AOur life span is restricted. Everyone accepted this as "biological" obvious. `Nothing lives forever!` However, in this statement we think of artificially produced, technical objects, products which are subjected to natural wear and tear during use. This leads to the result that at some time or other the object stops working and is unusable (`death` in the biological sense). But are the wear and tear and loss of function of technical objects and the death of living organism really similar or comparable?
BOur `dead` products are `static`, closed systems. It is always the basic materials which constitutes the object and which, in the natural course of things, is worn down and becomes `older`. Ageing in this case must occur according to the laws of physical chemistry and of thermodynamics. Although the same law holds for a living organism, the result of this law is not inexorable in the same way. At least as long as the biological system has the ability to renew itself it could actually become older without aging; an organism is an open, dynamic system through which new materials continuously flows. Destruction of old material and formation of new material are thus in permanent dynamic equilibrium. The material of which the organism is formed changes continuously. Thus our bodies continuously exchange old substance for new, just like the spring which more or less maintains its form and movement, but in which the water molecules are always different.
CThus aging and death should not be seen inevitable, particularly as the organism possesses many mechanisms for repair. It is not, in principle, necessary for a biological system to age and die. Nevertheless, a restricted life span, ageing and death are the characteristics of life. The reason for this is easy to recognise: in nature, the organisms either adapt or are regularly replaced by new types. Because of the changes of genetic material (mutations) these have new characteristics and in the course of their individual lives they are tested for optimal or better adaption to the environmental conditions. Immortality would disturb this system – it needs room for new and better life. This is the basic problem of evolution.
DEvery organism has a life span which is highly characteristic. There are striking differences life span between different species, but within one species the parameter is relatively constant. For example, the average duration of human life has hardly changed in thousands of years. Although more and more people attain an advanced age as a result of the developments in better medical care and better nutrition, the characteristic upper limit for most remains 80 years. A further argument against the simple wear and tear theory is the observation that the time within which organism age lies between a few days (even a few hours for unicellular organisms) and several thousand years, with mammoth trees.
EIf a life span is genetically determined biological characteristic, it is logically necessary to propose the existence of an internal clock, which in some way measures and controls the ageing process and which finally determines the death as the last step in a fixed programme. Like the life span, the metabolic rate has for different organisms a fixed mathematical relationship to the body mass. In comparison to the life span this relationship is `inverted`: the larger the organism, the lower its metabolic rate. Again this relationship is valid not only for birds, but also, similarly on average within the systematic unit, for all other organisms (plants, animals, unicellular organisms).
FAnimals which behave `frugally` with energy become particularly old, for example, crocodiles and tortoises. Parrots and birds of prey are often held chained up. Thus they are not able to `experience life` and so they attain a high life span in captivity. Animals which save energy by hibernation or lethargy (e.g. bats or hedgehogs) live much longer than those which are always active. The metabolic rate of mice can be reduced by a very low consumption of food (hunger diet). They can live twice as long as their well-fed comrades. Women become distinctly (about 10 percent) older than men. If you exam the metabolic rate of the two sexes you establish that the higher male metabolic rate roughly accounts for the lower male life span. That means that they live life `energetically` – more intensively, but not for as long.
GIt follows from the above that sparing use of energy reserves should tend to extend life. Extreme high performance sports may lead to optimal cardiovascular performance, but they quite certainly do not prolong life. Relaxation lowers the metabolic rate, as does adequate sleep and in general an equable and balanced personality. Each of us can develop his or her own `energy saving programme` with a little self-observation, critical self-control and, above all, logical consistency. Experience will show that to live in this way not only increases the life span but is also very healthy. This final aspect should not be forgotten.