Why are there no three limbed animals?

Discussion in 'Biology & Genetics' started by esbo, Sep 16, 2011.

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  1. Me-Ki-Gal

    Me-Ki-Gal Banned Banned

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    Lazy Designer theory . I like that . I think I will google that . See if I get a hit . Trippy

    O.K. back from my trip . I got a funny for ya . A mystic is a person that wants to understand the universe , but is to lazy to study physics .


    Ha Ha Ha Ha is that funny ? I thought so .
    Nothing concrete on a Lazy Creator . I will buy into it though . Path of least resistance seems right . Most bang for the buck so to speak . Sounds like the same reason Animals don't have 3 legs to Me . There are anomalies. I heard of them anyway . Humans with and extra leg growing out of there side . Left overs from absorbing a twin maybe . Why is there only one head . I mean come on . Can you imagine that . Your second head . This way no this way no this way no this way
     
    Last edited: Sep 17, 2011
    Me-Ki-Gal, Sep 17, 2011
    #21

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  3. Trippy

    Trippy ALEA IACTA EST Staff Member

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    Yeah, my theory is that if there was a designer they weren't so much as intelligent as they were Lazy. Everywhere you look, the same patterns repeated over, and over, and over again - it's like they just had the one good idea and said "I wonder what happens if you make this change here?"
     
    Trippy, Sep 17, 2011
    #22

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  5. Me-Ki-Gal

    Me-Ki-Gal Banned Banned

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    The life of an Artist . That is how Spidey does it , I am positive
     
    Me-Ki-Gal, Sep 17, 2011
    #23

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  7. chimpkin

    chimpkin C'mon, get happy! Registered Senior Member

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    Technically the animal here comes equipped with two rear limbs that have fused over time into a single caudal locomotor appendage, leaving this animal to move around with three limbs:

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    chimpkin, Sep 17, 2011
    #24
  8. Anti-Flag

    Anti-Flag Pun intended Registered Senior Member

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    Ask yourself what the advantages of having 3 limbs would be. Bipedal pairs obviously provide better motion as that's how most animals have evolved - but in the cases it doesn't then obviously there are some odd numbered limbed creatures.
     
    Anti-Flag, Sep 17, 2011
    #25
  9. Fraggle Rocker

    Fraggle Rocker Staff Member

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    No Orly, you miscounted. We have ten of each. Some mammals (such as the highly successful artiodactyls, the order that includes most, but not all, of the well-known grazing animals), most birds, and many other vertebrates have eight.
    No, that's not correct. The pelvis of the cetacean has atrophied almost completely leaving behind only a couple of vestigial bone fragments that float uselessly, unattached to anything. The hind legs have disappeared completely. The tail of the cetacean is, indeed, his tail and nothing more.

    Notice that his tail is articulated to move up and down and the fins are aligned to provide leverage in that direction, whereas the tail of the fish moves sideways and is aligned that way. If the cetacean tail were a fusion of the tail and two legs it would probably have a much greater range of motion.

    . . . . To return to the OP and the raging argument:

    I don't think I'm insulting evolutionary biologists to say that we really don't know why bilateral symmetry won the contest for the blueprint for all the higher phyla. Perhaps it was a survival advantage, but there's no reason to assume that it could not possibly have been instead an accident of genetic drift or a genetic bottleneck.

    Survival of the fittest is certainly an important factor in evolution, and very likely the most important factor. But that doesn't mean that sheer chance doesn't also play a role occasionally.

    I suspect that bilateral symmetry was indeed a survival trait in larger land-living animals. Surely it gives them a balanced locomotion that they could not achieve with an odd number of limbs.

    Because mass is proportional to the cube of linear size whereas muscle strength is only proportional to the square, larger animals are at a disadvantage in moving their weight around with their legs. The arrangement has to be very efficient. But smaller animals don't have that problem and can be "designed more whimsically," as it were.
     
    Fraggle Rocker, Sep 18, 2011
    #26
  10. Orleander

    Orleander OH JOY!!!! Valued Senior Member

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    but only 5 on each appendage. Why not 6?
     
    Orleander, Sep 18, 2011
    #27
  11. esbo

    esbo Registered Senior Member

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    No it looks to me like one limb has moved up his back to form the dorsal fin,
     
    esbo, Sep 20, 2011
    #28
  12. esbo

    esbo Registered Senior Member

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    Why not it is an efficient platform.
    3 legged stools camera tripods etc....
     
    esbo, Sep 20, 2011
    #29
  13. esbo

    esbo Registered Senior Member

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    esbo, Sep 20, 2011
    #30
  14. ULTRA

    ULTRA Realistically Surreal Registered Senior Member

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    Fossil evidence clearly shows bilateral budding of fronds/leaves going back some 3bn years or so. This is a pattern most easily engineered into simple dna, as working out an assymetrical design has no advantages. Nature will usually take the simplest route to a working design, and basal symmetery is the easiest to reproduce.
     
    ULTRA, Sep 20, 2011
    #31
  15. wlminex

    wlminex Banned Banned

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    . . .what kind of leaves were around 3 by, or so, ago? . . . plants came later, I think.
     
    wlminex, Sep 20, 2011
    #32
  16. ULTRA

    ULTRA Realistically Surreal Registered Senior Member

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    Plants were the first biological entities to colonise Earth. Animals came some time later. I recall seeing very early fossil remains of plants clearly showing bilateral symmetry though I can't remember what they were called just now. A quick search of the interweb might prove fruitful. David Attenborough did a very good documentary on early life, well worth a look.
     
    ULTRA, Sep 20, 2011
    #33
  17. wlminex

    wlminex Banned Banned

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    . . . .well . . . algae were probably around then . . . not terrestrial (above-ground) plants. Maybe called Eukarophytes?
     
    Last edited: Sep 20, 2011
    wlminex, Sep 20, 2011
    #34
  18. ULTRA

    ULTRA Realistically Surreal Registered Senior Member

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    No, that's right. Terrestial plants came later. However there were some "plants" distantly related to sponges that were neither true plant nor true animal. Even in early protozoa you can find symmetry though, it's something pretty well welded into our DNA at an early stage. I find nothing odd in this. It's gonna produce plants and animals that are easily reproducable in huge numbers without much effort. There's nothing strange about it.
     
    ULTRA, Sep 20, 2011
    #35
  19. wlminex

    wlminex Banned Banned

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    . . . .could be . . . I'm an igneous petrologist . . . not a paleontologist . . just curious!
     
    wlminex, Sep 20, 2011
    #36
  20. ULTRA

    ULTRA Realistically Surreal Registered Senior Member

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    Also, think of a cell dividing. A cell with more symmetrical components will be able to divide much more simply than one with random components. this leads to less errors and hence greater survivability. When a simple cell divides, it basically forms 2 poles that generate microtubules. Half of the dna is drawn into the poles by the microtubules that grab onto the dna and split it in two, and the cell divides. If a cell was assymetrical, it would produce uneven results meaning the daughter cell was incomplete. This would put it at a functional disadvantage.
     
    ULTRA, Sep 20, 2011
    #37
  21. wlminex

    wlminex Banned Banned

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    you're right about bilateral cell division . . . . reminds me of mitochondria . . . .
     
    Last edited: Sep 20, 2011
    wlminex, Sep 20, 2011
    #38
  22. Me-Ki-Gal

    Me-Ki-Gal Banned Banned

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    yeah path of least resistance. Simplest rout . I think there is some strong merit there . Coral isn't that an ancient life form . Those mushroom looking things , Ancient coral like structures . Shell fish evolved around one of those billion years . I am thinking most the animals were shell type shallow sea creatures. Small shell fish. Mass extinction comes to mind . Were most of them suckers were wiped out . Method of destruction unknown ? Maybe we got an idea now ?
    Bush did it
     
    Me-Ki-Gal, Sep 20, 2011
    #39
  23. ULTRA

    ULTRA Realistically Surreal Registered Senior Member

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    Heehe! I don't think even he's that old, though I could be mistaken!
     
    ULTRA, Sep 20, 2011
    #40
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