At the age of twelve years, the human
body is at its most vigorous. It has
yet to reach its full size and strength,
and its owner his or her full intelligence;
but at this age the likelihood of death
is least. Earlier, we were infants and
young children, and consequently more
vulnerable; later, we shall undergo a
progressive loss of our vigour and
resistance which, though imperceptible
at first, will finally become so steep
that we can live to no longer, however
well we look after ourselves, and however
well society, and our doctors, look after
us. This decline in vigour with the
passing of time is called ageing. It is
one of the most unpleasant discoveries
which we all make that must decline in
this way, that if we escape wars, accidents
and diseases we shall eventually 'die of
old age', and that this happens at a rate
which differs little from person to person,
so that there are heavy odds in favour of
our dying between the ages of sixty-five
and eighty. Some of us will die sooner,
a few will live longer--on into a ninth
or tenth decade. But the chances are
against it, and there is a virtual limit
on how long we can hope to remain alive,
however lucky and robust we are.
Normal people tend to forget this process
unless and until they are reminded of it.
We are so familiar with the fact that man
ages, that people have for years assumed
that the process of losing vigour with
time, of becoming more likely to die the
older we get, was something self-evident,
like the cooling of a hot kettle or the
wearing-out of a pair of shoes. They have
also assumed that all animals, and probably
other organisms such as trees, or even
the universe itself, must in the nature
of things 'wear out'. Most animals we
commonly observe do in fact age as we do,
given the chance to live long enough;
and mechanical systems like a wound watch,
or the sun, do in fact run out of energy
in accordance with the second law of
termodynamics (whether the whole universe
does so is a moot point at present).
But these are not analogous to what
happens when man ages. A run-down watch
is still a watch and can be rewound.
An old watch, by contrast, becomes so
worn and unreliable that it eventually
is not worth mending. But a watch could
never repair itself--it does not consist
of living parts, only of metal, which
wears away by frintion. We could, at one
time, repair ourselves--well enough,
at least, to overcome all but the most
instantly fatal illnesses and accidents.
Between twelve and eighty years we
gradually lose this power; an illness
which at twelve would knock us over,
at eighty can knock us out, and into our
grave. If we could stay as vigorous as we
are at twelve, it would take about 700
years for half of us to die, and another
700 for the survivors to be reduced by
half again.
ALEX COMFORT The process of ageing