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Author | Topic: Does Neo-Darwinian evolution require change ? | |||||||||||||||||||||||||||||||||||||||
Coyote Member (Idle past 2127 days) Posts: 6117 Joined: |
There has not even been much change in the Genome of most anything since the time of Adam. Adam is a myth. And you're right, very little change. Edited by Coyote, : No reason given. Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
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Dr Adequate Member (Idle past 305 days) Posts: 16113 Joined: |
Cost of selection puts a limit on what natural selection can do because it tells us that selection has a cost, you cannot select Ad Infinitum. If, in a given species in a given generation, 5000 individuals can be killed by selection and still maintain the population size stable, then that is the maximum ''cost'' you can pay in that generation to filter the deleterious mutations. But that is not the limit of purifying selection. The minimum genetic casualties required to remove a new deleterious mutation from the gene pool is one (1) (ONE). Which keeps the population stable at least with respect to that particular mutation.
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RAZD Member (Idle past 1426 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Hi slevesque, you certainly stirred up an hornet nest this time eh?
I understand all these, but I don't see how it answers what I'm asking. Which is that given the high mutation rates, how can it stay at that optimal peak when every single offspring will have inherited so many mutation (the majority deleterious, most only very slightly). Whichever one natural selection ''chooses'', it will still be less fit then it's parents were. Two things: First, not all the population will be at the peak. If you look at the bell curves mentioned by AZPaul3 in Message 36, you will see that in each case the vast majority of individuals will still not be at the optimum. This is partly due to shifting optimum points and partly due to the non-direction of mutations. Some will be towards the peak, some will be away, some will be neutral, the further they are away, the stronger will be the selection against their continued success. Second, one generation of offspring may be forced away from the peak for the optimumest individuals, but that leaves room for the next generation to move back towards the peak, while selection acts against any further movement away from the peak: result is oscillation around the mean optimum values. The stasis involves the whole population, with all the various hereditary lineages involved in these oscillations for all of their relevant hereditary traits, they average out, and thus the population as a whole will still form a bell curve around the optimum adaptations. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
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Iblis Member (Idle past 3917 days) Posts: 663 Joined:
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slevesque writes: Of course this is all probabilities talk, since obviously population size goes up and down. But it cannot for too long downwards, because genetic meltdown is never far away. Faith used to back her affected agrument by incredulity with specious appeals to "genetic meltdown". Her favorite example was the amazing cheetah.
He's had it rough as the poster-child for reduction of genetic diversity. Due to depopulation, isolation and inbreeding his genetic variability is so low that skin grafts between unrelated animals do not result in immunological rejection! And so on, there are a lot of lovely fables in this area. But contrary to popular belief, this is nothing new for the cheetah. It began thousands of years ago, toward the end of last ice age, in a fairly ordinary genetic bottleneck. And as result of this process, the cheetah has become the least "feline" of all the big cats. In another million years or so, he may look something like this:
Or this:
The misadventures of these fellows actually provides the key to your whole puzzle. You see, when the gene pool is large and conditions remain stable, the overwhelming majority of even the effective, non-neutral mutations are quickly lost in the shuffle. They are outnumbered and as they provide no selection advantage, there is no reason for them to be preserved. When the gene pool is greatly reduced however, either due to large-scale changes in the environment in terms of selection factors or to the spreading out of outliers of a population into a new area or niche, this changes. The cow's primary source of genetic diversity is, other cows with somewhat different genes. The cheetah's, though, is mutation. Each new trait produced by mutation is valuable to a reduced species and likely to be preserved, resulting in large-scale morphological changes over a relatively short period of time. Still in the high thousands and millions though. And this is the main factor underlying Gould's "punctuated equilibrium". For ten million years, everything is fine. Then things change; and when they do, things change. Eerie. But not mysterious, simple statistics.
PaulK writes:
Message 18 The next important fact is that P.E. is a prediction of evolutionary theory - or to be more precise Mayr's theory of speciation (still felt to be the main mechanism by which new species form). Mayr's mechanism starts with a small population becoming isolated from the main body of a species. Large populations are slow to evolve, by drift or even selection - this smaller population can change far more rapidly. If this smaller population thrives and evolves to form a new species and if it is able to return it may overrun the territory of the ancestral population, giving the appearance of a change more sudden than it actually was. Since most of the evolution happens relatively rapidly (but still "gradually" by human standards) and in a small region it is not uncommon for it to be missed - either absent from the fossil record for one reason or another, or simply not found by us. As I've demonstrated, Paul has already given you the answer to both longterm stability and rapid change. Why can't you see it?
slevesque writes: I know the basics of Ponctuated equilibrium, and I don't see how all you said about it affects what I'm talking about. Cleopatra.
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
You have yet to show this. Also, as a population dwindles over a few generations this can reduce the deleterious mutation load far easier than in a growing or stable population. And even so, it does not stop the mutation load from accumulating, since every single individual that would survive would still have inherited multiple mutations.
You can have a cycle of booms and busts that negate genetic meltdown. And if high selective pressure breaks down the mutational load, relaxed selective pressures accelerate it. And so, at the end of the day, if you had a population of x individuals, and you finish with x individuals, putting boom and bust cycles in between won't really have changed anything.
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
You can also reduce a mammalian population from millions to a few thousand and re-establish the species. Unless you are implying tht mammalian populations can sustain as much intense selective pressures as E.Coli, you'll have to explain to me what this has to do with what you quoted.
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Taq Member Posts: 10038 Joined: Member Rating: 5.3 |
Unless you are implying tht mammalian populations can sustain as much intense selective pressures as E.Coli, you'll have to explain to me what this has to do with what you quoted. In the short term, yes. The American Bison went from 10's of millions to just a few thousand and they are now making a comeback. The same for the walrus. Other species, such as the cheetah, show definite signs of a sever bottleneck indicative of intense selection.
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
Yes, in the most egregious cases it kills the individual. But in the majority of instances Natural Selection simply means reduced or enhanced reproductive success. But taking Natural selection as that it kills (or totally prevents from reproducing) is taking it at it's most powerful form. Taking it in simply reduced or ehanced reproductive success only makes matters worse.
In the case of the dancing population curves any changes or group of changes that move the apex of the curve away from the optimum (which is set by the present environment) will correct itself by those in the population closer to that optimum having more babies and moving the curve over time back toward that optimum. And this is done for each of the thousands of attributes. It is a self-correcting mechanism. Yes, but even taking those in the population closer, their babies will be farther then there parents because of the high mutation rates. And, even if we take the babies of that generation which are closer then the rest of the other babies, they will still be farther then their parents. etc. etc. I perfectly understand the pendulum effect with small mutation rates. As I said, I can see such things happen in E.Coli population because there mutation rates are under 1mpipg. What I'm saying is, with higher mutation rates, no pendulum effect will happen. The mutations will always force a population to drift away from the optimal peak, and NS will resist this drifting but, even when taking it in it's most powerful form (kill the less fit, only the most fit reproduce) it still cannot stop it.
{abe} And just to be pointed about it... Nothing can ever overwhelm Natural Selection (selection pressures) regardless of perceived cost. It is a nonsensical notion. Any change, rate of change, high or low that has any effect on reproductive success is part of the Natural Selection phenomenon. If the changes enhance reproductive success then these are said to be "selected for" while any that reduce reproductive success are deemed "selected against" regardless of how many there may be or how fast the come. Cost of selection is certainly a very important notion in population genetics.
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Taq Member Posts: 10038 Joined: Member Rating: 5.3 |
And even so, it does not stop the mutation load from accumulating, since every single individual that would survive would still have inherited multiple mutations. And for each round of genetic recombination in the gametes there is a loss of multiple mutations. Also, individuals with a higher load of deleterious mutations will be selected against allowing for selective sweeps.
And if high selective pressure breaks down the mutational load, relaxed selective pressures accelerate it. And so, at the end of the day, if you had a population of x individuals, and you finish with x individuals, putting boom and bust cycles in between won't really have changed anything. The bust cycle resets the mutational load, so yes it has changed. You are only measuring the load since the last bust cycle instead of the origin of all life.
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
Ok I think I got misunderstood there. What I was saying was: The % of functioning genome has been ever increasing in the past few years, as I'm sure you know. Right now, anyone can safely say that at least 30% of the genome is functional.
What I said concerning ENCODE was simply that it ''opened up the possibility'' that the entire genome had a function. I'm not saying it proved anything, and I certainly know the difference between functional and transcribed. Therefore, all I'm saying is that when seeing how genetics has been unravelling the secrets of previously thought ''junk DNA'', and how more evidence comes to open the possibility that maybe the whole genome is functional, I think it is the idea that any part of the genome is junk that should be regarder with great skepticism, not the other way around.
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Taq Member Posts: 10038 Joined: Member Rating: 5.3 |
But taking Natural selection as that it kills (or totally prevents from reproducing) is taking it at it's most powerful form. Taking it in simply reduced or ehanced reproductive success only makes matters worse. You are forgetting about genetic recombination and selective sweeps. If selection is looked at through the lens of reproductive success then you up the chances of hitting a beneficial or compensatory mutation that can then spread through the population separately from the background of slightly deleterious mutations found in the individual in which the beneficial mutation occurred. IOW, you up the chance for beneficial mutations.
As I said, I can see such things happen in E.Coli population because there mutation rates are under 1mpipg. Are you taking the size of the E. coli genome into account? The human genome is 1,000 times larger than the E. coli genome.
Cost of selection is certainly a very important notion in population genetics. So is the deleterious nature of these mutations. If their affect is so slight as to be a non-factor then it really doesn't matter.
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
YEC. There is the problem. The empirical evidence overwhelmingly supports an old earth, with life starting some billions of years ago. That evidence is absolutely incompatible with the idea of this genetic meltdown in a few hundred generations. Put simply, if the genome hasn't melted down in 3+ billion years, we don't need to worry about it. I hate discussing with you because it is so blatantly obvious that you argue in bad faith. Other evidence, and how they are interpreted, does not erase evidence from other fields of science. If you feel the evidence from other fields show life has been going on for billions of years, then you can't just ''not worry about it'' when seeing that it conflicts with another field. You have to identify what is wrong in that field, were is the missteps. That is what everyone here, except you, is doing. And it is obviously the right approach.
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Taq Member Posts: 10038 Joined: Member Rating: 5.3 |
What I said concerning ENCODE was simply that it ''opened up the possibility'' that the entire genome had a function. To use the analogy I used before, this is like saying that since you can hear static on your radio that this opens up the possibility that there is a radio station on every part of the dial.
Therefore, all I'm saying is that when seeing how genetics has been unravelling the secrets of previously thought ''junk DNA'', and how more evidence comes to open the possibility that maybe the whole genome is functional, I think it is the idea that any part of the genome is junk that should be regarder with great skepticism, not the other way around. At the same time, there are sections of the genome that have accumulated mutations at a rate consistent with neutral drift. These include processed pseudogenes which were the first to be called "junk DNA". If they do serve a function it is probably independent of the actual DNA sequence. The more we learn of genetics the easier it is to find junk DNA. Even more, scientists have removed over 2.3 million base pairs from the mouse genome with no visible change or loss of function. This is one half the size of the E. coli genome. Obviously, there is much more vestigial DNA in the eukaryotic genome than in the prokaryotic genome. "We deleted two large non-coding intervals, 1,511 kilobases and 845 kilobases in length, from the mouse genome. Viable mice homozygous for the deletions were generated and were indistinguishable from wild-type littermates with regard to morphology, reproductive fitness, growth, longevity and a variety of parameters assaying general homeostasis."Megabase deletions of gene deserts result in viable mice - PubMed
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
But that is not the limit of purifying selection. The minimum genetic casualties required to remove a new deleterious mutation from the gene pool is one (1) (ONE). Which keeps the population stable at least with respect to that particular mutation. Of course, and the most deletirious mutations will be wiped out of each generation without any problem. But some individuals most survive and reproduce, and what I'm sayign is that the high mutation rates imply that those individuals will have inherited lots of mutations, and although they may have the least deleterious set of mutations to have appeared in that generation, doesn't mean they still don't have those mutations.
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slevesque Member (Idle past 4661 days) Posts: 1456 Joined: |
Second, one generation of offspring may be forced away from the peak for the optimumest individuals, but that leaves room for the next generation to move back towards the peak, while selection acts against any further movement away from the peak: result is oscillation around the mean optimum values. But this is statistically very unrealistic. If a generation moved away from the peak by 50 mutations, in a genome of 3 billion, it is extrememly improbable that the next generation will move back towards the peak on not simply farther away.
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