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Author Topic:   The End of Evolution By Means of Natural Selection
Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 31 of 851 (552031)
03-26-2010 2:01 AM
Reply to: Message 11 by Taz
03-25-2010 4:07 PM


Re: Not a simple addition and subtraction problem
Hello Taz:
If you start with twenty alleles in a population for one gene and one of them becomes crucial for a particular environment and therefore gets selected, either rapidly or slowly depending on the selection pressure, you will lose the other nineteen alleles as the one selected comes to determine this particular trait.
But this isn't how evolution works. The other 19 alleles don't just disappear unless there are selective pressures against them.
You're still thinking in black and white.
Well, I'm trying to keep things simple at least for starters to try to prevent just this sort of misunderstanding, but I guess nothing will work. The 19 other alleles are FOR THE SAME TRAIT, which is clear enough in the quote if you read very carefully, but since it is a very high number of alleles for one trait I can understand that I contributed to the problem by trying to be all-inclusive of all possibilities in this simple layout.
Of course the one selected allele WILL over time eliminate all the other nineteen in the population if it contributes that much adaptive benefit that it is passed on to that much greater an extent than the others FOR THAT SAME TRAIT. In other words there IS selective pressure against these nineteen in the form of this highly desirable and successful single allele. I am NOT talking about a zillion other alleles for other genes in the population.
What happens is by some selective pressure, say environmental or predatory, begins to favor one trait out of the 20, we will begin to see a steady increase of that one trait in the population. But the other 19 still remain, perhaps in lower number than before.
The other 19 in this case remember are COMPETITORS at this same gene locus. They will remain until they are replaced by "the steady increase of that one trait in the population."
In other words, despite selective pressure favoring one or two or a few traits doesn't mean the overall variation of the gene pool will necessarily decrease.
Nor have I said that it would. Again, I'm focusing on ONE selected allele for the purpose of demonstrating that its selection will either rapidly or eventually replace all competing alleles for the same trait. This isn't meant to be a complete picture of how evolution works but an example pared down to its essentials to make the point I want to make.
The graphic for genetic drift that I linked from Wikipedia in my OP is the model for everything I've been saying here. They isolated a single gene, gave it two alleles equally divided among twenty individuals and showed how drift eventually replaces one with the other.
Edited by Faith, : No reason given.

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 Message 34 by Dr Adequate, posted 03-26-2010 2:10 AM Faith has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


(1)
Message 32 of 851 (552032)
03-26-2010 2:05 AM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


Then if you think mutation can save the day, all that happens is that the mutated allele gradually eliminates all the other alleles, once again eliminating genetic diversity.
This is only what happens to one gene of course, but the trend is inexorable.
By looking at just one gene, and by considering the moment of fixation as an end state instead of just more of the middle of the process, you've ignored equilibrium heterozygosity.
You may get a new trait but you'll always get it at the expense of all the other genetic possibilities ...
Well this is where your argument really breaks down, isn't it? Because the fixation of an allele in one population doesn't magically cause its fixation in another. So long as there's room for adaptive radiation, the diversity will in fact increase. Your argument applies only when the ecology has reached such a climax of diversity that one species can only be replaced by one other species, instead of diverging into two.
The production of additional net diversity has, I suppose, to stop at some point --- just as someone climbing Mount Everest must eventually reach a point where he can't get any higher. But this is not a valid argument that it is impossible to climb up Mount Everest, only an argument that it is impossible to climb up when you're on the summit.

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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 33 of 851 (552033)
03-26-2010 2:09 AM
Reply to: Message 12 by subbie
03-25-2010 4:11 PM


Dog breeding as per usual.
Consider the dog example while we're at it. Every breed of dog MUST show reduced genetic variability compared to its population of origin because if you want it big you're going to have to eliminate everything that tends to smallness, if you want it good natured you have to eliminate everything that breeds for ferocity, and so on
This is only true if the "first dog" had all possible dog genetic information, and subsequent dogs were created by taking out all the stuff that wasn't necessary for that breed of dog. This idea is ridiculous.
While you might be right about the original genetic situation (it's a possibility but there may be other ways it happened) there is nothing in my quote that doesn't describe what is actually observable in domestic breeding. As I recall, either Dawkins or Coyne described this in one of their books (which I've been reading recently) -- there's nothing odd about what I'm saying, it's strictly factual. That is, if you want to maximize certain characteristics of your dog in its offspring, what you have to do is make sure it can't breed with dogs that have different characteristics. It's a process of eliminating what you don't want. Elementary my dear Subbie.
Edited by Faith, : No reason given.

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Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 34 of 851 (552034)
03-26-2010 2:10 AM
Reply to: Message 31 by Faith
03-26-2010 2:01 AM


Re: Not a simple addition and subtraction problem
This isn't meant to be a complete picture of how evolution works ...
Good, 'cos it isn't.
... but an example pared down to its essentials to make the point I want to make.
And if you gave the ostrich as your sole example of a bird, "pared down to its essentials", then this would assist you to make the point that it is impossible for birds to fly.
It would not, however, provide you with a valid form of argument.

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 Message 31 by Faith, posted 03-26-2010 2:01 AM Faith has replied

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 Message 35 by Faith, posted 03-26-2010 2:13 AM Dr Adequate has replied

  
Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 35 of 851 (552035)
03-26-2010 2:13 AM
Reply to: Message 34 by Dr Adequate
03-26-2010 2:10 AM


Re: Not a simple addition and subtraction problem
My my my, Dr. A with his flat assertive pronouncements as if from on high, how very scientific of you.

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 Message 34 by Dr Adequate, posted 03-26-2010 2:10 AM Dr Adequate has replied

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 Message 37 by Dr Adequate, posted 03-26-2010 2:17 AM Faith has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 36 of 851 (552036)
03-26-2010 2:16 AM
Reply to: Message 33 by Faith
03-26-2010 2:09 AM


Re: Dog breeding as per usual.
That is, if you want to maximize certain characteristics of your dog, what you have to do is make sure it can't breed with dogs that have different characteristics. It's a process of eliminating what you don't want.
* sigh *
But this process may reduce the diversity in each breed of dog but increases the number of breeds of dog, thus producing a net increase in diversity.
The net result is that breeding by humans has quite visibly and obviously increased the diversity of the dog/wolf species.

This message is a reply to:
 Message 33 by Faith, posted 03-26-2010 2:09 AM Faith has replied

Replies to this message:
 Message 51 by nwr, posted 03-26-2010 8:44 AM Dr Adequate has replied
 Message 102 by Faith, posted 03-28-2010 6:47 AM Dr Adequate has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 37 of 851 (552037)
03-26-2010 2:17 AM
Reply to: Message 35 by Faith
03-26-2010 2:13 AM


Re: Not a simple addition and subtraction problem
My my my, Dr. A with his flat assertive pronouncements as if from on high, how very scientific of you.
If you are really unable to find a single error in anything that I've written, you could convey this best by agreement followed by silence.

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 Message 35 by Faith, posted 03-26-2010 2:13 AM Faith has replied

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 Message 39 by Faith, posted 03-26-2010 2:38 AM Dr Adequate has replied

  
Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 38 of 851 (552039)
03-26-2010 2:36 AM
Reply to: Message 13 by Taz
03-25-2010 4:17 PM


Taz and reinventing the wheel
A decimated population such as the seals which were hunted to near extinction, may actually come back in large numbers, but they will come back with much reduced genetic variability compared to their original population. Surely this is obvious?
No, it's not obvious, because you are using it in the wrong way. It's like saying each individual atom of my computer is colorless therefore my computer is colorless. There's a fallacy for that. Try to guess what it is.
Offending Taz's sense of propriety probably. I can see that I'm going to be up against denials of the obvious here for some time.
It SHOULD be obvious, Taz. It's a BOTTLENECK!!! There were very few individuals of the original population left, from which a new very large population grew, OF COURSE based entirely on the blending of the limited genetic diversity in those few. Sheesh!
While it is true that the seal population came back with less genetic variation than before, we're talking only a couple generations. You are trying to apply a couple generations of seal as an example of evolution. If I didn't get drawn in by your honest tone, I would have said strawman.
Please bear in mind that I did not discuss ANYTHING OTHER than the situation as it NOW EXISTS. I did not extrapolate to the future as you are insisting either that I did or I should or who knows what. What NOW EXISTS is a very large population of seals with reduced genetic diversity as a result of the bottleneck they experienced because of the hunters.
If you want to take this into the future somewhat compare them to the cheetah. How many generations has it struggled along on its reduced genetic diversity because of the bottleneck it experienced? At what point, how many years or how many generations or whatnot, do you expect to see variability increase in the population? And it would be nice if you could include some actual FACTS in your discussion. (I see that by the end of your post you do at least include some speculations if not facts -- 50 generations you say).
What happened with the seal population you described is called a bottleneck, where an event triggered a loss of many traits and the resulting allele frequency is completely different than the one before. In this particular case with the seal, the event is called over-hunting.
Too bad you missed that I already made that perfectly clear.
Because we know for a fact that each individual in that population carries at least several mutations compared to its parents,
DO YOU KNOW THAT "FOR A FACT???" Have you sequenced the DNA of a good sample of the seals? Or are you aware of a scientific report on that very experiment? And of what quality are these mutations and are they getting passed on or eliminated in further reproductions? Etc. etc. etc. Do the cheetahs carry several such mutations too?
This is NOT something you "know for a fact," this is something you ASSUME because of your preconceptions.
But after all that, EVEN IF THERE WERE SUCH AN INCREASE IN VARIATION IN THE POPULATION THROUGH MUTATION, and if you'd read more of this thread than you obviously did you'd know I've discussed this very situation many times already, EVEN IN THAT CASE, if from among these new traits one is selected and is reproduced at a higher rate than its competitors for a number of generations, it will eliminate any competing alleles for that trait/gene that may already be present anyway. The principle I'm talking about operates whenever selection or isolation of a trait occurs. It doesn't matter how much variability you get in between such events. If speciation is going to occur, alleles are going to have to be eliminated.
if left undisturbed it is inevitable that genetic variation in that population will increase given enough time. By enough time, I'm talking about at 50 generations or so, not a couple.
You don't know if it WILL, even over 50 generations, you just assume that it must. But again, if it does, this is not the subject I'm focused on here. I'm talking about how the selection and isolation processes reduce this very variability no matter how it is originally acquired.
As a side note, the rattlesnake population in the southwest are going through a bottleneck event as we speak. People there are hunting down every rattlesnake they could find, which are usually the ones that make a lot of noise. The very trait that helped keep their ancestors from being trampled on are now working against them with humans. There are reports of increasing number of silent rattlesnakes crawling around. Goddamn rednecks...
Yes? This is typical natural selection/evolution. And what's happening is that the allele(s) for noisy rattlers are BEING ELIMINATED FROM THE POPULATION allowing a new phenotype, a deadly silent nonrattler, to emerge.
I'm sure that one day in the distant future, our children's children will label this period as the great bottleneck era for most species on Earth. Man has been changing and molding population genetics to our liking. I'm sure we'll look back one day and realize the vast changes we've made to wild populations everywhere.
Could be, I haven't been following that aspect of the situation, But whether human beings or something else in nature is bringing about the changes, such change always happens through the elimination of some traits which is the reduction of genetic diversity I'm talking about.
(I must apologize if I sound exasperated. I'm not up to rewriting this. It's just frustrating to be so indignantly told I'm wrong when you've completely misunderstood what I've said.)

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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 39 of 851 (552040)
03-26-2010 2:38 AM
Reply to: Message 37 by Dr Adequate
03-26-2010 2:17 AM


Re: Not a simple addition and subtraction problem
I haven't got down to your posts, Dr. A, but I will, I will. Patience.
Edited by Faith, : No reason given.

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 Message 37 by Dr Adequate, posted 03-26-2010 2:17 AM Dr Adequate has replied

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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 40 of 851 (552041)
03-26-2010 2:59 AM
Reply to: Message 14 by PaulK
03-25-2010 4:37 PM


Re: There is Addition as well as Subtraction
This isn't a simple addition and subtraction problem.
At heart it is. Granted there are complications in the details, but there is no doubt that there is addition as well as subtraction.
No doubt at all, PaulK, nor have I implied that there is no addition, I'm simply talking about what happens when the existing variation is acted upon by selection or isolation.
If you start with twenty alleles in a population for one gene and one of them becomes crucial for a particular environment and therefore gets selected, either rapidly or slowly depending on the selection pressure, you will lose the other nineteen alleles as the one selected comes to determine this particular trait.
And that allele will still be subject to mutations and new alleles will be derived from the one survivor.
How unfortunate! This poor allele was selected only to be morphed into something else after doing its duty for the species? Wouldn't the adaptive benefit its selection conferred on the population then be lost again? What kind of "evolution" is going on here?
Sorry, it's past my bedtime. I may have to answer your post again tomorrow to do it justice.
But I AM trying to make a point. If you have THAT much mutation going on, even to the point that the allele that is selected for its adaptability is mutated away, it's hard to see that anything deserving of the name evolution is really going on here. You've got changes galore but a scattered mix of them rather than evolution in a particular direction. That's why I called this "stasis" before. The population in this condition is not evolving. It may even be reverting to an earlier condition from the sound of it.
Meanwhile other genes will also be mutating, producing new alleles. There is addition as well as subtraction.
Indeed there is, but what is going on in the rest of the population is not my subject here, as I'm trying to keep the focus on what happens when there is SELECTION and ISOLATION, not increased variation.
What you get from mutation is the raw material for evolution, you do not get evolution. Any number of writers on this subject will tell you that, especially Dawkins I believe. I suppose I should look it up at some point.
It would make no sense to add new alleles for that trait either, as it has been selected because of its value for the species. Selection REQUIRES the elimination of alleles. Addition would only kill selection and kill evolution. Addition means stasis, not evolution. Selection (or isolation of a portion of the population) is essential for evolution to occur.
Addition certainly does not mean stasis. It cannot, because addition is the arrival of new alleles, not previously existing in the population. That is an example of change, not stasis. Selection gives direction to change, making it more than a random walk but mutation and drift ensure that change would happen, even in the absence of selection.
You are right, the word was not apt. Of course mutation is change. But it's not evolution. Evolution requires selection from among those variations.

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Replies to this message:
 Message 42 by PaulK, posted 03-26-2010 3:26 AM Faith has replied
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Faith 
Suspended Member (Idle past 1444 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 41 of 851 (552042)
03-26-2010 3:10 AM
Reply to: Message 16 by subbie
03-25-2010 5:01 PM


Re: (Subbie) Am I ignoring reproductive isolation?
The point I'm making is that WHEREVER EVOLUTION IS GOING ON, THAT'S WHERE you'll have a reduction in genetic diversity, and that is completely at odds with the theory of evolution.
This is simply not true. As an example, let's discuss Darwin's Finches, 15 different species of tanagers that Darwin found on the Galapagos islands. The most important difference among the various species is the size and shape of their beaks. These differences did not come about by the elimination of alleles, but by changes in alleles in different populations, resulting in different species. Thus, in this example, evolution resulted in an increase in genetic diversity. In fact, this sort of increase in genetic diversity is what is most commonly seen in speciation events.
I want to address this:
These differences did not come about by the elimination of alleles, but by changes in alleles in different populations, resulting in different species.
My understanding of speciation is that, just as with domestic selection, the selected trait is isolated from other alleles for that trait so that it can disperse through the new population down the generations and thus come to characterize the new species. If the alleles for different kinds of beaks were not eliminated you would not have this new species.
This is what must have happened with each of the finch types. A beak type got selected for its usefulness with a particular kind of function, and that got passed on and came to characterize a whole population because the alleles for the other beak types were eliminated from the reproductive pool. The same thing happened with other beak types as each found its peculiar adaptation and became isolated from the other types.
It's not exactly that there were "changes in alleles" but that those alleles that were already available in the original population and probably haphazardly expressed phenotypically at that stage -- quite a few types obviously -- were selected down to a single type for each new population, and in the process all the other beak types were eliminated.
The principle I'm hammering away at does hold up you see.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.

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Replies to this message:
 Message 48 by Percy, posted 03-26-2010 8:05 AM Faith has replied
 Message 49 by Dr Adequate, posted 03-26-2010 8:07 AM Faith has replied
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 Message 63 by Dr Adequate, posted 03-27-2010 1:18 AM Faith has replied
 Message 64 by subbie, posted 03-27-2010 1:38 AM Faith has replied

  
PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 42 of 851 (552043)
03-26-2010 3:26 AM
Reply to: Message 40 by Faith
03-26-2010 2:59 AM


Re: There is Addition as well as Subtraction
If there is addition as well as subtraction you have to show that the subtraction outweighs the addition. That's simple fact.
quote:
How unfortunate! This poor allele was selected only to be morphed into something else after doing its duty for the species? Wouldn't the adaptive benefit its selection conferred on the population then be lost again? What kind of "evolution" is going on here?
No, that's not necessarily true. There must be plenty of variations that would not compromise the adaptive change. Some might build on it further, some might confer some other benefit - possibly where the protein is used in some other role entirely - and a lot will just do nothing. Given the facts that proteins often have multiple uses, that neutral mutations are common, that much of the structure of a protein is not critical to it's function the assertion that any additional variation will disable an adaption seems hard to justify.
And, of course, in some cases the fixed trait becomes unnecessary and can be lost.
quote:
Indeed there is, but what is going on in the rest of the population is not my subject here, as I'm trying to keep the focus on what happens when there is SELECTION and ISOLATION, not increased variation.
You cannot consider variation without considering a population. And you can't ignore increases in variation - they are a critical factor in your argument. Maybe you think that I'm talking about the case where a subpopulation is split off and becomes a new species - and that I am counting both the variation in that population and in the remaining parent population. But that would be completely incorrect. Others are making that argument, not me. Did you forget that species have many genes ? Or that genetic variation must be considered over the whole genome, over a population ?
quote:
What you get from mutation is the raw material for evolution, you do not get evolution. Any number of writers on this subject will tell you that, especially Dawkins I believe. I suppose I should look it up at some point.
I have no idea why you find the need to tell me something that I already know. Nothing in my post disagreed with this in the slightest. You must remember that your whole argument is based on assuming that the supply of new variation must be inadequate.

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 Message 40 by Faith, posted 03-26-2010 2:59 AM Faith has replied

Replies to this message:
 Message 103 by Faith, posted 03-28-2010 7:04 AM PaulK has replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 43 of 851 (552051)
03-26-2010 6:46 AM
Reply to: Message 26 by nwr
03-25-2010 9:14 PM


I'd say that you are reading too much into that demonstration. It is giving an exaggerated example as an illustration. The complete removal of an allele in 5 generations of drift is improbable, even with a population size of only 20. With larger populations it is even more improbable. Generally, you would expect drift to show up as a slow change in frequency, rather than complete elimination. I'm not a biologist, but I think it is still controversial as to whether genetic drift is significant enough to even be important.
I don't think you will find anyone in evolutionary genetics who doesn't think drift is an important factor affecting genetic variation, the question has always been over the relative importance of drift against selection or other factors affecting variation in specific evolutionary elements such as speciation or following a bottleneck.
As for drift eliminating variation, if your allele has a low frequency initially then the chances of it being eliminated by drift are much higher. That is why so much variation is transient since a de novo mutation is by its very nature of very low frequency and therefore highly prone to loss through drift.
I am as interested in the evidence as you are. If some of our biologist members can produce relevant evidence, that would be useful. It is almost certain that the experiment has been done with drosophila - that is, severe selection to reduce variation, and then observation of the increase in variation over future generations.
There are many experiments where inbred lines have been used to identify novel mutations affecting specific traits, but I don't know of any studies where looking at the recovery of variation was the primary focus in the absence of any sort of intervention such as the introduction of an immigrant individual. The effects of even a single immigrant in raising levels of genetic varaition are one of the reasons why the existence of variation in other populations is such an important point.
TTFN,
WK

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 44 of 851 (552052)
03-26-2010 7:04 AM
Reply to: Message 38 by Faith
03-26-2010 2:36 AM


Re: Taz and reinventing the wheel
DO YOU KNOW THAT "FOR A FACT???" Have you sequenced the DNA of a good sample of the seals? Or are you aware of a scientific report on that very experiment? And of what quality are these mutations and are they getting passed on or eliminated in further reproductions? Etc. etc. etc. Do the cheetahs carry several such mutations too?
This is NOT something you "know for a fact," this is something you ASSUME because of your preconceptions.
We do know this "for a fact" and, no, as far as I know the experiment has never been carried out on seals. But it has been carried out in humans and a variety of other mammals, in vertebrates, in multiple strains and species of bacteria and archaea and even in non-living viruses. All show multiple mutations from their parents.
The fundamental principle of scientific investigation is that you can generalise discoveries to novel situations. We don't have to rediscover the first and second law of thermodynamics everytime we look at a new chemical reaction, for example, and we don't need to investigate DNA replication in seals to assert that they exhibit mutations because we already know that it's a general property of living systems.

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Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 45 of 851 (552054)
03-26-2010 7:38 AM
Reply to: Message 19 by Faith
03-25-2010 5:54 PM


Re:
Faith writes:
[I'm] constructing an argument to show that selection and isolation single out a particular trait by eliminating all its competition and ultimately make that trait characteristic of a new population that emerges from these processes.
This argument couldn't be more wrong. The alleles for a gene are not involved in a competition where only one is left standing. If that were the case then extinction would be an extremely common event because a species ability to survive across changing environmental landscapes is dependent upon variability. Great variability increases the likelihood that at least some subset of a population will survive an environmental change.
If it were really true that more beneficial alleles eliminate those that are less beneficial or even deleterious then alleles for genetic diseases would have disappeared long ago, and yet genetic diseases like cystic fibrosis persist.
You need to find solutions consistent with both your religious views *and* reality.
--Percy

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