Cause of aging

Iuval Clejan clejan at jump.net
Mon Aug 24 22:44:43 EST 1998


Steven B. Harris wrote:

> In <35DF9398.67C47B6C at jump.net> Iuval Clejan <clejan at jump.net> writes:
> >
> >I don't believe aspens or any plant is immortal. They just have an
> >interesting way of living, with each new generation living on top of
> the
> >old dead generation.
>
>     I really don't care what you believe.

I don't care if you care what I think as long as you stimulate my thinking
or teach me something, which you may have done.


> If you don't know anything
> about aspens, why don't you read a book?

I have. I went back and reread the relevant pages, since it's been a while
It is called "How and Why we Age", by one Leonard Hayflick, heard of him?
Maybe you don't care what he thinks either, but just in case you do here
are some quotes:

(Talking about redwoods, sequoias and bristlecone pines in particular,
which have older individual trees than the aspens)
"That is why, if you are past your 30th birthday, I insist that you are
older than what some mistakenly call the world's 'oldest' trees" (p 35)
Do individual aspens also form concentric rings with the younger
generation living on top of the older DEAD generation? I thought so (don't
all trees do that?), but perhaps you or someone else  could save me from
spending more time on this, and tell me the answer, if they know.

And again, on page 36- "Many trees and shrubs propagate by sending up new
plants from their roots as the roots spread underground. This process may
be repeated for centuries or even millenia. If the original tree dies.."
(which surely it does at some point-my own words) "..how old are the
remaining trees? Although most of the parental plant's tissue may be gone,
the daughter's represent its direct physical continuation. Trees like the
aspen, the coast redwood, and some elms and bushes like the creosote
propagate in this fashion."

p 37: "Are aspens, creosote bushes, prairie grasses, or fairy rings
immortal? Do the individuals age? When is each born and when does each
die? There are no simple answers.
    One could also make a powerful argument that even trees and plants
that propagate only by seeds are immortal. The seeds, although they
eventually separate from the plant, are a physical continuation of the
parent and give birth to living progeny. This argument applies equally
well to humans and other animals, whose 'seed' also separates from its
producer, fuses with another cell, and starts a new individual.
Individuals may die, but the germ plasm is immortal."

So I had forgotten that the aspen brings a new generation forth by sending
out shoots instead of (of in addition to?) seeds. But I think you would
have a hard time arguing that an individual aspen is potentially immortal.
You would have to then concede that an individual human is also
potentially immortal (as long as he and his descendents keep reproducing).
The differences between detaching the seed from the individual, and
sending out shoots a few feet a way (which are still connected by the
roots to the original live individual at the time of their sprouting) is
probably purely semantic.

I actuallt also looked in Peterson's field guide to N American trees, and
it also mentions for both bigtooth and quaking aspen (but perhaps you have
another species in mind) that they are "short lived" I guess they are
using the standard definition of lifespan, referring to the individual not
the germ cells or cell lines. Also it is not clear if they are short lived
because they age or just get outcompeted or diseased.

The question of whether the aspen, and a number of other organisms age is
still open.



>
>
>                                        Steve Harris, M.D.


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