From: Joao Magalhaes (joao.magalhaes@fundp.ac.be)
Date: Fri Dec 06 2002 - 04:12:36 MST
Hi!
At 20:46 05-12-2002 -0800, Reason wrote:
>Just to be contrarian, how about aging being a function of damage due to
>rate of energy processing? That doesn't have to be particularly genetic. I
>seem to recall that most mammals go through the same number of heartbeats in
>a lifetime (ballpark) irrespective of size. So you could do some math based
>on scaled energy costs of circulatory systems per cell in the body, and you
>could find that mouse/human is 25/1. Or more probably not, but I just wanted
>to point out that biochemical/biomechanical stuff based on simple physical
>laws relating to size and volume could be just as important.
I faced these arguments by one of the referees when I published my
Experimental Gerontology paper earlier this year. My response to the
referee was something like this:
"The rate of living theory was an old theory proposing an inverse
correlation between metabolic rates and longevity. Yet there are so many
exceptions that one wonders if the theory should not be the other way
around. Birds, for instance, have higher temperatures and metabolic rates
than mammals and yet age slower than same-sized mammals. Bats too age
slower than expected from their metabolic rate. On the other hand,
marsupials age quite fast for their low body temperatures. It is true an
inverse correlation can be found between metabolic rates and the longevity
of some mammals, but the rate of living theory, as it stands, cannot be
accepted."
This is the most popular view nowadays and I don't think many
gerontologists out there defend the rate of living theory. Also, I am not
aware of any proof that mammals go through the same number of heartbeats
throughout their lifetimes. I read that mice have about 350 beats per
minute, or roughly 5-fold that of a human. Yet mice age 25-times faster
than humans and live about 20-times less. Actually, I was looking for the
murine heartbeat on the Net and found something even better to disprove
your hypothesis: "Your dog's heartbeat should range between 60 - 80 beats
per minute for a large dog, 80 - 120 for a small dog. Your cat should range
between 110 - 130 beats" Yet I know small dogs live longer than bigger dogs
and cats, in general, live longer than dogs. I actually remember reading
about this in Hayflick's book, but it was together with the old myths of
gerontology which are simply not true.
All the best.
Joao Pedro de Magalhaes
The University of Namur (FUNDP)
Research Unit on Cellular Biology (URBC)
Rue de Bruxelles, 61. B-5000 Namur. Belgium.
Fax: + 32 81 724135
Phone: + 32 81 724133
Website on Aging: http://www.senescence.info
Reason's Triumph: http://www.jpreason.com
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