Why do we die?

Discussion in 'Biology & Genetics' started by Norsefire, Feb 2, 2008.

  1. Enmos Staff Member

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    Yup and that is why I said that we die to make place for others

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  3. marnixR in hibernation - don't disturb Registered Senior Member

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    logic alert : you're confusing the CONSEQUENCES of someone dying (i.e. freeing up resources for the next generation) with the REASON(s) why death happens

    saying that we die BECAUSE we want to make space for others is a teleological argument with very little substance
     
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  5. Enmos Staff Member

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    No it isn't, it may be programmed in our DNA to live for a certain approximate amount of time. Because history has shown that populations fare better then, in relation to resources.
     
    Last edited: Feb 18, 2008
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  7. Norsefire Salam Shalom Salom Registered Senior Member

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    Can't one live longer if they put off reproduction ( I think for females at least) until very old ages? I head that over the course of many generations, lifespan will increase significantly.
     
  8. marnixR in hibernation - don't disturb Registered Senior Member

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    the watchword being : MAY be programmed - that's still far from proven
     
  9. blobrana Registered Senior Member

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    It seems to me that DNA is essentially eternal, and that lifeforms are only temporary vessels for the code.
     
  10. draqon Banned Banned

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    thats why we shouldn't meddle with our DNA
     
  11. marnixR in hibernation - don't disturb Registered Senior Member

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    huh ? how's that follow ?
     
  12. francois Schwat? Registered Senior Member

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    Wow, that kind of surprised me. Good answer, draqon.

    There's another tantalizing explanation for why we die. I think it was proposed by Peter Medawar sometime in the 70s. He suggested that all of the ill effects of old age, that is, weaker muscles and bones, loose skin, hair loss, dementia, loss of motor control, etc., are the effects of the accumulation of sublethal genes. By sublethal gene, I mean a gene that doesn't necessarily kill you, but increases the probability of you dying.

    The idea is that genes don't care much whether a person lives forever once he has reproduced. So as a result, the selection of genes for this or that trait is weak after a person has reproduced. This is why genes like the ones causing Huntington's Disease exist. Huntington's Disease usually "turns on" when a person is in his 30s, an age when most people have already reproduced, so it's easy to see how that lethal gene can be handed down to offspring.

    The other idea behind this theory is that the vast majority of mutations are deleterious. And as explained, there is significantly less selection pressure going on after a person reproduces and it continues to lessen as the person continues to age. So as a result, because there's little selection pressure against sublethal and deleterious genes, they accumulate and accumulate. They're always there, but they're not always "on"; they turn on or at least express themselves in a pernicious way later on in the organism's senescence, just like does the gene for Huntington's disease. In fact, it may even be true that these genes which later on gang up and kill us were genes that helped us in our youth, maybe coded for eye pigment or who knows? It happens though, because what an organism does in its old age isn't as important to its genes as what it does in its youth.
     
  13. Enmos Staff Member

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    Some aspects of it are proven though..
    On the micro scale, programmed cell death is scientific fact.
    On the macro scale, such as in populations, things may just work the same way.

    Also, evolutionarily seen it makes sense to have organisms live shorter than they could have otherwise. For instance, if a species would arise that could potentially live forever (meaning they don't age) it's environment would be void of food sources pretty quickly. This leaves the species competing amongst each other for food, and they will eventually die out because of starvation.
    And then there is the thing of adaptability. Even if a species would manage somehow to avoid starvation the species would eventually fall prey to diseases or any other environmental pressures because of too little variation in the population.
    Natural selection does not benefit immortal organisms.
    Besides, a truly immortal species can never exist.. there would still be predators, diseases, accident.. etc.

    Edit:
    Long-lived species in nature today have very low reproduction rates.. I should think that's a pretty good indication that the longer the organism lives the more pressure it puts on it's population.
    Short-lived species with lots of offspring is one solution, long-lived species with little offspring is another..
    In this light a nearly immortal (as in VERY long-lived) species would hardly ever reproduce.. a great risk to the survival of the species.
     
    Last edited: Feb 18, 2008
  14. marnixR in hibernation - don't disturb Registered Senior Member

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    agreed on the micro scale
    as for the macro scale, it all depends on whether you think that group selection is a major force in natural selection

    look at the various combinations possible

    short-lived, few offspring : doesn't look like a good evolutionary gambit to me
    short-lived, many offspring : obviously a successful and very common gambit
    long-lived, few offspring : the second most successful gamit, but in the long run (as you pointed out) in danger of extinction through small populations
    long-lived, many offspring : presumably would lead to overpopulation followed by population crash
     
  15. Enmos Staff Member

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    I do.. or rather natural selection on populations, not necessarily coherent groups.

    Exactly.. sooo.. you agree ?
     
  16. marnixR in hibernation - don't disturb Registered Senior Member

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    yes
     
  17. Letticia Registered Senior Member

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    The longest-lived known animal, the quahog (400-year old specimen found recently) follows just that strategy. No risk of population crash because of very high infant mortality. Or you could say population crashes in every generation -- before reaching maturity.

    In general, species' lifespan seems depended on its mortality rate from other reasons. For a mouse, expending energy on tissue repair year after year is pointless, as an owl will get it soon anyway. Nothing preys on great cats, but they depend on fairly changeable food source where risk of death from starvation is fairly high. So for them lifespan beyond 30-40 years is excessive. Tortoises and large parrots have no predators either, and very stable food source hence their 100+ lifespan. Adult quahog has it best -- no predators at all, and EXTREMELY stable environment (deep seabed).

    So it looks like optimum lifespan is roughly your expected life expectancy before something non-age related takes you. And it can be VERY long.
     
  18. Letticia Registered Senior Member

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    Now that I think of it, trees follow the same strategy. Very long lifespan, many offspring, very high infant mortality, and very low death rate in adulthood -- at least before humans invented axes. A creature which is nearly unkillable has no reason to age -- or rather, has good reasons to invest in repair mechanisms which stave off aging.
     
  19. cosmictraveler Be kind to yourself always. Valued Senior Member

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    We die because we just can't take all the assholes that are around us and make us pule!
     
  20. Enmos Staff Member

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    Btw. whence this newly found insight ?
     
  21. CharonZ Registered Senior Member

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    Ehem, there is quite some truths accumulated in this thread.
    I assume the real question is rather why we age and not death per se (as for the latter there are more options than aging). ATM there is no real definite answer, but a number of hypotheses exist.

    Anyway, it has been put forward several times that basic metabolic processes (as respiration) damage cells. In addition DNA replication is prone to errors which may accumulate and thus result in cell aging.An interesting point put forward by SAM is the observation that there are in fact immortal cells. Cancer cells for instance and most uni-cellular organisms are basically immortal. So why can't multi-cellular organism be the same? One answer is that multi-cellular organisms require a higher level of regulation, especially with regards to (DNA)-replication. As already mentioned, cancer cells are essentially deregulated cells which eventually can cause the death of the whole organism. So if cells were allowed to divide infinitely (e.g. by fiddling with the telomeres and a number of transcription factor) one might increase the living time of each individual cell, but the risk of deregulation would increase.
    Basically it is a kind of trade-off.
     
  22. cosmictraveler Be kind to yourself always. Valued Senior Member

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    no, you know what i meant
     
  23. Aivar A.R. Registered Senior Member

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    so... the "evolutionaly" cause is a metareason. It's the "real" cause of death, but definitely not the direct cause of old age.

    Direct causes, then, are...
    1) End strands of DNA (telomeres) wearing off, so part of DNA gets lost over repeated regeneration.
    2) Smaller scale mutations, caused most naturally by oxydative stress.
    3) A possible suicide gene which's sole purpose may be killing us off?

    And then: since the previous halt healthy cell regeneration, organs start withering, becoming less effective, eventually causing the failure of one or more organs, which causes a domino effect.


    How not to die of old age?

    Apparently, then, antioxydants help. But not entirely. You'd also need to either make sure DNA replication is done without any errors ever occurring (probably impossible, for a living being, but good nutrition should decrease the errors), or find a way to inject your own, unbroken DNA into you.

    And maybe virally reprogram a possibly suicide gene.

    Can anyone here explain how the low-carb diet works, or post a link to where it's thoroughly explained? Or explain how the yoga anti-aging principle works? I'm guessing it somehow "halts the burn-out" or something.


    Most importantly... I'm pretty much convinved that most of our modern sufferings are caused by overpopulation. So just think of what must happen, when we no longer age?? The overwhelming corruption... and wars... that's scary. Especially since I'm pretty sure we'll figure out how to not age, in my natural lifespan.


    Oh yes, I forgot: then there are cells which (maybe) do not reproduce. Nerve cells. Brain cells. They take damage over time, but there's no fixing them. Which means none of the previously mentioned methods would really rejuvenate those cells, only conserve them. Then again, I heard a rumor that the very latest research shows that nerve cells do regenerate, only very slowly... anyone's welcome to share their knowledge on that.
     
    Last edited: Feb 22, 2008

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