 For the 4th of July, on the 5th of July. | 5. Jul 2011 @ 14:45  |
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It is almost impossible to write off any possibility for certain. But in that case I would have you directed to Russell's teapot first, please.
And in any case, while the (human and its) genetics might well be put together by a divine being, one can but wonder at the circumspect or indeed ineffable route it is employing in the case of ensuring the time of a person's death. Even if the divine being would be only concerned with humans as species the solution wouldn't make any particular sense.
When I said divine being, I wasn't thinking of one plotting away in the heavens, rather something more akin to Spinoza's conception (or more accurately, what I in my part-time blundering way understand of it). So I'm not really saying that God/nature has our time of death calculated, but that we are designed (see that passive voice is a 'dead' give away) to pass away naturally at some point, leaving our DNA to endure - as long as our offspring have the sexual appetite for it, that is.
I see now.
And that's mostly the point I am against, in my post.
From what I have read about genetics and related subjects (which isn't much, I admit), I have a distinct impression that the fact of our systems going down steadily is only "designed" in that respect that it is not (broadly speaking) evolutionary critical that humans survive past the age of raising their children, therefore, there seems to be no natural selection of long-lived humans.
That would change, if more people raised kids later in life though. And, of course, we must take into account secondary advantages of having groups with long-living humans -- as long as their long lives benefit the group as whole.
It's interesting though, that no living creature lives forever - that the potential causes of our death are there in the DNA of all living organisms from the start (I say 'potential' because I am excluding deaths at the hands of others, natural disasters etc.).
As for natural selection of long-living adults, there is a nice contradiction in that although you are likely to live longer in a society that looks after your health and social needs, you are less likely to be needed to share the burden of caring for grandchildren in such a society, and there is, therefore, less scope for natural selection to play its part.
Interesting also, that when it comes to the sexual imperative to reproduce, I would say it is the ones that feel it most that have kids younger (OK, I feel I am on the border of crass generalization - but I just feel there is some truth to it - the romantic abandon, if you like).
> It's interesting though, that no living creature lives forever - that the potential causes of our death are there in the DNA of all living organisms from the start.
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Well, first of all, I do believe I have read not very long ago about some creatures (I think it was a type of fish or shark) that are currently believed to be able to theoretically live on forever, barring enemies and disasters. Might've been some type of shark, they apparently have a terrific immune system.
Secondly, the potential causes of our death are indeed frequently in our DNA: each strand of DNA in each of our cells, as I was surprised to learn, is around 6 feet long and contains 3000 million genes (aka letters). One particular letter goes wrong, and bang, you got sickle-cell anaemia.
However, the point that sharks (or other semi-eternal fish or creatures) seem to bring about is that it is not _neccessary_ that we should have this limitation of living with detoriating bodies.
I do believe we are quite close to collapse finding how to improve our genetic system in ways that could give us longer lifespans without the unpleasant effects of old age. Smarter immune systems, better secondary chains of command, it seems we could achieve these things at least in lab in our lifetime, DNA-preserve-us!
> As for natural selection of long-living adults, there is a nice contradiction in that although you are likely to live longer in a society that looks after your health and social needs, you are less likely to be needed to share the burden of caring for grandchildren in such a society, and there is, therefore, less scope for natural selection to play its part.
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Well, from the perspective of natural selection, the only criteria for long life as evolutionary trait would seem to have your own children late in the life. I mean -- if you only get children when young, then you pass your genes anyway, even if you have some genetic screwup that kicks in at, let's say around 30. If you also have children when older, then you have qualified as somebody who can give genes that have better chance to live for longer (since you did).
OK, I will keep my eyes open for that shark - if it is the case, then I find it a little unsettling - as if a natural law has been proven false.
Regarding the natural selection of genes which result in greater longevity, then I would say that there is another factor at play, as well. If grandparents have this longevity gene, and are active and caring in their old age, then in a situation in which this could give their grandchildren an advantage, this gene will be selected for (as their DNA will have been passed on to their offspring and their offspring's offspring).
Doubtless, there are a lot indirect advantages that can be passed on to next generations by longevity. It does seem also that a lot of people ARE in fact living longer, although it would probably be more due to the living conditions and better knowledge of the body requirements.
Regarding the fish -- it really depends on what you call living. AFAI understand, there are bacteria that also have the possibility to live near endlessly; however, you would be hard pressed to determine the "original" speciman, due to their multiplication by division. I wouldn't be surprised if the further down the chain of complexity you go, the more there would be organisms that can survive eternally, assuming external factors are favourable.
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