TED Conversations

Anuraag Reddy

AIESEC India

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Why evolution could never solve aging?

Maybe aging is an essential mechanism to clear out the old and make way for the new like cells within a body?

Maybe every form of life is already close to the upper limit of life expectancy?

Maybe aging is in the nature of carbon based life and metabolism?

Maybe we genetically sacrifice our longevity to survive the stresses of competition.

Emerging Questions:
Is it that our metabolic processes are over-compensated for dominance in their sexual prime which prove detrimental for longevity?

Is it that genes leading to different lifespans are mixed indefinitely in nature that it was never possible to select for it?

Isn't an organism with a longer span of mating at an advantage?

My hypothesis:
In the absence of change in ones environment, or competitive stresses an organism would eventually adapt itself to survive longer.

If every organism is a product of evolution then there must of course be underlying mechanisms within itself to aid such an adaptive process.

Under the influence of adaptive pressure, it would encourage mutation or variations in order create successful variations and also increase the number of life-cycles and so reducing the lifespan.

Under the influence of competitive stress, the dominance would lead to reproductive success and not the span of mating during ones lifespan.

In the absence of change in ones environment leading to adaptive pressure, or competitive stresses from rivals to prove dominance. Species would evolve longer lifespans.

Just a Theory though! But it would predict that

Lifespans of living fossils which have undergone little change in time should be greater than their relatives which have recently evolved.

Life having evolved on geographically isolated places far from intense competitive pressures should have greater lifespans.

Living things higher up in the food-chain or with few natural enemies should have greater lifespans.

Life span in pair bonding species should be higher than tournament species.

Topics: aging evolution
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  • Nov 20 2011: I must say, first - I don't know why we need to view aging as a problem. "The problem of aging". I see no problem with old age and eventual death. I'm very interested in the reason for a line of questioning like this.

    At any rate, evolution and aging have, in my view, very little to do with the other. Natural selection no longer comes into play after child-bearing age. As much as I hate to personify it, evolution doesn't really care about old people. According to natural selection and the survival of a species it doesn't matter in the least if you survive after rearing your offspring.

    It's against a population's best interest to prolong life past a certain point, most especially if child-bearing years are lengthened. The vast and overwhelming majority of animals on this planet will make offspring if age and health allow. The scenario that's painted by older creatures being able to continue to give birth is one of, eventually, a nearly infinite spring of life into a world of very finite resources, and eventually that little experiment would lead towards a stripping of natural resources, hunger, crowding, etc.

    Aging and eventual death keeps the genetic pool fresh and ensures a homeostatic planet with balanced resources. Prolonged life or immortality eventually means an overburdened planet.
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      Nov 20 2011: I like your explanation, considering a majority of recent opinions on this thread cite that aging and eventual death are required to maintain a balance of resources.
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      Nov 20 2011: I basically agree with George's reply, but will point out that post-reproductive (older) individuals can still make a considerable contribution to the survival of the group or of individuals within the group, and as such they can have significant impact on the evolutionary course of the group and the species. It may be correct to say that when the older individuals reach a point where they are more burden than help to the group, then they no longer impact the group's evolutionary course. But keep in mind that all of a species' characteristics, including their behavior - such as their degree of caring for older members, play a part in the evolutionary game.
      The initial question of why debilitating aging occurs is still interesting. We know that during our lifetimes mutations occur in our DNA, both through copying errors whenever our cells divide, and through the ionizing effects from various sources of radiation. Preventing such mutations completely would have been metabolically costly and might not have been possible for complex organisms. As it is, there are many redundancies in our bodies that minimize the effect of mutations for many years, and these are certainly the result of evolution operating to give us the long length of life that we have. An interesting study is of "aging" in simpler systems like bacteria, which are very resistant to debilitating mutations, yet are highly adaptable to changing conditions. A puzzling paradox.
    • Nov 22 2011: Your explanation unfortunately assumes that which is sets out to explain, i.e., that at some stage an organism's "child-bearing age" ends.

      That an organism's child-bearing age usually does end is manifest, and so universal in our experience that it seems natural. But that it does is an aspect, or perhaps a phase, of aging, the phenomenon we seek to explain.
      • Nov 22 2011: I'm afraid that I haven't unfortunately assumed anything, if the condition of a limited child-bearing age is manifest and universal in our experience. There's no reason to believe that something like menopause is anything but natural, seeing as how we have extremely limited examples of evidence to the contrary. Menopause and aging go hand in hand, certainly, but it's wildly illogical to assume that either of these things are unnatural.

        The simple fact is that the key to successful life on this planet is adaptability. Without the ability to adapt to changing conditions, an organism will eventually fall prey to the tumultuous environment that we all live in. If an organism doesn't eventually stop giving birth, then it continues to pass its own unchanging genetic structure on through the world, and evolution slows down immeasurably and becomes stunted.

        Aging and eventual death are a part of this world, and they are the mechanisms that allow for growth in the species overall.
        • Nov 22 2011: Limited child-bearing age, menopause, etc. are the phenomena that we are trying to explain. They can't be the reason for themselves. Supposing that they exist to explain why they exist is a circular argument.

          Your second argument (like that of several explanations above) is that if there were no aging a catastrophe would eventually occur (or would have occurred), specifically, that if organisms did not age and die then evolution would slow down and life would fail to adapt. That's not a workable explanation, because evolution doesn't have any foresight. To explain why a biological phenomenon evolved you need to describe the mechanism by which organisms that had the causative mutation flourished and proliferated in competition with the rival alleles. Preventing a catastrophe in the future is not a way to survive and reproduce in the present.

          To explain the evolution of senesence you have to explain a mechanism by which mutations that cause senescence proliferated when they were new and rare. Making room for a new generation is not such a mechanism, because most of the benefits to fall to the more numerous offspring of non-aging rivals. That isn't a competitive benefit to the mutants. Preventing a catastrophe to either the species, the ecosystem, or life itself isn't an explanation either, in the first place because saving the world, the region, or the species is not a competitive advantage to the mutants of their rivals, and in the second place because there is no mechanism for a possible catastrophe in the future to either prevent specific mutations or to save the lives and increase the progeny of specific mutants or to suppress their rivals in the present, Evolution does not provide protection against extinction, which is clear when you consider that most species that ever evolved have gone extinct.
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          Nov 23 2011: This looks like an evolutionary dead-end, I can't reply to Brett but Go Evill! lol

          I side with you, as evolution doesn't have a foresight, nothing evolves for the good of the species, it is individual fitness that matters and there must be a reason for the development of senescence and its efficacy as a trait.

          Males can continue to mate until death, the child bearing/rearing hypothesis only applies to human females.
    • Nov 23 2011: "Natural selection no longer comes into play after child-bearing age. (...) According to natural selection and the survival of a species it doesn't matter in the least if you survive after rearing your offspring."

      Hey, which species are you talking about? Our own or all the others -- or are you putting all in the same basket?

      As far as our species is concerned, do you mean that its perennity is granted by the sole production of offspring, as with animals? How about inventions, technology, science, infrastructures -- all those "children" born out of the human brain?

      It seems to me you're in great need of some enlightenment -- which you might find in my reply to Christopher Henningsen in this discussion.

      Comment on Brett Evil's reply to your comment:

      Both of you (and most of the commentors in this discussion) are talking about limited child-bearing age as if natural selection had led to prevent the transmission of genes coding for exceptional longevity -- whereas in actual fact evolution has preserved the option of selecting these genes by not limiting the age of male fertility (as far as I know, for us humans)!
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    Nov 25 2011: Aging has been solved. . . . . by Death.
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    Nov 25 2011: Why aren't ant's or bee's being researched? They are clearly masters at manipulating age when it comes to queens. I just watch this interesting talk by Deborah Gordon on digs ants and the queen ant live 15 times longer than other normal ants and it's not because of a special DNA. They use the same ant DNA.
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      Nov 25 2011: If you mean "average lifespan" is makes sense that queen ant lives longer than the others ants which are more susceptible to disease, get killed, have worst food, work more, etc. all kind of environmental and behavioral factors.

      this is the tedtalk about it: http://www.ted.com/talks/deborah_gordon_digs_ants.html
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        Nov 25 2011: I don't think it's just average life spans. As I understand it the queens life longer by default.
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          Nov 25 2011: If you meant "Maximum life span" it has to be something related to DNA. From what I understand yes they share a common DNA while they are at a larva stage but the level of care and nourishment the larvae receive will determine their eventual adult form.

          "Analysis of ... new ant genomes suggests that chemical modification of certain sections of DNA could be responsible for the differential development of queens and workers. As an ant larva develops, DNA methylation ... may switch off the genes that control reproductive capacity and wing growth." AND I WOULD ADD IT ALSO SWITCH THE RATE OF AGING.

          SOURCE: -Newly Decoded Ant Genomes Provide Clues On Ant Social Life, Pest Control-
          http://www.sciencedaily.com/releases/2011/01/110131153244.htm
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        Nov 27 2011: Well stated comments about the queens there, Adrian. It is what the future 'queen' is fed, in some species that 'grow' her to be a queen in the first place.

        So in 'essence' it is what she eats, the enzymes in the food (and other properties) that affect her genome.

        Also, in regards to human evolution-the topic on this forum question- there are some who theorize that 'food' may have contributed to our own evolution, so I understand.

        Interesting thought, yeah?

        Maybe the related 'humanlike' species who eventually formed us started to consume a new diet that introduced different enzymes, vitamins etc. that helped to shape our own genome?

        Anyway, totally unrelated-unrelated. I think we are all queen bees who can lead or follow-humans that is.

        And food (and other phenomena) is important to not only our own brain function but the shaping of our progeny (ie look up stuff in epi-gentics). Just a thought out there.
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      Nov 27 2011: On a related note-There is a jelly fish that has 'infinite' life. Yep. It lives forever if it can keep from disease and being killed. It just renews it's life by "reverting to its polyp state." Yeah, amazing, right? I love jelly fish. This one is really pretty too but there are so many beautiful ones.

      Article about these little guys:

      http://green.yahoo.com/blog/guest_bloggers/26/the-world-s-only-immortal-animal.html
    • Nov 27 2011: A more philosophical approach of queen bees' longevity may yield some interesting findings considering that drones are left to starve after one of them has fecundated the queen -- which reminds us that bees are living in matriarchal societies.

      By analogy, patriarchal societies might feature an exceptionally long-living king male dedicated to churn out "the 'children' born out of the human brain", as explained in my first comment, hinting at the "unchallengeable leadership of the very one who willl be living longest" predicted in the same comment.

      Fortunately, money can be used to virtually extend the remaining life-span by packing more years into it through subcontracting the more time-consuming tasks involved with the bearing and rearing of major inventions, so as to get these tasks done in parallel time.

      Now, since money can help densify your life, the question of how to achieve exceptional longevity becomes that of whoses life deserves being densified. The first answer coming to my mind is that society should stop spreading big money randomly through lotteries, and instead try to get the masses financing the densification of the remaining years of, say, an outstanding elderly inventor... with a sample of his (my) revolutionary aircraft as the jackpot for the winner!

      Yet, alas, if this kind of lottery could get me to sell my invention to, say, Boeing, they'd probably kill it in order to preserve the long-term success of the current assets of the Boeing-organism...
  • Nov 22 2011: The best explanation I ever saw for this question was mostly mathematical. I'll try to summarize it here, but I may mangle it a bit.

    The thing is, human population has been expanding for as long as anyone can remember, but established species always have stable populations. In an expanding population, having more children indefinitely would be beneficial, but in a steady one, each mating pair can only have a finite number of offspring. If a species grows for too long, it presumably destroys its niche, so there needs to be an upper limit on how many offspring a species can typically have, depending on how many die before mating age. This is a question not of individual fitness but of species wide fitness

    If we accept this premise, it's fairly easy to see why death is beneficial to the individual. Imagine a species where the typical mating pair can produce 3 children on average, can reproduce for three generations, and reaches sexual maturity in one. A pair that has 3 children in its first generation will have nine times as many descendants by the third generation as one that has 3 children in the third generation. Evolutionarily, it's better to reproduce early rather than late (unless the population is shrinking, but never mind that now). 'Natural Causes' encourage early reproduction.

    I don't remember the math, but the paper I read explained to my satisfaction at the time that given the above conditions (which admittedly don't apply to humans since we don't have a stable population yet) there would always be an optimum age for an individual of a species. the exact age would depend on various factors, but it would always be finite.

    I really haven't done the theory justice and unfortunately don't remember the name of the paper, but I thought it was interesting enough to share anyway. Hope someone enjoyed the read!
    • Nov 23 2011: "A pair that has 3 children in its first generation will have nine times as many descendants by the third generation as one that has 3 children in the third generation. Evolutionarily, it's better to reproduce early rather than late,"

      In a more generic style your first phrase reads: the comparative growth rate of two populations will be higher in the population where the women's average child-bearing age is lower.

      As to the higher growth rate through early reproduction being an evolutionary advantage, I doubt it always is -- especially since human intelligence has entered the scene resulting in democracy based on the predominance of the majority's will.

      Now, since when should the reason of the majority be the better one, knowing that wisdom is a rather rare virtue among humans? That's probably what Churchill meant with his famous statement about democracy being the worst system of government, except all others...

      How come that the change of paradigm with the emergence of human intelligence versus the previous state of unconscious animal intelligence has been paid so little attention in this discussion?

      I invite you to reflect upon the hypothesis that while outnumbering other species may constitute an advantage in the vegatal and animal worlds, it may well have become a handicap in the human world where information, as based on unlimited accumulation, is taking the lead on the genetic code based on the relentless yet imperfect reproduction of a finite set of elements.

      And by accumulation I don't mean piling up books, but the virtually unlimited storage capacity of the human brain -- not by the sheer number of informations, but by the ever more complex correlations it can establish during a lifetime; an advantage which is likely to be developed by those who live longer, and ultimatley even to grant unchallengeable leadership to the very one who willl be living longest -- if not, at last, to an omniscient computer.
      • Nov 23 2011: An excellent hypothesis concerning future human evolution, but I don't fully understand your point about outnumbering other animals being a handicap to humans. I would think that nearly all human evolution has been an arms race against either germs or other humans, with other races playing an increasingly less competitive role. I don't think you are wrong, the current trend towards smaller families is an excellent indication that your idea has merit, but I don't understand your logic. Would you be willing to elaborate on this idea?

        On another note, I think a distinction must be made between memetic and genetic evolution. Though memetic evolution is becoming more and more fashionable as an area of study, there is far less history to study- the oldest known surviving texts are only a few thousand years old, and oral traditions mutate so quickly that it's difficult to study their history at all. Genetic history however is millions of years old with excellently preserved examples, and still seems to have many mysteries. I wouldn't sell it short !-)
        • Nov 25 2011: "I don't fully understand your point about outnumbering other animals being a handicap to humans."

          Sorry, the last part of my hypothesis should read: "while outnumbering other species may constitute an advantage in the vegetal and animal worlds, outnumbering other ethnic groups may well have become a handicap in the human world."

          An example of this questioning is whether China's success is based on outnumbering other nations or on the one-child-per-couple policy -- I for one would favor the second guess.


          As to outnumbering being a problem within the human species, here's another example: according to my very personal analysis of the evolution of communism, the Soviet rulers failed because they did not calculate their quinquennal plans by computer -- instead, they left this task to an army of human calculators who ended up outnumbering the decision makers of the real economy, when they became a state within the state, compromizing central governance.

          The Chinese communist rulers still calculate quinquennal plans, but since they do it by computer they manage to remain a small crew in charge of the nation's destiny.

          Small is purposeful!

          However, there seems to be a moral issue related to predation: predators carry genes coding for keeping their numbers small versus the lifestocks they prey on, in order not to reach a statistically significant ratio beyond which natural selection among their preys would start to work against them.

          But does a small number of rulers mean they have to be predators? And does a small minority have to consist of rulers at all?

          Here's a clue: there are much less pollinizing insects than plants offering nectar -- and, in Nature, symbiosis is largely predominant over predation.

          Predation is an epiphenomenon on the decline in both the animal and human worlds -- symbiosis is our future!

          Mainstream symbiosis is about sedentarity teaming with mobility -- and most of the mobile symbiots are flying animals!

          Our future is in the airspace
      • Nov 26 2011: Regarding the amount of complex passageways one can establish in a ever-maturing brain-I believe the number is limited due to the fact that if too many passageways are formed and intertwined, there is simply not enough space for them to avoid clashing, creating a responding amount of chaos. For the passageways, or coorelations to remain efficient and become more so, it would take a significant amount of energy, which, as one ages, is very hard to sustain without damaging other areas needed to survive.

        I am by no means an expert on this subject, but to me it seems this is the reason functions of the brain tend to almost "rust" in a sense, in most cases the apparent change affecting memory and physiological functioning.

        To comment on a special I saw - I believe it was the Discovery channel or something and involved Adam from Mythbusters (awesome, I know)- it would make sense that at some point, we would have to find a way to "replace" our body parts, but I honestly don't know how feasible it would be to actually repair a brain without disrupting the circuitry.
  • Nov 22 2011: Peter Medawar suggested an explanation for aging in "An Unsolved Problem in Biology" [1952], which, as refined by G.C. Williams in 'Pleiotropy, natural selection, and the evolution of senescence' [1957], seems adequate and convincing as a core explanation.

    First, observe that many genes have more than one apparent effect (a phenomenon called "pleiotropy"), and that some genes may have one effect that promote survival, reproduction, and the successful raising of offspring and another effect that inhibits it. Whether a gene proliferates over evolutionary time is the result of its average net effect in a particular environment. Second, observe that an organism's genes are expressed differently at different times in its life-cycle. Consider, for example, that a caterpillar and the butterfly it develops into have the same genes.

    Now think of a gene like that for Huntingdon's Chorea in humans, which increases fecundity in young people but causes disability and death in middle age. It should be fairly obvious that such a gene can produce an increase in the rate of its proliferation by trading off length of reproduction for rate of reproduction. In conditions where such genes flourish there is an evolutionary pressure in favour of aging.

    We ought to expect multiple instances of such genes to spread through any gene-pool. Once they are established there is a selective pressure that favours genes that adapt the organism to senescence, such as the genes that are supposed to switch women's efforts from bearing children to raising grandchildren after menopause. Indeed, senescence in animals is so ubiquitous that we must suspect that it is a primitive feature, and that major aspects of ontogeny are adapted to producing a mortal organism, that at least some of the processes of senescence consist of processes of development and growth continued past the point at which other processes dictated senility. See Hamilton, W.D. (1966) 'The moulding of senescence by natural selection'.
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      Nov 23 2011: Hey Brett!
      I believe this post has received less credit than it deserves, so I would like to bring more attention to it. I will read further about "Pleiotropy."

      It is possible that organisms must be trading off longevity to be more competitive in their sexual prime, so they could leave more copies of themselves. All traits were selected for having their advantage, but later in the course of evolution when such traits become more common in the population, competition drove such traits to be expressed around the time of mating, even if it was self-mutilating in the long run.

      Like they say it is better to burst like a cracker than burn like a candle. Reproductive impact mattered more.
  • Nov 21 2011: This is neat. We just were talking about this in one of my forestry classes. As some trees can live very very long lives. Some, it seems, live forever. The prime example is bristlecone pine ( I think Pinus longaeva D. Bailey). It lives forever and hypothesized that some individuals have cells with DNA that have "forgotten" the death or shutting down activation. It seems that the trees cells just live forever and ever. The downfall of this tree is it can only grow in one place with such a evolved trait as it is very in-efficient and cannot compete.
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      Nov 22 2011: whoa! That is interesting... A living fossil that doesnot compete.
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    Nov 17 2011: That question gave me a lot of time to think these two days ago.....

    I have just seen one talk about that.

    http://www.ted.com/talks/aubrey_de_grey_says_we_can_avoid_aging.html

    He says: "Aging is not a product of selection, evolution; aging is a producto of evolutionary neglect. We have aging because it's hard work not to have aging".

    Please see it; however that question is eating up my head all the time.

    Maybe aging is part of nature, maybe living matter always ages.... it doesn't care how long it takes, but it always happens.
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    Nov 17 2011: My guess about this is that every organism's life is as short as its genes can afford.

    Humans live longer than chimps after menopause, since babies require grandparents as well as parents. (Menopause is 3 years before death in chimps = you die knowing that the last child has been carried to autonomy... Menopause is about 20 years before death in humans = you die knowing that the last child's child has been babysat)
    Longevity has a cost, you know, for the genes. The shorter the life the better. Why is that?

    Well, having offspring means that your genes are now competing for food and sex, and one can understand how the genes would benefit from the non-reproducing organism to be dead. I read of some fish that ages immediately after reproduction, an hormonal booby trap.
    Remember that your genes are in all your relatives, unequally distributed of course. But cousins, siblings and children share your genes and if you can't provide their survival into the next generation, let them take care of it. If there's nothing you can do to help anymore, then get out of the picture ; more of everything for everyone.

    Makes me think about our old people. Once our kids have been babysat by our parents, the best thing they can do to help is to die, isn't it?

    So what lives forever is not subject to natural selection, since no replicator has any advantage of lingering once it's made a copy of itself. Especially if such replacing produces variation that might be beneficial.

    Until recently, no form of life has emerged from something else than natural/sexual selection, so immortal living organisms cannot have evolved.
    In fact, immortal living organisms can only be created by ... I hate to say this... intelligent design!
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      Nov 18 2011: Isn't an organism with a longer life and a longer sexual prime at an advantage? Or maybe breeding after a certain age would mean passing on damaged genes which would prove detrimental on the long run?
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        Nov 18 2011: It works this way if there are no or few factors which introduce evolutionary pressure. Why do turtles live so long? They have hardly any enemies so the longer their lifespan the more offspring they can produce - selection for longevity.
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        Nov 18 2011: - Isn't an organism with a longer life and a longer sexual prime at an advantage?

        I suppose it has something to do with sexual prime overlap. I your prime lasts ages, then it will largly overlap with your children's prime. So children whose parents leave the scene are likely to reproduce more since there is less competition, and thus the genes encoding this trait are selected.

        But there are more possible explanations, depending on the species. One of these might have to do with the number of offspring. Sometimes it may be an advantage to have few offspring and thus have more energy available to ensure their safety. Other organisms such as trees have tremendously long sexual primes and produces hudge quantities of seeds, because of the low cost of offspring in the vegetal kingdom. Thus, yeah, trees would benefit from near immortality and near infinite procreation, in this sense.
        But one thing about trees, though : two generations are never rivals over sunlight or minerals, since
        a seed that has fallen at the base of it's shadowing parent is just about doomed. So a succesful descendant is one that has landed far away, and it can only grow where it's not bothering its procreator.

        All this is just deduction, not proper scientific information, so someone who knows the first thing about biology might rake me over the coals.
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      Nov 18 2011: Does that mean my kids are being kind to me by not having kids yet?
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        Nov 18 2011: Perhaps they need their mother a little longer before she turns her attention to grandchildren (since concentration of energy on grandkids is a hell of a lot more fruitful at this point, evolutionnary speaking of course).

        Or perhaps there's no lady out there as great as mom...
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          Nov 19 2011: Gerald, for a hairless creature you are very sweet.
  • Dylan F

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    Dec 6 2011: A beautiful principle of evolution is that its designs only have to work well enough - well enough for the genes of an individual to propagate to successive generations. Perhaps the sheer evolutionary costliness of immortality for a mammal has proven too much and a higher metabolism was favored as a more engaged nervous system could live long enough to sufficiently reproduce.

    Although the mechanisms responsible for aging are not exactly known, it is clear that it's a complex matter involving many different biochemical factors. To overcome such a feat by natural selection may simply be too improbable to ever occur or it may need not ever occur because of easier solutions (higher metabolism = shorter life, but more strength, speed, intelligence for more reproduction = more genes in the gene pool to favor shorter life).

    But, on the other hand, evolution has stumbled upon a species capable of redesigning its very own nature with the potential of reaching conscious immortality. So maybe the question is "When will evolution solve the problem of aging?"
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      Dec 8 2011: You seem to be in favor of the Antagonistic pleiotropy theory: Late-acting deleterious genes may even be favored by selection and be actively accumulated in populations if they have any beneficial effects early in life.

      A likely possibility and well arrived at. :)
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    Dec 1 2011: Not all organisms age.

    Dieing is a selection step within the process of evolution. If you would implement any of the evolutionary algorithms you would understand it better. http://en.wikipedia.org/wiki/Evolutionary_algorithm

    Human race managed to escape evolutionary pressure by not of adapting, instead we are changing our environment (irrigation, shelter, heating, clothing, sanitation etc.).

    That being said, I still wish I would not have to die someday...
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    Nov 22 2011: Actually, aging is a more recent feature of evolution: If you look at simple one celled organisms, there are quite a lot of them who don't age at all (and can live very very very long).
    Their metabolism is rather slow... (and indeed, their environment is similar for thousands of years)

    Metabolism tends to cause damage (as energy transformation can be a violent process, suite difficult to control)

    Once you have sexual reproduction, it does not matter what happens with the parents once reproduced, so damages due to metabolism need not be repaired (no evolutionary gain, maybe even a drawback as it might consume more energy compared to those who don't have it, and as such may be slower to reproduce).

    So I go for the metabolism and sacrifice hypothesis ;-)
  • Nov 22 2011: From what I understand second law of thermodynamics necessitates aging. DNA and the associated organisms are highly ordered and they eventually need to turn to dust (i.e., simple, uniform, unordered molecules). I doubt that evolutionary process can ever overcome this unstoppable equilibriating drive.

    From a purely evolutionary basis, here's another explanation. Let's posit that evolution always tends to produce longer living organisms given the current environment. But by introducing a new product of evolution into the environment, the environment itself changes. The extreme example is that humans whose basic DNA structure has remained unchanged for millions of years today live and breathe a totally different environment than what they were made to live in. In that sense, evolution is always chasing its tail in search of the perfect organism.
    • Nov 22 2011: Nothing's DNA structure remains unchanged for millions of years. Homo sapiens sapiens has probably not existed as a species for millions of years (I noted in another post that the average life of a mammal species is only one million years).. And we were not "made" to live in any specific environment. We arose as a species in the emerging savanahs of Africa, but obviously have experienced great success in colonizing vastly different environments.

      There are no goals for or purpose to evolution so the ideas ot it "chasing its tail" or "searching for the perfect organism" is meaningless. There is no perfection, and no species is static genetically. Even cockroaches or dragonflies, which have persisted as Genera for millions of years have not been spared the slow changes (and the birth and death of whole species) brought about through evolution.
  • Nov 21 2011: You really came up with an interesting question. However, it is my belief that your theory/line of reasoning has a number of important flaws.

    The law of natural selection would suggest that genes for enhanced health and longer reproductive period, which are linked with higher longevity and reproductive success, are likely to be passed on to future generations, which suggest a predisposition of lifecycles to become longer.

    However, longevity cannot become infinitely long at least for 2 reasons: (1) individuals are also part of a population (a group of other organisms of the same species) and a community (a group of other organisms of different species living together and interacting) which may lead to stress, competition for resources, predation, parasitism, etc (2) cumulative death rate - even if you assume that death rate will remain constant through the lifecycle (which it obviously doesn't) less individuals will make it to old age.

    the problems with your hypothesis is that you suggest

    1) "Under the influence of adaptive pressure, it would encourage mutation or variations in order create successful variations and also increase the number of life-cycles and so reducing the lifespan." ...

    there is no such a thing which encourages mutation. Mutations are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication.

    2) "Under the influence of competitive stress, the dominance would lead to reproductive success and not the span of mating during ones lifespan."

    Competitive stress is well documented from biological studies to decrease reproductive rates

    3) "In the absence of change in ones environment leading to adaptive pressure, or competitive stresses from rivals to prove dominance. Species would evolve longer lifespans."

    very simplistic & suggests an unrealistic picture that the environment, populations, species and the interactions of all these can remain constant with time
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      Nov 22 2011: If every organism is a product of evolution, then every organism has come long enough and must have developed a genetic predispositions to adapt themselves. This may not happen all the time, but there must be genes which would spring into action in the event of stress or environmental changes to cause changes in the progeny.

      The organism/offspring would definitely benefit from having a variant that may be better adapted to its environment. I only postulate this on the grounds that if natural selection is the most important factor for evolution, then it would have definitely developed tricks to benefit evolution itself, and this is just a prediction.

      I have heard a leading cause of cancer is stress, stress does have a mutative effect.
      • Nov 22 2011: I think that there is some confusion of terms here ...

        every inherited trait is the product of a mutation that, may lead to deleterious effect and hence less likely to be passed to the next generation or, which could enhance the performance of the individual in an environment and hence very likely to be passed to the progeny.

        Mutations are within the genes, or the code made of bases (A,C,G,T) within the DNA, and to be expressed they need to "written" into proteins which have a particular function.

        I would suggest you define stress, but yes stress does have a mutative effect and this has been proved for a number of organisms.

        my take to your question "Why did evolution never solve aging?" is that organisms cannot live forever due (1) increasing entropy (state of disorder in molecules/systems/etc)- the random loss of molecular fidelity, and accumulation to slowly overwhelm maintenance systems (2) genetic factors themselves - ageing has been suggested to be a genetic disease. This may suggest that once past the reproductive stage genes are more likely to persist in the offspring of a particular organism, and (3) the environment - living and non-living which could directly and indirectly cause death. And coupled with ageing due to genetic or entropic causes death rate is more likely to increase in senescent stages
  • Nov 21 2011: Unless an organism produces offspring through its entire life (and specifically unless it produces a greater number of offspring as it ages, which is almost never the case) there is no selection pressure towards longevity. Indeed, the number of surviving offspring this would lead to would very likely be detrimental to the environment and cause negative selection pressure.

    Increasing lifespan decreases the need for replacement of the individual through reproduction, and probably slows the changes in alleles in a population that might confer longevity.

    In humans increases in longevity are the result of better nutrition, standard of living and health care. these things probably prevent selection for the very kinds of changes that would increase longevity in a "wild" population. It seems pretty clear that genes for better eyesight, genes for more efficient immune systems, genes for better problem solving abilities (Jarrod Diamond addresses this) are NOT being selected for, while genes that predispose us to degenerative disease and birth defects are not being selected against. These two things have a definite affect on longevity.
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    Nov 21 2011: 1 - Aging controls population, and eliminates those organisms that are no longer better suited to the environment.
    2 - The illusion that evolution is there to solve problems is just that, an illusion. Evolution is merely the name we have given to the process by which living species adapt to their environments and in general become more complex. In order for evolution to work, honestly, the species needs to keep dying to make room in the environment for the young.
    3 - If you must look at evolution as a process that benefits something, I think Richard Dawkin's has it pretty much wrapped up in the selfish gene. It is not the individual but the genes which are served worse or better by a trait, and aging is extremely beneficial to the adaptation of species, which in turn is beneficial to the survival of the majority of genes in that species. A species that does not age becomes either stuck in an adaptive rut, or consumes all the resources.
    • Nov 22 2011: I agree with adaptation and it being key for a species to survive, however, in order for the change in people to accompany the change in environment, the change has to take place genetically and chronologically. As the environment changes over time so does the change across species. It's important to add the dimension of time into this discussion. As well consider that as complex as we are, our engineers did not design our cells to adapt quickly, perhaps this measure of speed of adaptation is what causes aging.
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        Nov 23 2011: Our engineers? Intelligent design by committee? Surely that just applies to camels?
    • Nov 22 2011: To a certain extent evolution can be seen as an artifact of the existence of genetic material. It mutates, it accidentally doubles itself, it becomes corrupted by bits left behind by virus and bacteria and so on. That is the stuff of evolution. And an unstable environment ,that exerts pressure on organisms that are trying to reproduce and successfully raise (or simply leave behind) their offspring, is the engine that drives it.

      Incidentally, species appear to have discrete lifespans. For a mamalian species the average seems to be one million years, though some may last as long as 5 or 10 million. They either diverge, or the lineage simply stops. At no more than 250,000 years old, we probably have a ways to go yet, but who knows. All too often people indulge the notion that there is some grand purpose for our species, or that we represent the apogee of evolution. This is hubris and nothing more.
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    Nov 21 2011: Hi Anuraag,

    I read your hypothesis and i don't grasp what competitive advantage may derive from living longer. It would require too many simultaneous genetic adaptations to enhance the lifespan of all the different types of cells in the body in such a way that an older individual would be stronger and healthier than a young one. Somehow i doubt that all those could arise at the same time.

    So once reproductive age has been reached, a younger individual would still be at advantage against an older one (better mobility, better chance of healthy offspring) so evolution would tend to reinforce individuals who reproduce right after their bodies reach maturity (post puberty), and who are around the peak of their fitness. Two individuals reproducing from age 15 to 40 would probably have more offspring (and healthier) than a single individual reproducing from 15 to 65

    cheers
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    Nov 18 2011: This is interesting but I honestly do not understand the question?

    Forgive my ignorance but what does aging have to do with evolution in the sense of evolution solving this "problem"?

    I honestly do not see the correlation between the two but I would love to know more about it
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      Nov 19 2011: evolution leads to adaptations within organism to survive in ones environment. A genetic predisposition to age and die doesn't seem to be beneficial or advantageous in anyway, or is it?
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        Nov 19 2011: It is.
        Evolution has little to do with any individual in particular.
        The living cell has to survive.
        Everything that secures the procreation of the initial cell in a better way is favored and becomes dominant.
        If a short life can do this or a long life doesn't matter much to the life force on earth as long as it serves its purpose.
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        Nov 21 2011: Hi Anuraag. I like your questions. I too have pondered the very same thing. Here's my two cents.

        Can you imagine how many billions of people would be on this planet without the benefit of aptosis? We started as a cell. Our cell formed a community of cells. The community of cells formed other communities. Those communities grew more complex. Each community worked to conquer more of the environment to its benefit. Through evolution some communities (organism) developed further (conquered more environment, not just adapt to it) and became fish, birds and even man. Each time the organism left a blue print of what worked best to control more of the environment and imprinted this information into the cells it used to pass on to the next generation.

        In nature, death is a benefit and it is needed. Cancer is a cell that forgot to die which is why it kills the organism in which it lives. If the organism (people) were to start acting like cancer we would destroy the environment much in the same way cancer destroys the environment it lives in--the human body. I'm not a math major, but if someone knew a way to calulate the number of people that would be alive today if we could live for 100, 200, 300 years etc. and only dying of natural causes that number would have to be 70 Billion or so.
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        Nov 21 2011: I must say, I am impressed, I never thought of it in that way.

        I would say it is as long as we can procreate and that is obviously one of the reasons as to why we reproduce.

        Most of the biological complexities on the planet are given a genetic predisposition to live and die.

        What do you think? Do you think living longer would be advantageous?

        For human beings there is really no benefit to live to 100 and this is also the case with other animals.
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          Nov 22 2011: Today if we have to excel at anything we do, we have to spend a majority of our life learning, look at doctors and scientists. There is so much we have discovered already that we have to specialize among specializations to be good at something. There is just not enough time, and as time passes fewer and fewer will achieve their goals.

          We need longer lives, we need to stay mentally young but maybe we should also control birth and manage our resources.
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    Nov 18 2011: I am now 3 minutes older than I was when I started reading this. The only problem I see is that it was 3 minutes wasted
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    Nov 17 2011: What Paul said: "Why did evolution never solve the problem of aging?

    Where's the problem..? Is that not a person centered problem based on fear..?

    ---

    Maybe a more fruitful question is: Why do we see aging (and death) as a problem? [If we do.]
    • Nov 18 2011: I also don't feel death to be so malign. The ideas that new life must take its place are compelling indeed. But what could immortality contain? In us humans, our cognitive functions decline with age. Maybe there is something more substantial than spreading your genes. But wouldn't it be painful, to see your loved ones pass away, constantly experiencing forms of trauma or emotional/psychological pain. I think we must evolve more as a species as far as how we treat each other, how we use our resources.. And on & on. Since the industrial revolution, man sought to gain command over the natural world. Early technologies did not think of adverse effects to climate? If an organism could live forever, how much resources would that require. It would be something with a much lower metabolism, possibly even seasonal hibernation. As a child you dream of endless opportunities. Nature could not sustain the human species, given it's history. We would have to turn back and respect our natural world's health more. I don't believe we could psychologically survive immortality if it were possible until the human psyche evolved proportionately. Some trees live up to 9,550 years but they have a more harmonious relationship to natural world. Why would a form of life so detrimental to it's planet ever discover a solution, we would likely ravage the earth for resources, and destroy it's ability to sustain life before we found a way using science. The entire human relationship with reality, each other, and perceptual reality would have to drastically change before immortality would even be feasible
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    Nov 17 2011: Why did evolution never solve the problem of aging?

    Where's the problem..? Is that not a person centered problem based on fear..?
    It is the ability to swap (genetic) information andcreate new variants that gives the best chance of some of your population surviving uncertain environmental changes.. So if new variations on a theme need to be constantly recreated in a finite system then old ones need to be broken down and reassembled..

    Those that fit best into the current system of resources and limitations will prosper, others will not.
    So the evoultionary process favours the combinations of information which currently work well and is not interested in the individual body that carries them.. If the body is successful enough to reproduce it will likely pass it's propitious combinations on..

    It is only our personal psychological attachments that think that we exist as seperate individuals that can be preserved.. This may well be nothing more than a cultural trend.. Certainly form any wholistic spiritual perspective it is not a thruth.
    The 'self' is illusury. Even if the body did last indefinitely the thing that controls it would continue to change.

    That said and in response to your last point there are many life forms that do, or at least can, live forever..
    Many 'individual' trees, Bristlecone Pines etc don't seem to have aging mechanisms.. Many forest forming trees and grasses, like bamboo, also continue indefinately..

    Also animals do it.. don't know so many examples but remember hearing recently that Lobster cannot be aged and can theoritecally at least continue in cycles of renewal as long as conditions allow.. I would not be surprised at all if it is not infact quite common in many animals..?

    Paul
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    Nov 17 2011: Give it time.....
  • Dec 6 2011: If we're approaching this from a human genetic standpoint then you have to consider that genes won't propagate, quickly, to enact change when there isn't a selective pressure. Almost all human genetic changes are going to be of rates unoticeable to us, barely perceptibly above the norm, because of the cultural influences upon sexual health and family life.

    As for aging you have to ask yourself is there really a significance currently to a longer period of sexual activity to your offspring surviving? How is that limited by things like the menopause and old men losing virilence? And does a longer period of sexual activity actually have any real statistically relavent effect upon the average number of children a person has.

    I very much doubt a longer lifespan actually will contribute to the number of children produced in a western community with good sexual health education. A brief observation is that women are making choices about when to have children increasingly closer to the onset of menopause so they can accomplish a greater number of goals in their youth. If you expand the aging process in a means that produces a greater period of youth I can only conclude that women will continue to choose to have children closer to when the threat of not being able to ever have children compels a desire to do so.
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      Dec 8 2011: This is another socioeconomic selection trend that is well observed, definitely interesting and something new to this conversation.

      There is also a tendency for son's of rich, successful older men having sons who have better chances of mating themselves.

      Both should definitely be leading to longer lives at least among st humans.
  • Steve G

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    Dec 6 2011: Being more a philosopher than a scientist, I can best address why aging isn't a "problem". Perhaps you can draw scientific conclusions. 1. Other people are environmental factors, and in today's world, the ideas held by people also become environmental factors which in a real way effect biological evolution. If people were not to age and die, that environment would begin to homogenize (peoples ideas don't change with any predictability or guarantee), and with less environmental variety, there would be less to adapt TO. 2. The gene pool stays the same longer - similar problem: the opportunities for different types of mutations becomes limited.
    Some of your hypotheses seem to favor this kind of homogeneity - a problem is that it is a little self-contradictory to speak of evolution in an environment in which change becomes a non-factor. If such "favorable" conditions did occur, evolution would almost certainly stop too - thus nothing new, including new lifespans. (It is important to consider that while adaptation and mutation certainly will always be the condition of living things, the term "evolution" is almost always used to describe, only with 20/20 hindsight, such a mutation that we qualify as "good". Also, barring such ephemera as "the human ego", where is the evidence that living longer is an improvement? )
    And importantly, if Evolution is your ruler, then measuring by that ruler indicates that the proper lifespan for each living entity = well.... it's current lifespan.)
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    Dec 2 2011: Evolution's aim is not to prolong the lives of the living, but to facilitate reproduction and improve such beings. In order to have a world in which species are constantly progressing and moving toward better versions of themselves, the death/life cycle is a necessity. In fact, the faster we are replaced by newer beings, the faster evolution and adaptation can progress. The very thought of creatures that have yet to be improved upon living long lives goes against evolution. Evolution would only produce immortality/anti-aging if it had created a perfect being that could no longer be improved upon. But, seeing as that will never happen considering the constantly changing universe, immortality never will either.
  • Dec 1 2011: Species are locked into a predator-prey arms race, so the survival strategy would be genetic variation within the species, and strategic alliances with other species. Living for a long time would be like standing still in the middle of a battlefield. In our species we are no longer fully part of this predator-prey arms race, so we see our lifespan increase. Those living to 100+ can be sequenced and their genetic information can be used to increase the lifespan of our species.
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    Nov 27 2011: there are some species of animals that live for hundreds of years. and some scientists even ague that viruses may possibly be the oldest funtional biological structures on the planet, they solved the problem of death by ceasing to live = "nonlife", making them the most deadly and lethal earthly threat to all living organisms, they are like zombie vampires that hijack your cells and multiply within that cell hundreds of millions of times until they explode out of it. they couldnt be much more perfect.

    michael behe after charles darwin's findings came up with the theory of irreducible complexity which theorizes that through selection and temination, structures become ever more efficient and simple. what this means for complex organisms is less friction on moving parts, faster regeneration periods, less genetic flaws, longer life spans etc.

    Death IS an evolutionary advantage becuase of the fact that, becuase of environmental constraints, it makes room for more "experiments" (humans) to be produced. much like in the movie "evolution" the aliens were replicating in a practically exponential rate and rapidly evolving as a result. however thats a convenience of death, not it's purpose! evolution IS moving towards longegity, so long as we can produce the resources needed for our species to thrive. ---Mars here we come
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        Nov 27 2011: HI Tony
        Interesting perspective , enjoyed it.
        Just curious with your SATAN & GOD proposition..... so how you see it I mean the whole kingdom of living being result of GOD's will or evolution ?

        If SATAN can do anything whats so ever is it than again GOD's will ?
        If not SATAN is more powerful to over rule GOD's will......

        Curious to hear your thoughts
      • Nov 29 2011: Tony, I'd like to ask you just one thing. Are you here to preach or to contribute to the conversation here.
        We are talking about scientific facts of evolution and not about theological hocus pocus. Forgive me for being so crude but, I believe its necessary. You have brought up the irrelevant topic of christian mythology, about god and satan here when we are talking about evolution increasing longevity of evolved creatures. I dont think you quite understand the topic here, We are talking about random mutations that occur in living organisms that allow them to survive in their surroundings better. Its not something that the organism chooses to do or makes an effort to do. Evolution is based absolute randomness. When you bring in gods and satan into the picture you're effectively bringing intelligent design into the argument which, is absolute nonsense in itself. If all organisms were designed as version 1.0 and 2.0 we should see less random vestigial organs and vestigial construction in the biological makeup of organisms. For the time being I can give a few examples with regard to us humans, the human eye has its photo-receptors : the cones and rods facing backward with the retinal nerve passing right through it which creates the blind spot. Another being the vestigial organs such as the appendix, coccyx, nipples in males etc.
        Good and evil is a social construct and not something that the natural world exhibits. It might be disheartening but there is no other purpose that anyone is born with in life other than to ensure the species survives. All purpose that we find are what we give ourselves. So I urge you to give yourself purpose rather than to wait for it, and to indulge in a scientific debate when we are discussing science. Its good to believe in things that make you feel good, but one must always know when to draw the line as to the limit that it governs your understanding and way of life. You should govern your beliefs and not let your beliefs govern you. Cheers
        • Dec 3 2011: Stating those words to bring Tony 'into line' must have made YOU feel good. Do you see this self indulgence at Tony's expense as more virtuous or less emotionally driven than his? He seemed to simply refer to our convenient blindness to one side of a polarity that exists in all things. Eg. When we are trying to 'be right' in expressing our viewpoint, we are conveniently unaware we are concurrently aversive to 'being wrong'.

          Sure, in logic and science we draw lines. We 'draw a line' by saying everything must be rational and in accordance with rules or natural laws. But, by 'drawing the line' we create the very problem we wish to resolve. Fundamentally, THERE IS NO LINE. The idea of 'life' being a notable eg.

          THERE IS NO 'LIFE'.
          Some time ago humans 'drew a line' and said; "There is a distinction between the animate and the inanimate." We called things on one side of the divide 'LIFE' and on the other side, 'NOT LIFE'. Then right up to this day,we are trying to find 'the origin of life'. I suggest we don't find 'the origin of life' because we made 'life' up. WE ARE THE ORIGIN. Our logic, made it up! The concept of life only exists inside logic and we generate our logic. So try considering logic as just a self licking ice cream of self generated 'lines'. It cannot ever be the whole truth. A benefit of this idea is: THERE IS NO DEATH.

          So if you want to go down the rationalist's path to pull someone like Tony 'into your line', then be prepared to go all the way with rationalism. You will see that even your logic is funded by 'self drawn lines', or better put, 'irrationality'. I know mine is.

          "There are only two mistakes one can make along the road to truth; not going all the way, and not starting." Buddha.

          So give the religious a break; at least they are couragous enough to accept some irrationality. And as an aside: The accepted scientific wisdom of today is that everything in this universe came from nothing. Now IF THAT is possible, then pray tell, what is not?
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          Dec 4 2011: I would keep myself as far away from this argument as possible but there is one rational man out here that I can entertain. They are all just theories whether religious or scientific, each plausible to a different mind but at least we can look back and say we have found a missing link from the dark ages.
          A lexicon acquired from brushing through a scientific manual doesn't make these people a formidable opposition to science or progressive thinking. So do think twice before you commit to entertaining their arguments.
    • S Das

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      Dec 8 2011: Julius N., good point about the virus. Others took a sidestep to your comment, but let me challenge it directly.

      Virii are living, so they do impact evolutionary aging. I'll explain by first saying: All life requires energy. Energy is the "lifeforce" of evolution and of living systems. Life requires two things: specific matter-structures and specific energy-types.

      Without energy, life ceases. We see this when an animal stops getting energy (eating), it dies (turns to dust, into simpler matter).

      Likewise, when energy is added [to certain configurations of matter], life begins/resumes.

      This is very apparent in a virus, which can be dormant (having insufficient energy to animate/activate), or can be "living" (active) if its environment or a host-cell gives it the right energy. Virii are very unique forms of life, since they can easily move from being "living" to "dead", and back and forth.

      We also see this in more complex life. Some of you might know of Dolly, the first lifeform we cloned (she happened to be a sheep). Well, the hardest part of figuring out how to clone was not the genetics, manipulating cells, or their structures. The most difficult part was how to "breathe life into the clone"... how to jump-start that cloned cell to make it start dividing. It was no simple feat. We know now, all it took was a bit of energy. They "jump-started" the cloned cell with an electrical current. This is another example of energy being added to "a clump of lifeless matter"... to make it living. And this was done to a clump of matter more complex than a virus -- maybe the most complex bit of matter we humans can repeatedly bring to life.

      The ease with which life can be controlled (enlivened or killed) depends on the complexity of the matter composing it. A virus is relatively very simple compared to all life we know, so it can easily be enlivened or killed. For this reason, more complex structures are harder to bring to life.

      Virii =life. Prions =nonlife.
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        Dec 8 2011: it doesnt seem to me that your challenging my comment at all, but rather challenging the idea that viruses ARE living organisms. my previous comment served the purpose of proposing that through evolution viruses have become irreducibly complex, meaning they couldnt be any simpler and carry out the same function. and the same status of optimum efficiency in achieving a objective which allowed bacteria to evolve into viruses is also constantly happening in every complex organism. 30 million years from now our anatomy will be much simpler than it is today, it will be much more efficient. our bodies will repair themselves faster, our organs will optimize their energy use etc.

        but in response to your comment i feel that viruses are neither "enlivened or killed" but rather take on form of active nonlife and non active non life(we do not yet know how to kill a virus). and since viruses are as much living as they are dead, they cannot either be categorized as living or dead. viruses are no longer comprised of systems. they dont have common anatomical charactristics of any living organism on the planet, the function they serve shouldnt be confused with the sturctures that allow that body to perform those functions. its not that im any more right than you are [in a philosophical sense] but our current standards by which we categorize life and non life have NOT been modified to make room for viruses to be categorized as either.
  • Nov 26 2011: Life requires death. Why? from a biological perspective- the purpose of life is to procreate. what is the point of reproduction? genetic recombination. evolution is primarily to become the best version of something(at particular time)- not make that something immortal.
    it is a personal urge to stay alive. moreover death, as many people on this discussion have said,maintains supply and demand ratios.
    this is my take on life- a bunch of chemicals not knowing what they are doing.
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    Nov 25 2011: I like the question. My view is that we forget "the what" that is survivng. It is the gene. The body is like a husk it can be discarded once the genetic material has been supported suuficiently to survive and do it all again. The life span of a gene is unimaginably longer than its incubator. You could easily develop a eugenics program that would result in longer life spans by simply not allowing anyone to bare children until 50 years old and out of the successful offspring lift the barrier once again and then again etc etc. (I use the word eugenics without moral content) If there are any biologists out there who want to prove this in a breeding program on animals I would be delighted to hear the results
  • Nov 24 2011: I'm not an expert,but I feel that the answer to the question of "Why evolution hasnt solved the issue of aging." is a simple one. The answer lies in what exactly evolution is : Evolution is the modification of features in a species over generations, governed by the concept of natural selection and survival of the fittest. When an organism doesnt die, a new generation of the species does not arise, and so evolution cannot occur. Slight mutations in every generation is what leads to evolution.Bye definition the next generation that does survive has to be better equipped to survive than the previous one. The younger organisms of the species have almost no chance of survival without initial support from the mature of the species.That said, I feel that evolution had almost come to a snails pace in comparison to it previous snails pace, which makes it extremely slow in the case of Homo sapiens, thanks to medicine. Its not just the fittest who survive and reproduce but rather almost everyone does, regardless of their strengths or weaknesses. But evolution is still taking place, the rise and fall in the number cancer cases might be an indicator to this. The body is trying to advance in its ability to repair damaged tissue. But the mutations have not reached a stable maturity for the species to move in a particular direction, by having the weaker part of the species overtaken by the stronger. Besides modern medicine would allow us to replicate it in the weaker set of our species too once it stabilizes if we dont artificially find a way to stabilize it first.
  • Nov 23 2011: It strikes me that extended aging is in fact a specific evolutionary DISADVANTAGE.

    On the one hand; It is clear that in animals that care for their young there is a specific advantage to parents surviving until their young are mature, and it there is even an arguement for survival well beyond procreative fecundity (as in humans where females typically survive not only long enough to rear their own young but even to assist in rearing their grandchildren).

    On the other hand; survival of an "unevolved form" of any animal over several reproductive cycles results in the potential for excess competition. While the "survival of the fittest" would favour the more evolved form any capability to learn would provide a potentially outweighting counter advantage to the less capable but "better informed" older generations.

    The consequence of this would be that the species as a whole would fail to evolve and ultimately have insufficient variation within it's population to address "shocks" and thereby be at risk of extermination.

    Following this thinking;
    Animals which don't care for their offspring would have life expectancies ranging from slightly longer than the time required to reproduce (such as the mayfly or the salmon) increasing to address potential risks associated with the development cycle (predictable life-cycle giving a short life while high risk of failure to develop gives longer life requirement)

    Animals which do care for their young would have a life expectancy of betwen say 2 and 4 rearing cycles (2 to allow their offspring to be fully reared up to say 4 to avoid excess competition with their own great grandchildren).

    The other expectation that this thinking would establish is that the more generations a particular animal "cares for" the longer its likely lifespan. (Humans, Elephants etc which care across generations tend to have multi-generational lifespans)
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      Nov 23 2011: I do agree that the affect of age on child-rearing is a significant advantage that proliferated through the population and developed species that adapted such an ability. This is a trait that is advantageous to unique species in unique situations.

      How would you explain the Galapagos turtle? I believe it is one of the longest living vertebrate yet abandons its eggs. It could also be that it is an isolated or rare occurence as well.

      A theory must be simple and able to explain everything but there can be few exceptions which should be explained by other superimposed factors. It must hold true for a majority of populations, measurable by controlling for other traits which affect the same characteristic.

      Is it possible that species started growing older long before they developed the behavior of grand-parenting? Uniquely Humans and Elephants are species which have barely any competition and adapt their environment and so have to face less adaptive pressures.

      Although there are other similarities as well, we have acquired learning so a longer learning period is definitely a benefit. But the greater apes have them too but have little impact on their environment and so have to face adaptive pressures. :)
      • Nov 24 2011: Anuragg, the case of the Galapagos tortoises face an extremely hisk of failure of breeding with young being very heavily predated with only about 1 in 1000 laid eggs survivng to maturity. Given an average clutch size of about ten eggs and four clutches per year it is easy to see how a simple replacement birthrate would require about 50 years of reproductive life so an average age of circa 70-75. The actual wild avaerge age of about 100 would yield an average of three adult offspring per female so provide for a slow population growth while resources permit. In this case the high level of predation requires that parent is extremely long lived.

        It is of course possible that species started to grow older independently of behaviour my point is that being long lived, while an advantage for an individual and potentially an adaptaion to allow for either long periods of dependency as in many "higher mammals" or high levels of predation in the young (sexually immature), once it has achieved that purpose it ceases to provide further evolutionary advantage (capacity for an organism to adapt to its environment such that its genetic inheritance can be preserved) and can indeed, in cases where learning is involved, provide a specific evolutionary disadvantage by alowing the unadapted ancestors generations out compete their potentially more appropriately adapted descendants.

        My expectation is that species which have extended their life-spans beyond the point where it is delivering evolutionary advantage (as opposed to individual advantage) will be more vulnerable to evolutionary shocks (environmental changes/novel predation/novel diseases etc.) and therefore more likely to fail to respond to those shocks.

        In the case of humans the pre-christian era book of psalms estimates the lifespan of the human as three score years and ten (70 years) the latest UN global estimates suggest the current human average life expectancy is 67.2 years (82 in Japan down to 40 in swaziland)