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 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 we 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 course of time 'wear out'. Most animals we commonly observe do in fact age as we do if they survive long enough; and mechanical systems like a wound - up watch, or the sun, do in fact run out of energy in accordance with the second law of thermodynamics (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 stops working altogether. It is rather like the human body. A person who has been doing strenuous physical work for a long time may find that his or her body no longer responds as well as it used to; but if he or she takes a long rest, the body will recover some of its vigour. There is a difference between a worn - out watch and a worn - out body. An old watch cannot be made new again; but a human body can be restored to a certain extent, and, if we take good care of it, it can remain in fairly good condition for a long time.
Our so - called 'control of nature' is a phrase full of conceit. It implies that nature is something outside us, which we can control. We forget that we ourselves are part of nature, and that as we do to nature, nature does to us. Our very life depends on our body's adjustment to the changing environment. We are not much different from other animals in this respect. When we are cold, we shiver and try to get closer to a heat source. When we are hot, we sweat and try to find a cooler place. We do these things because our body has been adjusted to the environment in which we live. We also have a built - in thermostat which regulates our body temperature. When our body temperature rises, we sweat more; when it drops, we shiver more. This is how our body keeps itself in balance. If we interfere with this natural adjustment, for example, by wearing too many clothes when we are cold or by not wearing enough when we are hot, we will get sick. So, we can say that our body has a certain amount of self - control. But this self - control is limited. If we are exposed to too much cold or heat, our body will not be able to adjust itself, and we will die. So, we should respect nature and let our body do its job. We should not be too conceited about our 'control of nature'.