• Question: why do different animals have a different life span

    Asked by nishilgamer1213 to Frank, Ian, Isabel, Jared, Zena on 10 Mar 2015.
    • Photo: Zena Hadjivasiliou

      Zena Hadjivasiliou answered on 10 Mar 2015:

      This is a very interesting question that we don’t yet fully understand. One theory says that life span depends on the metabolic rate. According to this theory, animals that have lower metabolic rates are more likely to live longer. So for example, elephants that are large and have slow metabolic rates (they breathe more slowly and their hearts beat more slowly) live much longer than other mammals. But this theory is not supported across species. For example, some birds have very high metabolic rates but they live very long lives!

    • Photo: Jared Parnell

      Jared Parnell answered on 10 Mar 2015:

      As Zena mentioned, this is a very difficult question to answer and one we don’t really understand. It might also have something to do with the way cells reproduce, each cell contains DNA and this needs to get copied to every new cell that is produced. Telemeres are like little caps on the end of our strands of DNA, and it is a theory that when cells divide these get a bit weaker until they can no longer hold the DNA together and it gets damaged, causing ageing.

      An interesting example is a tiny Japanese jellyfish called a Turritopsis dohrnii (I have no idea how you say that), which appears to be able to self-heal. They can return to a child-like state and then begin ageing again. It is a theory that these jellyfish could live forever, but this hasn’t been proven! It is the only known species that might be able to do that!

    • Photo: Isabel Pires

      Isabel Pires answered on 10 Mar 2015:

      I agree with both Zena and Jared when they say it is a very interesting yet difficult question and that there can be many aspects to consider, such as metabolic rates and the way cells divide.

      Another interesting aspect to think about is how well the cells can repair the DNA when it is damaged by things such as sun light, nasty byproducts of metabolism or just when things go wrong during cell division. It is thought that older cells cannot repair their DNA as well and this is associated with the organism ageing.

      Cancer cells are quite different and interesting because they can overcome all these issues, which is the reason they are so dangerous. They can divide over and over again (because they have lots of telomerase), they can change their metabolism and they can ignore deficient DNA repair and actually get more mutations that way that allow them to survive, for example. If given enough food and space to grow, in a lab setting cancer cells are virtuality immortal! This is why they are so nasty…

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