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Thread: Evolution Question -

  1. #1
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    Evolution Question -

    This was posted on digg today and it got me thinking:

    Richard Dawkins explains the Halibut

    A Halibut has two eyes on the same side of its head. A distant ancestor of the Halibut was a normal-looking fish with an eye on each side of its head. But that distant ancestor (let's call him H1) had one essentially useless eye, an eye that pointed down into the sand. As Dawkins explains, that lead to the evolution of the modern Halibut (let's call him H3) with an eye on each side of the head. Now here's my question.

    There is an intermediate stage between H1 and H3. Let's call this Halibut H2. H2 has an eye that's halfway between H1 and H3 **but** H2's other eye still points down into the sand. So, H2 has started along the road that will lead to H3, but it isn't there yet.

    H2's eye still points into the sand. So what possible selective advantage does it have over H1? There has to be some selective advantage, otherwise we wouldn't have continued along to H3. But I can't for the life of me figure out what it could be.

    edit: sorry about the title. I meant the title to be descriptive of the thread. Soemthing like, "Evolution Question - A Halibut's Eye"

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    Quote Originally Posted by tofu View Post
    So, H2 has started along the road that will lead to H3, but it isn't there yet.
    If it happened gradually, wouldn't the first small deviation in the position of the eye give the side-laying owner an advantage that a smaller lift of the head gets that eye exposed?

    That might be a benefit always, but especially when under attack and fleeing, maybe that slight difference made a corresponding slight difference in getting eaten, and in reproducing.
    0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 ...

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    There needn't be a evolutionary advantage at every step. For any animal, there is a little drift between eyes. There will be certain selective pressures to keep towards symmetry (signals fitness towards a mate, perhaps makes visual observations clearer) in most organisms. This pressure is off in a halibut-type fish. One eye can drift all over the place.

    Indeed, in a halibut-type fish, all sorts of symmetry-breaking is possible and perhaps beneficial. A general symmetry-breaking mutation might even be selected for and might promote a switch of eyes in another single mutation.

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    Quote Originally Posted by Kwalish Kid View Post
    There needn't be a evolutionary advantage at every step.
    Yes, there needs to be a selective advantage at every single step. That's sort of the whole point of evolution. There are always more individuals than the ecosystem can support. Only the strongest (that is, the most fit) survive.

    There doesn't have to be an advantage for every trait or adaptation. Plenty of species carry vestigial traits. But if you're going from point A to point B, or in this case, from H1 to H3 then yes, there absolutely has to be a selective advantage to H2.

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    Quote Originally Posted by tofu View Post
    But if you're going from point A to point B, or in this case, from H1 to H3 then yes, there absolutely has to be a selective advantage to H2.
    Must a propagated mutation offer an advantage, or can it simply not offer a disadvantage?
    0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 ...

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    An advantage for stage 2 is only needed if there ever actually was a stage 2. Sometimes there can be a single mutation that went from "before" to "after" without any intermediate stages. That really can only happen with small changes, but this one actually is small. Single mutations are already known to cause equally severe or more severe facial deformities anyway.

    But here's a gradual explanation anyway, offered by Darwin in TOoS. In order to use both eyes while lying on one side, it had to twist its neck so its head was rolled to a different angle from the rest of its body (or even deform the head by muscular action if the head was cartilagenous). The farther up around the curve of the skull the low-side eye was located, the less twisting was required. Reduced twisting was advantageous (because it not only reduced joint stress and used less muscular energy but also allowed the fish to lie more thoroughly flat instead of just mostly flat), so eye-lopsidedness became advantageous by enabling reduced twisting.

    Also, the original might not have always laid perfectly flat on the ground; they might have simply cruised near the bottom, tilted over as low as they could get, so that a gradually more upshifted eye allowed them to tilt their bodies lower and lower until it finaly became possible to land on the ground instead of cruising slightly above it.

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    Not that it changes the argument much, but don't halibut start with their eyes in a normal position (one on each side of the head)?

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    Quote Originally Posted by Musashi View Post
    Not that it changes the argument much, but don't halibut start with their eyes in a normal position (one on each side of the head)?
    Yes, they do. After birth they are swimming upright.
    As they grow, the eye starts to move on the other side (right side) and the fish starts to swim tilted until he swims totally flat. They pass through this metamorphosis in their first year of life.

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    Quote Originally Posted by tofu View Post
    Yes, there needs to be a selective advantage at every single step. That's sort of the whole point of evolution. There are always more individuals than the ecosystem can support. Only the strongest (that is, the most fit) survive.

    There doesn't have to be an advantage for every trait or adaptation. Plenty of species carry vestigial traits. But if you're going from point A to point B, or in this case, from H1 to H3 then yes, there absolutely has to be a selective advantage to H2.
    Perhaps, but you may simply not be "tuned in" to that advantage. A peacock's tail is a definite disadvantage for an individual peacock's survival. But as S.J. Gould has pointed out....

    "Our world overflows with peculiar, otherwise senseless shapes and behaviors that function only to promote victory in the great game of mating and reproduction. No other world but Darwin's would fill nature with such curiosities that weaken species and hinder good design but bring success where it really matters in Darwin's universe alone -- passing more genes to future generations."

    As to halibut, I'm not really tuned in to their particular evolution. I think Delvo makes good points.
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Cougar View Post
    Perhaps, but you may simply not be "tuned in" to that advantage. A peacock's tail is a definite disadvantage for an individual peacock's survival. But as S.J. Gould has pointed out....

    "Our world overflows with peculiar, otherwise senseless shapes and behaviors that function only to promote victory in the great game of mating and reproduction. No other world but Darwin's would fill nature with such curiosities that weaken species and hinder good design but bring success where it really matters in Darwin's universe alone -- passing more genes to future generations."

    As to halibut, I'm not really tuned in to their particular evolution. I think Delvo makes good points.
    This reminds me very much of my situation. I have spend most of my life bearly able to function because of depression. Once I had stabilized on my medication, I ask the doctors why natural selection hadn't bred this obvious flaw out of the population. I was told that it was because many of us so afflicted were so productive. What was a disadvantage for me personally was good for the species...

    thanks a lot Darwin!!

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    This reminds me very much of my situation. I have spend most of my life bearly able to function because of depression. Once I had stabilized on my medication, I ask the doctors why natural selection hadn't bred this obvious flaw out of the population. I was told that it was because many of us so afflicted were so productive. What was a disadvantage for me personally was good for the species...

    thanks a lot Darwin!!

    If you were a hunter gatherer you probably would not suffer from depression. Its prevalence appears to be the result of our modern lifestyle. For example depression used to be very rare in China but has now become a major problem as they have modernized. The genes that predispose one for depression in our society may have been beneficial for hunter gatherers, similar in the way that our desire to overeat helped hunter gathers to survive but gives us heart disease.

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    Quote Originally Posted by Lurker View Post
    This reminds me very much of my situation. I have spend most of my life bearly able to function because of depression. Once I had stabilized on my medication, I ask the doctors why natural selection hadn't bred this obvious flaw out of the population. I was told that it was because many of us so afflicted were so productive. What was a disadvantage for me personally was good for the species...

    thanks a lot Darwin!!
    Also, in humans, we are so boneheaded about survival that genes that might be considered a disadvantage or weakness are not bred out.

    And that really is the case in evolution. It isn't JUST that strong genes prevail. That can be a case but not always.

    Weak genes or non-advantageous are passed on just fine as long as the carriers of the genes survive.

    In the case of the halibut, as long as the species survived- so did its genetic material.
    If we took a known weak creature like a snail and put it in an area of lots of crows. Snails would not survive well in that area,
    However take that snail and put it in an are that has no predators to the snail- and it will do a lot of damage maybe but thrive.
    It is in fact a current problem in many places where man has interferred with the natural selection process.

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    Quote Originally Posted by tofu View Post
    Yes, there needs to be a selective advantage at every single step. That's sort of the whole point of evolution. There are always more individuals than the ecosystem can support. Only the strongest (that is, the most fit) survive.

    There doesn't have to be an advantage for every trait or adaptation. Plenty of species carry vestigial traits. But if you're going from point A to point B, or in this case, from H1 to H3 then yes, there absolutely has to be a selective advantage to H2.
    If the selective pressures of the organism make H1 and H2 equally fit, then the population at large can support both H1 and H2 types. If H2 types can then gain the trait of H3, there the advantage comes in.

    This follows from your second paragraph.

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    Quote Originally Posted by tofu View Post
    Yes, there needs to be a selective advantage at every single step. That's sort of the whole point of evolution. There are always more individuals than the ecosystem can support. Only the strongest (that is, the most fit) survive.

    There doesn't have to be an advantage for every trait or adaptation. Plenty of species carry vestigial traits. But if you're going from point A to point B, or in this case, from H1 to H3 then yes, there absolutely has to be a selective advantage to H2.
    I am not convinced that this is true. I recall reading "Darwin's Finches" or a similarly-titled book a while back where a group was studying finches methodically. They noted that during times of plenty, there was substantial variability in the types of beaks that existed, whereas during times of rarity, only those that were very specialized (and whose specialization lead to getting more food, for example) tended to survive.

    Thus, it is possible that birds with a short fat beak could, in times of plenty, develop variants where birds had a longer, thinner beak, which, by further variation, could develop a small twist in the beak. Then, as food grows scarce, those birds with more twisted beaks could successfully compete against short-fat-beaked birds by eating a different class of nuts. Then, you would have the twisted-beak birds coming from the fat-beaked birds with an intermediary that has an advantage to neither specialization (and the intermediary would likely diminish during scarce food times).

    Note that I am not claiming that this is in fact how the beaks developed; I provided a (fictional) example of how not every step must maintain advantages. I'd add that it would be circular to dismiss the thin, untwisted beaked-birds as a step because they died off, because they were, in the example, the requisite middle step in the progression of beak development.

    I'm sorry for bringing finches into a halibut discussion, but I'm working from memory and the example can be applied without sounding too fowl or fishy.

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    Quote Originally Posted by mr obvious View Post
    I am not convinced that this is true. I recall reading "Darwin's Finches" or a similarly-titled book a while back where a group was studying finches methodically. They noted that during times of plenty, there was substantial variability in the types of beaks that existed, whereas during times of rarity, only those that were very specialized (and whose specialization lead to getting more food, for example) tended to survive.

    Thus, it is possible that birds with a short fat beak could, in times of plenty, develop variants where birds had a longer, thinner beak, which, by further variation, could develop a small twist in the beak. Then, as food grows scarce, those birds with more twisted beaks could successfully compete against short-fat-beaked birds by eating a different class of nuts. Then, you would have the twisted-beak birds coming from the fat-beaked birds with an intermediary that has an advantage to neither specialization (and the intermediary would likely diminish during scarce food times).

    Note that I am not claiming that this is in fact how the beaks developed; I provided a (fictional) example of how not every step must maintain advantages. I'd add that it would be circular to dismiss the thin, untwisted beaked-birds as a step because they died off, because they were, in the example, the requisite middle step in the progression of beak development.

    I'm sorry for bringing finches into a halibut discussion, but I'm working from memory and the example can be applied without sounding too fowl or fishy.
    Look at human variation.

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    Quote Originally Posted by Neverfly View Post
    Look at human variation.
    i think most human variations can be attributed to the event that almost made the human species go extinct. when it happened, we had spread out of Africa and into Europe and Asia. and maybe even into Australia. then something happened that killed of 95% (or thereabouts) of all humans and isolated the survivors to small populations cut off from everyone else by thousands of miles.
    i'm thinking it might have been a super volcano eruption, but can't remember at this point. i'm sure someone will jump in and pick this apart and correct what i got wrong..
    anyways, this, i think, is why we have the different "races" within the human species. the people that survived in Africa tended to look different and have different adaptations to their environment than the group that survived in Europe and on the other side of Asia. if the populations had remained isolated for a longer period of time, then people from Europe wouldn't be able to breed with people from the other end of Asia or in Africa. they would have been distinct species, but i have no idea how long that would have taken to happen..

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    Quote Originally Posted by novaderrik View Post
    i think most human variations can be attributed to the event that almost made the human species go extinct. when it happened, we had spread out of Africa and into Europe and Asia. and maybe even into Australia. then something happened that killed of 95% (or thereabouts) of all humans and isolated the survivors to small populations cut off from everyone else by thousands of miles.
    i'm thinking it might have been a super volcano eruption, but can't remember at this point. i'm sure someone will jump in and pick this apart and correct what i got wrong..
    anyways, this, i think, is why we have the different "races" within the human species. the people that survived in Africa tended to look different and have different adaptations to their environment than the group that survived in Europe and on the other side of Asia. if the populations had remained isolated for a longer period of time, then people from Europe wouldn't be able to breed with people from the other end of Asia or in Africa. they would have been distinct species, but i have no idea how long that would have taken to happen..
    yes, I was tempted to nitpick this but...

    Generally you are making sense so I'll shut up.

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    Generally when we are talking about evolution, to get from A to E steps B C and D must be useful for the organism otherwise they won't be selected for and spread through the population. It is quite common for a creature to be stuck with an inefficient arrangement simply because the intermediate steps aren't useful. For example insect eyes aren't as good as our camera type eyes, but insects can't evolve camera eyes because that means they would have to have intermediate stages where they would be carrying around primitive eyes that are worse than current insect eyes which would simply be a waste of energy to grow and carry around and would be a disadvantage. The only way insects could develop camera eyes would be perhaps for insects that live in caves and have completely lost their eyes to evolve eyes again. Then it might be possible for them to evolve camera eyes as each step along the way would then have advantages.

    Now usually each step must be useful, but random variation also occurs. These can be changes that are neither really good nor bad but merely different but sometimes these random variations might turn out to be useful and then become selected for. For example my friend can drink from a beer bottle using his toes. This might not sound all that useful from a survival point of view, but if the human race was attacked by a virus that damaged our hands then my friend and his decendants might end up being some of the most successful people on the planet.

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    Quote Originally Posted by Ronald Brak View Post
    Generally when we are talking about evolution, to get from A to E steps B C and D must be useful for the organism otherwise they won't be selected for and spread through the population. It is quite common for a creature to be stuck with an inefficient arrangement simply because the intermediate steps aren't useful. For example insect eyes aren't as good as our camera type eyes, but insects can't evolve camera eyes because that means they would have to have intermediate stages where they would be carrying around primitive eyes that are worse than current insect eyes which would simply be a waste of energy to grow and carry around and would be a disadvantage. The only way insects could develop camera eyes would be perhaps for insects that live in caves and have completely lost their eyes to evolve eyes again. Then it might be possible for them to evolve camera eyes as each step along the way would then have advantages.

    Now usually each step must be useful, but random variation also occurs. These can be changes that are neither really good nor bad but merely different but sometimes these random variations might turn out to be useful and then become selected for. For example my friend can drink from a beer bottle using his toes. This might not sound all that useful from a survival point of view, but if the human race was attacked by a virus that damaged our hands then my friend and his decendants might end up being some of the most successful people on the planet.
    yes good points, however, I'd like to point out the use of the words "useful" and "selected." (I know YOU know this... )

    There is no commitee that "selects" what is good or bad. The ONLY selection is: If It Dies. If it dies it can't pass it on.
    If you take the WORST creature with the WORST genetic material, but continually keep it alive- put it on life support if you have to- and breed it...
    Its species will continue to survive as well as any other healthy well adapted species.
    That given, a variety of environments and situations can give cause to the survival of some rather odd creatures. Time tested.
    How many other Odd creatures did not survive that we havent found the fossils for yet? The halibut is one that did- how many did not when the circumstances were different?

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    http://en.wikipedia.org/wiki/New_Zealand_mud_snail

    From the Rock snot thread, a good example of envirnoment, predators and selection at work.

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    Quote Originally Posted by novaderrik View Post
    i think most human variations can be attributed to the event that almost made the human species go extinct. when it happened, we had spread out of Africa and into Europe and Asia. and maybe even into Australia. then something happened that killed of 95% (or thereabouts) of all humans and isolated the survivors to small populations cut off from everyone else by thousands of miles.
    i'm thinking it might have been a super volcano eruption, but can't remember at this point. i'm sure someone will jump in and pick this apart and correct what i got wrong..
    anyways, this, i think, is why we have the different "races" within the human species. the people that survived in Africa tended to look different and have different adaptations to their environment than the group that survived in Europe and on the other side of Asia. if the populations had remained isolated for a longer period of time, then people from Europe wouldn't be able to breed with people from the other end of Asia or in Africa. they would have been distinct species, but i have no idea how long that would have taken to happen..
    Sorry, Novaderrik, but that is completely wrong. The human species is thought to possibly have gone through a bottleneck, but that was before we left Africa!

    The evidence, by the way, is based on the fact that we are much less genetically variable than other species.

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    But that must mean that life was designed!!




    Just kidding.

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    Quote Originally Posted by Ronald Brak View Post
    If you were a hunter gatherer you probably would not suffer from depression. Its prevalence appears to be the result of our modern lifestyle. For example depression used to be very rare in China but has now become a major problem as they have modernized. The genes that predispose one for depression in our society may have been beneficial for hunter gatherers, similar in the way that our desire to overeat helped hunter gathers to survive but gives us heart disease.
    Perhaps... however, the condition I suffer is genetic in nature. It is unlikely that I would escape the condition as a result of other lifestyles... It appears that I am programmed for low levels of serotonin and norepinephrine...

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    Question

    Isn't the level of those neurotransmitters increased by physical activity?

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    Quote Originally Posted by Disinfo Agent View Post
    Isn't the level of those hormones increased by physical activity?
    This is true, but for some the body appears to be designed for lower levels... so, the highs are at low levels and the lows are very deep.

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    Question

    What I was thinking was that since most of our ancestors probably were physically more active than many of us today, that might have been enough to raise their levels of neurotransmitters to 'bearable' levels... Just a random idea, though.

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