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One-eyed animal

  1. Nov 13, 2003 #1
    What animal normally develops with only one eye?
     
  2. jcsd
  3. Nov 13, 2003 #2

    Another God

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    Is this a trick question?


    I can't think of any (since at least most animals that have eyes tend to be symetrical), but my mind is tending towards flat fish. Since they are flattened side on, I am wondering if they have lost one of their eyes...actually, no, i think their eye sockets get distorted and it comes around to be on the same side... but maybe one of them has managed to 'remove' its eye in its evolutionary past or something.
     
  4. Nov 13, 2003 #3
    Is it a capertillar?
     
  5. Nov 13, 2003 #4
    Another God,

    My guess is that a universal minimum of two eyes provides evolutionary redundancy for all-important vision in case of an accident. Don't euglena (the most primitive example of eyes I could think of) have an eye spot(s)?

    Mentat,

    have you heard of the Polyphemus moth? Named after the Cyclops that Ulysses killed. It has at least two real eyes, though, as do all caterpillars to my knowledge.
     
  6. Nov 13, 2003 #5
    Actually, I just heard of that Polyphemus moth, that's why I mentioned caterpillars. But I guess I was wrong on that one...

    Do you have an answer, or are you actually asking?
     
  7. Nov 13, 2003 #6

    iansmith

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    Yes they have an eye spot but it is an organell and euglena are unicellular organism. It allow the cell to go toward or away from the ligth. The spot actually detect where the minimun ligth is coming from.

    As far as i know there is not such thing as one eye animal. 2 is the minimun requiered.
     
  8. Nov 13, 2003 #7

    Njorl

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    So, did someone ask you this verbally? If so, possible answers are:

    pig
    chimpanzee
    squid
    pigeon
    lion
    tiger
    etc.

    Njorl
     
  9. Nov 13, 2003 #8

    Another God

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    I'm not a fan of this "Minimum 2 required' phrase....it makes it sound like things can't live without two eyes...

    There is an undoubted evolutionary advantage in having 2 eyes over one, and since we are symetrical it makes sense that everything should have 2 eyes... But I am ready to accept that it was just another evolutionary accident frozen in time on account of its practicality.

    Something I learnt the other week: Predators tend to have eyes on the front of their head, good for focusing on a single prey animal. Prey animals tend to have their eyes on the side of their head, good for all round vision, preparing them for attack from any side.
     
  10. Nov 13, 2003 #9

    FZ+

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    Worms? We can consider the light sensitive end to be an "eye"...
     
  11. Nov 13, 2003 #10
    How could I possibly stay away from a topic about eyes?

    I heard tell of a One-Eyed-Flying-Purple-People-Eater, but excluding that, I can't say I've ever heard of a One-eyed critter. Cell division, Pairing off of the sexes,..., things like to come in twos. The Fer-De-Lance often travel in pairs, so you have to on your guard if you bump into one. The "Ayes" have it...


    pineal eye?; http://ebiomedia.com/gall/eyes/many.html
     
  12. Nov 13, 2003 #11
    Mentat,

    I'm jest-asking. The Polyphemus moth has a prominant "eye spot" as protective coloration on each wing. Birds spear the spot, not the moth!


    Another God et al.,

    Are two eyes more an outcome of symmetry or redundancy needs?

    Have you heard of the extreme birth defect in humans involving the development of only one eye centered at the forehead? The visual cortex there must maintain some semblance of bilateral symmetry, with one withered optic nerve. Extreme retardation and death accompany this "cyclopia."
     
  13. Nov 13, 2003 #12
    I cast my vote for Symmetry.
     
  14. Nov 13, 2003 #13

    Another God

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    symmetry is almost certainly the cause. Once the two eyes are there though, it makes sense to make the most of them, and so in the case of predators (which our eye configuration appears to point us out to be) it gives great focus. It allows predators to have an almost perfect judge of distance around the 10m mark... Meanwhile, the prey animals have used their two eyes to create a complete view. In rthe prey case in particular, there is nothing redundant about the eyes, each eye has been made somewhat necessary. With the predator case, there is better, more accurate vision with two, but you could live with just one. Redundancy isn't a strong theme.
     
  15. Nov 16, 2003 #14
    The physical environment could influence the organism's development (not just genes)

    from the book Evolution as Entropy by the zoologists Brookes and Wiley - certain species of fish, when it grows in fresh water, develops two eyes, but if you place the young fish in salt water, it grows up to have only one eye.
     
  16. Nov 16, 2003 #15

    FZ+

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    Hmm... but it seems that multi-eyes were more common with the more primative creatures of the sea, eg. jellyfish etc. At what point did they go back down to two eyes, or were the two-eyed creatures the result of a seperate evolutionary development?
     
  17. Nov 16, 2003 #16

    iansmith

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    For the jelly fish it is still is symmetry. The jelly fish as a radial symmetry and has an eye for each plane, more or less.

    Scientist think the eye evolved 40 times. How many times did it evolve to have 2? Also what is interresting in anthropods, arachnids have multple eyes whereas insects and crusteceans have 2 eye.
     
  18. Nov 17, 2003 #17
    That's the point, AG. If the "evolutionary accident" of having two eyes proved infinitely superior to having just one, then it could be considered a "minimum requirement" for surviving species, that they have two eyes (or none, like some species of fleas that live in wells).
     
  19. Nov 17, 2003 #18
    Well, I was making a joke, since "Polyphemus moth" sounded like some rare breed that nobody usually hears about...so, I say "of course I've heard of that" :smile:.
     
  20. Nov 17, 2003 #19
    That makes me wonder though...some insects have "complex eyes", don't they? Wouldn't one such complex eye be sufficient, without the other?

    Also, there are species of lizard (or is it chameleon?) that can see individually through each eye. That is, they can see one set of things in one eye, and another in the other eye. Thus, they can look behind them, and in front of them, at the same time. Couldn't something like this prove that it is alright to live with just one eye?
     
  21. Nov 17, 2003 #20

    NateTG

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    How about parralax? Two eyes make depth perception a whole lot easier.
     
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