On Mon, 26 Jun 2000, Bryan Moss wrote:
> Not exactly related to your post but: how much "age-related"
> damage to the brain do you think might be caused by the
> failure of the aging body supporting the brain rather than
> the aging of the brain itself? In other words, if we can
> only replace the body, and lack a way to treat the brain,
> how far will this get us?
Well,  below, estimates that:
"approximately 10% of all neocortical neurons are lost over the
life span in both sexes"
so, I suppose if you assume this is due to the body not supplying
it with what it needs (glucose, O2, amino-acids, lipids, etc.)
then you could make the argument that this is failure of the body
to support the brain. But I think aging is highly organ specific
because nature "primarily" evolves individual programs within each
organ. So IMO, I would guess that much more of this is actual
aging of the brain. Now, strokes and lack of blood supply are due to
failures of the endothelial/immune systems and not the brain per se.
Since some people (~20%?) do die from things going wrong inside your
your brain, there is a fraction whom a cloned body probably isn't
going to help much (it might even hurt them if the aged endothelial
system cannot tolerate a stronger heart.
Sapolsky would argue that at least some of the cell loss in the
brain is not due to 'aging' (brain or body) per se, but results
from environmental[adrenaline] stress. So it is really the
the accumulation of environmental experiences ('scars of life').
The 10% loss above, would argue that you should be able to get out
to several hundred years, if you can live with a smaller brain
and *if* loss doesn't accelerate (!?!). There are clearly a large
number of individuals whose body wears out long before their brain
and for them a clone body would certainly be nice. It isn't a universal
1. Pakkenberg B, Gundersen HJ, J Comp Neurol 1997 Jul 28;384(2):312-20
"Neocortical neuron number in humans: effect of sex and age."
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