the phylogeographic challenge to creationism

But that isn't what evolution says. Unless your talking about "evolutionism", wich could be just about anything you want it to be as there is no such thing.Those two species do have a common ancestor. Otherwise it just ain't evolution. What predictable reduction in genetic diversity? Are you talking about creation? That sure isn't what evolution says is happenning. We do understand about mutations and natural selection? Phenotype or genotype? Perhaps you forgot my explanation for this Faith? In that case here it is: From: Natural Limitation to Evolutionary Processes threadNatural selection does NOT ALWAYS cause a reduction in variation because hidden variation is ALWAYS present in continuously varrying traits. Natural selection can INCREASE variation. How about an example of how this can come about, eh?Suppose you have an environment that favors larger beaks in birds. We'll let + equal the gene for large beaks and - as the gene for small beaks. Because deeper beaks is determined by genes at many loci, a population of even large beaked birds + have some small beak genes -. Now when the birds with the smallest beaks die, alleles for the small beaks are removed from the breeding popuation. This may increase the frequency of the + gene at every loci, but because even the larger beaked birds have some - alleles, variation still remains. Reproduction shuffles these genes within the population and because + genes are more common, individuals in future generations will have more + alleles. Because the more + genes you have the deeper your beak, the population will show a shift to larger beaks, and the new generations biggest beaks will be bigger than the previous generation. If this continues the same thing happens again. The individuals with the biggest beaks will have beaks even larger than the previous generation. As you can see you have MORE variation. This process can even be reversed.An example I have seen used is an experiment on oil content within seeds. The experiment conducted on corn showed that oil content could be increased, after 80 generations, beyond the initial oil content of 4-6%. The researchers were also able to reverse the process and select for low oil content instead. This showed that selection could INCREASE the initial range of variation.
(From Boyd and Silk, ibid, p. 74 with the citing found in the url below) Evolution: Online courseAnd finally, where do you think our domestic dogs have come from? If they come from wolves and we SELECTED traits then of course you should be able to see that we do have MORE dog breeds and MORE variation in this species.It is hidden variation that is selected FOR in many situations of natural selection...It is EXPRESSED variation that is selected for. Hidden variation is later expressed through reproduction/recombination.and:I apologize if I misunderstood what you were saying. It seemed to me that you were talking about variation. Specifically a reduction in variation due to genetic drift/ NS.
I do think I percieve what you are saying and perhaps a misunderstanding about alleles that you might have. In your first post you talked about a reduction in alleles: This is infact not the case. There is no genetic reduction, or reduced allotment of alleles, as if they are somehow reduced. Instead there is a shift in the frequency of alleles by selection working on the expressed alleles. This may or may not cause a reduction in the "FREQUENCY" of an allele, but that is because the frequency of a selected allele is increased. So if we see in our finches with small beaks that they are selected against, we still have a population of larger beaked birds that may have the small beak alleles. In the case of a drastic reduction, such as a bottleneck the allele frequency may shift so much that the allele for small beaks doesn't exist in the population, but the number of alleles for that trait are still there, they may all be large beak alleles.To express this visually, suppose you have a population of birds that vary in beak size according to expressed alleles, as shown below (with - allele for small beaks and + allel for larger beaks). Now remember we are talking about continuouly varrying traits or multiple alleles affect a trait (such as height in humans.)(numbers in parenthesis show hypothetical population)(5) (11) (20) (30) (21) (10) (3)
-- -- -- -+ -+ -+ ++
-- -- -+ -+ -+ ++ ++
-- -+ -+ -+ ++ ++ ++Now if some selection pressure caused the smallest beaked birds to die off you still have - genes in all but the largest beaked birds. There was no "reduction" in the alleles that affect beak size but a reduction in the FREQUENCY of the - allele.This I think is the misperception you have about some reduction.As far as there being a reduction in variability. Variability is the "ability" to vary. What is stopping a mutation to act on or change one of the alleles, even if they were all + alleles? If a mutation acts or changes one of these alleles it will remain hidden and reshuffled among the population if it isn't detrimental to the reproduction of the species UNTIL selective forces act in such a way that this NOVEL ALLELE becomes expressed. This novel allele may or may not help the species to survive.(edited to clarify beak chart a bit)This message has been edited by DBlevins, 11-27-2005 09:55 PM

Where do we get phenotype variation from?As far as the rest of my post goes, please feel free to read it when you are able. I don't want you to feel ganged up upon, even though you and I have had this conversation before. You didn't answer me the last time I gave you this explanation so I thought I'd bring it up again. I linked to the thread where we talked about this before.This message has been edited by DBlevins, 11-27-2005 11:43 PM

I hope you don't feel like you are being piled upon by me. I just want you to understand that selection does not ALWAYS reduce variation. If you read through my post here and hopefully read the link I provided you would see what I am talking about. Natural selection does NOT ALWAYS cause a reduction in variation because hidden variation is ALWAYS present in continuously varrying traits. Natural selection can INCREASE variation. Here is example of how this can come about.Suppose you have an environment that favors larger beaks in birds. We'll let + equal the gene for large beaks and - as the gene for small beaks. Because deeper beaks is determined by genes at many loci, a population of even large beaked birds + have some small beak genes -. Now when the birds with the smallest beaks die, alleles for the small beaks are removed from the breeding popuation. This may increase the frequency of the + gene at every loci, but because even the larger beaked birds have some - alleles, variation still remains. Reproduction shuffles these genes within the population and because + genes are more common, individuals in future generations will have more + alleles. Because the more + genes you have the deeper your beak, the population will show a shift to larger beaks, and the new generations biggest beaks will be bigger than the previous generation. If this continues the same thing happens again. The individuals with the biggest beaks will have beaks even larger than the previous generation. As you can see you have MORE variation. This process can even be reversed.There is no genetic reduction, or reduced allotment of alleles, as if they are somehow reduced. Instead there is a shift in the frequency of alleles by selection working on the expressed alleles. This may or may not cause a reduction in the "FREQUENCY" of an allele, but that is because the frequency of a selected allele is increased. So if we see in our finches with small beaks that they are selected against, we still have a population of larger beaked birds that may have the small beak alleles. In the case of a drastic reduction, such as a bottleneck the allele frequency may shift so much that the allele for small beaks doesn't exist in the population, but the number of alleles for that trait are still there, they may all be large beak alleles.Now if some selection pressure caused the smallest beaked birds to die off you still have - genes in all but the largest beaked birds. There was no "reduction" in the alleles that affect beak size but a reduction in the FREQUENCY of the - allele.This I think is the misperception you have about some reduction.An example I have seen used is an experiment on oil content within seeds. The experiment conducted on corn showed that oil content could be increased, after 80 generations, beyond the initial oil content of 4-6%. The researchers were also able to reverse the process and select for low oil content instead. This showed that selection could INCREASE the initial range of variation.
(From Boyd and Silk, ibid, p. 74 with the citing found in the url below) Evolution: Online course

Would you agree that sickle cell anemia is a disease? Would you say that having this "disease" could be diadvantageous in an area without malaria? Do people with SCA have an advantage over people without SCA in malaria prone regions? Do you know what change'(s) in DNA created SCA?If you don't get my point. Even something that might be 'deleterious' in one region is not necessarily 'deleterious' in another.Though I don't want this to get you off track. Would you agree that something that is considered deleterious can still be passed down to offspring?

Perhaps you need to reread my posts. That is NOT the case. There is ALWAYS hidden variation. While you might eliminate the extreme end of a range of variation that possess only one type of allele, you have to contend with the fact that that allele is not necessarily eliminated from the population. There will be others in the population who continue to carry that allele even though it isn't expressed.Same with mutations. You may cary mutations that aren't expressed unless something in the environment changes, etc. You'd still have a chance to pass that mutation on to your offspring, and they would also have novel mutations, and so on, and so on. What other forms are you talking about? You are clearly wrong in your assertion that eliminating the small beaked birds eliminated their genes. As I said, there is always HIDDEN VARIATION in the population so that even if you eliminate a set of organisms who carry a certain gene, that doesn't mean the gene is eliminated from the population. It can still become expressed later. That was the point of the oil seed experiment, even though they had ELIMINATED the low oil producing seeds that GENE or set of GENES that made those seeds produce low oil amounts STILL EXISTED in the other seeds! Even after 80 GENERATIONS they still had that HIDDEN VARIATION, and the experimenters could go from one range of oil production to another. The GENES for oil production were not ELIMINATED but were not EXPRESSED. No you haven't. The genes for small beaks still exist and if environmental conditions change you can again see small beaked birds from the population because of the HIDDEN VARIATION. As your posts suggests, you have a misunderstanding of the processes themselves. You may have forgetten that there is hidden variation ALWAYS.

Now I realize this is from your reply to Mammuthus, but I thought it bears replying to on this end because it was rather boggling.I am actually rather confused as I am unsure of what you are saying here. Are you saying that the process of speciation reduces future genetic diversity? That the very process of selection keeps any future genetic possibility from happening, that it somehow reduces the ability of DNA to create novel genes? And this reduction of Genetic potential over-rides everything else?Let me know if I am misuderstanding your posts.By the way, just because all the smaller beaked birds are killed, doesn't mean the small beaked bird gene is eliminated from the population. Just to be clear: The feature is eliminated but NOT the gene.I could very well be wrong in my understanding that you think ALL the genes for small beaked birds would disappear with the killing of all the small beaked birds. IE. Therefore the extinction of small beaked birds in a population would keep any small beaked birds in that population from existing again.

This will have to be a short post as I have a final paper draft due toady and class, so here it goes. I wonder if you actually read through the complete articles or picked and choosed what you wanted to paste. I also wonder if there is not some cognitive dissonance working here (IE you read it but unconsciously picked and chose what portions to paste without attempting to understand the article.)The article you quoted goes on to say that you should be careful to distinguish how you measure genetic diversity.

quote:

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Finally, Avise (1994) notes that the level of genetic diversity in one marker class (e.g. allozymes) may not reflect genome-wide diversity. It is important to distinguish among measures of genetic diversity. For example, inbreeding (here connoting mating between relatives) within a population will reduce observed heterozygosity but does not alter overall allele frequencies. In other words, all else being equal (and ignoring possible purging of deleterious alleles), such inbreeding reduces one measure of genetic variability (observed heterozygosity) while the other (allelic diversity) remains the same.
  —Canadian Wildlife service

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(my bold.)And as far as Evolution is concerned, you are correct in stating that it is change in frequency of alleles over time. This is also something you conveniently seemed to gloss over in your use of the link you provided. Namely:

quote:

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Genetic drift: The genetic make-up of a population may change over time because of chance differences in the survival or reproduction of individuals with different genotypes and sampling errors of gametes from one generation to the next ” this process is known as random genetic drift or simply genetic drift...

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Changes in allele frequencies via genetic drift are entirely at random; thus, different populations within a species may follow independent evolutionary trajectories. In other words, genetic drift alone can result in evolution (a change in allele frequencies), although only natural selection produces adaptive evolutionary change...

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While genetic drift leads to a decrease in genetic diversity over time, it is still also an evolutionary constructive process. Which addresses your point below: In short, evolution, described as the process of the change in allelic frequency over time, still occurs without mutation via genetic drift. The caveat being that without mutation and natural selection you don't adapt to environmental changes and eventually go extinct.