those elusive 'barriers'

Discussion in 'Creation vs. Evolution' started by Helen, Jul 27, 2003.

  1. Helen

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    Although it is certainly intuitive that variation can only go so far, the challenge is thrown up time and again regarding the biblical 'kind': "Prove it. Where are the genetic barriers which forbid changing beyond a certain point?"

    I'm going through a lot of material today, doing some research for some upcoming presentations. This was in an email I had not noticed before:

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    A recent paper in Science (July 4, 2003), "Low Potential for Climatic Stress Adaptation in a Rainforest Drosophila Species," indicates that fruit fly species subjected to "intense selection for over 30 generations" "lack[] the ability to evolve further resistance." This seems to imply that even under extreme selection pressure, there are inherent genetic limits the amount of change possible in an organism. The abstract concludes that, "[t]he low potential for resistance evolution highlights the importance of assessing evolutionary potential in targeted ecological traits and species from threatened habitats," implying that species just can't naturally evolve very far very fast in response to environmental changes! The abstract is as follows:

    Low Potential for Climatic Stress Adaptation in a Rainforest Drosophila Species

    A. A. Hoffmann,* R. J. Hallas, J. A. Dean, M. Schiffer

    The ability of sensitive rainforest species to evolve in response to climate change is largely unknown. We show that the Australian tropical rainforest fly Drosophila birchii exhibits clinal variation in desiccation resistance, but the most resistant population lacks the ability to evolve further resistance even after intense selection for over 30 generations. Parent-offspring comparisons indicate low heritable variation for this trait but high levels of genetic variation for morphology. D. birchii also exhibits abundant genetic variation at microsatellite loci. The low potential for resistance evolution highlights the importance of assessing evolutionary potential in targeted ecological traits and species from threatened habitats.

    Centre for Environmental Stress and Adaptation Research, La Trobe University, Bundoora, Victoria 3086, Australia.

    (From "http://www.sciencemag.org/cgi/content/abstract/301/5629/100")
     
  2. mdkluge

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    As is often the case Helen misunderstands fundamentally the issue. No one disputes that some variations in some directions are limited. It's physically impossible, for example, for a fruit to contain more than 100% fructose, or less than 0%, and other more complex physical limitation constrain the possible levels of fructose concentration still further. Similarly physical constraints prevent human beings from exceeding some hight or weight. Variation along particular lines is indeed limited. However, variation can take untold many forms (not an infinite number, byt very many) so that the variation can become excedingly large, although not literally infinite. But variation of a single trait need not be unbounded.
     
  3. Helen

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    1. Thank you for the ad hom -- you are really an expert there!

    2. So you can't have more than 100% of something or less than 0%? My dad used to have a name for that kind of statement: the triumphant discovery of the obvious.

    3. The rest of your response is a great case of hedging a response.

    In the meantime, it seems that boundaries exist not only intuitively, but in the real world, too.
     
  4. The Galatian

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    I guess Helen has made the triumphant discovery of the obvious, then.

    Not all organisms are capable of evolving a suitable response to envirionmental pressures. In fact, in the history of the Earth the great majority of them have not been able to do this.

    They became extinct.

    "Triumphant discovery of the obvious", indeed.
     
  5. Peter101

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    &gt;&gt;&gt;&gt;&gt;&gt;Although it is certainly intuitive that variation can only go so far, the challenge is thrown up time and again regarding the biblical 'kind': "Prove it. Where are the genetic barriers which forbid changing beyond a certain point?"&lt;&lt;&lt;&lt;&lt;&lt;

    It is not intuitive to me, that variation can only go so far. There is no limit to the number of mutations that can take place, and therefore there should be no limit to the amount of variation that can take place. Helen speaks as if the amount of possible variation is fixed in the genes. I don't see how that can be so, since mutations can and will take place without end and without limit. In other words, I would contend that the huge amount of variation seen in dogs was not all present in their wolf ancestors but has been acquired through mutations after the first wolves were domesticated.

    The substantial physical variation found in humans was not carried in the genes of the first humans but has been acquired by mutation in the last few tens of thousands of years. This fits well with what is known of human migrations. Blacks remained in Africa and therefore retained or acquired black pigmentation as a sunscreen. Their descendents, 30 or 40 thousand years ago, migrated to the north, where mutations allowed them to become lighter and to take advantages of some of the benefits of having lighter skin in northern latitudes.

    It is interesting that those races that have a history of keeping dairy cattle are also those races who can tolerate drinking milk while races, such as the Chinese, without a history of dairying cannot drink milk because of the lack of a certain enzyme for milk digestion. As someone has said, nothing makes sense except in the light of evolution.
     
  6. Paul of Eugene

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    Lessee. Helen found proof that flies can only go so far in being drought resistant and no further.

    From this she draws the conclusion that there is a kind barrier that cannot be crossed.

    The logic escapes me.
     
  7. Helen

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    Didn't go so far as that, actually, Paul. You folks have asked for evidence. There is one piece of it, that's all.
     
  8. The Galatian

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    Does the fact that other insects have evolved resistance to dessication mean anything?

    It seems that this is a new elaboration of "Oh, yeah? Well show me a dog evolving into a horse!" argument.

    It presupposes the Cartoon Theory of Evolution.
     
  9. Helen

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    LOL, I have never asked anyone to show me a dog evolving into a horse, so please don't try to lie about that, Galatian. I have asked for anyone, however, to show me any time where some variation or group of variations is great enough to cause the scientists to say, "That is now no longer a ....." -- whatever type it was originally.

    Speciation is not evolution, by the way. You may have a new species of canine, or a new species of fly, or whatever, but the grouping of 'canine' and 'fly' etc. remain, showing that the animal still belongs to that original group. That is an indication of kind.

    As far as insects go, if the exoskeleton was not there to resist moisture loss in the first place, they wouldn't have survived at all.
     
  10. Paul of Eugene

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    The pace of evolution is slow enough we can barely observe speciation, so I don't think we'll see a natural evolution of a new kind in our lifetimes. But I've got a question for you, Helen - suppose somebody somewhere succeeds in breeding bacteria to become a multibodied form instead of single celled. Would that count as crossing the kind barrier to your way of thinking?

    I don't know that anybody is even trying to do that right now, it seems to my little head like a worthwhile research project.
     
  11. ChurchBoy

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    I am really curious. What is the Cartoon Theory of Evolution?
     
  12. UTEOTW

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    I wish I had the whole paper to read, though I imagine it would be over my head.

    But let's see if I am reading this correctly, per the abstract. They found that the particular species of fruit fly has a range dessication resistence. They then took samples of the most resistive and found that these that were already most resistive did not become any more resistive when environmental pressures were applied over 30 generations. Finally, they did genetic analysis where they found that this group of flies being tested had a lot of genetic variability in general but had very little variablity in the genes that caused the resistence to dessication.

    So we have shown that there is a limit to how extreme this particular trait can become. That seems to make sense, especially over a few generations and given that the most resistive genes in this population had already been selected for in this population. I would like to know if the authors think that more resistence would be possible over more generations or if this was considered to be an endpoint.

    But even if this is a limit that cannot be crossed even if given a much larger number of generations, in-my-humble-uneducated-in-this-field-opinion, I do not see how this limits change between species, genera, families, orders, etc. It is a limit on a particular trait.

    Helen, I appreciate what you are doing here. It is refreshing to see a YEC pulling material from recent science and using it in context to advance a case. This is a reasonable response to the challenge you are attempting to answer. I just do not see how it helps you though I can see how you see that it helps you. If you see what I meant by that last statement. [​IMG]
     
  13. Peter101

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    &gt;&gt;&gt;&gt;&gt;&gt;&gt;Speciation is not evolution, by the way. You may have a new species of canine, or a new species of fly, or whatever, but the grouping of 'canine' and 'fly' etc. remain, showing that the animal still belongs to that original group. That is an indication of kind.&lt;&lt;&lt;&lt;&lt;&lt;&lt;

    I think that if you admit that new species can be formed, then you have conceded the whole argument.
     
  14. Paul of Eugene

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    I am really curious. What is the Cartoon Theory of Evolution? </font>[/QUOTE]Churchboy, when an evolutionist speaks of the cartoon theory of evolution, she/he is talking about an oversimplification of the theory of evolution that leaves out key elements and adds in spurious elements such as sudden appearance of whole new parts in all their finished, detailed glory out of nothing.
     
  15. Helen

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    No one is arguing speciation, Peter. In fact I have posted before about how easily a new species can be declared. The argument is about common descent. Please stop this baiting and mocking.
     
  16. UTEOTW

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    Helen

    I think that the point is that you admit to new species and even genera and that there have been what would be called new species emerge while we were watching so to speak. So why not new families if given a bit longer time? Or new orders given an even longer time? The fossil record preserves good evidence of new families and new orders arising from others. So why are these interpretations wrong, what interpretation better fits the evidence, and what prevents new families and orders but allows new genera and species in short periods of time?

    It seems to me that what your abstract shows is a limit on how much a particular trait can change in a short period of time. It is not clear to me how this relates to limits on new families and above.
     
  17. DM

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    Actually, it's a very brief, clear, and straightforward paper. I doubt it would be over your head. Essentially, they already know that a number of generalist, widespread species of Drosophila have high heritability and variability in dessication resistance, but they are asking whether this can be applied to more specialist species restricted to high-humidity habitats that may face habitat dessication in the future. As the abstract says, they found that these flies have very low heritability and genetic variability *for this one trait*, and *in contrast* to other, generalist Drosophila species. Additionally, these flies are about as highly genetically variable for morphological traits as widespread generalist flies are.

    So it seems that the conclusions that Helen was trying to draw are not in fact supported by the paper itself. In this one trait, selection has acted to limit future potential, which could be a problem for the flies *if* their habitat dries out. As Galatian has already pointed out, this is hardly a major surprise, since the vast majority of species do not make it. However, morphological variability in general is high, so we are still left to wonder where these so-called "barriers" are supposed to be.


     

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