Why do animals vary so much in life span?

  1. I was curious, why is it that dogs will live somewhere in the 10-20 year range, but humans make it to 80, and animals vary so much?
  2. jcsd
  3. mfb

    Staff: Mentor

    Why do you expect a similar lifespan for completely different animals, adapted to completely different conditions?
  4. What factors do you think might affect aging?
  5. Well I suppose it would have something to do with the complexity of the organism. It seems larger animals live longer than smaller ones generally (whale vs. house fly). Still, why is the life cycle of a dog so relatively short? I want my doggy to live forever =(
  6. Ryan_m_b

    Staff: Mentor

    Humans can live to 80 yet a horse only lives 20-30 years. Elephants can range from 75 to 105 times the mass of a human but they too only live around 80 years. Given this do you think there is something missing from your proposal about size and complexity? I'd suggest first looking up what the processes of ageing are and then trying to figure out why they might be different for different animals.
  7. mfb

    Staff: Mentor

    Significant differences can be found between different classes of animals - mammals tend to live long, but unicellular organisms can be immortal. The size-correlation is a side-effect: Many large animals (especially animals relevant for food, media coverage and so on) are mammals, many small ones are not.
  8. May I suggest the book "Cheating Time" by Roger Gosden. It's a nice non-technical book and makes for a good read. And the first few chapters are relevant to your question.
  9. I remember hearing once that if you measure lifespan in heartbeats instead of years, most animals (or was it just mammals?) come in at about the same number, about 2*10^6 or something.
  10. Ryan_m_b

    Staff: Mentor

    Given an average human heartbeat of 60bpm that means a human life expectancy would be 3 weeks. This doesn't make any sense regardless of how many beats one proposes.
  11. mfb

    Staff: Mentor

    As not animals have a heart, it cannot be a similar number for all animals.

    In addition, we should not compare the average lifespan - this is determined by the availability of food, predators, accidents and so on. The maximal lifespan is harder to evaluate, but better to compare.
    There are several known correlations with various biological rates.
  12. Pythagorean

    Pythagorean 4,483
    Gold Member

    Size, heart rate, and oxidative stress are the three wive's tales I always hear. (Acknowledging two of these have already been brought up in this thread).
  13. The fundamental determinant of the mean life span of a species in genetic. I don't think you can pin down individual traits consistently across species and genera that explain comparative life spans. Most research along these lines is in small rapidly reproducing organisms such as bacteria and insects.

    Last edited: Jan 18, 2013
  14. The simple, but admittedly not very helpful, answer is evolution. Dogs who live to be 80 don't leave any more descendants than those who live to be 20.
  15. Evo

    Staff: Mentor

    This has come up before. And as someone mentioned, there seems to be a correlation with heart rate and life span. I can't find the refernce i used last time, but this has a table. Scroll down to Lifetime Heartbeats and Animal Size.


    Also here. It also has a table.

  16. mfb

    Staff: Mentor

    It has a table, but I would not trust the graphs or mathematics there. It looks like a homework project with the target "we have to find some relations to get a good grade".

    The life expectancy of humans is a bit special anyway.
  17. Evo

    Staff: Mentor

    Yeah, it's not the study I originally found a few years back. The second goes into more detail.

    Here's a peer reviewed study published in The Journal of the American College of Cardiology.


    And I see more studies referenced on the page.
    Last edited: Jan 25, 2013
  18. Evo

    Staff: Mentor

    I found a free paper and it goes into the difficulties in determining the effects.


    Paper was published http://www.ncbi.nlm.nih.gov/pubmed/15855403 in The Journal of Experimental Biology.

    There are many peer reviewed papers that deal with the topic. There is no definitive answer AFAIK, but size and heart rate do seem to be a factor.
  19. epenguin

    epenguin 2,496
    Homework Helper
    Gold Member

  20. Mute

    Mute 1,390
    Homework Helper

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