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Author Topic:   The End of Evolution By Means of Natural Selection
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.2


Message 46 of 851 (552056)
03-26-2010 7:53 AM
Reply to: Message 45 by Percy
03-26-2010 7:38 AM


Re:
quote:
You need to find solutions consistent with both your religious views *and* reality.
But Percy, her argument isn't even consistent with her religious views. Even if the animals on the ark were modern species rather than the "kinds" preferred by most YECs, every species would have suffered a bottleneck. And according to Faith's argument they cannot recover from that. YECs need a mechanism to generate variation even more than evolution does to explain why we don't see evidence of that bottleneck.
This point was brought up in the original discussion so Faith has no excuse for ignoring it.

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Dr Adequate
Member (Idle past 285 days)
Posts: 16113
Joined: 07-20-2006


Message 47 of 851 (552057)
03-26-2010 7:57 AM
Reply to: Message 39 by Faith
03-26-2010 2:38 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.
Well, good, I look forward to it.
But what I find rather odd is that before you've actually gotten round to discussing one single thing that I've actually said, you've put up a snide remark pro tem.
It is you, I think, who needs to learn the lesson of "patience". If I'm wrong, then you can analyze my wrongness at your leisure. I'm not going to rush you. If, on the other hand, I'm not wrong, then you shouldn't have rushed to write a post contemning me personally when my whole offense was to write something so correct that at present you are utterly unable to dispute it.

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Percy
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Posts: 22394
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 48 of 851 (552059)
03-26-2010 8:05 AM
Reply to: Message 41 by Faith
03-26-2010 3:10 AM


Re: (Subbie) Am I ignoring reproductive isolation?
Faith writes:
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.
This isn't the way it works. For Darwin's 15 different tanager species there were not 15 different alleles for the shape of beaks, one for each species. Bird beaks are controlled by the expression of the Bmp4 gene. All the different beak shapes are the result of different timing and spatial controls on the expression of the Bmp4 gene. Expression of the Bmp4 gene is under the control of regulator genes with names like Shh and Fgf8.
In other words, beak shape is under the control of more than one gene and more than one type of gene, and bird gene pools of any species possess a great deal of variation. This is why beak expression is so plastic under the influence of changing environmental pressures.
--Percy

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Replies to this message:
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Dr Adequate
Member (Idle past 285 days)
Posts: 16113
Joined: 07-20-2006


Message 49 of 851 (552060)
03-26-2010 8:07 AM
Reply to: Message 41 by Faith
03-26-2010 3:10 AM


Re: (Subbie) Am I ignoring reproductive isolation?
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.
* sighs again *
In the case that you bring up, the action of evolution may well have diminished the variation within species, but it also produced more species. Thus increasing genetic diversity.
The interesting thing about what you're doing is that you appear to be committing the fallacy known as "moving the goalposts" inside your head, but without ever doing so explicitly. In your line of argument, as soon as radiative adaptation starts happening, you move the goalposts and it becomes two separate examples of evolution, both of which are conservative.
Edited by Dr Adequate, : No reason given.

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 Message 41 by Faith, posted 03-26-2010 3:10 AM Faith has replied

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


Message 50 of 851 (552061)
03-26-2010 8:25 AM
Reply to: Message 1 by Faith
03-25-2010 1:07 PM


Thanks Faith, this was a very clear demonstration that you haven't bothered to use any of the intervening 5 years since you started the other thread to actually learn anything more about evolutionary genetics.
Given your determination to address everybody's responses and your determination to be wrong about pretty much everything I'm not sure how you expect to be any less swamped this time around. It seem to me that a topic like this would really be much more suitable for something like a great debate.
To address some specific points from your OP ...
It seems to be generally overlooked that for evolution to occur, alleles must be eliminated, thus reducing genetic diversity.
Not overlooked, simply not true. Evolution can very readily occur without any alleles being eliminated.
But I realize this has to be demonstrated.
Having said this you then go on to do nothing of the sort. The fact that genetic drift and selection can both lead to the fixation of an allele within a population in no way means that they must or that this forms an 'inexorable' trend.
You have no evidence, you have no demonstration, all you have is your totally uninformed assumption about what happens, one that is plainly contradicted by the evidence.
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.
Not true, to be 'established' a trait just needs a sufficient frequency that it will not be readily eliminated from the population by the vicisitudes of genetic drift. Other alleles absolutely do not have to be eliminated for this to happen, although obviously their relative frequencies will change somewhat.
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.
As others have pointed out that is just flat out fantasy, cheetahs aren't an example of extreme genetic reduction due to being 'wonderfully selected' but due to a severe population bottleneck back in their evolutionary history.
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.
How can you justify basing an argument on ignoring all the evidence and just lying to yourself like this repeatedly for five years?
*ABE* Just to add, this ...
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.
The entire basis for your 'model' is a simplistic demonstration on wikipedia with a population size of 20 individuals? This sort of behaviour is why people consider creationists and IDists a joke.
TTFN,
WK
Edited by Wounded King, : No reason given.

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 Message 1 by Faith, posted 03-25-2010 1:07 PM Faith has replied

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 51 of 851 (552065)
03-26-2010 8:44 AM
Reply to: Message 36 by Dr Adequate
03-26-2010 2:16 AM


Re: Dog breeding as per usual.
Dr Adequate writes:
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.
To be fair to Faith, I think she is making a different point.
She is arguing that as the biosphere branches out, producing more variety, eventually it will reach dead ends where no further evolution is possible beyond those dead end points.
Looking at it in terms of a tree analogy, Faith is saying that as the tree branches out, it will reach the point where the peripheral twigs have lost their ability to sprout new twigs. You are responding "but there are lots of twigs as a result of prior branching" and that seems to miss her point.
I do think her point is mistaken, and I have said so in earlier posts in this thread.

This message is a reply to:
 Message 36 by Dr Adequate, posted 03-26-2010 2:16 AM Dr Adequate has replied

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 52 of 851 (552066)
03-26-2010 9:01 AM
Reply to: Message 9 by Faith
03-25-2010 3:58 PM


Faith writes:
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.
I am inclined to doubt the "eliminate everything that tends to smallness" part. Breeding reduces the frequency with which those genes appear in the population, but it does not eliminate them. That is why you get atavism (or reversion). Dog breeders have to continue with their program of artificial selection to avoid this problem.

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Dr Adequate
Member (Idle past 285 days)
Posts: 16113
Joined: 07-20-2006


Message 53 of 851 (552073)
03-26-2010 10:12 AM
Reply to: Message 51 by nwr
03-26-2010 8:44 AM


Re: Dog breeding as per usual.
She is arguing that as the biosphere branches out, producing more variety, eventually it will reach dead ends where no further evolution is possible beyond those dead end points.
Well, this is why I wrote in post #32:
me writes:
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.
Now, in case you've never met Faith before, then you should know that Faith is a creationist. She is not trying to argue that futher evolution is impossible now (which would merely be silly) but that evolution was impossible in the first place (which is downright crazy).
In effect, you are trying to twist her words so that they mean something nearly reasonable, whereas the thing that she's actually trying to say is gormlessly stupid.

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 Message 51 by nwr, posted 03-26-2010 8:44 AM nwr has replied

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nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 54 of 851 (552082)
03-26-2010 11:07 AM
Reply to: Message 53 by Dr Adequate
03-26-2010 10:12 AM


Re: Dog breeding as per usual.
Dr Adequate writes:
Now, in case you've never met Faith before, then you should know that Faith is a creationist.
Oh, yes, I have met her before - online, but not in person.
She has freshly been reinstated as a member here, so I'm for giving her a fresh start. That is, I treat her as asking honest questions and wanting to learn. I don't doubt that she is still a firm creationist, and wanting to refute evolution. Yet, I do think she deserves straightforward answers that don't refer back to her history at this forum.
Dr Adequate writes:
In effect, you are trying to twist her words so that they mean something nearly reasonable, whereas the thing that she's actually trying to say is gormlessly stupid.
Hmm, no. I am just being polite and responding to what she asks, rather than responding to what we might assume to be her ulterior motive.

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


Message 55 of 851 (552084)
03-26-2010 11:43 AM
Reply to: Message 54 by nwr
03-26-2010 11:07 AM


Re: Dog breeding as per usual.
Yet, I do think she deserves straightforward answers that don't refer back to her history at this forum.
I'm not sure this is fair, what is mostly being referred back to is the thread on this exact same topic that Faith herself referenced in her OP. She isn't making any new arguments or bringing in any new evidence this time round.
All she has to do to get her straightforward answers is re-read the thread from 5 years ago.
TTFN,
WK

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Blue Jay
Member (Idle past 2698 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


(2)
Message 56 of 851 (552085)
03-26-2010 11:59 AM
Reply to: Message 40 by Faith
03-26-2010 2:59 AM


Re: There is Addition as well as Subtraction
Hi, Faith.
I don’t really want to pile it on too thick, but I wanted to add one point that I don’t think has been adequately addressed so far. Forgive me for the length and the detail. After this post, I’ll stop and hopefully that will make it easier for you to keep up with the demands placed on you here.
Faith writes:
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.
The thing you’ve neglected is time. You’ve got this Heisenberg-like problem, where you’re trying to address what’s happening in evolution right now, and you’ve neglected the fact that right now is just one tiny piece of the process.
Even as selection starts acting on specific traits, mutation is still acting in the genome as well. And, while selection often takes many generations to play out to its end, the work of a mutation is done after a single cell division. Each individual will most likely contain several dozen new mutations, many of which will constitute new alleles or alter the expression patterns of existing alleles. And, some of these mutations can remain hidden in recessive alleles for a very long time: it’s very hard to entirely weed out a deleterious allele that doesn’t always express it’s deleterious effects.
So, while selection is going about the business whacking 19 of your 20 alleles, organisms with those 19 alleles are still persisting for a good number of generations beyond the introduction of the champion allele, and mutating at many, many times the rate of selection for that champion. Furthermore, since there isn’t just one beneficial trait in an organism, there isn’t just one champion allele. So, organisms with those 19 alleles may also have other traits that are beneficial or superior, and can compensate for their inferiority at the locus you’re addressing, which will further reduce the rate of selection-mediated extinction of the 19 inferior alleles.
The result is that we should expect a large diversity of alleles to persist for a long time, even in the presence of a superior mutant. And, extending the time of persistence extends the chance for new beneficial mutations to be associated with those inferior alleles, and the chance that some environmental fluctuation will alter the selection environment such that it favors one or more of the inferior alleles.
If evolution were allowed to proceed to its stable, climax equilibrium point, then we might experience what you suggest. However, the environment is very complex, very dynamic, and very much in flux constantly. As such, we should expect there to be cycles, balancing acts and fluctuations in the success of the champion allele in conquering its rivals.
-----
I hope this is helpful to you, Faith. Anyway, have fun debating, and I look forward to other discussions and debates with you in the future.
Edited by Bluejay, : Small addition.

-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.

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Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.7


Message 57 of 851 (552090)
03-26-2010 1:13 PM
Reply to: Message 41 by Faith
03-26-2010 3:10 AM


Re: (Subbie) Am I ignoring reproductive isolation?
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.
Mutations in each generation guarantee that new variation in beaks will continue to appear through time. Also, environments are almost never static so that alleles that were previously driven towards high frequencies may be selected against in the future.
So for evolution to end, as you claim, you would require two things. First, mutation must stop. I know of no species that breeds true. All species acquire new mutations in each generation. Second, you need the environment to be completely static. Can you name one environment that doesn't change over time? I can't.

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 Message 41 by Faith, posted 03-26-2010 3:10 AM Faith has not replied

  
Faith 
Suspended Member (Idle past 1445 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 58 of 851 (552095)
03-26-2010 2:04 PM
Reply to: Message 17 by Percy
03-25-2010 5:11 PM


Re: (Subbie) Am I ignoring reproductive isolation?
Good morning, Percy.
It's taking forever to get through the posts, but I do want to get to all of them if I can.
Genetic diversity can go in any direction after reproductive isolation.
Got to answer this right off the bat. The point I keep trying to get in focus here is the genetic diversity CAUSED BY reproductive isolation. What happens AFTERWARD is another subject. Reproductive isolation is THE way new phenotypes/variations get established, whether the mechanism is natural selection, genetic drift or bottleneck etc. Reproductive isolation keeps the selected -- whether randomly or adaptationally -- alleles from being mixed with others that would perpetuate the characteristics of the old population, so that a new population with new characteristics can emerge.
This is how a ring species forms for instance -- a few migrate away from the original population and start their own population and if there is no gene flow with the original population due to geographic or other kinds of barrier, after a few generations the new population will come to have its own peculiar characteristics that set it apart from the original population. This is just the effect of the alleles already present in the new population coming to expression, in most cases a relatively small portion of the original gene pool, whereas in the original population other alleles dominated the phenotype.
For example, consider a relatively homogeneous population that becomes divided in two when a river changes course. There are now two populations, both with pretty much the same alleles and allele frequency.
That can happen I'm sure, if the original population was large enough that dividing it fairly equally wouldn't much change the frequencies, but then it's not an example of what I'm talking about here. But perhaps you are making a different point.
Mutations experienced in one population will no longer be shared with the other and the populations will evolve along different paths. If this continues for a sufficient period then they could lose their mutually interfertile quality and become two species.
OK, I can see that mutation appears to be the explanation for all change in the minds of evolutionists here so that it's hard to get across what seems to me to be the much more common scenario I've been spelling out -- that an already-present complement of alleles is split between the populations and it is this that brings about the differences between the two as they go their separate ways mixing their genes in isolation from each other. It's the already-present alleles that "are no longer shared" between the populations, not mutations. The already-present alleles are sufficient to establish two different varieties without any help from mutations, and even to establish separate species according to the definition that they can no longer interbreed.
This wouldn't happen in the case where the alleles are equally distributed between the two as you define this situation, however. I believe my scenario is recognized by all the major writers on this kind of thing, though, it's only here that I'm running into this dependence on mutation to power all variations.
It's kind of curious, really. Many sources on the subject give the usual definition that it's relatively rare, usually deleterious, responsible for thousands of genetic diseases and known to have been beneficial in only a few odd circumstances that involve playing off a detriment against a benefit and so on, and yet people here talk as if mutation is the engine of evolution. And I get the impression you don't all agree with each other about exactly how it works, either.
If both populations thrive then diversity could increase in both. But if one or both populations suffer some disaster such as flood or famine or an invasive predator or disease that greatly reduces population size, then diversity would be reduced. It all depends upon what happens to the populations.
IF mutation is the source of all variation and IF it occurs at a sufficient rate that enough useful mutations become established in a population to affect the phenotype while the larger proportion of deleterious mutations are eliminated by selection, then you'd be right that diversity could increase (over a few thousand years or what though?) but this is so hypothetical I don't really see the point.
And you've also got one or both of these populations suffering from a disaster which could cause a bottleneck, or a predator or disease, all reducing the population size and of course these reduce genetic diversity just as natural selection does or migration of a small portion of the population as in ring species and so on and so forth, which is where I've been trying to focus from the beginning.
When you get a smaller number from a population isolated that's when you get reduced genetic diversity. It's what has to happen in natural selection and it's what happens in speciation. {edit: not ALL natural selection, I hasten to add, as some doesn't reduce the population but simply works its way through a population -- but sometimes it does isolate a small portion of a population:} You get a new phenotype, even such a dramatically new phenotype with such changed genotype that it can no longer interbreed with the former population.
Even if there are some mutations that contribute to the variation from which the new phenotype emerges, the bulk of the contribution is from the already-present alleles, and in any case it's when natural selection or any of the other isolating processes are at work that the phenomena I'm talking about occur, and since these are intrinsic to evolution then evolution depends on reducing genetic diversity in order to get a new variation or species and you can see that this chain of events MUST be self-limiting.
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.
Edited by Faith, : typo

This message is a reply to:
 Message 17 by Percy, posted 03-25-2010 5:11 PM Percy has replied

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Faith 
Suspended Member (Idle past 1445 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 59 of 851 (552108)
03-26-2010 3:15 PM
Reply to: Message 18 by Rahvin
03-25-2010 5:17 PM


Rahvin 2, part 1
Hi Rahvin. Actually, observed evolution does demonstrate [reduced genetic capacity for variance] 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.
You seem to have an odd understandong of what natural selection entails. The Theory of Evolution predicts that extinctions will happen. Endangered species are the result of a set of adaptations that no longer apply in a changing environemnt. Since mutation is largely random, the process of developing new traits is slow, and changes in the environemtn can be relatively rapid, there will always be cases where changes in the environemnt will occur too rapidly for a population to adapt effectively, and they will either be killed outright or gradually out-competed for resources by better-adapted species.
The fact that evolution can rationalize extinctions has nothing to do with my presentation of the mechanisms of natural selection and other isolating factors, which is perfectly orthodox from everything I've read on the subject.
There may be many reasons for extinctions in any given case, but reduced genetic diversity IS definitely one of them, as any conservationist could tell you.
None of it has anything to do with some sort of reduced potential for adaptation. You certainly haven't provided any evidence that there is any finite limit for genetic variance over long timescales. You've simply asserted it to be so.
Actually I have very clearly spelled out the sequence that does occur in actual reality, which IS the evidence, and it ought to be recognizable to anyone who knows anything about these things. If you reduce a population to a few members, anyone with any knowledge of population genetics should recognize that as a condition of reduced genetic diversity. Rahvin, that is FUNDAMENTAL, I certainly didn’t make it up and I know you know it too.
The seal population was drastically reduced in numbers, therefore drastically reduced in genetic diversity, therefore its regenerated population numbers are also reduced in genetic diversity as they all inherited the reduced diversity of their few founder ancestors. Whether further diversity can be recovered or not is another subject, but as it stands they are a large population with MUCH less genetic diversity than their original population, and it appears they are doing just fine and are not threatened with extinction. This is obvious and I know you know this; you just for some reason are throwing in irrelevancies that only obscure the point.
All I’m doing is taking something that IS recognized but not generally recognized in the context of its effect on evolution theory. I’m pointing out the effect.
Reductions in the numbers of a given population does indeed result in a "genetic bottleneck" where extant genetic diversity is lost.
See, I knew you knew it.
If families A B and C die out while family D lives, certainly the currently available genetic diversity inthe total population has been reduced. But that says absolutely nothing about the potential of mutation.
No, it doesn’t, nor have I claimed it does.
The only real problem with a reduction in genetic diversity as in a non-extinction die-off is the danger of recessive traits being passed around and expressed, not some "mutation barrier." If a population is shrunk to a sufficient degree, the lack of genetic diversity can threaten the population's longevity because of those rexcessive traits until reproduction allows natural mutation to restore diversity. Human beings had an extreme population bottleneck some thousands of years ago, yet look at our diversity today.
I have not said one thing about a mutation barrier Rahvin. * You seem to be making this up as you go. Yes, of course many recessive traits will come to the fore in a condition of drastically reduced genetic diversity, but why is that necessarily a bad thing? A whole population of blue-eyed humans can result from such a bottleneck, right? It’s most likely what happens when some breeder comes up with a brand new trait never before seen — it’s usually attributed to a mutation, but in fact it’s probably just a very rare recessive allele that found its very rare mate and got expressed.
As for the human bottleneck it’s quite possible that the loss of diversity nevertheless left us with enough genetic variability to continue without the help of mutations. I know that flies in the face of uniformitarian assumptions, but it IS a possibility. The same would be true of all other living things too.
I know I don’t have to answer every post down to the last detail but I’d like to try for a while. I’m sure I’ll reach a point where I’ll stop doing that eventually. For now I’m going to stop answering your very long post but I’ll be back with the rest of it next, however long that takes.
Cheers.
--------------------------------------------------------
*I just realized where you get this notion of a "mutation barrier." Since you like everyone else here think exclusively in terms of mutation as the source of all variation, when I say that the condition of speciation with its drastically reduced genetic diversity makes further evolution impossible you figure I'm saying mutations can't happen. Well, I DON'T think of this as a barrier to mutation, I think of it as a barrier to further natural selection; but I DO assume that mutations are not going to save the day in this condition, and I believe the example of endangered species ought to make that only too clear to you too. Even those who believe mutation is going to save them assume this won't happen for a long long time. But they are threatened NOW. When endangered species are rescued they are rescued IN their condition of genetic reduction. They are protected so that they can reproduce and increase in numbers -- BUT this does not restore their genetic diversity. And as far as I've seen mutation is not coming along to help them with this.
Edited by Faith, : No reason given.
Edited by Faith, : to add last paragraph from the asterisk
Edited by Faith, : Spacing corrections
Edited by Faith, : No reason given.
Edited by Faith, : No reason given.

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Faith 
Suspended Member (Idle past 1445 days)
Posts: 35298
From: Nevada, USA
Joined: 10-06-2001


Message 60 of 851 (552129)
03-26-2010 6:14 PM
Reply to: Message 18 by Rahvin
03-25-2010 5:17 PM


Rahvin 2 part 2 bacteria and so on
Rahvin 1, part 2
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.
What's your criterial for a "significant change?" We can easily get child populations that no longer interbreed, change the color of their eyes, etc.
OK, I’ll drop the significant, I forgot what I had in mind there anyway, but the challenge was to show that you didn’t lose genetic diversity by these changes and you haven’t given the slightest hint about that. According to everything I know about genetics there’s no way you didn’t lose genetic diversity; it’s how one GETS new varieties, breeds, species. You can’t have the alleles for the other colors of eyes in a population characterized by one particular color. Elementary my dear R.
But remember, Faith: in any observed "branching" of populations into divergent and distinct subgroups (whether actual speciation has occurred or not), total genetic diversity has increased, even if each indivdual subgroup now has less diversity than the parent population.
1) I’m ONLY talking about the subgroup, because it demonstrates what happens when you have selection or other forms of genetic isolation, major engines of evolution, and what you get is genetic reduction along with the development of a new phenotype characteristic of the new group.
2) Even if the parent population were very large you still may have a LITTLE reduction in genetic diversity when it loses a subgroup because that group may take a rare allele with it and the parent population will no longer have it.
3) Even if the impact on the parent population is negligible genetically speaking because the loss of the alleles in the subgroup is not large enough to have affected it, you do NOT have an increase in genetic diversity in the parent population. Where on earth are you getting that idea?
4) And it’s the same if you are talking about separately branching subgroups -- there is also no source of genetic increase here either. There may be little or no loss if the two populations are about equal in size and the parent population was very large, as in the hypothetical example Percy gave, but you certainly do NOT have an increase in ANY case. Yet here you are pronouncing this as if it were a known fact. Seems to me others here should be able to correct you instead of leaving it to me. This is simply flat-out false. You do NOT get a genetic increase from any of the processes that split populations, you get either no effect or you get a reduction.
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.
It's both.
Well, to be clear, what you actually described was not both, but the appearance in a culture of a drug-resistant variation apparently out of thin air, otherwise known as a mutation.
The experiment involves growing a large population of bacteria from a single cell. All of the child bacteria should be identical clones of the original. The population is then exposed to an antibiotic, which drastically reduces the population - in effect, it eliminates all genetic diversity except for those organisms which include a resistance to the antibiotic. It's used to demonstrate the fact of mutation (since a new trait that was not present in the original parent forms; it's a new trait that was not inherited, the very definition of a mutation)...
Yes, I grasped that. It’s an argument for mutation. It’s come up before, even at EvC a few years ago. All I can do is accept it as given, I don’t dispute it, though with more knowledge I might raise some questions about what’s really going on there. In any case I’m not sure what the point is. I’m not abandoning my argument because of what bacteria do. I’m not talking about bacteria and I’m not at all sure their genetics should be so readily assumed to apply to sexually reproducing animals. I’m talking about cheetahs and seals and eagles and seagulls and chipmunks and salamanders and it’s only an evasion to switch the topic to bacteria.
But it also works well to discount your assertions. When the population is allowed to continue to grow with regular exposure to the antibiotic, the resitance trait remains expressed by the vast majority of the population because those without it are quickly killed off. But when the antibiotic is removed (an environemntalchange) the resistance no longer confers any survival advantage, and will slowly decrease in representation among the growing population.
In other words, even after genetic diversity is reduced in a population reduction, diversity will continue to increase.
But it doesn’t in sexually reproducing animals, and uncritical extrapolating from bacteria or even fruit flies is questionable to say the least, at best irrelevant even if applicable: the cheetah’s diversity is NOT increasing and isn't going to in human time.
HIV treatment is particularly sensitive to this fact. Believe me, I wish HIV had a "mutation threshold" that could not be passed. Unfortunately, that;s not the way it works. Once a strain of HIV develops resistance to a given antiviral drug, it can and will continue to mutate rapidly, and can develop resistances to new drugs as well. This is why HIV treatment usually involves two or more completely different antiviral medications right from the beginning - if resistance to Drug A develops, the retrovirus should still be susceptible to Drug B, and so on. It;s effective so long as the selective pressure is continued by continuing to maintain a high level of all of teh medications in teh patient's body...but as soon as the pressure is lessened (say, within a month or two off of the meds), the viral population will have grown and diversified to the point that the patient now risks resistance even to both drugs.
Again, I’m not at all sure you have any warrant for assuming that what happens with HIV can be extrapolated to all living things.
In any case, I KNOW that what I’ve said about selection leading to reduced genetic diversity for the examples I’ve given is correct and you can only answer me effectively by focusing on my kind of examples.
Their ability to evolve a drug-resistant strain even when reduced to a single allele
Not a single allele. A single cell. Very different.
Hm. But doesn’t the fact that this cell IS drug resistant, while all the others aren’t, mean that it possesses a particular genetic formula — an allele or alleles — that the others don’t have, that codes for this protection?
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?
Essentially, yes. See above. Populations that have been reduced to a single member (in other words, zero genetic diversity) will spawn populations with lots of diersity, even to the point of acquiring resistance to medications.
There is some confusion here I believe, that needs sorting out. I suspect you are merely ASSUMING a growth in diversity along with the growth in population and don’t have any evidence that this is actually the case. I can’t just take your word for it. If you do have evidence, please describe it.
In order to get an ENTIRE population resistant to medications you MUST have eliminated all the genetic types that DON’T have that capacity, and this is a condition of reduced genetic diversity, NOT increased diversity. If you got a single cell with this ability after all the others were eliminated, its offspring with that capacity are not going to be more diverse, they are going to have the genetic capacity of this founder cell.
Again, I suspect you are ASSUMING a growth in genetic variability, in any case you are not demonstrating it. All the logic of genetics I’m aware of leads to the conclusion that a decrease in diversity is the necessary outcome of selection. Bacteria may be different in some crucial ways, where apparently something else can happen from time to time, a new genetic possibility just sort of gallop in from the ether or something just in time to save the fort, I’m not at all clear about this, but whether it can or not you still haven’t shown any genetic increase in the total population.
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.
Evolution never stops.
In a SENSE evolution never stops but in another sense it does. Populations often do reach a state of equilibrium from which they are not evolving in any appreciable way for long long periods of time, even granting that there is always some degree of change from generation to generation. AND, as I am suggesting, it also stops at a certain degree of genetic depletion which often occurs at speciation. If you have a large number of fixed loci you are NOT going to get further evolution in any sense that matters. You ASSUME that mutation changes things at this point. Except in bacteria and possibly fruit flies (?) it simply DOES NOT. Oh MAYBE in thousands or millions of years. How hypothetical can you get and still think you are talking about reality?
But I’m trying to keep the focus on the processes that lead to speciation, and that means the selecting and isolating processes; the variability in the population is simply the raw material that these processes operate on. Listen, if I have to I KNOW I can find some major evolutionist saying just this, I’m not saying anything new here. And you know it too, only you only know it in a context that fits your assumptions and you seem to forget it when your focus shifts -- or something like that.
So long as mutations are passed down from parent to child, natural (or artificial, in teh case of lab experiments) selection will continue to increase the frequency of beneficial traits while decreasing the frequency of traits that are not beneficial.
And here you are stating what I AM TRYING TO KEEP IN FOCUS though in different terms than I would use. We don’t need the mutations part, the normal scattering of alleles in a large population is sufficient for selection to operate as described. I doubt that selection is the most important engine of evolution myself, genetic drift being possibly more important, and I’ve found plenty of evolutionists saying the same thing, but the basic formula is correct enough though I would rewrite it:
So long as a variety of naturally occurring alleles are passed down from parent to child, selection and other isolating processes will continue to increase the frequency of the selected or isolated traits, while decreasing the frequency of traits that are in competition with them.
And here I’m going to stop again in this marathon slog through your long long post. More later. Sorry to go on at such length but you’ve raised a bunch of issues I can’t just ignore.
Edited by Faith, : To add italics
Edited by Faith, : to correct a quote format

This message is a reply to:
 Message 18 by Rahvin, posted 03-25-2010 5:17 PM Rahvin has not replied

  
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