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Author Topic:   The End of Evolution By Means of Natural Selection
Faith
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Posts: 34503
From: Nevada, USA
Joined: 10-06-2001
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Message 1 of 851 (551948)
03-25-2010 1:07 PM


I've been wanting to see if I can do a better job on my original topic here: Natural Limitation to Evolutionary Processes . As I've reread that old thread I see I got overwhelmed and defensive and didn't do a very good job of thinking through my answers. In some cases I never got back to answering some people at all, Pink Sasquatch in particular, and I'd like to try again.

In a nutshell: Evolution is said to be powered by natural selection, and some say other processes contribute as well, such as genetic drift. You will also find in definitions of evolution on some websites the statement that variability is necessary for evolution to occur. My argument is that natural selection and genetic drift, all the processes that select or isolate a portion of a population, do bring about the change called evolution but also always reduce genetic variability, which is the opposite of what evolution needs.

Paul K answered my opening post on that thread this way:

If you accept for the sake of argument that new variation is entering the population through mutation then what happens depends on the rate at which new variations appear against the rate at which variation is lost through selection. Only if the rate at which variation is lost is greater than the rate at which new variation enters the population will there be a net decrease in variation.

This is the answer that is always given to this argument, and Pink Sasquatch gives another version of the same answer in her post that follows PaulK's. I answered in turn many times that increase in variation (sometimes called "information") doesn't prevent this ultimate reduction -- you can have as much variability as mutation or any other source of genetic variability can provide, but the processes that select and isolate, which are considered essential to evolution, inevitably work to reduce the needed genetic variability, and this spells the end of evolutionary processes. It seems to be generally overlooked that for evolution to occur, alleles must be eliminated, thus reducing genetic diversity.

But I realize this has to be demonstrated.

Genetic drift is demonstrated at Wikipedia with a series of jars representing subsequent generations of a population through which drift occurs, demonstrating that while the population starts out with equal proportions of blue and pink alleles, over time drift completely eliminates the pink ones leaving only the blue, a complete elimination of one allele.

The same thing happens but more systematically if natural selection is doing the eliminating.

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. There is no way to get a trait established in a population if alleles in competition with the allele for that trait are not eliminated.

However, there's usually more going on than just the establishment of a single allele. Even in natural selection for a single trait you have to remember that individuals carry these traits and their alleles, and its the individual that is selected for its trait. This individual's genome is full of other genes for other traits, so when it passes on its selected allele it also passes on all the rest and over time if this trend continues the population will simply become more like that individual all around and alleles for that individual's traits will all have been reduced or eliminated, substantially reducing the genetic variability in the gene pool as a whole.

However, it is possible of course for the single allele to work its way through the population without remaking the whole population in the image of this individual, if it is that particular trait that has special reproductive value from generation to generation. This seems to be the point Pink Sasquatch was making. Then you will only have eliminated alleles for that trait. You'll have a population of frogs with better ability to catch flies as she was saying, but you'll be pretty far short of a new species. Small changes occur in populations all the time for various reasons without getting anywhere near speciation.

With a bottleneck, or domestic selection, on the other hand, where a phenotype is selected (or randomly isolated in the case of bottleneck) and is completely reproductively isolated, then you get the dramatic changes in many traits at once, and when you have that you also have dramatic genetic reduction for all those traits. Often this situation leads to inability to interbreed with former populations and is known as a new species.

I've always liked the cheetah example because it is a case of a wonderfully selected animal that demonstrates extreme genetic reduction, to the point of fixed loci for many traits.

But whether we are talking only about a change in a single trait or in many traits at once, the trend is ALWAYS toward genetic depletion. You can add as many new alleles as you think mutation can come up with at any point in this progression, but when these selection and isolating processes go to work on them the very same thing happens. You may get a new trait but you'll always get it at the expense of all the other genetic possibilities, and when this occurs with many traits you eventually get speciation, fixed loci, and such limited ability for further variation evolution is for all intents and purposes at an end.

To my mind this absolutely spells the end of evolution. Evolution itself defeats evolution.

Edited by Faith, : to fix url

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Admin, : Fix quote: [q] => [qs]


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Admin
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Message 2 of 851 (551962)
03-25-2010 1:56 PM


Thread Copied from Proposed New Topics Forum
Thread copied here from the The End of Evolution By Means of Natural Selection thread in the Proposed New Topics forum.

  
PaulK
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Joined: 01-10-2003
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Message 3 of 851 (551966)
03-25-2010 2:22 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


quote:

This is the answer that is always given to this argument, and Pink Sasquatch gives another version of the same answer in her post that follows PaulK's. I answered in turn many times that increase in variation (sometimes called "information") doesn't prevent this ultimate reduction -- you can have as much variability as mutation or any other source of genetic variability can provide, but the processes that select and isolate, which are considered essential to evolution, inevitably work to reduce the needed genetic variability, and this spells the end of evolutionary processes. It seems to be generally overlooked that for evolution to occur, alleles must be eliminated, thus reducing genetic diversity.

This response really makes no sense. If there are increases in variation and decreases in variation the net change in variation will be the difference between them. Only if the decrease is greater than the increase will there be a net decrease in variation. This is simple, obvious fact and flatly denying it is pointless.


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Coyote
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Posts: 6117
Joined: 01-12-2008


Message 4 of 851 (551971)
03-25-2010 2:45 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


The end of evolution (again)
To my mind this absolutely spells the end of evolution. Evolution itself defeats evolution.

To be replaced by what?


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.

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Rahvin
Member (Idle past 43 days)
Posts: 3964
Joined: 07-01-2005


Message 5 of 851 (551972)
03-25-2010 2:59 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


Hi Faith. Welcome back.

The problem behind your theory is that it's contradicted by real-world observations. Your predictions are invalidated, because observed evolution has not been reducing genetic capacity for variance.

Year after year, undergraduate students directly observe evolution in action as they show changes in allele frequency in fruit flies. Other students observe the case of drug resistance spontaneously forming in a population of bacteria.

The process doesn't stop. Variation continues, unimpeded. There is no reduction in the possibilities derived from mutation guided by natural selection. At no point to we reach an evolutionary "endpoint" where no more change is possible.

And that's just the examples that we directly observe. The fossil record and the other extant life we see today has variety beyond comprehension.

The genetic and morphological evidence for common ancestry of virtually every living thing on the planet is overwhelming, to the point that it's better established than the Theory of Gravity. Given that this is the case, and populations continue to diversify into distinct sub-groups before our very eyes, it would seem that your premise, that evolution should grind itself to a halt through some sort of genetic entropy, is falsified.


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subbie
Member (Idle past 132 days)
Posts: 3509
Joined: 02-26-2006


Message 6 of 851 (551973)
03-25-2010 3:02 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


You are ignoring a key aspect of evolutionary diversification; reproductive isolation.

You are correct that if one trait becomes so dominant in a population that it drives competing traits out of existence, that would result in a decrease in variability in that population. What you don't address is the fact that there are still other populations that possess the "eliminated" traits. To illustrate this, let me expand on the Wiki example you use.

Let's say we take a relatively homogeneous population and separate it into two jars, and keep track of the pink and blue alleles. It's entirely conceivable that either the pink or the blue might disappear from one population over time through nonselective processes. It's even possible that the pink might disappear from one and the blue from the other. However, since these populations were reproductively isolated from one another, overall there has been no total loss

While separating the populations into two jars is an artificial isolation, this type of isolation happens all the time in the real world. It is this isolation that creates different species. (Well, not entirely true, as speciation can occur over time as well, but that's not really relevant to this discussion. I mention it only so someone else doesn't come in and point out the error.)

I doubt that few here would disagree that from, time to time, some traits will disappear from some populations, and as a result, the total variability in that population is reduced. However that is not nearly the same thing as saying that evolution "inevitably work[s] to reduce the needed genetic variability."


Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. -- Thomas Jefferson

For we know that our patchwork heritage is a strength, not a weakness. We are a nation of Christians and Muslims, Jews and Hindus -- and non-believers. -- Barack Obama

We see monsters where science shows us windmills. -- Phat


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Faith
Member
Posts: 34503
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 7 of 851 (551974)
03-25-2010 3:11 PM
Reply to: Message 3 by PaulK
03-25-2010 2:22 PM


Not a simple addition and subtraction problem
Hello Paul K.

This isn't a simple addition and subtraction problem.

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.

One allele causes the subtraction of nineteen, reducing genetic diversity. If it happens to have been a mutation, an addition, it will still have the same effect, subtracting twenty in that case.

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.

Variability may remain in the rest of the population, as Pink Sasquatch emphasized, but that isn't evolution. Evolution requires this subtraction process. And again, NS keeps subtracting everything except what it selects for its survival/reproductive value.

If you start with twenty alleles in a population for one gene and 10% of the population migrates to new territory taking five of those alleles with them, you've already lost fifteen and the new population will develop a characteristic phenotype from the five it had, along with whatever proportion of other alleles for every other trait in the population that also went with it. This may be the most common way speciation occurs. Ring species apparently develop this way. New populations are formed from a few members of the previous population, and at each migration new traits come out as many alleles from the old population are left behind. Again, you only get new phenotypes by favoring particular alleles at the expense of others. That can occur by losing them altogether in a migration as well as by selection and drift within a population.

I believe my little drawings at the links show this. Simply denying it isn't evidence against it.


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Phage0070
Inactive Member


Message 8 of 851 (551975)
03-25-2010 3:16 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


Faith writes:

My argument is that natural selection and genetic drift, all the processes that select or isolate a portion of a population, do bring about the change called evolution but also always reduce genetic variability, which is the opposite of what evolution needs.

That is true; if only a subset of the population reproduces then the variability in the set that did not reproduce is lost.

Your argument appears to be based on the concept that because a subset of all possible mutations is being selected, the population must necessarily trend toward a single genetic standard. To illustrate where this goes wrong, consider this hypothetical bloodline:

An organism has 5 genetically distinct offspring (they each have their own unique variations). Two of these do not reproduce, the remaining three having been "selected". These three in turn have 5 genetically distinct offspring each, 2 each of which do not survive (6 lost, 9 reproducing).

You seem to be claiming that because the theoretical possibility of having 25 genetically distinct organisms descended from 5 bloodlines is being reduced through selection, that the genetic diversity must necessarily trend toward zero. The problem is that in this example we are left with 9 genetically distinct organisms descended from 3 distinct bloodlines, when we started out with one.

The series [1, 3, 9] does not appear to trend toward zero in my view.


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Faith
Member
Posts: 34503
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 9 of 851 (551980)
03-25-2010 3:58 PM
Reply to: Message 5 by Rahvin
03-25-2010 2:59 PM


Hi Faith. Welcome back.
The problem behind your theory is that it's contradicted by real-world observations. Your predictions are invalidated, because observed evolution has not been reducing genetic capacity for variance.

Hi Rahvin. Actually, observed evolution does demonstrate this when you focus on endangered species. It is probably not Natural Selection that has brought about their endangered condition since supposedly that would be adaptive and not endangering, but it is brought about by processes that isolate a small portion of the genetic variation formerly available to the whole population, which is just a more drastic version of what NS does. As I imply above in my response to Paul K I believe perfectly viable healthy populations can develop from such random reductions in genetic diversity, as most likely is the case in Ring Species. 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? Unfortunately in many cases such a situation does threaten the survival of a species and conservationists are always having to deal with these situations.

Year after year, undergraduate students directly observe evolution in action as they show changes in allele frequency in fruit flies. Other students observe the case of drug resistance spontaneously forming in a population of bacteria.

It's certainly true that we don't have to worry about fruit flies and bacteria becoming endangered species. You are going to have to prove to me that you can get significant changes in fruit fly phenotypes without a reduction in genetic diversity, that is, you can bring about a new population characterized by this change without losing genetic diversity.

As for bacteria I'm not enough up on the genetics involved, but what you are describing is some sort of mechanism for increasing their variation, not the selection that reduces it, which is what I'm focusing on. Their ability to evolve a drug-resistant strain even when reduced to a single allele is very interesting but it MUST be accompanied by a severe genetic reduction leaving ONLY the allele for that particular strain no matter how the original came about. Or are you claiming that you see a multiplication of new alleles from a condition of total genetic depletion? Again, even if you are, again this is increased variation, not selection and when you have it you no longer have evolution, you no longer have a drug-resistant strain or whatever else you were aiming to get. It's selection and isolation that bring the desired trait to expression in the phenotype, drug resistance in the case of bacteria, and this always involves decreased genetic variability. At least you haven't shown me how it doesn't.

The process doesn't stop. Variation continues, unimpeded. There is no reduction in the possibilities derived from mutation guided by natural selection. At no point to we reach an evolutionary "endpoint" where no more change is possible.

There may, hypothetically anyway, be no "reduction in the possibilities derived from mutation," but when you add "guided by natural selection" you are implying something that can't in fact happen. Natural selection "guides" by doing what I've been describing, by eliminating all that variation mutation has brought about so that the selected variant can come to characterize the population.

And that's just the examples that we directly observe. The fossil record and the other extant life we see today has variety beyond comprehension.

{Edit: I have to add in here somewhere a warning to myself as well as you that it's easy to get the terms "variation" and "variability" and related concepts confused with each other and even lose the whole point. This has happened to me and I'm trying very hard to avoid it but it will probably still happen. The fact that there is lots of VARIETY in nature, in phenotypes even within the same species, is a different matter from the amount of genetic VARIABILITY that is present in a population}

The fact that great variety exists in nature is a very good thing, but this doesn't change the fact that when evolution occurs in a population it HAS to reduce genetic diversity. That's the only way you get a new variety. I have to postulate that there used to be much much more variability in all species than there is today in most species, BECAUSE of the evolution that has been going on creating new varieties (or "species" if they can't interbreed with their parent population) over millennia. Some species retain enormous variability nevertheless -- dogs for instance. The most amazing varieties of dogs have been brought about and yet they can still interbreed -- THAT's enormous built-in variability there. But other species don't have that much variability, or have lost it in their successive branchings down the centuries.

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. Dogs as a species have enormous genetic variability but a particular dog variety or species has to have very little. You are ELIMINATING alleles in order to bring about your favored breed. Assuming that natural selection operates in a similar fashion in nature, that's what has to happen there too. You are not going to get a new variety, breed or species without a loss of genetic variability. This is really a law of genetics.

The genetic and morphological evidence for common ancestry of virtually every living thing on the planet is overwhelming, to the point that it's better established than the Theory of Gravity. Given that this is the case, and populations continue to diversify into distinct sub-groups before our very eyes, it would seem that your premise, that evolution should grind itself to a halt through some sort of genetic entropy, is falsified.

The evidence for common ancestry is going to have to be rethought if it turns out that evolution beyond a series of built-in variations is impossible because of the laws of genetics.

Edited by Faith, : No reason given.


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nwr
Member
Posts: 5590
From: Geneva, Illinois
Joined: 08-08-2005


Message 10 of 851 (551981)
03-25-2010 4:05 PM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


Faith writes:
My argument is that natural selection and genetic drift, all the processes that select or isolate a portion of a population, do bring about the change called evolution but also always reduce genetic variability, which is the opposite of what evolution needs.

That's not quite right. Yes, selection reduces variation. As far as I know, genetic drift does not affect variation. And mutation increases variation.

You are correct, that if there were only processes that reduce variation, then eventually evolution would run out of variation and would stop. But as long as there are also processes that increase variation, there is no reason to expect evolution to stop.

As far as I know, what is mostly noticed is that variation stays fairly constant. A bottle neck, such as caused by isolation of a small population, can result in reduced variation. But the variation is rebuilt during succeeding generations.

The type of argument you are making could perhaps be used to suggest that the theory overemphasizes selection and underemphasizes the production of new variation. But you won't be able to refute evolution this way, because the empirical evidence shows that variation does build up again if it has been reduced - unless, of course, that particular line goes extinct.


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Taz
Member (Idle past 1680 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


(1)
Message 11 of 851 (551983)
03-25-2010 4:07 PM
Reply to: Message 7 by Faith
03-25-2010 3:11 PM


Re: Not a simple addition and subtraction problem
Faith writes:

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.

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.

Try to think of it like capitalism. Just because Bill Gates began to dominate the silicon valley market doesn't mean all other software companies went belly up. In fact, despite Microsoft's attempts to stamp out their competitions, we still have giant software corporations all over the place. Even in cases of monopolies in the past, no one single commercial entity of a particular market has ever dominated the entire market.

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.

Now, if we're talking about the bottleneck effect... that's a different story.

Edited by Taz, : Fixed my damn grammar...


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subbie
Member (Idle past 132 days)
Posts: 3509
Joined: 02-26-2006


Message 12 of 851 (551984)
03-25-2010 4:11 PM
Reply to: Message 9 by Faith
03-25-2010 3:58 PM


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.


Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. -- Thomas Jefferson

For we know that our patchwork heritage is a strength, not a weakness. We are a nation of Christians and Muslims, Jews and Hindus -- and non-believers. -- Barack Obama

We see monsters where science shows us windmills. -- Phat


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Taz
Member (Idle past 1680 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 13 of 851 (551985)
03-25-2010 4:17 PM
Reply to: Message 9 by Faith
03-25-2010 3:58 PM


Faith writes:

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.

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.

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.

Because we know for a fact that each individual in that population carries at least several mutations compared to its parents, 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.

Added by edit.

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...

Added by edit.

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.

Edited by Taz, : No reason given.

Edited by Taz, : No reason given.


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PaulK
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Posts: 15843
Joined: 01-10-2003
Member Rating: 2.7


Message 14 of 851 (551988)
03-25-2010 4:37 PM
Reply to: Message 7 by Faith
03-25-2010 3:11 PM


There is Addition as well as Subtraction
quote:

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.

quote:

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. Meanwhile other genes will also be mutating, producing new alleles. There is addition as well as subtraction.

quote:

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.


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Faith
Member
Posts: 34503
From: Nevada, USA
Joined: 10-06-2001
Member Rating: 1.1


Message 15 of 851 (551989)
03-25-2010 4:45 PM
Reply to: Message 6 by subbie
03-25-2010 3:02 PM


(Subbie) Am I ignoring reproductive isolation?
Hi Subbie:

You are ignoring a key aspect of evolutionary diversification; reproductive isolation.

I usually have reproductive isolation uppermost in my mind as THE factor that brings about the new phenotype BY ensuring the reduction in genetic diversity or variability. Isolation is THE engine here, not just Natural Selection, which is really a very weak form of isolating factor, or genetic drift or bottleneck but all these processes. They all isolate a portion of a population with respect to a selected trait in the case of NS, or randomly with respect to some unknown factors in the case of genetic drift, or randomly with respect to whatever complement of alleles are contained in the new population in the case of bottleneck and founder effect. It's the isolation from other alleles that does all this. It effectively eliminates all those other alleles from the population under consideration. Alleles can be eliminated by killing them off as in a catastrophe that leaves only a few living members of a species, or by keeping them from affecting the evolving population one way or another. Absolutely reproductive isolation is not being ignored, it's of the essence of what I'm describing. But I'm not smart enough to be able take up more than one piece of this puzzle at a time.

You are correct that if one trait becomes so dominant in a population that it drives competing traits out of existence, that would result in a decrease in variability in that population.

Well, take that a bit further and agree with me that this IS what natural selection must do if a new adaptive trait is to be established. That is, this IS evolution by natural selection. (There are certainly less drastic versions of this, such as the "peppered moths" example that adapt to the color of their resting place, which as far as I know have always retained the ability to revert to the previous type and so, while they are an example of natural selection, they aren't an example of evolution to the point of speciation where you actually get a new "species.")

What you don't address is the fact that there are still other populations that possess the "eliminated" traits. To illustrate this, let me expand on the Wiki example you use.

Let me just comment before I get to the Wiki example that I haven't addressed this YET. I've certainly had it in mind. In the case of Ring Species, alleles no longer possessed by one population in the series can be found in the former populations. Same in the case of a bottleneck where a small number of individuals are merely separated from a much greater number -- the greater population will retain what the new population has lost. The new population will develop a "new look" like Darwin's Galapagos turtles, and soon not be able to interbreed any more with the old population because of genetic differences, and they will have much reduced genetic diversity compared to the mother population.

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. It should be exactly at the point a species is evolving that you are getting increasing variability, but in reality you are getting the opposite. You may have tons of variability/diversity left in the mother population but that's not the evolving population.

Let's say we take a relatively homogeneous population and separate it into two jars, and keep track of the pink and blue alleles. It's entirely conceivable that either the pink or the blue might disappear from one population over time through nonselective processes. It's even possible that the pink might disappear from one and the blue from the other. However, since these populations were reproductively isolated from one another, overall there has been no total loss

This is correct, as I anticipated in my paragraph above. Again, it is the separated populations that are evolving, through genetic drift in this case apparently, and it's where we see evolution that we see the reduction in genetic diversity. If you recombine these two populations before they've reached such genetic incompatibility that they can't interbreed the evolution stops. Gene flow interferes with evolution. You've got to have isolation and reduced genetic possibilities for evolution, for change in the phenotype, to occur.

While separating the populations into two jars is an artificial isolation, this type of isolation happens all the time in the real world. It is this isolation that creates different species. (Well, not entirely true, as speciation can occur over time as well, but that's not really relevant to this discussion. I mention it only so someone else doesn't come in and point out the error.)

I agree. From what I've read, speciation most often occurs from this sort of random isolation of populations, as in ring species. Yes, it can also occur within a population by factors that bring about reproductive isolation even there, as you point out, but the example of simple geographic isolation without the possibility of gene flow (=reproductive isolation) appears to me from my reading to me THE main way speciation comes about.

Again, the point I am making is that wherever you can point to an evolving population due to such isolating or selecting factors, you are inevitably going to have reduced genetic diversity. It doesn't matter how much diversity is left in OTHER populations. The point is that WHERE THE POPULATION IS EVOLVING THAT IS WHAT IS INEVITABLY HAPPENING.

I doubt that few here would disagree that from, time to time, some traits will disappear from some populations, and as a result, the total variability in that population is reduced. However that is not nearly the same thing as saying that evolution "inevitably work[s] to reduce the needed genetic variability."

If what you mean by some traits disappearing from some populations is that those populations are evolving with respect to those traits, the phenotype is changing, the gene frequencies are changing etc., then the variability that is lost as a result IS the same thing I'm talking about. No matter how slight the tendency, the tendency is ALWAYS in the direction of reducing genetic variability. And if genetic variability is needed for evolution, as it is, then there you have it.


This message is a reply to:
 Message 6 by subbie, posted 03-25-2010 3:02 PM subbie has responded

Replies to this message:
 Message 16 by subbie, posted 03-25-2010 5:01 PM Faith has responded
 Message 17 by Percy, posted 03-25-2010 5:11 PM Faith has responded

  
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