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Thread: why salamandra can regenerate her tail?

  1. #1
    Banned adi chicago's Avatar
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    why salamandra can regenerate her tail?

    why a salamandra can regenerate her tail after an injury and we humans cannot regenerate the spinal cord?
    • Dum spiro, spero.
      • Translation: "As long as I breathe, I hope."

  2. #2
    I am speculating here but if loosing the tail is not fatal then tailless individuals will live and those that can regenerate tails may have an evolutionary advantage. Loosing your tail can save your life, as demonstrated by some Lizards which shed their tails when confronted with predators, leaving the predator to catch the tail whilst they escape alive. If a salamandar escapes from a predator by having its tail bitten off then being able to lose your tail again, if caught by another predator, would certainly be advantageous and the ability to regenerate a tail could be selected for. However as spinal cord injuries have been almost universally fatal throughout almost the entire history of mammals the implication is that a dead individual has been unabele to regenerate their spinal cord. There has thererfore been no possibility to select, in evolutioinary terms, the genes for this regenerative ability. Even if individuals survived the initial trauma they were left paralysed and likely to die from inability to collect food or to escape predators. Any surviving males have been left incapable of ejaculation and therefore reproduction and the females were also far less likely to reproduce succesfully, so it has not been possible to pass on the genes that made them more likely to survive and this has eliminated the possibility of evolving the ability to regenerate the spinal cord.
    Last edited by Adrian; 11-14-2006 at 03:58 PM.

  3. #3
    I agree with Adrian but unfortunately there are some flaws to the argument.

    An animal can evolve abililty to regenerate only if it can survive the injury. If true, lizards should not not regenerate their feet as well as they can regenerate their tail. A lizard needs its feet to survive more than it needs its tail. Likewise, a salamander should not regenerate its tail as well as it could its feet because a salamander needs its tail to swim more than it needs its legs.

    From personal experience, I know that a lizard does regenerate its tail very well. Likewise, I have studied regeneration of the legs of salamander and know that they do regenerate beautifully. However, I have read papers that suggest that the salamander will regenerate its tail and a lizard will regenerate its legs. It would be of interest to compare the extent, speed, or completeness of regeneration.

    But, if the above hypothesis is correct, the question is why we did not evolve the ability to regenerate those appendages that we don't need for survival but would give us some advantage. For example, probably millions of fingers are amputated every year somewhere around the world but the instances of regeneration of the fingers by adults is very rare. Note that are some reports that some children have regenerated the distal phalange of their fingers. I have a nephew who regenerated part of his finger as his child, for example. However, reports of adults that regenerate their fingers are very rare.

    Perhaps the reason why adults do not regenerate their fingers is because loss of a finger or two and lack of regeneration does not necessarily reduce the survival and reproduction of individuals. Some tribes cut their fingers off to mourn the death of loved ones. I suppose if the women were to marry only men who were able to regenerate their fingers, such a tribe may evolve the ability to regenerate their fingers.

    It is also worthwhile noting that the tail of a salamander does not have any spinal cord in it, just like our sacral segments contain only spinal roots. So, it is not about regenerating the spinal cord but rather the regeneration of a tail. Apparently, the regeneration of the tail involves the same mechanism and principles as regeneration of the legs. Stem cells are involved.


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