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  1. #1
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    The level of selection

    At what level does Natural selection occur? This is a question I've been asking myself recently and as I have started to look at the papers on the matter I find that there is a quite a bit of controversy on this matter amongst evolutionary biologists.

    By level of selection I refer to the "unit" at which Natural Selection works. For instance, the "unit" could be the individual organism. Natural Selection therefore works upon each individual organism and selects for those organisms which are best adapted, meaning, those organisms that have the greatest reproductive success.

    However, many have argued that it also works at the group level and can select for groups of organisms that share certain traits as opposed to each individual.

    Another possibility is that it works at the genetic level, i.e. better known as the "selfish" gene.

    I for one find the individual level to be the most likely and best explanation.

    At the genetic level there is some merit to the idea of the "selfish gene" as there are genetic elements that seem to operate in a fashion that would not necessarily be beneficial to the organism. The two best examples are transposons and B-Chromosomes.

    Transposons are genetic elements which are capable of moving throughout the genome. They operate in various ways, my personal favorite being the transposons which encode proteins that excise the transposon and then reincorporate somewhere else in the genome. These elements dont really serve any benefit to the organism. However, if they insert themselves into a critical gene, causing a knockout mutation, they pretty much screw themselves by killing the plant or at least hindering its ability to reproduce. The other example are B-Chromosomes which are small chromosomes that pretty much lack any functional genes and as far as we know, serve no real purpose. These are primarily found in plants, and can be tolerated to a small degree, however, too many and they once again hinder the plant and screw themselves in the process.

    The reason I dont fully accept the selfish gene idea, that genes are essentially the unit of selection is because they are fully dependent upon the organism as a whole for their continuity.

    Group Selection on the other hand proposes selection at the level of the group and favors groups of individuals that are best able to survive as a whole.

    Once again however, I find this one to be a bit of a stretch. Ultimately the group is made up of individuals and it is the individuals which breed, which reproduce, which must survive. If one individual is more successful in reproduction than another in the same group, then that individual is the one whose genes will become more predominant. Even if the group does aid survival, selection is still operating upon the reproductive success of each individual. An example of this can be found in the practice of infanticide amongst higher organisms, in particular primates. The practice where a male may kill off the offspring of another male within the same group. Once again, despite there being a group we find selection occurring at an individual level as opposed to a group level.

    For these reasons I do not find either the "selfish gene" or the "group selection" model convincing and favor the idea of selection at the organism level.

    What do you guys think? Any opposition? I hope so, but dont expect much.
    I typically cite original research papers and reviews that are available only to a personal or institutional subscriptional. If you wish a PDF copy of the papers I cite, send me a request.

  2. #2
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    Re: The level of selection

    Quote Originally Posted by chadn737 View Post
    For these reasons I do not find either the "selfish gene" or the "group selection" model convincing and favor the idea of selection at the organism level.

    What do you guys think? Any opposition? I hope so, but dont expect much.
    I'm not the kind of guy to be giving animal behavioralists funding, but in this case Chad, the evolution of eusocial animals, mammalian group dynamics and the evolution of alturism, all offer key insights into this question.
    Before I go further, I have potatoes on. But right quickly, your own theory has a flaw. You deny group selection, yet an organism is simply a bacterial colony that has specalized its members. Meaning humans are basically many smaller organisms operating for group evolution. To the point that individual cells will commit suicide?
    On the other front, you utilize the evidence of selfish genes inability to survive without the group to point of the key flaw in individual survivability.

    Believe it or not, I think I have a solution, but the potatoes are burning


    Alright. Lets get cracking. Ok, chad, first you are awesome sauce for advancing humanity's understanding.
    Now, if we consider it from a game theory perspective in which all players are rational and the game has no ending (rational meaning : tries to have the most kids, live longest), then we interpret the question of "level of selection" to be an entirely misdirecting thought.
    Consider the ant, who does not ever breed, but labouriously works for those who do. What motivates this? Surely such a subsurvent strain of the species, with selection operating at the level of the organism, would die out quickly and the queen-ant would predominate. Why does this not happen?
    I would argue that group selection is focusing individual selection. I mean, consider the wolf pack, all of whom's members work extremely dilligently to hunt, care, and provide for, ultimately, the alpha couple's pups. How could such an arrangement evolve?

    The thing that drives this, I beleive Chad, is simply the nature of greater good. Queens who evolved many docile daughters for every 1 fellow queen, although on the surface sacrificed a massive advantage to queens who produced only other reproductively viable offspring, on the level of daily interaction (many docile daughters can swarm and kill many queens as queens usually operate individually). So the queens who evolved the most obedient daughters florished despite having key flaws in there genes should there daughters betray them. The unit of selection was sort of the queen, but it was really group dynamics that supported that selection.
    Hence, we find that queens who breed for the good of the group are capable of overwhelming those who breed for there own good, however if any of the queen's daughters betrayed her during a critical stage in the nesting she would quickly fail.
    This is arguably how multicellular life evolved.

    Therefore, the unit of selection is the group up until an individual member's benefit for betayrel outweighs the negatives of such an activity. Therefore, the concept of a definitive "unit of selection" does not reflect how evolution operates in a multi-member species.


    Link- Tit for tat - Wikipedia, the free encyclopedia
    This is the game theory concept I was alluding to
    Last edited by Turtleflipper; November 8th, 2007 at 02:57 PM.

  3. #3
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    Re: The level of selection

    Quote Originally Posted by chadn737 View Post
    However, if they insert themselves into a critical gene, causing a knockout mutation, they pretty much screw themselves by killing the plant or at least hindering its ability to reproduce.
    This situation applies to individuals within a group too. If an individual does the wrong thing, they can screw themselves and kill the whole group (or at least hinder the groups ability to reproduce its individuals).


    I'd also point to the example of bees. Many of the individuals are not able to reproduce, but overall the group benefits by this condition, and ironically the trait of "not being able to reproduce" is passed on genetically and overall aids in the replication of the species.


    Utlimately, I'd agree with Turtle,

    Quote Originally Posted by Turtleflipper View Post
    Therefore, the concept of a definitive "unit of selection" does not reflect how evolution operates in a multi-member species."
    (although I don't know why he was wearing potatoes).
    Quote Originally Posted by Turtleflipper View Post
    Before I go further, I have potatoes on.

    Contrariwise, if it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic.

  4. #4
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    Re: The level of selection

    IMO, it makes sense to talk about selection at all three levels.

    Individual highly beneficial genes will, all else being equal, become more common in a population over time. This is because, on average, their hosts will have an above average chance of doing well. In this sense, an individual gene can be selected.

    Individual selection is obvious.

    Group selection, IMO, seems equally apparent. Groups that do well (and the individuals that comprise those groups) survive and thrive. Groups that cannot survive disappear. It's the same thing, just at a higher level, with groups competing instead of individuals.
    Freedom is you choosing for yourself. Law is the government choosing for you. The two are opposites.

    Pray - To ask that the laws of the universe be annulled in behalf of a single petitioner confessedly unworthy - Ambrose Bierce
    Faith - Belief without evidence in what is told by one who speaks without knowledge about things without parallel - Ambrose Bierce

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    Re: The level of selection

    Quote Originally Posted by Castle View Post
    Individual highly beneficial genes will, all else being equal, become more common in a population over time. This is because, on average, their hosts will have an above average chance of doing well. In this sense, an individual gene can be selected.
    ).
    This makes no sense, as although one gene may randomly form that kicks ass, it is not replicated to any special extent inside the cell. It reachs the Hayflick limit, and dies. Unless the random gene directly effects the longevity or survivability of the cell, no advantagoius mutation can ever predominate in the body (natural selection is not allowed to operate at that level)
    Note: the random kickass gene that effects the longevity of the cell is usually cancer, and thus showcases Chad's earlier point that the "selfish gene" is not a solid idea about selection (it would kill itself by not cooperating).

  6. #6
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    Re: The level of selection

    Quote Originally Posted by Castle
    IMO, it makes sense to talk about selection at all three levels.

    Individual highly beneficial genes will, all else being equal, become more common in a population over time. This is because, on average, their hosts will have an above average chance of doing well. In this sense, an individual gene can be selected.

    Individual selection is obvious.

    Group selection, IMO, seems equally apparent. Groups that do well (and the individuals that comprise those groups) survive and thrive. Groups that cannot survive disappear. It's the same thing, just at a higher level, with groups competing instead of individuals.
    Proponents of group selection never advocate it as being a sole level of selection, but rather that selection can occur at this level. Those who oppose this seem to do so more on the grounds that its still individual selection with the added dynamics of the group involved.

    The selfish gene concept is a little different. Its hard to pin this one down, quite frankly, because it doesnt appear to be widely used terminology. However, Dawkins argues that organisms are little more than vehicles for genes and so it would appear that he takes the more extreme position that genes really do constitute the primary level of selection.


    _________________________________ Post Merged _________________________________


    Quote Originally Posted by Turtleflipper
    This is arguably how multicellular life evolved.
    The distinct problem I see here is that multicellular life is genetically identical. In other words the same genetic sequence in your brain can be found in your liver, in you fingers, and ultimately in you sperm or eggs.

    So that even though a cell in your brain may not reproduce, the same genetic material is still reproduced, as opposed to say a group of genetically heterologous individuals.

    Similarly in eusocial organisms, the worker ants or worker bees are essentially clones of the Queen. So in many ways its analogous to multicellular life, where the whole works to the preservation of the same genetic material.

    In contrast you have the example of the Wolf Pack where it is composed heterologous members. However, ask yourself what is the basis for being an alpha female or an alpha male? These individuals compete with the rest of the group for that position. So while group dynamics are involved, selection at the individual basis is still going on based on which member can take control.
    Last edited by chadn737; November 8th, 2007 at 04:30 PM. Reason: Automerged Doublepost
    I typically cite original research papers and reviews that are available only to a personal or institutional subscriptional. If you wish a PDF copy of the papers I cite, send me a request.

  7. #7
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    Re: The level of selection

    Quote Originally Posted by CHAD
    At what level does Natural selection occur?
    I hate to oversimplify it, but my answer is.

    Natural selection occurs at every level that a natural selective pressure is applied.
    All the fuel for selection would have to be found at a genetic level.
    So group selection, is just mass genetic selection.

    A volcano irrupts killing everyone on an island.. isn't exactly natural selection. (unless there is a "Dumb enough to live next to an active volcano Gene"
    A whale eating 80% of a school of fish.. isn't exactly natural selection. (unless there is a "Be lucky" gene)

    If natural selection isn't on the genetic level.. then what is being selected?
    To serve man.

  8. #8
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    Re: The level of selection

    Quote Originally Posted by Castle
    IMO, it makes sense to talk about selection at all three levels.

    Individual highly beneficial genes will, all else being equal, become more common in a population over time. This is because, on average, their hosts will have an above average chance of doing well. In this sense, an individual gene can be selected.

    Individual selection is obvious.

    Group selection, IMO, seems equally apparent. Groups that do well (and the individuals that comprise those groups) survive and thrive. Groups that cannot survive disappear. It's the same thing, just at a higher level, with groups competing instead of individuals.
    I forgot to mention that there is also the idea of multi-level selection which is essentiall what you have just proposed. However, its just now starting to gain some development conceptually as far as I understand. Unfortunately evolution is not my area of expertise. I'm familiar enough with a lot of the basics and some more advanced concepts. Im even more familiar with its applications to molecular biology and biochemistry, but where the latest research and opinions in the field lie is not something I keep a real close tap on.

    In fact this debate is actually the result of a personal effort of late to familiarize myself more with the subdiscipline of evolutionary biology.
    I typically cite original research papers and reviews that are available only to a personal or institutional subscriptional. If you wish a PDF copy of the papers I cite, send me a request.

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    Re: The level of selection

    Quote Originally Posted by chadn737 View Post
    The distinct problem I see here is that multicellular life is genetically identical. In other words the same genetic sequence in your brain can be found in your liver, in you fingers, and ultimately in you sperm or eggs.

    So that even though a cell in your brain may not reproduce, the same genetic material is still reproduced, as opposed to say a group of genetically heterologous individuals.
    ...haha, this will be awesome....(I've been long considering the evolutionary function of eusociality and cannot wait for the ensuing debate!)

    Alturism through eventual benefit, I agree. However, as cancer shows, at any time a cell can reject (in the evolutionary sense of "growing" eyes) the arrangement and become cancerous, perpetuating itself over its fellows.
    Here, I believe, is the problem. You assume that individuals of identical genetic makeup are the same entity.
    This is not supported by other examples of asexual species, who do not obey eusocial concepts and openly compete among the species (despite all being genetically identical).
    Quote Originally Posted by chadn737 View Post
    Similarly in eusocial organisms, the worker ants or worker bees are essentially clones of the Queen. So in many ways its analogous to multicellular life, where the whole works to the preservation of the same genetic material.
    .
    This hypothesis is contradicted by the existence of "super colonies", many ant colonies with total numbers of upwards of 100 million individuals, of varying genetic makeups between colonies, operating together, or at the least, not actively attacking each other as most ant-nests are prone to do.
    Quote Originally Posted by chadn737 View Post
    In contrast you have the example of the Wolf Pack where it is composed heterologous members. However, ask yourself what is the basis for being an alpha female or an alpha male? These individuals compete with the rest of the group for that position. So while group dynamics are involved, selection at the individual basis is still going on based on which member can take control
    .
    Yes, but... you assume a constant level of competition that does not exist. When the alpha is weak or impaired, a dominance struggle will often break out, but until such a time, the other animals will obey. If it is simply a case of perpetual struggle, how do you explain the willingness to surrogate mother cubs from the alphas? Surely wolves would kill the cubs of the alphas the second they leave if we follow your thinking to its conclusion?
    No non-identical species would willingly protect cubs of different genetic makeup, if I may extent your thoughts in this post.
    Yet they do!

  10. #10
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    Re: The level of selection

    Quote Originally Posted by chadn737 View Post
    At what level does Natural selection occur? This is a question I've been asking myself recently and as I have started to look at the papers on the matter I find that there is a quite a bit of controversy on this matter amongst evolutionary biologists.

    By level of selection I refer to the "unit" at which Natural Selection works. For instance, the "unit" could be the individual organism. Natural Selection therefore works upon each individual organism and selects for those organisms which are best adapted, meaning, those organisms that have the greatest reproductive success.

    However, many have argued that it also works at the group level and can select for groups of organisms that share certain traits as opposed to each individual.

    Another possibility is that it works at the genetic level, i.e. better known as the "selfish" gene.
    That was an excellent statement of the various positions. As has already become evident, those positions are not mutually exclusive. Well done.
    I for one find the individual level to be the most likely and best explanation.
    For me, it is the easiest to understand. Perhaps that is because it is the oldest and the first that I learned. That was back when it was the only explanation.
    At the genetic level there is some merit to the idea of the "selfish gene" as there are genetic elements that seem to operate in a fashion that would not necessarily be beneficial to the organism. The two best examples are transposons and B-Chromosomes.

    Transposons are genetic elements which are capable of moving throughout the genome. They operate in various ways, my personal favorite being the transposons which encode proteins that excise the transposon and then reincorporate somewhere else in the genome. These elements dont really serve any benefit to the organism. However, if they insert themselves into a critical gene, causing a knockout mutation, they pretty much screw themselves by killing the plant or at least hindering its ability to reproduce. The other example are B-Chromosomes which are small chromosomes that pretty much lack any functional genes and as far as we know, serve no real purpose. These are primarily found in plants, and can be tolerated to a small degree, however, too many and they once again hinder the plant and screw themselves in the process.

    The reason I dont fully accept the selfish gene idea, that genes are essentially the unit of selection is because they are fully dependent upon the organism as a whole for their continuity.
    I agree. I just don't grasp the idea of the selfish gene. I do understand that a single gene, alone or in combination with certain alleles of other genes, might be lethal at many stages of development and may cause failure to form a viable embryo, foetus, or offspring. But that isn't what Dawkins meant.
    Group Selection on the other hand proposes selection at the level of the group and favors groups of individuals that are best able to survive as a whole.
    I do better with this concept. While natural selection is generally a matter of competition within a population, group selection is a matter of competition between populations.
    Once again however, I find this one to be a bit of a stretch.
    I don't.
    Ultimately the group is made up of individuals and it is the individuals which breed, which reproduce, which must survive. If one individual is more successful in reproduction than another in the same group, then that individual is the one whose genes will become more predominant. Even if the group does aid survival, selection is still operating upon the reproductive success of each individual.
    While that is indeed true, you have not actually addressed the question of group selection. Why are there Eastern Meadowlarks and Western Meadowlarks, even though they produce hybrids where the meet? Why are there Common Grackles in the east and north, and Great-tailed Grackles in the south-west and western Gulf Coast, as well as Boat-tailed Grackles in Florida and the Gulf Coast? Could it be that each species has certain genetic traits that are more suitable for their particular environment? Could it be (gasp!) species selection?

    (I really like Grackles. They are beautiful in sunlight - all species are iridescent in bright light, both males and females. And while they have been described as 'back yard bullies', because they are so aggressive, they have been driven out of my yard by the doves [5 species]. You can get within a couple feet of a Grackle, and if you throw them something to eat, and then hold more out to them in your hand, they will eat out of your hand. But I digress.)
    An example of this can be found in the practice of infanticide amongst higher organisms, in particular primates. The practice where a male may kill off the offspring of another male within the same group. Once again, despite there being a group we find selection occurring at an individual level as opposed to a group level.
    I don't see how any of that applies to the concept of group selection. Natural selection is the result of competition between individuals in the same population. Group selection is the result of competition between similar populations. What you explain seems to be more a case of the selfish gene, the desire to pass on ones own genes by eliminating the competition.
    For these reasons I do not find either the "selfish gene" or the "group selection" model convincing and favor the idea of selection at the organism level.
    As stated, I find both natural selection and group selection understandable. I just don't quite grasp gene selection.

    Let me inject here, lest the ignorant misunderstand, what we are talking about. We are discussing only one mechanism of evolution - selection. We are talking about various aspects of that single mechanism - gene selection, natural selection, and population selection. Each of these mechanisms acts on the genetic diversity that is produced by several other mechanisms of evolution. We are not arguing about whether or not evolution is true or not - evolution is an observation. We are talking about why it happens.
    What do you guys think? Any opposition? I hope so, but dont expect much.
    Why would you expect opposition? Given the excellent nature of you statement, I would expect discussion, either supporting or conflicting with your position. Since you didn't expect much, I guess I have wasted my time. At this point, I'm going to post anyway.
    From The Treaty of Tripoli, Art. 11, negociated under Washington, passed unanimously by the senate, and signed by Adams -- "As the Government of the United States of America is not, in any sense, founded on the Christian religion;"

 

 

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