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Medical Why do we die of old age?

  1. Oct 2, 2007 #1
    It would perhaps seem more beneficial for organisms to have evolved so as to live forever, excluding of course any trauma induced from injuries, or being consumed by predators.

    Life is so complex, what stopped it from simply acquiring the ability to live forever?
     
  2. jcsd
  3. Oct 3, 2007 #2
    Since organisms are inevitably going to be killed, either by predators or by accidents, evolution has favored early reproduction instead of longevity. Both reproduction and maintenance of the body require a lot of energy, so it's sort of one or the other, and evolution has generally favored reproduction. Because of limited maintenance of the body, it eventually breaks down, and we die of old age.

    Some animals, such as turtles and rockfish, have what's called 'negligible senescence', which means that they don't show signs of getting older, or their body breaking down. Essentially they've evolved so as to live forever.

    For a great primer on the topic, check out the Wikipedia article on senescence
     
  4. Oct 3, 2007 #3

    jim mcnamara

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    More succinctly -
    There is no selection pressure for genes that make you live longer than it takes to successfully reproduce and rear young. It is a mammalian trait, BTW, because mammals have to care for young. Some other groups of animals die when they reproduce - eg. many insect species, anadromous fish. Which is tantamount to the same idea.
     
  5. Oct 3, 2007 #4
    I think it is coded into the DNA by the designers. Once you reach 25-30 years of age your body starts going downhill. If we can ever figure out the genome maybe we can figure out a way of stopping it.
     
  6. Oct 3, 2007 #5
    But wouldn't living longer allow you to reproduce and rear more young? As humans we typically raise one set of young, but other organisms reproduce regularly. For example, sea turtles nest every two to four years -- the longer they're alive the more offspring they can reproduce. Isn't that a selective pressure for longevity?
     
  7. Oct 3, 2007 #6
    Because it isn't the individual that is important, it's the genes.

    As long as the individual lives long enough to reproduce and raise its young, its genes will be perpetuated.

    If there was set of genes that caused the death of its carrier before its offspring are able to survive on their own, it would quickly disappear from the gene pool. But any set of genes that caused death later would not be removed, since they have already been passed on before they activate.

    For example, if there were different sets of genes in humans that favored death around 50, 60, 70 and 80 years of age, there would be no particular reason for one to become more abundant than the other, since the vast majority of reproduction and child raising will be done by then. Essentially, there is no reason based on gene-centered natural selection for us to live longer.
     
  8. Oct 14, 2007 #7
    I know a lot of genes involved in cancer suppression are also related to aging. Right now it seems the ability to repair the body and the ability to guard against cancer are antagonistic. So it may be that a limited life span of a certain length was selected for because it allowed the highest portion of organisms to live to reproduce. A shorter limit culled them too quickly, while a higher limit left too many dying prematurely of cancer. But the third bowl of porridge was just right.
     
  9. Oct 18, 2007 #8
    Reproducing more and rearing more young would defeat the purpose.

    The reason humans and other mammals have evolved to reproduce very little is because, though they only have a few offspring, they invest a great deal of time and effort into those few offspring to make sure that they also reach maturity and reproduce.

    Having more offspring would mean fewer resources available for all of them, and less time for the parents to dedicate to each one; effectively reducing the likelihood that any of the children will survive to reproduce.
     
  10. Nov 24, 2007 #9
    What acvwjohn stated is right. Just a curiosity: our cells have a division limit, because every time our dna replicates before cell division, a piece of each cromossome is lost (in the telomere). But there is a gene that prevents this (produces a proteín telomerase, if i am not wrong), that is silenced in our somatic cells. This gene is usually unsilenced in cancer cells (it is there as a consequence, it doesn't causes cancer!!). I hope my explanation is cientificaly acurate and understandable... Since this isn' t a biology forum I assume most people wouldn't understand the concept completely if I used the standard names.
     
  11. Nov 25, 2007 #10

    Chronos

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    The hayflick limit is the quick answer. Even turtles, sharks and trees eventually succumb to old age. All living things are programmed to die to create space for their offspring.
     
  12. Dec 27, 2009 #11
    If that's the case then surely organisms that do not reproduce would not die?
     
  13. Dec 29, 2009 #12
    yep, we calll them machines.
     
  14. Dec 29, 2009 #13
    Even machines succumb to old age, they wear out and break eventually even if they are maintained.
     
  15. Dec 29, 2009 #14
    I agree our body is like a machine which ages and deterioates with time.
     
  16. Dec 29, 2009 #15
  17. Jan 19, 2010 #16
  18. Jan 25, 2010 #17
    Is living forever even possible, whether or not the genes for such a purpose are present? What is known from why we die of old age is explained by the commonest causes of death with cardiovascular disorders ranking top. Some critical regulatory process or organ gives way and we simply die regardless of how good or bad health we had maintained over the past years!
     
  19. Jan 25, 2010 #18
    The entire biosphere can be considered to be a 4 billion year old organism.
     
  20. Jan 26, 2010 #19
    Whether or not the genes for such a purpose are present, living forever probably even possible. Near death experiences and out of body experiences may probably gives us clue. But no one likes to leave the genes and live like a ghost.

    Cardiovascular disorders are commonest causes of death. This is probably because of reduced heterosexual activity. The heart needs sex hormones. Higher sexual activity is linked with increased sex hormone levels.

    http://www.albany.edu/news/pdf_files/Hughes article.pdf
    http://www.ncbi.nlm.nih.gov/sites/entrez/15216425

    Asexuality (sexual abstinence) is associated with short stature, low education, low socioeconomic status, poor health and later onset of menarche in women.
    ( http://www.ncbi.nlm.nih.gov/sites/entrez/15497056 ) Another article says that deprivation of sexual activity in girls after the puberty probably induces physical and functional damage. ( http://www.ncbi.nlm.nih.gov/sites/entrez/642847 ) Sexual abstinenceis associated with death. Early cessation of sexual intercourse was found to be associated with an increased mortality risk among men. http://www3.interscience.wiley.com/journal/120047525/abstract?CRETRY=1&SRETRY=0

    Reduced frequency of orgasm is remarkably associated with coronary artery disease.
    http://www.ncbi.nlm.nih.gov/sites/entrez/1005633


    Repeatedly mated experimental field crickets increased their longevity to 32%. http://www.ncbi.nlm.nih.gov/sites/entrez/11430659

    Why not humans?

    We really need research on human subjects.
     
  21. Jan 26, 2010 #20
    I need less physics and more sex.
     
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