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  1. #1

    Default Evolution (and randomness)

    I went to see an eye doctor today, and being a physicist I got thinking about what a complex system the eye is. How does something like that evolve?

    It's all good having small changes in cells and stuff. But what kind of mutation creates a lens system accidentally? And how much more random processes does it take to breed a creature with a perfectly functioning lens system with aperture control and receptors?

    There is no reason for a creature with a half constructed lens system to have an advantage over any others of it's species. And I can't see it evolving in one step.

    These parts of evolution have always puzzled me. I don't believe in intelligent design or anything, I'm looking for science answers. I've never taken biology. What are the generally held theories on evolution these days, and how do they describe the processes driving it.
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  2. #2
    DoubleplusUngoodNonperson
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    I don't think complexity starts with new mutations - it HAS to begin small and subtle for reasons you stated. Basically, somewhere along the line a biological mutation was made in cells that made those particular cells react/sensitive to different forms of electro magnetic radiotion. Think of something starting off with small/simple structure.... like primitve spider eyes or something, that was the first photo-sensitive cells that gave advantages. the rest could just be developmental history

  3. #3
    Habitual Fi LineStepper JocktheMotie's Avatar
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    [YOUTUBE="http://www.youtube.com/watch?v=Yj_lNQerUJ4"]Evolutionary steps of the Eye[/YOUTUBE]

    Here you go.



  4. #4

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    Cool . Thanks to both of you.
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    Senior Member Feops's Avatar
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    Can't wait to get home and view that clip. I'd love to hear how something so complex came about.

    At a guess.... basic photosensitivity seems simple enough. An attaction to light (energy) would be a basic survival trait. Plants do that just so they don't grow stupid and they don't have eyes.

    From there, perhaps multiple distinct photosensitive patches to discern direction? From there, I could see a socket developing to better estimate depth and focus energies on increasingly specialized photosensitive patches for color and shade. There would be huge evolutionary pressure as the blind would be destroyed quickly.

    Little stumped at this point on how the ball could form. Maybe a film, then a lens, then increasingly specialized lenses?

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    4x9 cascadeco's Avatar
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    In the 'Blind Watchmaker', Dawkins devotes a handful of pages to this very subject - the eye.

    Basic premise is that an organism with even the most basic 'vision' - photosensitivity - could have some sort of survival advantage over one with none at all.

    Using humans as an example -- someone with vision impairment, who requires glasses but still sees fuzzy shapes and can navigate around objects without glasses, is going to obviously be in much better shape than someone whose vision is so impaired that they can only see vague shadows/lights. And someone who can only see vague shadows and hardly anything at all is going to be a bit better off than someone who can't distinguish anything at all.

    And...just remember it's not like evolution is something that has a set goal in mind. It's nothing more than those individuals who have better survival mechanisms, and thus produce more offspring (in theory), who will then shift the overall gene pool of the population to include their traits. So then slowly the entire population shifts in that direction over time.
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  7. #7
    Senior Member sculpting's Avatar
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    Many species of bacteria actually posses a photosenstive clump of cells at one end that allow them to sense light. Also I think I'd look towards really simple sea based animals and see if they had the same features.

  8. #8

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    Here is a series of lectures that is rather illuminating.

    RichardDawkins.net

    Accept the past. Live for the present. Look forward to the future.
    Robot Fusion
    "As our island of knowledge grows, so does the shore of our ignorance." John Wheeler
    "[A] scientist looking at nonscientific problems is just as dumb as the next guy." Richard Feynman
    "[P]etabytes of [] data is not the same thing as understanding emergent mechanisms and structures." Jim Crutchfield

  9. #9
    Senior Member Qre:us's Avatar
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    The evolution of the eye is quite fascinating as the eye is such a complex organ. Convoluting this matter is also how the eye does what it does....which we have yet to get a clear picture about. Esp. in terms of visual perception where the retinal image is not a direct translation by the brain (as what the image is on the retina, we do not 'see'), but, rather there is *something* going on with visual processing that allows us to see what we see. E.g., why are images upside down on our retina? What is the evolutionary advantage of this method versus direct translation of a right-side image on retina, to, processing in brain?

    It's not simply about figuring out how the eye came about, but, to comprehensively answer this question, we must first find out HOW the eye/brain works, and work backwards.

    * aside - I think it was Stratton and another dude, Kohler, who made these upside down glasses (glasses inverted images/world), and had peeps wearing them. With practice, we can get used to navigating in an upside down world. this raises quite a few questions regarding visual perception and what it means for the interpretation of images by the eye to the brain.

  10. #10
    Gotta catch you all! Blackmail!'s Avatar
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    Quote Originally Posted by nozflubber View Post
    like primitve spider eyes or something, that was the first photo-sensitive cells that gave advantages.
    Actually, some spiders developped very efficient eyes through evolution, with stereoscopic, binocular and even color vision. Think for instance to the jumping spiders (Salticidae). Even if their range is more limited than ours, their accuracy is quite similar. Thus, you can tell when these spiders are staring at you.



    Even if these animals are very tiny, they have a huge brain compared to their body mass, and it is mostly dedicated to image processing.

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