Hi!
You wrote:
>On Wed, 15 Dec 1999, Joao Pedro de Magalhaes wrote:
> One always has
>to be careful however that the cause-of-death isn't "aging" per se.
>In Drosophila, as in Elephants, the "wear-and-tear" theory seems to
>explain most of the causes of death. Drosophila lose their wings
>and mouth parts and Elephants lose their teeth. Michael Rose has
>commented that one of the reasons his flies live so long is that
>they have huge fat reserves. Their eating parts wear out and they
>survive on their remaining fat reserves. Starvation does not equal
>aging.
"Aging" per se is what I call senescence. I define aging as an inevitable loss of viability and increase in vulnerability (from Comfort's book). Now, mechanical senescence (e.g. wearing of joints, molar erosion, etc.) does affect aging in both drosophila and elephants. But the fact remains that senescence also exists in both species (although it can be caused by different factors). As far as we are concerned, I think that in order to avoid death before, say, 200 years, we have to solve not only senescence but also other causes of aging and post-mortem lethal genes (e.g. mechanical senescence happening after our current lifespan). It's a lot of work -- I'm not going to be unemployed for centuries!
>> Many non-aging species do appear to grow indefinately (lobsters, certain
>> turtles, etc.). In fact, Bidder's hypothesis was that species with unlimited
>> growth would not age (constant expansion or death, a bit transhuman once you
>> think about it).
>
>Hmmm, if you have a ref for Bidder, I'd appreciate it, this isn't ringing
>a bell in my brain.
It's an old theory and since there are exceptions, the idea has been discarded by many. The reference is:
Bidder, G. P. (1932) Senescence. Brit Med J 2:583-585
>The problem as I see it is that if you grow
>indefinately, you eventually exceed the local food resources and die.
I like to call it ecological senescence. And don't forget that if you grow too big you'll might have to change your diet.
>You do need to have increasing reproductive capacity so that
>the fraction of "longevity" genes in the reproductive population
>gets preserved. The "short-lived, faster-reproducing" variants of
>your species will win in the competition for resources unless you can out
>reproduce them.
There are species with reproductive senescence that appear not to age (e.g. sharks). Perhaps senescence never evolved in these species. From mathematical models you can argue that they'll eventually age either by mechanical or even ecological senescence, but the fact is that senescence might have not developed in sharks at all, despite their reproductive senescence.
>> Although there are exceptions to this rule, the truth is
>> that non-aging species' cells do undergo mitosis (one good exaple is the
>> molting in lobsters).
>
>Isn't this only the outer surface of the lobster though?
I'm not sure (lobster anatomy is not my speciality, at least not at dinner). In my writings I have that molting occurs in all hard tissues -- perhaps inner cartilage is also included, I don't know. Still, it's clear that some tissues do undergo mitosis in all long-lived species.
Best wishes.
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