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Thread: Hummingbird changes - Natural Selection

  1. #1 Hummingbird changes - Natural Selection 
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    Video about Chris Schneider, biologist studying hummingbirds in Ecuador:
    http://www.pbs.org/wgbh/evolution/li...1/2/e_s_4.html

    Toward the end, it states:
    "You cannot make your arm longer (to reach a book on a shelf up high).
    Hummingbirds cannot make their bills longer.
    Their bill length is determined by the DNA they inherited from their parents."

    But at the beginning, it says: "Natural Selection will result in changes in wing shape that allow hummingbirds to fly longer distances, or
    it'll affect the length and shape of the bill."

    Isn't that contradictory?
    At what point are the bills changed, if the hummingbird itself cannot change it?


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    WYSIWYG Moderator marnixR's Avatar
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    what a pitiful example of genetic determinism
    in that view every member of a species is genetically and morphologically a clone of another, which is clearly not the case

    variability in hundreds of characteristics is all around us, and if hummingbirds, within the range of their species, make a better living out of having a longer beak then the average beak length of the population will become longer - after all, the better-fed hummingbirds will tend to leave more offspring, and hence the inherited longer beaks of their offspring will start to dominate the numbers in the local population

    remember, it's not you that makes your arm longer, but over time longer arms in the population will become more common if it means they can reach the cookie tin on the top shelf and you can't


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    Thanks for your reply.
    I'm not a professional scientist; just trying to understand evolution.

    Personally, I have a characteristic of wanting to know how things work.
    In the PBS web site http://www.pbs.org/wgbh/evolution/library/
    I selected "Evolution of Diversity", then "Species and Speciation", then "Evolving Ideas: How Does Evolution Really Work?"

    In this video, they say:
    "Natural Selection - the key evolutionary mechanism Darwin identified is really four processes:
    1. Genetic variation
    2. Overproduction of offspring
    3. Struggle for existence
    4. Differential survival and reproduction"

    They are not saying that members of a species are clones.

    Applying this to hummingbirds (HB).
    Do the HB have DNA that includes the genetic variation for short and long bills, straight and curved bills?
    Is this the first ingredient - "Genetic Variation"?

    Starting with a mixture of flowers and HB:
    In time, most of the short flowers die and long flowers persist.
    So the HB with long bills start to dominate the population.
    In time, most of the long flowers die and short flowers persist.
    Will the HB with short bills then start to dominate the population?

    That's the impression I get - Natural Selection works with characterisics inherited by the member.

    The video says at the beginning:
    "In our research we're trying to understand how new species arise.
    What we're finding is that Natural Selection seems to be an incredibly important factor in generating new species."

    I'm sold on NS being a filter that generates trends in populations.
    What are the other factors that actually generate new species?
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    WYSIWYG Moderator marnixR's Avatar
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    that's about it - genetic variation begets physical difference (there's obviously also the influence of embryology and availability of various food stuffs)

    but remember the only action natural selection has on a single individual is whether that individual will survive, how long it will live and how much offspring it will have

    change through natural selection acts on populations by differential survival and reproduction rates depending on their physical characteristics, which vary in (a substantial) part due to variation in their genetic make-up
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by marnixR
    change through natural selection acts on populations
    Is this the same thing as what the video said:
    "Natural Selection will result in changes in wing shape that allow hummingbirds to fly longer distances, or
    it'll affect the length and shape of the bill."

    What I described in previous post: Natural Selection of available (inherited) characteristics within the hummingbird. There are no real changes - there is only a selection of available options!

    It's like ordering a car with certain available engines, number of doors, colors etc.
    I can select whatever options fit my requirements this year.
    With a different environment next year, I may select other options.
    But I cannot change the options. If they offer only a 4 and 6 cylinder engine, I cannot select a V8 with more power. Or a bigger gas tank so I can travel further.

    Now, if the car company perceives that some new options may sell more cars, they invest in tool changes, factory-line changes, ordering new supplier products, etc. to change the available options.

    From my understanding of DNA, the equivalent effort in living things is to have a modification of genetic material.
    This is a separate factor from NS.
    It must be done before NS.
    It is more complicated than NS.

    Why do they say NS makes changes?
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  7. #6  
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    Quote Originally Posted by gs99
    Quote Originally Posted by marnixR
    change through natural selection acts on populations
    Is this the same thing as what the video said:
    "Natural Selection will result in changes in wing shape that allow hummingbirds to fly longer distances, or
    it'll affect the length and shape of the bill."

    What I described in previous post: Natural Selection of available (inherited) characteristics within the hummingbird. There are no real changes - there is only a selection of available options!

    It's like ordering a car with certain available engines, number of doors, colors etc.
    I can select whatever options fit my requirements this year.
    With a different environment next year, I may select other options.
    But I cannot change the options. If they offer only a 4 and 6 cylinder engine, I cannot select a V8 with more power. Or a bigger gas tank so I can travel further.

    Now, if the car company perceives that some new options may sell more cars, they invest in tool changes, factory-line changes, ordering new supplier products, etc. to change the available options.

    From my understanding of DNA, the equivalent effort in living things is to have a modification of genetic material.
    This is a separate factor from NS.
    It must be done before NS.
    It is more complicated than NS.

    Why do they say NS makes changes?
    Who is 'they'? Not biologists, that's for sure.

    Mutation causes variation, or 'changes' if you like. Specifically, it generates new alleles, new versions of genes. Natural selection changes the frequency of a given allele in a given population based on its fitness to the environment and relative to other alleles.
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    Quote Originally Posted by TheBiologista
    Who is 'they'? Not biologists, that's for sure.
    It's a biologist (Chris Schneider) in the PBS video who says
    "The primary way that evolution occurs is through the action of Natural Selection.
    We're trying to understand how new species arise."
    http://www.pbs.org/wgbh/evolution/li...1/2/e_s_4.html

    The video repeats the idea "Natural selection - changes - generates new species".
    It mentions Genetic variation but not Genetic modification.

    Quote Originally Posted by TheBiologista
    Mutation causes variation, or 'changes' if you like.
    Some definitions of "primary": of first rank or importance or value; of or being the essential or basic part.

    Can evolution work without these mutations that cause genetic modification?

    If not, then it seems that Schneider should say "The primary way that evolution occurs is through genetic modification by means of mutations.
    The new genetic material is then available for Natural Selection."

    Wouldn't that be a more accurate way of explaining how evolution works?
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    Quote Originally Posted by gs99
    Quote Originally Posted by TheBiologista
    Who is 'they'? Not biologists, that's for sure.
    It's a biologist (Chris Schneider) in the PBS video who says
    "The primary way that evolution occurs is through the action of Natural Selection.
    We're trying to understand how new species arise."
    http://www.pbs.org/wgbh/evolution/li...1/2/e_s_4.html

    The video repeats the idea "Natural selection - changes - generates new species".
    It mentions Genetic variation but not Genetic modification.

    Quote Originally Posted by TheBiologista
    Mutation causes variation, or 'changes' if you like.
    Some definitions of "primary": of first rank or importance or value; of or being the essential or basic part.

    Can evolution work without these mutations that cause genetic modification?

    If not, then it seems that Schneider should say "The primary way that evolution occurs is through genetic modification by means of mutations.
    The new genetic material is then available for Natural Selection."

    Wouldn't that be a more accurate way of explaining how evolution works?
    More accurate than those other statements, yes. Though still somewhat inaccurate.
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    WYSIWYG Moderator marnixR's Avatar
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    let's put it this way : genetic variation comes from imperfections in the copying of DNA whenever eggs / sperm are made / combined
    this genetic variation is a major factor in creating a variation in phenotype when expressed during embryological development
    this variation leads to differential survival / reproductive success, and may change the overall genetic make-up in a local population of a species

    and that, in a nutshell, is what evolution amounts to
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  11. #10  
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    Quote Originally Posted by marnixR
    and that, in a nutshell, is what evolution amounts to
    Is nutshell a euphemism for scrotum?
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  12. #11  
    WYSIWYG Moderator marnixR's Avatar
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by marnixR
    and that, in a nutshell, is what evolution amounts to
    Is nutshell a euphemism for scrotum?
    if there is such a thing as a euphemism for scrotum
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Going back a few days...
    Quote Originally Posted by marnixR
    what a pitiful example of genetic determinism
    Please explain this. What part is pathetic, and why?
    Or is the whole concept (genetic determinism) viewed as obsolete?
    Isn't that how traits are inherited?


    Quote Originally Posted by marnixR
    in that view every member of a species is genetically and morphologically a clone of another, which is clearly not the case
    I thought that only offspring of an asexual parent is a clone.
    In the case of hummingbirds, why would every member be a clone?
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    Quote Originally Posted by gs99
    Going back a few days...
    Quote Originally Posted by marnixR
    what a pitiful example of genetic determinism
    Please explain this. What part is pathetic, and why?
    Or is the whole concept (genetic determinism) viewed as obsolete?
    Isn't that how traits are inherited?
    genetic determinism is dead in the sense that it's not just genes that decide how an individual will turn out - it's always an intimate interplay of genes and environment
    hence even identical twins don't end up totally identical (even if they are more similar than other human beings)

    Quote Originally Posted by gs99
    Quote Originally Posted by marnixR
    in that view every member of a species is genetically and morphologically a clone of another, which is clearly not the case
    I thought that only offspring of an asexual parent is a clone.
    In the case of hummingbirds, why would every member be a clone?
    the implication of the logical chain which says that, if some organism is genetically identical to another, they will also be morphologically identical, would be that for all intents and purposes they may as well be clones, even if the product of sexual rather than asexual reproduction - obviously, in reality nothing could be further from the truth
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    "(Richard) Strohman was a leading critic of genetic reductionism, the idea that a single gene corresponds with a single trait or disease. He
    advanced the idea of epigenetic control, meaning that the genes are directed by something beyond the genes. As he put it,
    "another kind of information management system must be present rather than genetic determinism." Clearly this is true. For
    example, the well known fact that the chimpanzee genome is 98.5 percent identical with the human genome indicates that genes
    alone are not determining the phenotype, but rather some program beyond the genes that makes the same genes manifest in different
    ways in different species."
    http://www.amnation.com/vfr/archives/013965.html

    Quote Originally Posted by marnixR
    genetic determinism is dead in the sense that it's not just genes that decide how an individual will turn out
    There are many traits and diseases related to a single gene. Can that be denied?
    Why shelve Genetic Determinism just because we don't understand how some things work?

    Strohman said "another kind of information management system must be present rather than genetic determinism."
    Why couldn't it be "another kind of information management system must be present in addition to genetic determinism."?

    Epigenetics is "above" (in addition to) genetics in DNA.

    Quote Originally Posted by marnixR
    it's always an intimate interplay of genes and environment
    1. The article about Strohman doesn't mention environment, neither does this:
    "As scientists discover more about the "epigenome," a layer of biochemical reactions that turns genes on and off, they're finding
    that it plays a big part in health and heredity."
    http://www.wired.com/medtech/health/news/2005/08/68468
    2. Environment can't work on a chimpanzee embryo to change it into a human embryo.
    3. With what environment can genes inside the nucleus "always have an intimate interplay"?

    From what I've seen, the Epigenome determines when certain genes are expressed and may be a supervisor of multiple genes. But it doesn't change the DNA that is inherited, whether the theory of Genetic Determinsim is dead or not.
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    Quote Originally Posted by gs99
    There are many traits and diseases related to a single gene. Can that be denied?
    single gene traits and diseases are in a small minority - most traits are due to a combination and interaction of various genes
    as for diseases, what makes the news is that scientists have found a "gene for ...", what often doesn't get reported that subsequent research often finds that a variety of genetic defects have been found associated with schizophrenia, alcoholism, etc.

    Quote Originally Posted by gs99
    1. The article about Strohman doesn't mention environment, neither does this:"As scientists discover more about the "epigenome," a layer of biochemical reactions that turns genes on and off, they're finding that it plays a big part in health and heredity."
    the way i see it, the switching on and off of genes depends on chemical gradients in the cell, which i include as part of the environment in which the gene expresses itself
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by marnixR
    single gene traits and diseases are in a small minority - most traits are due to a combination and interaction of various genes
    It appears these three concepts need to be recognized when studying genetics (the terms are not new):

    1. Monogenic Determinism for single-gene traits. Although a minority, it is the oldest. Replaces "Genetic Determinism".

    2. Polygenic Determinism for multiple-gene traits. An example is provided in this definition of polygenic:
    "Pertaining to two or more genes. As opposed to monogenic.
    Eye color is polygenic. It is determined by a number of genes."
    http://www.medterms.com/script/main/...rticlekey=4986

    3. Epigenetics (newest) for cases where parts of the epigenome affect the operation of genes.

    Or do they think epigenetics are involved in every case, thus making all genetics much more complicated?

    Back to the hummingbird, where possibly all three types of genetic changes occur...

    Quote Originally Posted by marnixR
    variability in hundreds of characteristics is all around us, and if hummingbirds, within the range of their species, make a
    better living out of having a longer beak then the average beak length of the population will become longer - after all, the
    better-fed hummingbirds will tend to leave more offspring, and hence the inherited longer beaks of their offspring will start to
    dominate the numbers in the local population
    remember, it's not you that makes your arm longer, but over time longer arms in the population will become more common if it
    means they can reach the cookie tin on the top shelf and you can't
    Do you know if the beak gene(s) provide both "short" and "long" alleles?
    If they do, I can see how one or the other could dominate due to Natural Selection.

    But if they do not provide that variety of options:
    How does the change come to exist?

    The longer beaks cannot "start to dominate the numbers in the local population" unless they appear in one member first, then spread to others.
    The beaks belong to individual members, not the population.

    How does the hummingbird start the process of getting a different beak that it needs?
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    Do you know if the beak gene(s) provide both "short" and "long" alleles?
    As I understand it, it is not one for long and one for short, but rather one for "length".
    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
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    Quote Originally Posted by KALSTER
    As I understand it, it is not one for long and one for short, but rather one for "length".
    You're saying the beak gene merely specifies the variable (length) but not the value (short or long).
    I would think there are many other genes that describe size (of other parts of the organism).
    At what point does the member provide all the values?

    In Mendel's observations of the pea plant, one trait was stem length: Tall or Dwarf.
    http://www.bio.miami.edu/~cmallery/1...4.1.traits.jpg

    I'm assuming a similar concept holds true for other genes.
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  20. #19  
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    Quote Originally Posted by gs99
    In Mendel's observations of the pea plant, one trait was stem length: Tall or Dwarf..
    Mendel got lucky.
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    Quote Originally Posted by Ophiolite
    Mendel got lucky.
    Agreed; it's more complicated if the size is determined by multiple genes.

    "Inheritance of quantitative traits or polygenic inheritance refers to the inheritance of a phenotypic characteristic that varies
    in degree and can be attributed to the interactions between two or more genes and their environment. Though not necessarily genes
    themselves, quantitative trait loci (QTLs) are stretches of DNA that are closely linked to the genes that underlie the trait in
    question."
    http://en.wikipedia.org/wiki/Quantitative_trait_locus

    Could it work like this?
    The QTLs have the values that will be utilized in the size allele.
    Say the values are like 1, 2, 4, 8, and 16.
    Depending on the environment, the organism calls for values 4 and 8 which cause a specific amount of growth (12).
    The QTLs are inherited DNA, so there are specific values that can be selected.
    They do not generate new values.
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    But if they do not provide that variety of options:
    How does the change come to exist?
    If no genetically based variation in beak length ever exists, on any basis (such as a general difference in body size, differentiated response to diet or light or common infectious microbe, etc), then no such change would come to characterize an evolved future population.

    But as Darwin observed, very few natural populations of anything exist without genetically based variations in colors, reactions to circumstance, size and growth rate of all body parts including internal organs, shape and arrangement of various parts and pieces, etc.

    I doubt that all the hummingbird beaks in any large population of a species of the birds have exactly the same genetic specifications of length. That would be a remarkable situation, worthy of note in itself.
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    Quote Originally Posted by iceaura
    I doubt that all the hummingbird beaks in any large population of a species of the birds have exactly the same genetic
    specifications of length.
    I didn't mean to say that; genetic variation of beak length obviously does exist.
    If it's a monogenic trait, there would be at least two sizes (short and long).
    If it's a polygenic trait including QTLs, there would be variable sizes that match a normal distribution.
    http://staff.jccc.net/pdecell/evolution/polygen.html
    Either way, it's inherited in the normal way via meiosis and reproduction.

    This Normal Genetic Variation is described often in many biology books.
    Natural Selection can work with Normal Genetic Variation to cause certain traits to dominate due to the environment.

    But with only this kind of genetic variation, can new species arise?

    In the PBS video they mention "genetic variation" as one of the processes of Natural Selection.
    http://www.pbs.org/wgbh/evolution/li...1/2/e_s_4.html
    They explain that each bird can only have a bill size that is inherited.
    This sounds like Normal Genetic Variation.
    However, the title of the video is "Evolving Ideas: How Evolution Works"

    Therefore the "genetic variation" needs to include something that is not normal.
    I call it "Modified Genetic Variation".
    The video does not explain this concept.
    Without it, I don't see Natural Selection producing new species. Perhaps I have a mental block.

    They talk about the difference between monogenic and polygenic traits. Why don't they explain the difference between normal and modified genetic variation?

    Is there a scientific term for Modified Genetic Variation? Is "mutation" the only source? Where is it explained?
    What are the steps needed to make changes, to provide new options?
    I think that is needed for people to understand how Natural Selection works to create new species of hummingbirds.
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    Quote Originally Posted by gs99
    But with only this kind of genetic variation, can new species arise?
    Yes.

    The source of the step by step genetic variations can be anything that changes the genetic material in a reproductive cell - from heat to virus infection. The selection agency at each step can also be drawn from a wide variety - sexual preference to prevailing wind speed to meteor impact.

    Neither must be the only one throughout the evolutionary sequence - mix and match, down through the years.
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    Quote Originally Posted by iceaura
    anything that changes the genetic material in a reproductive cell - from heat to virus infection.
    However, I was referring to the normal genetic variation that's inherited.
    The staggering amount of genetic variation normally provided by meiosis and fertilization.
    Scientists have spent much time discovering how it works; they've explained it often in biology books.

    The question was
    With only this kind of genetic variation, can new species arise?
    With no "heat or virus infection", my answer is NO.

    To explain how things work, it seems important to acknowledge the two kinds of genetic variation I described.
    They're different.

    Perhaps some persons see a benefit of having one bucket for all genetic variation.
    To me that's like saying all traits are caused by single genes, when it's known that most are polygenic.
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    There are many traits and diseases related to a single gene. Can that be denied?

    yes, since it would depend on which gene we are talking about in what species

    Why shelve Genetic Determinism just because we don't understand how some things work?
    Because determinism is often inaccurate when looked at in detail.


    Strohman said "another kind of information management system must be present rather than genetic determinism."
    Why couldn't it be "another kind of information management system must be present in addition to genetic determinism."?

    Because that would eliminate viable options, without checking them to be invalid first.



    1. The article about Strohman doesn't mention environment, neither does this:
    "As scientists discover more about the "epigenome," a layer of biochemical reactions that turns genes on and off, they're finding
    that it plays a big part in health and heredity."


    I assume the article you are referring to is written by a fallible human.


    2. Environment can't work on a chimpanzee embryo to change it into a human embryo.
    If there is a point to this statement it isn't obvious.

    3. With what environment can genes inside the nucleus "always have an intimate interplay"?

    The womb, the egg, the blood, the radiation, gravity, you name it.


    From what I've seen, the Epigenome determines when certain genes are expressed and may be a supervisor of multiple genes. But it doesn't change the DNA that is inherited, whether the theory of Genetic Determinsim is dead or not.

    Actually epigenetic changes can be inherited. Try reading a text book in biology. It is no secret.
    "Kill them all and let God sort them out."

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    point 1
    gs99: There are many traits and diseases related to a single gene. Can that be denied?
    spuriousmonkey: yes, since it would depend on which gene we are talking about in what species

    I was referring to monogenic traits and diseases. This 2006 article "Genetic medicines: treatment strategies for hereditary disorders" says:
    "The treatment of the more than 1,800 known monogenic hereditary disorders..."
    http://www.nature.com/nrg/journal/v7...s/nrg1829.html

    What are they talking about? I get the impression that each of these disorders are caused by a single gene.

    Have all these disorders been shown not to be caused by a certain gene?

    point 2
    spuriousmonkey: Because determinism is often inaccurate when looked at in detail.

    I'm not sure what you mean.

    Define "Genetic determinism"
    Genetic determinism is the belief that genes determine physical and behavioral phenotypes. It is usually
    taken to mean "that the genotype completely determines the phenotype, that is, the genes completely determine how an organism
    turns out" or that genes alone determine human traits and behaviours. However, nowadays practically every geneticist has
    disavowed genetic determinism. While it is well established that most phenotypic variability is strongly influenced by genes, it
    is clear that environment also plays an important role and that epigenetic mechanisms of inheritance also exist.
    http://en.wikipedia.org/wiki/Genetic_determinism

    The words I underlined were probably added when new discoveries were made to explain polygenics.
    I think geneticists would agree with this term today if those words are left out or replaced with "partially".

    It would then agree with the last sentence (bold added):
    (a) It is well established that most phenotypic variability is strongly influenced by genes
    (b) environment also plays an important role
    (c) epigenetic mechanisms of inheritance also exist

    Type (a) includes genes working alone or with others.
    The less important (b) environment and (c) epigenome may affect how genes are expressed.

    But if you look at this in detail, it does not work without genes.

    Would you not agree that genes are the primary part of determining the phenotype?

    Can you see why the general term "genetic determinism" is not inaccurate if we view it in this way?

    edit, Add this line:
    I recognize that the current definition of "Genetic Determinism" does not agree with the the latest understanding of genetics etc..
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  28. #27  
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    Quote Originally Posted by gs99
    What are they talking about? I get the impression that each of these disorders are caused by a single gene.

    Have all these disorders been shown not to be caused by a certain gene?

    Not at all, these disorders are shown to be caused by a mutation in a certain gene. That doesn't mean the end result can be be necessarily reversed with one step. Sometimes maybe, often not.




    point 2
    spuriousmonkey: Because determinism is often inaccurate when looked at in detail.

    I'm not sure what you mean.

    [/quote]

    Because stochastic regulatory mechanisms for instance, wouldn't be deterministic. They may seem so at first glance.

    One of the areas where stochastic regulation has been suggested for instance is the regulation of maintenance of stem cells.

    Determinism in molecular biology is really something from the 90s and it is still king in molecular biology. Because people are slow to change. Unfortunately determinism cannot explain many current problems, and they have invented keywords to hide the inability to penetrate function, such as "redundancy".

    Of course the currently picture starts leaning towards noise when talking about regulation of genes, whereas we would very much prefer this one-on-one relationship you are so keen on.

    regulatory networks are intertwined with each other, and with totally different regulatory principles, such as transcription factor regulation is accompagnied by microRNA regulation. And there is so much noise in the system, that researchers cannot even unravel it in a meaningful manner because they are most sticking to the deterministic dogma. When I pull a lever here, I can predict an outcome there.
    "Kill them all and let God sort them out."

    - Arnaud Amalric

    http://spuriousforums.com/index.php
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    Quote Originally Posted by spuriousmonkey
    Not at all, these disorders are shown to be caused by a mutation in a certain gene.
    Isn't that the same as saying that the disorder is determined by a certain gene?

    In regards to monogenic traits, this web site mentions a few we know about:
    tongue rolling, handedness, mid-digital hair, PTC sensitivity, earlobe attachment, widow's peak, and polydacytly.
    http://www.landmark.edu/institute/gr...instructor.pdf
    Aren't they saying these traits are determined by genes alone?

    Why can't we say "genetic determinism" is true in some cases?
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  30. #29  
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    Quote Originally Posted by gs99
    Quote Originally Posted by KALSTER
    As I understand it, it is not one for long and one for short, but rather one for "length".
    You're saying the beak gene merely specifies the variable (length) but not the value (short or long).
    I would think there are many other genes that describe size (of other parts of the organism).
    At what point does the member provide all the values?

    In Mendel's observations of the pea plant, one trait was stem length: Tall or Dwarf.
    http://www.bio.miami.edu/~cmallery/1...4.1.traits.jpg

    I'm assuming a similar concept holds true for other genes.
    A lot creatures can change features after birth that would normally be seen as purely genetic. I understand there are some alligators that, if you keep them in too small a cage to fit their full adult size, they will stop growing. That doesn't mean their offspring will be smaller than they would have been. (Unless their offspring are also placed in a similar cage, of course) So there is a difference between environment determining something about you, and environment determining something about your offspring.

    Natural selection works only be selecting against. It's sort of like how the direction of flowing water as it goes down hill is determined entirely by the barriers it encounters, which constrain its direction to the course of least resistance.
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    Quote Originally Posted by kojax
    I understand there are some alligators that, if you keep them in too small a cage to fit their full adult size, they will stop growing. That doesn't mean their offspring will be smaller than they would have been.
    I'll state a few assumptions:
    The size is a polygenic trait, involving QTLs.
    The small cage environment had no effect on the genes or natural selection.
    The offspring inherit the size genes with about the same values as the parents.

    But I could be wrong.

    ps. Have no idea if epigenetics are involved.
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    Quote Originally Posted by spuriousmonkey
    Because stochastic regulatory mechanisms for instance, wouldn't be deterministic.
    Define deterministic:
    "of knowable outcome: having an outcome that can be predicted because all of its causes are either known or the same as those of a previous event"
    http://encarta.msn.com/dictionary_18...rministic.html

    I continue to learn and appreciate that many steps are needed to make things related to cells and genes.

    For example, when a cell divides there are countless regulatory mechanisms in each and every phase.
    But there is a deterministic predictable outcome - a new cell with all the features of the parent.

    I don't understand where stochasticity comes into play.
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    Quote Originally Posted by gs99
    With only this kind of genetic variation, can new species arise?
    With no "heat or virus infection", my answer is NO.
    With no mutations allowed, only recombination of existing alleles can happen - that might be able to produce a new species, but only in unusual circumstances (a recessive allele that sterilizes the homozygous except in combination with a homozygotic mate, an extreme founder effect, etc.)

    But the answer is still "yes", simply unusual.

    Meanwhile, most geneticists regard mutations as "normal". I don't know why you would not - they are very common, after all.
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    With only this kind of (normal) genetic variation, can new species arise?
    Quote Originally Posted by iceaura
    With no mutations allowed... the answer is still "yes", simply unusual.
    On the other hand,
    Quote Originally Posted by TheBiologista
    Mutation causes variation, or 'changes' if you like. Specifically, it generates new alleles, new versions of genes. Natural
    selection changes the frequency of a given allele in a given population based on its fitness to the environment and relative to
    other alleles.
    To me, that sounds like an opposing viewpoint.


    Quote Originally Posted by iceaura
    Meanwhile, most geneticists regard mutations as "normal". I don't know why you would not
    At my stage, I'm learning what is described in biology sources - how things are supposed to work.
    This is what I call "normal".
    When I read the diagrams of any process, I don't see mutations being explained.
    Just as we categorize traits as monogenic, polygenic etc. to know the difference.
    I categorize "normal" as being different than "mutation".

    Quote Originally Posted by iceaura
    they are very common, after all.
    How do you know how common they are?

    I do have many questions about mutations that I want to include in a new thread.

    I'm really impressed that these matters have been discovered, normal or mutation.

    The original question of this thread related to a PBS video of hummingbirds to explain how evolution works.
    They claimed that Natural Selection was the primary force that creates new species.
    Whereas I can see NS acting on "normal" genetic variation to provide dominating trends,
    Many of you may disagree, but I don't see that as evolution.
    So I don't think the video did a good job explaining how evolution works.

    Thanks to all who posted here; I have learned a lot.
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