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Thread: Question on evolution

  1. #1 Question on evolution 
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    Hi,

    So I was thinking about evolution the other day after watching a documentary
    on Charles Darwin and there's something that I just could not figure out .

    Natural selection is one of the ways by which evolution can occur right ?.
    An example would be how micro organisms develop immunity to antibiotics
    over time (because the ones with mutations that allowed them to be resistant to
    the antibiotics lived on).

    What I am confused about is the beak variation that Darwin found in Finches on Galápagos Islands, the beaks varied depending on the diet of the Finches.

    What I don't understand is how the change in beak was triggered, if I'm not wrong some birds needed bigger stronger beaks to crack open seeds etc but did not have them and eventually developed them overtime. So there was a requirement there,
    how does the change get triggered at a genetic level ? Does the bird's body realise that bigger beaks are needed and therefore makes changes at a genetic level ?


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  3. #2  
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    Beak size is not something that is constant in a population. If one looks at any population of birds, one will find a number of different types of beaks, within a certain range. In the Galapagos, there are different food resources available on different islands. Some beak shapes do better on different islands. Birds that stay on a particular island and have a beak shape that is better than others will tend to get more resources and thus tend to breed more.

    Occaisionally, mutations can arise that change beak shape or the sexual shuffling of genes can change beak shape, usually these changes are small. Whether or not these changes persist depends on the conditions on an island.


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  4. #3  
    Forum Professor Zwirko's Avatar
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    It's not easy to put together a precise molecular sequence of events, but some work has been done. Here's two papers that describe some work in this area:

    Bmp4 and Morphological Variation of Beaks in Darwin's Finches
    Abzhanov, Arhat; Meredith Protas, B. Rosemary Grant, Peter R. Grant, Clifford J. Tabin
    Science 3 September 2004:
    Vol. 305 no. 5689 pp. 1462-1465

    Quote Originally Posted by Science Magazine
    Darwin's finches are a classic example of species diversification by natural selection. Their impressive variation in beak morphology is associated with the exploitation of a variety of ecological niches, but its developmental basis is unknown. We performed a comparative analysis of expression patterns of various growth factors in species comprising the genus Geospiza. We found that expression of Bmp4 in the mesenchyme of the upper beaks strongly correlated with deep and broad beak morphology. When misexpressed in chicken embryos, Bmp4 caused morphological transformations paralleling the beak morphology of the large ground finch G. magnirostris.
    The calmodulin pathway and evolution of elongated beak morphology in Darwin's finches
    Abzhanov, Arhat; Winston P. Kuo, Christine Hartmann, B. Rosemary Grant, Peter R. Grant and Clifford J. Tabin
    Nature 442, 563-567 (3 August 2006)

    Quote Originally Posted by Nature
    Our results indicate that local upregulation of the CaM-dependent pathway is likely to have been a component of the evolution of Darwin's finch species with elongated beak morphology and provide a mechanistic explanation for the independence of beak evolution along different axes. More generally, our results implicate the CaM-dependent pathway in the developmental regulation of craniofacial skeletal structures.
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  5. #4  
    Forum Radioactive Isotope skeptic's Avatar
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    Beak size is related to food choice. If a bird has a small beak, it is restricted to easily cracked foods. if the beak is bigger, it is able to crack larger seeds and nuts. This may widen its food choices, and improve its survival chances.

    Of course, if large seeds and nuts are not abundant, the bird may be better off with a small beak better able to prize out smaller items. It all depends on what is available, and beak size evolves to fit the food choices.
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  6. #5  
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    how does the change get triggered at a genetic level ? Does the bird's body realise that bigger beaks are needed and therefore makes changes at a genetic level ?

    No individual bird's beak changes in a heritable way once it has been born. I.e. the flow of information does not reverse from phenotype to genotype. Sorry for stating this, I know that you most probably already are aware of this. Just wanted to clarify since the above sounded distinctly Lamarckian.

    Cheers
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    Quote Originally Posted by tridimity
    how does the change get triggered at a genetic level ? Does the bird's body realise that bigger beaks are needed and therefore makes changes at a genetic level ?

    No individual bird's beak changes in a heritable way once it has been born. I.e. the flow of information does not reverse from phenotype to genotype. Sorry for stating this, I know that you most probably already are aware of this. Just wanted to clarify since the above sounded distinctly Lamarckian.

    Cheers
    Actually, I'm not sure he did know, so good point.

    Long story short: There are natural variations in beak size among a population. Those with beaks more suited for certain food sources will be better at utilizing that food source and produce offspring that would on avergae also be more suited to utilizing that food source. The offspring of that finch then on average have beaks that are larger, as the median of the variation is more offset towards larger. Then the next generation's beak size varies from a base median that might be larger still, and so on.

    Here is a little thought experiment:

    Take a die with seven sides, numbered accordingly, with 4 as the median. A result can be 4 or either larger or smaller than 4. If after the first throw the number is say 5, then take a new die with numbers ranging from 2 to 8, with the median at 5 and start over.

    In nature, natural selection would drive the median beak size higher of the finches capable of gaining an advantage from the alternative food source (more successful offspring). Sexual selection might help drive beak size as well, as females that choose males based on beak size will have more viable offspring on average; offspring that on average in turn have females that will choose partners based on beak size and might have larger beaks in general across the sexes.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  8. #7 What Darwin Got Wrong 
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    The explanatory power of natural selection is exactly the topic of Jerry Fodor's book, What Darwin Got Wrong. It's definitely worth looking at. And it is NOT religious. Fodor and his co-author proclaim their atheism in the introduction.

    Basically, they argue that genetic research is finding so many instances of "coextensive" genes -- genes that must travel together because they are tied to a common "master" gene -- that it effectively puts a leash on possible phenotypic variations from which natural selection can choose.

    Another argument has to do with "selection for" particular traits. Nature does not have a deliberating mind, so it cannot select "for" anything in particular. Were polar bears selected for being white or for matching the environment? Why aren't penguins white? What if the polar environment had been green? Natural Selection theory does not have sufficient explanatory power to answer these kinds of questions.

    The concepts of "trait", "adaptive advantage", and "fitness" can all be debunked. Something else is going on.
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    To starlarvae

    Fodor was not anti-evolution. He simply wrote a book trying to tidy up some of the concepts of evolution. His title was designed, not to rubbish Darwin, but because the marketing types thought that title would attract more buyers.

    Polar bears are white because they hunt prey on land, over the polar ice. Camouphlage is needed.

    Penguins are not white because they do not hunt prey on land, and there is no predator that hunts them on land (sea leopards hunt them in water) so camouphlage is not needed.
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    Quote Originally Posted by skeptic
    To starlarvae
    Fodor was not anti-evolution. He simply wrote a book trying to tidy up some of the concepts of evolution. .
    You are right that he is not anti-evolution, nor did I imply that he is. It's hard to argue with fossils.

    But he definitely set out to do more than "tidy up". Fodor's attack is directed at the concept of natural selection and its inability to account for how phenotypes got to be how they got to be. He says that natural selection is an incoherent concept. NatSel is central to the Darwinian paradigm. If it is marginalized, then the game is up for grabs.

    Quote Originally Posted by skeptic
    Polar bears are white because they hunt prey on land, over the polar ice. Camouphlage is needed.
    Yes, this is the accepted story. If the arctic ice were plaid, would polar bears be plaid?
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  11. #10  
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    Quote Originally Posted by skeptic
    Penguins are not white because they do not hunt prey on land, and there is no predator that hunts them on land (sea leopards hunt them in water) so camouphlage is not needed.
    Actually, penguins are camouflaged for the water. They're dark on top and light underneath so that they're less easily seen from below when looking into the lighter, upper waters and less easily seen from above when looking down into the darker, deeper waters. It's called countershading.

    And this is related to what starlarvae said, because penguins are not white, but their coloration is selected for their environment.
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  12. #11  
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    Starlarvae

    Natural selection is far from being an incoherent process. It is not the sole process involved in evolution, with artificial selection, genetic drift and horizontal gene transfer having an effect. However, you cannot have evolution without natural selection. The details of the mechanisms of natural selection may require careful study, but the overall process is real.
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  13. #12  
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    Quote Originally Posted by skeptic
    Starlarvae

    Natural selection is far from being an incoherent process. It is not the sole process involved in evolution, with artificial selection, genetic drift and horizontal gene transfer having an effect. However, you cannot have evolution without natural selection. The details of the mechanisms of natural selection may require careful study, but the overall process is real.
    Those that survive survive, and so their traits get handed on. Grandma knew that. We don't need a scientific theory about it.

    Fodor put it nicely. Selection can at most tune the piano, but it cannot compose the melody.

    Problem is, Darwinians tend to make natural selection the (overwhelmingly) primary mechanism behind phenotypes being what they are. Too many endogenous factors intervene, however. One needs to address Fodor's point about counterfactuals, or selectionism largely falls by the wayside.
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  14. #13  
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    Quote Originally Posted by starlarvae
    Quote Originally Posted by skeptic
    Starlarvae

    Natural selection is far from being an incoherent process. It is not the sole process involved in evolution, with artificial selection, genetic drift and horizontal gene transfer having an effect. However, you cannot have evolution without natural selection. The details of the mechanisms of natural selection may require careful study, but the overall process is real.
    Those that survive survive, and so their traits get handed on. Grandma knew that. We don't need a scientific theory about it.

    Fodor put it nicely. Selection can at most tune the piano, but it cannot compose the melody.

    Problem is, Darwinians tend to make natural selection the (overwhelmingly) primary mechanism behind phenotypes being what they are. Too many endogenous factors intervene, however. One needs to address Fodor's point about counterfactuals, or selectionism largely falls by the wayside.
    Whose Grandma?

    Darwin's Grandad had the idea that evolution existed, but he did not have the foggiest idea of any mechanism. Charles Darwin came up with the mechanism.

    Selection does a lot more than merely "tune the piano". While it is not the only mechanism at work, it is crucial to the whole thing.
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    It is a worthy reminder that Jerry Fodor's views have been widely addressed and refuted.

    Although Darwin himself was frustrated at the charge that he believed Natural Selection was the *only* proces at work during evolution (he didn't) Natural Selection remains the primary mechanism of the process.

    A far better reanalysis of evolutionary mechanisms comes from "Evolution: The Extended Synthesis" (2010, Muller and Pigluicci)
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  16. #15  
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    Quote Originally Posted by ProcInc
    It is a worthy reminder that Jerry Fodor's views have been widely addressed and refuted.
    Addressed, critiqued, assailed, what have you. But not refuted.

    Quote Originally Posted by ProcInc
    Although Darwin himself was frustrated at the charge that he believed Natural Selection was the *only* proces at work during evolution (he didn't) Natural Selection remains the primary mechanism of the process.
    What are other mechanisms of the process? What mechanisms sidestep natural selection?

    Quote Originally Posted by ProcInc
    A far better reanalysis of evolutionary mechanisms comes from "Evolution: The Extended Synthesis" (2010, Muller and Pigluicci)
    THanks for the reference. From the reviews on Amazon, it seems like something that could serve my purposes.
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  17. #16  
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    You forgot to put the Muuuhhhhhhhaaaaaaaa at the end of your post. It's okay you can borrow mine for the time being.
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  18. #17  
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    Quote Originally Posted by Darkhorse
    You forgot to put the Muuuhhhhhhhaaaaaaaa at the end of your post. It's okay you can borrow mine for the time being.
    Thanks. I couldn't decide between Muuuhhh(etc) or a simple "Heh-heh-heh"
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