection simply means that on average negative mutations will be weeded out and positive mutations will tend to get fixed. It does not mean that every deleterious mutation will disappear, juts most of them. If the mutation rate is too high, deleterious mutation will start accumulating, decreasing fitness. As a conclusion for this post, I'll add that point mutations are not the only way to generate variation in a genome. From the paper in the OP and talking about experiments done by other teams: "[...] increased adaptation to the existing conditions, as evidenced by increased population size and production, can be observed directly in experimental populations of Drosophila melanogaster. In these experiments, genetic variance has been increased by the additions of smell amounts of foreign genetic material by outcrossing."CharlesJ_{September 8, 2011
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And we also know that a lot of adaptation comes from behavioural changes.Joseph_{September 8, 2011
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"Neutral drift" does not provide variance in the first place, but it does serve to maintain variance in the population, even when the variants are not currently advantageous. It must happen sometimes that a brand new allele is also currently advantageous, but we know that a lot of adaptation occurs as already-existing traits become more or less advantageous in a changed environment.Elizabeth Liddle_{September 8, 2011
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"Liz Liddle seems convinced that neutral drift/draft is sufficient to provide all the genetic variance needed for evolution." Well, I don't know what Dr. Liddle's position is, but random events (or, yes, yes, some stochastic sampline of the same) clearly don't have the ability to provide all the genetic variance needed. "RM+NS just doesn’t have enough fire-power." NS doesn't have any fire power. All the variation has to come from the RM part. NS is just an after-the-fact label description of the differential survival. RM clearly isn't up to the task.Eric Anderson_{September 7, 2011
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You can say that it was NS. Fred Hoyle wrote a book on the "Mathematics of Evolution" and highlighted the role of NS as being, essentially, what is termed 'purifying selection'. But that's not how people usually think of NS. And that's not what the experimenters were expecting heading into the experiment. IOW, all this genetic variance amounted to, basically, a "genetic load", and nothing more. No extra fitness. Surely no "new species". RA Fisher's fundamental theorem says that fitness shouldn't decline, and that fitness is related to the amount of variance present. Well, here we had loads of 'variance', and no increase in 'fitness'. What happened? But, of course, why would we want actual facts to get in the way of a perfectly wonderful theory. Isn't that how science is supposed to work? ;)PaV_{September 7, 2011
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From the paper: “As expected, the size of the experimental populations declines under radiation. Population size is recovered rapidly when radiation is suspended.” “Following the cessation of the irradiation, the genetic loads of the irradiated populations were found to be elevated relative to the controls. These increased loads, however, disappeared within a year.” Seems like the populations were accumulating deleterious mutations faster than they could manage. My question is: by which mechanism do you think the deleterious mutations were weeded out after the irradiation stopped?CharlesJ_{September 7, 2011
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