**** Byegones for the delayed response and/or if previously posted ****
>>>> Date: Tue, 2 Nov 1999 06:15:30 -0800 (PST) <<<<
On Tue, 2 Nov 1999, Joao Pedro de Magalhaes wrote:
>
> Perhaps. But what about "use-related damage" or mechanical senescence that
> might not be derived from aging itself. For example: presbyopia, molar
> erosion, hardening of joints, and menopause.
These things are included of course. Whether or not you classify them
with "aging" is a semantic issue. I would probably include vision
changes (increasing the hazard function) and tooth loss as quite
significant. Elephants are supposed to go through many molars but
the replacment function is limited (whether by genetics or failure
of the replacement tissue is unclear), so for them this is clearly
an age-related cause of death. In humans it isn't so much tooth loss
but failure of taste & smell (leading to decreased interest in food)
and failure of the gut (leading to decreased nutrient absorption).
I'd put these as downstream from my previous reasons (telomere shortening
being the most likely upstream source of the failures).
I'm less concerned with things that are not "universally" fatal
(e.g. menopause) or can currently be treated (e.g. replacement joints
or teeth). If there is a reasonable strategy for fixing the consequences
of the problem (e.g. hormone replacement in women), then I would
want emphasis shifted to the next problem.
> Species that appear not to age
> have different physiologies that allow them to cope with these situations.
Yep, but the nice thing about nature is that we have examples of genetic
programs that solve some of these problems. Humans can "borrow" the
tooth replacement strategy of elephants or even better sharks. The
anti-cancer program of elephants or whales also would be useful.
> Even that we do not age, these problems might still affect us. Of course
> this depends on how you define aging but I think that senescence and certain
> age-related changes might be independent of one another (as predicted from
> evolutionary theory).
Precisely. To solve aging you have to knock off the problems one by one.
As you solve each, you will reveal something that was previously
unnoticed. Fortunately we have enough insights at this point that
we can work on the problems simultaneously.
Robert
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