So the cellular theories of ageing seem to focus on the faults which arise when, for one reason or another (free radical activity, or a built-in slowdown, or the onset of cellular mutation) cells become less able to repair, energize and detoxify themselves, causing alterations such as cross-linkage. Thus cells generally start to function at an increasingly poor level, and under certain circumstances start to mutate into cancerous forms.

Here are some of the theories which have been developed to describe the causes of ageing of the whole organism.

The simple wear-and-tear theory holds that we age as our non replaceable parts slowly wear out. This begs the question 'why' the wear-and-tear takes place, the causes of which lead us back to what is happening on a cellular level, possibly to free radical activity, cross-linkage of cells, inadequate protein synthesis, and accumulation of undesirable material in cells and tissues. Another facet of this same basic concept lays the blame for ageing on a combination of the accumulation of toxic debris (as our detoxification processes become less efficient) and the slow exhaustion of non-replaceable substances. The toxic build-up again describes a process without ascribing a cause, unless substance exhaustion is that cause.

The process of ageing is seen by some to be a result of hormonal and/or immune function changes. Once again we are asked to accept an effect as a cause. While hormonal disturbance can undoubtedly lead to a speeding up of ageing, in itself hormonal disturbance has to have a cause, and this may once more take us back to disturbance at the cellular and molecular levels.

These 'whole organism' concepts therefore seem to be seeing the process of ageing as part of the cause of ageing. It seems more probable that once cellular changes have become advanced (for whatever reason) and the consequent processes of 'wear-andtear' or hormonal/nervous system changes have started to become marked, that the process of decline becomes self perpetuating.

As I will show in the last chapter, some life extension methods aim specifically at restoring balance to imbalanced states which are a common feature of ageing, such as the slow build-up of excessive levels of vital substances such as serotonin and of the enzyme monoamine oxidize (MOA). Such methods often do influence the local imbalance but almost always fail to correct underlying trends. At such a stage, unless something is done to intervene and restore a degree of competence to what is faulty and malfunctioning at the cellular/molecular level, such as detoxification processes, protein synthesis etc., any organ dysfunction (liver, heart etc.) which has resulted from the cellular problems, itself becomes a 'further cause of ageing'. Comprehensive approaches, such as are offered by a calorie restriction diet seem able to improve (or retard) all (or most) levels of this vicious circle of decline, rather than just elements of it.

Integrated theories
To the credit of some experts in the field there have been many attempts to integrate elements of the theories listed above. This has led to the sort of scenario in which (for example) free radical damage to DNA is seen to result in altered nervous system and hormonal functioning and a consequent speeding up of the ageing process. Or, the involvement of negative changes (for whatever combination of cellular or disease-caused reasons) of the nervous system and the hormonal systems (neuroendocrine system) might be seen to severely compromise the immune (repair and defense) functions of the body, thus hastening aging