[00:01.51]Lesson 37
[00:03.35]The process of ageing
[00:12.02]What is one of the most unpleasant discoveries we make about ourselves as we get older?
[00:21.76]At the age of twelve years, the human body is at its most vigorous.
[00:27.41]It has yet to reach its full size and strength,
[00:30.64]and its owner his or her full intelligence: but at this age the likelihood of death is least.
[00:39.39]Earlier, we were infants and young children, and consequently more vulnerable;
[00:45.94]later, we shall undergo a progressive loss of our vigour and resistance which, though imperceptible at first
[00:53.59]will finally become so steep that we can live no longer,
[00:57.72]however well we look after ourselves, and however well society, and our doctors, look after us.
[01:04.70]This decline in vigour with the passing of time is called ageing.
[01:10.74]It is one of the most unpleasant discoveries which we all make
[01:14.92]that we must decline in this way, that if we escape wars, accidents and diseases we shall eventually 'die of old age',
[01:25.75]and that this happens at a rate which differs little from person to person,
[01:30.78]so that there are heavy odds in favour of our dying between the ages of 65 and 80.
[01:38.32]Some of us will die sooner, a few will live longer--on into a ninth or tenth decade.
[01:45.51]But the chances are against it,
[01:47.49]and there is a virtual limit on how long we can hope to remain alive, however lucky and robust we are.
[01:55.51]Normal people tend to forget this process unless and until they are reminded of it.
[02:01.84]We are so familiar with the fact that man ages,
[02:04.70]that people have for years assumed that the process of losing vigour with time,
[02:09.50]of becoming more likely to die the older we get, was something self-evident
[02:14.78]like the cooling of a hot kettle or the wearing-out of a pair of shoes.
[02:20.10]They have also assumed that all animals,
[02:22.80]and probably other organisms such as trees, or even the universe itself, must in the nature of things 'wear out'.
[02:32.39]Most animals we commonly observe do in fact age as we do,
[02:37.03]if given the chance to live long enough;
[02:39.34]and mechanical systems like a wound watch, or the sun,
[02:43.73]do in fact run out of energy in accordance with the second law of thermodynamics
[02:49.81](whether the whole universe does so is a moot point at present).
[02:54.42]But these are not analogous to what happens when man ages.
[02:59.58]A run-down watch is still a watch and can be rewound.
[03:04.26]An old watch, by contrast, becomes so worn and unreliable that it eventually is not worth mending.
[03:11.47]But a watch could never repair itself--it does not consist of living parts, only of metal, which wears away by friction.
[03:22.24]We could, at one time, repair ourselves--well enough, at least, to overcome all but the most instantly fatal illnesses and accidents.
[03:32.35]Between twelve and eighty years we gradually lose this power;
[03:36.90]an illness which at 12 would knock us over, at 80 can knock us out, and into our grave.
[03:45.22]If we could stay as vigorous as we are at twelve,
[03:48.78]it would take about 700 years for half of us to die, and another 700 for the survivors to be reduced by half again.