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Aging is a process that occurs begins after reproductive maturation puberty
and results from increasing random systemic molecular disorder. This disorder
has multiple causes, including damage by reactivereactive oxygen species,
also know as oxygen free radicals (see Oxidative
Damage Research Center),species but generally results from the diminishing
gradual loss of the energy necessary to maintain molecular structure and
function.
On the other hand, lLongevity determination, or a species' maximum life
span, on the other hand, is not a random process. It is governed by the
excess physiological capacity reached at the time of sexual maturation
that, through natural selection, was achieved to better guarantee survival.
Longevity, then, is only indirectly determined by genes. A species' maximum
longevity has been determined over time by natural selection.
The survival of a species depends on a sufficient number of members living
long enough to reproduce and, if necessary, to raise progeny to independence.
Natural selection favors animals that have greater survival skills and,
especially, redundant physiological reserve in vital organs beyond the
minimum needed to survive the damage that might be exacted by predators,
disease, accidents or environmental extremes.
Physiological capacity, beyond the minimum required for life, increases
the chances for animals to survive long enough to achieve reproductive
success, just as redundant vital systems in a complex machines like a
space probe, better insures that they the machine will achieve their its
goals. The amount of excess physiological capacity in animals, like the
amount of redundancy engineered into the space probe, provides the potential
for continued function beyond the primary goal of the space probe or beyond
reproductive success in animals.
Therefore, longevity determination is governed by the excess physiological
capacity reached at the time of sexual maturation that, through natural
selection, was achieved to better guarantee survival. Longevity, then,
is only indirectly determined by specific genes.
Thus, one important interpretation of the finding that a normal cell has
a limit on its ability to divide is that it this limit is a manifestation
of that cell's potential for longevity and thus reflects longevity determination
in the animal itself. So the biological losses that precede the loss of
normal cell division impacts on our understanding of aging, while the
absolute limit on the cells' division impacts on our understanding of
how longevity is determined. In a sense, these are opposing forces. Aging
processes work against the process that first determined longevity.
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