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Author Topic:   Evolution Requires Reduction in Genetic Diversity
JonF
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Message 16 of 1034 (691690)
02-24-2013 8:38 AM
Reply to: Message 10 by Percy
02-23-2013 9:03 PM


Re: Thanks for Acknowledgments of the Claim of Reduced Genetic Diversity
Of course there are other ways that speciation can happen.

Or polyploidy in plants, which can happen in a single generation, But nobody's impressed by plants.


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Percy
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Posts: 18249
From: New Hampshire
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Message 17 of 1034 (691693)
02-24-2013 9:57 AM
Reply to: Message 13 by Faith
02-24-2013 3:18 AM


Re: Thanks for Acknowledgments of the Claim of Reduced Genetic Diversity
Faith writes:

It's the distribution of the population of an entire species into subpopulations across distinct geographical regions with differing environments that results in reduced diversity in the subpopulations when compared to the entire species. That's what I meant earlier when I used the term "by definition." Practically by definition any subset of a population will have less diversity than the entire population.

Fine, that is true, but again nobody ever acknowledged that fact before...

It's central to ideas about how speciation occurs and was not only acknowledged but described in detail over and over again.

Also fundamental to modern concepts of evolution is that both increased and reduced genetic diversity *can* be a result of the evolutionary processes of mutation and natural selection (and this too has been said many times before). This is because mutation and natural selection are opposite forces. Mutation increases diversity, selection decreases diversity.

To make clear the point, a successful species whose range is increasing will experience burgeoning numbers and increasing diversity, while a failing species headed for eventual extinction will experience shrinking numbers and decreasing diversity.

...believe it or not "differing environments" is NOT what creates the new phenotypes.

Evolution does not describe environments as creating new phenotypes. Rather, an environment is more like the mold into which evolution is trying to find phenotypic fits.

The genetic situation itself is what creates the new phenotypes, the fact that a new mix of alleles forms the gene pool of the new population compared to the old.

Alleles are remixed during reproduction, providing additional variation upon which selection operates. And new alleles are a result of the imperfect copying that occurs during reproduction, and upon which selection also operates. Reproduction, mutation and selection, in other words evolution, are what create what you described as the "genetic situation."

The actual process of evolution by means of mutation and natural selection can only lead to increased diversity because there is nothing to prevent the imperfect copying of reproduction.

What you haven't yet grasped is that SELECTION always inevitably reduces genetic diversity.

I misspoke. What I meant to say is that change (not increasing diversity) is inevitable because of the imperfect copying of reproduction.

You can have mutations galore within a population but once you have selection of whatever mix of mutations -- or alleles however formed -- selection reduces genetic diversity in the new population. Selection brings a certain allele mix to expression in the phenotype BY ELIMINATING COMPETING ALLELES from the gene pool.

As I explained above, evolution can cause both increased and decreased diversity. Mutation and selection are working at cross purposes, mutations providing variation willy-nilly without regard to fitness, and selection pruning the variation that fits the environment least well. The environment plays a major role in deciding whether mutation or selection wins out as measured by allelic variation.

Each newly born person possesses, on average, approximately 100 random mutations, DNA sequences that are different from either parent. This is due to the imperfect copying of reproduction. As the human population grows variation can only increase because the mutational process is outrunning the selection process.

Actually they would evolve according to the particular mix of alleles in their gene pool, which may adapt to peculiarities in their environment certainly, but the environmental factor is not necessarily the driving factor.

Environment is not the only factor, but it is certainly the driving factor. This is self-evidently true because everywhere we look in nature there is adaptation to the environment. It's ubiquitous.

--Percy


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RAZD
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Message 18 of 1034 (691699)
02-24-2013 1:18 PM
Reply to: Message 13 by Faith
02-24-2013 3:18 AM


Ring Species -- Greenish Warbler -- and Genetic Diversity
What you haven't yet grasped is that SELECTION always inevitably reduces genetic diversity. That is the substance of my argument very oversimplified. You can have mutations galore within a population but once you have selection of whatever mix of mutations -- or alleles however formed -- selection reduces genetic diversity in the new population. Selection brings a certain allele mix to expression in the phenotype BY ELIMINATING COMPETING ALLELES from the gene pool. Yes it will take some time to work through this argument.

Of course selection reduces the variations in a breeding population, because it winnows out the variations that are least advantageous. But evolution is a two-step process:

If you keep one foot planted and only move the other foot you don't get very far. Move both feet and you can walk from the east coast to the west coast - even if one foot is placed randomly and the other is always directed in a westerly direction.

Think of it this way:

  1. increase variation by mutation/s
  2. decrease variation by selection
  3. repeat

Step randomly, step west, step randomly, step west ...

As an example, let's take the Greenish Warbler in Siberia:

http://www.zoology.ubc.ca/~irwin/GreenishWarblers.html

quote:
The greenish warbler ring species

Greenish warblers (Phylloscopus trochiloides) inhabit forests across much of northern and central Asia. In central Siberia, two distinct forms of greenish warbler coexist without interbreeding, and therefore these forms can be considered distinct species. The two forms are connected by a long chain of populations encircling the Tibetan Plateau to the south, and traits change gradually through this ring of populations. There is no place where there is an obvious species boundary along the southern side of the ring. Hence the two distinct 'species' in Siberia are apparently connected by gene flow. By studying geographic variation in the ring of populations, we can study how speciation has occurred. This unusual situation has been termed a 'circular overlap' or 'ring species'. There are very few known examples of ring species.

Plumage Patterns

West Siberian greenish warblers (P. t. viridanus) and east Siberian greenish warblers (P. t. plumbeitarsus) differ subtly in their plumage patterns, most notably in their wing bars, which are used in communication. While viridanus has a single wing bar, plumbeitarsus has two. Around the southern side of the ring, plumage patterns change gradually.

Genetics and history

Genetic data show a pattern very similar to the pattern of variation in plumage and songs. The two northern forms viridanus and plumbeitarsus are highly distinct genetically, but there is a gradient in genetic characteristics through the southern ring of populations. All of these patterns are consistent with the hypothesis, first proposed by Ticehurst (1938), that greenish warblers were once confined to the southern portion of their range and then expanded northward along two pathways, evolving differences as they moved north. When the two expanding fronts met in central Siberia, they were different enough that they do not interbreed.


As one subpopulation went west it accumulated mutations to the genes for plumage, size and mating songs, mutations that changed their original alleles to different ones. At each stage they had the same number of alleles, just a different mix from the original population.

As the other subpopulation went east is accumulated different mutations to the genes for plumage, size and mating songs, mutations that changed their original alleles to different ones. At each stage they had the same number of alleles, just a different mix from the original population, and a different mix from the other subpopulation.

P. t. trochiloides branches into P. t. ludlowii going west and P. t. obscuratis going east. Three subpopulations with different sets of alleles.

The process continues as P. t. ludlowii branches into P. t. nitidus going further west and P. t. viridanus going north, while P. t. obscuratis branches into P. t. plumbeitarsus and ending up with five subpopulations with different sets of alleles.

With the evolutionary two-step, the variations seen are fully explained.

Evolution Requires Reduction in Genetic Diversity

By selection/drift ... and

Evolution Requires Increases in Genetic Diversity

By mutations.

Enjoy.


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dwise1
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Posts: 3282
Joined: 05-02-2006
Member Rating: 8.1


Message 19 of 1034 (691711)
02-24-2013 3:30 PM
Reply to: Message 14 by Faith
02-24-2013 4:10 AM


Re: The effect of the flood bottleneck
See above. But again I would point out that even if it were true that new alleles are added by mutation, consider this: a mutation CHANGES an existing allele, it doesn't add something newer than a different expression of that particular gene.

Please review a description of the different types of genetic mutations that there are: Mutation: Classification of mutation types.

One type of mutation is allele duplication, in which a copy of a gene is inserted, such that where only one allele existed before there are now two. Consider the gene for skin color. If only one such allele existed then we would expect to be either black or white, but since multiple alleles for skin color exist we instead have a rich range of different shades of brown. This is an increase in diversity.

Then there are mutations that can change the function of a gene, for example alpha-lactalbumin, part of milk production, originated from lysozyme, an anti-bacterial protein. So when the gene for lysozyme changed to one for alpha-lactalbumin, it could no longer produce lysozyme. However, since the gene for lysozyme had been duplicated, mammals' ability to produce that protein was not lost.

It is by the duplication of genes to create multiple alleles that that trait is preserved as some of those genes then either lost functionality or gain new functionality.

You're only looking at what decreases genetic diversity and not at what increases it. Take the analogy of your household budget. You keep paying money out for bills, groceries, and other expenses. If that keeps up, you will end up with absolutely no money at all! Well, that is what you must conclude as long as you ignore the money coming in. Income balances against expenses; they both play a role that must not be ignored.


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Faith
Inactive Member


Message 20 of 1034 (691715)
02-24-2013 7:32 PM
Reply to: Message 1 by Faith
02-22-2013 6:14 PM


mutations
This is PaulK's last post (message 384) on the other thread which I didn't answer there:

But then you would be CHANGING your breed for some other breed.

So it would be evolution. That's supposed to be a problem ?

My point was that it just doesnít happen as much as you apparently think it should, as breeders arenít always having to fight new traits, at least after the breed is well established. Even in nature we see pretty homogeneous groups maintaining their character donít we? Populations of identical individuals keeping to their own kind, birds of a feather flocking together as the saying goes. Darwinís Galapagos turtles were of an identifiable kind, differing in identifiable ways from those on the mainland. His finches had something like four different styles of beaks that specialized in four different ways of getting food, and these types hung out with others of their same beak. There does seem to be a strong family inclination in nature.

But thatís not a particularly important point. the main point about mutations of course is the claim that evolution depends on increasing diversity which mutations supposedly supply. Iíve already argued that as soon as a trait is selected, whether it originated by mutation or by simple sexual recombination of existing alleles for that characteristic, whether by chance or conscious intent, that very selection reduces the genetic diversity of the breed or wild population. My claim is that this IS the definition of evolutionary change, there is no other, it can only proceed by reducing genetic diversity. Wherever there is any kind of selecting or culling process whatever, reduced genetic diversity is the result.

Taq said the same thing:

But then you would be CHANGING your breed for some other breed.

Exactly. You have novel changes arising from mutations that are then selected for. We call this evolution.

Again, the point was it doesnít happen at such a rate as to interfere with breeding programs. But the second point Iíd make here is that there seems to be this odd idea that it will always be the MUTATION that is selected for. Iíve noticed this before. I think itís probably just a case of imprecise thinking but thought Iíd mention it. Why should a mutation be any more likely to be selected than other alleles already in the population?

I think Iíve already made the most relevant comments about mutations though.

1) First that even if they do create new alleles, once they are selected the population loses genetic diversity by eliminating the competing alleles as it develops whatever new phenotype is favored by the allelic mix. Doesn't matter if it's a mutation that is selected or not.

2) And second even if they do create new alleles, they ARE just alleles, variations in the sequence along the gene locus, and whatever changes occur can only occur with respect to whatever that gene does. If it governs fur color then the allele may produce a new fur color. But you arenít going to get any changes beyond these limited changes within the purview of the gene itself and it really doesnít do more than a pre-existing allele would do anyway.

So in fact mutations don't increase diversity at all.


He who surrenders the first page of his Bible surrenders all. --John William Burgon, Inspiration and Interpretation, Sermon II.

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Faith
Inactive Member


Message 21 of 1034 (691716)
02-24-2013 7:37 PM
Reply to: Message 15 by vimesey
02-24-2013 4:47 AM


Re: Thanks for Acknowledgments of the Claim of Reduced Genetic Diversity
What you haven't yet grasped is that SELECTION always inevitably reduces genetic diversity.

But isn't the point that whilst selection often reduces diversity, mutation is adding diversity to a population at a greater rate.

Not really, as I've argued above. First they don't add anything really new to the gene pool, as they merely change the sequence of an allele for a given gene and can only be a variation on whatever that gene does, which the existent alleles already do quite well anyway, and second, selection eliminates the alleles that don't contribute to the phenotype anyway. In nature this most likely happens through mere geographic isolation. Anything that reproductively isolates a small portion of a population will act as a selection, bringing out new phenotypes based on the new gene frequencies, while the other alleles are not expressed and if the population is small enough eliminated altogether.

There is no way to get around the effect of selection or reproductive isolation, it always leads to reduced genetic diversity for a particular lilne of variation or breeding.

Edited by Faith, : No reason given.


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Coyote
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Posts: 6117
Joined: 01-12-2008


(3)
Message 22 of 1034 (691717)
02-24-2013 7:56 PM
Reply to: Message 20 by Faith
02-24-2013 7:32 PM


Re: Nonsense
My claim is that this IS the definition of evolutionary change, there is no other, it can only proceed by reducing genetic diversity. Wherever there is any kind of selecting or culling process whatever, reduced genetic diversity is the result.

So you are claiming that, in the diagram below, the 14 species that evolved from the common ancestor collectively exhibit less genetic diversity than the common ancestor?


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

Belief gets in the way of learning--Robert A. Heinlein

How can I possibly put a new idea into your heads, if I do not first remove your delusions?--Robert A. Heinlein

It's not what we don't know that hurts, it's what we know that ain't so--Will Rogers


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Faith
Inactive Member


Message 23 of 1034 (691718)
02-24-2013 8:12 PM
Reply to: Message 17 by Percy
02-24-2013 9:57 AM


Re: Thanks for Acknowledgments of the Claim of Reduced Genetic Diversity
Also fundamental to modern concepts of evolution is that both increased and reduced genetic diversity *can* be a result of the evolutionary processes of mutation and natural selection (and this too has been said many times before). This is because mutation and natural selection are opposite forces. Mutation increases diversity, selection decreases diversity.

In the balance the selective processes always win so that mutation actually as a matter of fact does not increase diversity in any way that facilitates evolution, and in a certain sense doesn't increase diversity at all. This is because the selection processes, and I'm including anything that creates a smaller population and isolates it, which can be geographic isiolation, will act on mutations just as on any allele, whichever happen to be in greater numbers dominating the new phenotype, the competitors being eliminated over time. Theoretically you could have many new alleles through mutation but they are still going to be selected and some eliminated and the overall genetic diversity reduced for any new subpopulation that is created from the larger population.

To make clear the point, a successful species whose range is increasing will experience burgeoning numbers and increasing diversity, while a failing species headed for eventual extinction will experience shrinking numbers and decreasing diversity.

You don't get evolution from an expanding population though. Where you get evolution is in the development of new phenotypes and that only comes about through some form of selection, a smaller population portion that gets reproductively isolated etc. All you have in the larger population is a nice healthy population. Also the increasing diversity is assumed, not witnessed. You may get variations of course, in fact you always will, but if it only when a smaller portion of the population gets isolated that the variations could actually develop into a new variety or breed. This could happen within the larger population by genetic drift or reproductive isolation of a particular variation through some sort of mating preferences too. But in any case you will have selection and selection is what reduces genetic diversity. Doesnt' matter how much diversity you start out with, doesn't matter how much might accumulated in a large population (which again I doubt. I don't think new genetic material occurs at all, although new traits certainly would).

...believe it or not "differing environments" is NOT what creates the new phenotypes.

Evolution does not describe environments as creating new phenotypes. Rather, an environment is more like the mold into which evolution is trying to find phenotypic fits.

My point was that the environment may hnot have any effect whatever. You will get new phenotypes, new varieties, new breeds, simply by the isolation of a smallish number of individuals from a larger population. The new gene frequencies all by themselves will bring about the phenotypic change, and this can occur in the same kind of environment as the parent population. Adaptation is not always at work in these selection processes, many new phenotypes are simply what happens when genes are shuffled.

The genetic situation itself is what creates the new phenotypes, the fact that a new mix of alleles forms the gene pool of the new population compared to the old.

Alleles are remixed during reproduction, providing additional variation upon which selection operates.

That is correct.

And new alleles are a result of the imperfect copying that occurs during reproduction, and upon which selection also operates.

I've been accepting this for the sake of the argument, and will go on accepting it although I don't think new alleles are ever formed. I think variation or the development of new breeds or phenotypes comes about simply by the changing of frequencies of the occurrences of the alleles in the population.

Reproduction, mutation and selection, in other words evolution, are what create what you described as the "genetic situation."

Yeah, OK. As I said I'm accepting mutation although I don't think it actually creates viable alleles. Again, doesn't matter how many new alleles did get created, selection will still have the effect I'm talking about of reducing genetic diversity as new phenotypes are formed.

The actual process of evolution by means of mutation and natural selection can only lead to increased diversity because there is nothing to prevent the imperfect copying of reproduction.

If it occurs at all, which I doubt, then you will get a temporary increase in diversity. If there is no selection the mutations will simply occur here and there in the overall population, and new traits may certainly develop from them, but the only way you'll get a new breed or variety is if there is selection, reproductive isolation, etc etc etc and that can't happen without reducing the genetic diversity.

What you haven't yet grasped is that SELECTION always inevitably reduces genetic diversity.

I misspoke. What I meant to say is that change (not increasing diversity) is inevitable because of the imperfect copying of reproduction.

OK

You can have mutations galore within a population but once you have selection of whatever mix of mutations -- or alleles however formed -- selection reduces genetic diversity in the new population. Selection brings a certain allele mix to expression in the phenotype BY ELIMINATING COMPETING ALLELES from the gene pool.

As I explained above, evolution can cause both increased and decreased diversity.

And as I have explained above in the end the diversity will be reduced as new phenotypes are created. Any increase in diversity will be temporary at best.

Mutation and selection are working at cross purposes, mutations providing variation willy-nilly without regard to fitness, and selection pruning the variation that fits the environment least well. The environment plays a major role in deciding whether mutation or selection wins out as measured by allelic variation.

It really doesn't play that major a role but I don't care, have that part of it your way for now. But WHENEVER you get selection you are ALWAYS going to get reduced genetic diversity. That's the only way you get new phenotypes.

Each newly born person possesses, on average, approximately 100 random mutations, DNA sequences that are different from either parent. This is due to the imperfect copying of reproduction. As the human population grows variation can only increase because the mutational process is outrunning the selection process.

It can never outrun the selection process if you understand what I'm getting at. First of course I don't believe any of those mutations are of any value to us, I believe they are all either "neutral" meaning all they do is damage an existing allele to no particular purpose, or they're deleterious. But again, going along with this belief that they are useful, they are still only going to provide a variation on an existing allele, within the purview of the gene locus, and there isn't all that much variety you could possibly get that isn't already expressed in alleles in the population anyway. But again, even if there is some increase in diversity, that diversity is going to get reduced with any selection/reproductive isolating event. This formula is NEVER going to bring about evolution as you envisage it. You get some variation on existing traits, nothing more than that, and whammo it all gets cut down to size by selection.

Actually they would evolve according to the particular mix of alleles in their gene pool, which may adapt to peculiarities in their environment certainly, but the environmental factor is not necessarily the driving factor.

Environment is not the only factor, but it is certainly the driving factor. This is self-evidently true because everywhere we look in nature there is adaptation to the environment. It's ubiquitous.

Yes there is adaptation to the environment but all you need for change to occur, for new phenotypes to develop, is the new gene frequencies created by a population split. Adaptation happens but the environment isn't the driving force in most cases. That would be severe natural selection and while it must happen to some extent, not nearly to the extent evolution supposes. Mere gene shuffling will give you new varieties in nature just as it does in domestic breeding.


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Faith
Inactive Member


Message 24 of 1034 (691719)
02-24-2013 8:15 PM


Request
Could I please request that posters not pile on here yet. I'm not feeling well and it's hard to get the little done I've already done. I really want to get to all of it and hope to eventually, but it gets harder when there are too many posting at once.

Thanks.


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Theodoric
Member
Posts: 5902
From: Northwest, WI, USA
Joined: 08-15-2005
Member Rating: 4.7


Message 25 of 1034 (691720)
02-24-2013 8:39 PM
Reply to: Message 20 by Faith
02-24-2013 7:32 PM


Re: mutations
So your whole argument basically comes down to this.

Don't confuse me with he facts my mind is made up*

* Not an actual Faith quote


Facts don't lie or have an agenda. Facts are just facts

"God did it" is not an argument. It is an excuse for intellectual laziness.


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herebedragons
Member
Posts: 1493
From: Michigan
Joined: 11-22-2009


(1)
Message 26 of 1034 (691731)
02-24-2013 11:26 PM
Reply to: Message 24 by Faith
02-24-2013 8:15 PM


Re: Request
Don't feel as if you have to respond to everyone. Limit yourself to only those that will help move your topic forward. Just ignore posts that aren't going the direction you want. For example, I don't think you are looking to have basic evolutionary theory explained to you, you are looking for reasons that your idea does or does not offer a valid explanation. Since you are proposing an alternate theory to the standard model, responses that explain the standard model really don't help you. No one should be offended if you don't respond to everyone. It can be overwhelming.

I hope to keep up this discussion with you, but don't have a lot of spare time right now. You'll have to be patient with me.

Feel better

HBD


Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for. But until the end of the present exile has come and terminated this our imperfection by which "we know in part," I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca

"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.


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herebedragons
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Posts: 1493
From: Michigan
Joined: 11-22-2009


(3)
Message 27 of 1034 (691734)
02-24-2013 11:58 PM
Reply to: Message 25 by Theodoric
02-24-2013 8:39 PM


Re: mutations
So your whole argument basically comes down to this.

Don't confuse me with he facts my mind is made up*

* Not an actual Faith quote

Actually Theodoric, I think she has a reasonably thought out argument here. I am not saying I agree with it, but it deserves more than ridicule. Few creationist do anything but repeat the B.S. they read on creationist websites, so its nice to see someone who has thought something through for themselves. Personally, I have never heard this argument before and it is kind of intriguing.

Maybe her mind is already made up ... but so what. Don't we all suffer from that???

HBD


Whoever calls me ignorant shares my own opinion. Sorrowfully and tacitly I recognize my ignorance, when I consider how much I lack of what my mind in its craving for knowledge is sighing for. But until the end of the present exile has come and terminated this our imperfection by which "we know in part," I console myself with the consideration that this belongs to our common nature. - Francesco Petrarca

"Nothing is easier than to persuade people who want to be persuaded and already believe." - another Petrarca gem.


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Faith
Inactive Member


Message 28 of 1034 (691737)
02-25-2013 2:45 AM
Reply to: Message 22 by Coyote
02-24-2013 7:56 PM


Re: Nonsense?
My claim is that this IS the definition of evolutionary change, there is no other, it can only proceed by reducing genetic diversity. Wherever there is any kind of selecting or culling process whatever, reduced genetic diversity is the result.

So you are claiming that, in the diagram below, the 14 species that evolved from the common ancestor collectively exhibit less genetic diversity than the common ancestor?

Not "collectively." I'm not even sure what that means. * The idea is that any ONE line of development of a new species will have reduced genetic diversity from its parent population. The smaller the new population the greater the phenotypic change and the greater the loss of genetic diversity.

It's possible of course that both parent and daughter population will be about the same size, in which case both populations would undergo both phenotypic change and reduced genetic diversity to about the same degree. In fact unless the parent population is a great deal larger in numbers than the daughter population both populations will alter in this same way to some extent so that I would think it could be hard in some cases to know which population was which unless you knew the actual history of the divergences.

That's a nice chart.

I've proposed a test for my view of this but I gather it wouldn't be easy, and in the wild the results might not be very reliable because of the factors I describe above. The test would be sampling the DNA of many individuals in both parent and daughter populations to see if I'm right that the genetic diversity is reduced in the daughter.

It would work better if it could be set up in a laboratory, but you should start with a population that has a lot of genetic diversity to begin with. Which you could only know by examining its DNA, and I don't know if that would require complete sequencing or if you could select particular genes to sample etc. On the Intro to Genetics thread I got the impression it might be a lot harder than I imagine.

Anyway the idea is that you start with a cage full of whatever this creature is, mice maybe, test the DNA and then separate out a small portion of individuals to separate cages, let them interbreed for enough generations so that each new population is characterized by its own phenotype and then check the DNA of each.

The numbers involved could of course rapidly become too much for a laboratory to keep.

You could also separate out a new portion from each of the new populations and do the same thing. You should have new phenotypes after some generations of mixing of each new population AND measurably less genetic diversity from their parent population which you had previously checked. I figure genetic diversity can often be recognized by how much hetero versus homozygosity is present.

* ABE: Collectively all the finch varieties together could have all the alleles of the original population, that is, all its genetic diversity. It's as separated varieties that their genetic diversity is reduced.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.

Edited by Faith, : No reason given.


This message is a reply to:
 Message 22 by Coyote, posted 02-24-2013 7:56 PM Coyote has responded

Replies to this message:
 Message 39 by Coyote, posted 02-25-2013 10:40 AM Faith has not yet responded

  
PaulK
Member
Posts: 14715
Joined: 01-10-2003
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(1)
Message 29 of 1034 (691738)
02-25-2013 3:34 AM
Reply to: Message 20 by Faith
02-24-2013 7:32 PM


Re: mutations
quote:

My point was that it just doesnít happen as much as you apparently think it should, as breeders arenít always having to fight new traits, at least after the breed is well established.

Then your point was both badly phrased and based on a misunderstanding of the timescales involved. We are talking of periods of tens or hundreds of thousands of years for natural species, not the few hundred we have limited records for. Indeed I don't think you can even get a good estimate of how many have occurred in the last few hundred years.

quote:

Even in nature we see pretty homogeneous groups maintaining their character donít we? Populations of identical individuals keeping to their own kind, birds of a feather flocking together as the saying goes. Darwinís Galapagos turtles were of an identifiable kind, differing in identifiable ways from those on the mainland. His finches had something like four different styles of beaks that specialized in four different ways of getting food, and these types hung out with others of their same beak. There does seem to be a strong family inclination in nature.

But let us note that these are all species and we've no reason to think that they are anything like as genetically impoverished as your breeds. A simple idea that they "all look the same" is hardly a measure of genetic diversity.

quote:

But thatís not a particularly important point. the main point about mutations of course is the claim that evolution depends on increasing diversity which mutations supposedly supply. Iíve already argued that as soon as a trait is selected, whether it originated by mutation or by simple sexual recombination of existing alleles for that characteristic, whether by chance or conscious intent, that very selection reduces the genetic diversity of the breed or wild population. My claim is that this IS the definition of evolutionary change, there is no other, it can only proceed by reducing genetic diversity. Wherever there is any kind of selecting or culling process whatever, reduced genetic diversity is the result.

But of course, the fixed allele is - generally - free to mutate too, perhaps modifying the trait or contributing to a new one. If you define evolution solely in terms of natural selection leaving out mutation then you get the result you want, but it's still a misrepresentation of the theory.

quote:

Again, the point was it doesnít happen at such a rate as to interfere with breeding programs. But the second point Iíd make here is that there seems to be this odd idea that it will always be the MUTATION that is selected for. Iíve noticed this before. I think itís probably just a case of imprecise thinking but thought Iíd mention it. Why should a mutation be any more likely to be selected than other alleles already in the population?

Of course we have evidence of mutations contributing to breeding programs and I very much doubt that there would be many records that let us work out where mutations have been removed by breeders, so I don't think you have enough information to make an argument here.

Your second point is another mistake. I find it very hard to believe that you've never seen any mention of deleterious mutations and I know that I referred to stabilising selection in a reply to you quite recently.

quote:

1) First that even if they do create new alleles, once they are selected the population loses genetic diversity by eliminating the competing alleles as it develops whatever new phenotype is favored by the allelic mix. Doesn't matter if it's a mutation that is selected or not.

THe assumption there is that fixation is a very rapid process, and there is not an extensive period where multiple alleles exist. Indeed unless being selected for it takes a considerable time for an allele to reach fixation by drift.

quote:

2) And second even if they do create new alleles, they ARE just alleles, variations in the sequence along the gene locus, and whatever changes occur can only occur with respect to whatever that gene does. If it governs fur color then the allele may produce a new fur color. But you arenít going to get any changes beyond these limited changes within the purview of the gene itself and it really doesnít do more than a pre-existing allele would do anyway.

What genes - and perhaps more importantly regulatory sequences do - can be quite subtle. And it can be possible to build on new traits, too - cumulative change is a major point in evolution However I don't really see the point you're trying to make even after that. A new variation is a new variation in whatever it is. You seem to be saying "just because it's different doesn't mean that it's different" which is rather obviously wrong.


This message is a reply to:
 Message 20 by Faith, posted 02-24-2013 7:32 PM Faith has responded

Replies to this message:
 Message 34 by Faith, posted 02-25-2013 8:41 AM PaulK has responded

    
Faith
Inactive Member


Message 30 of 1034 (691739)
02-25-2013 3:49 AM
Reply to: Message 19 by dwise1
02-24-2013 3:30 PM


Re: The effect of the flood bottleneck
I'm not ignoring it, DWise, I'm answering it. It doesn't matter how much genetic diversity you create or think you create, or how much was already present (which is my point of view since I don't think mutations create anything beneficial), you are still only creating the genetic material that will be affected by selection just as I've been describing.

It doesn't matter what diversity you begin with, what created it, how much there is, when a smaller population gets isolated it's going to undergo exactly what I'm describing here: that is, to get new phenotypes, such as all those finch varieties in Coyote's chart, the new population will naturally also have reduced genetic diversity from the original.

Sure you may have mutation-created alleles in the new mix (if anything other than damage actually occurs by mutation, which again of course I don't believe), but even if you do they are still going to have to either become part of the new phenotype while the gene pool as a whole loses genetic diversity, or they will themselves have been eliminated in the population split.

The increase in diversity ends up amounting to very little if anything at all.


This message is a reply to:
 Message 19 by dwise1, posted 02-24-2013 3:30 PM dwise1 has not yet responded

Replies to this message:
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