The inevitability of aging and the fear of dying have haunted the human race, and its been a human dream to retard aging and defy death. Aging is a complex syndrome that is progressive, deleterious, universal and so far irreversible. It is much like 'biological entropy', which increases with time, just as a block of ice would melt in an isolated environment, such as a room, in room temperature.
It has been argued that animals in the wild, do not suffer aging; they either fall prey (killed), die of starvation, or become victims of accidents. Aging only affects humans and zoo animals. Aging is, sometimes, also referred to as senescence.
With age; our strength, stamina, speed and skill diminishes, the encoding and retrieval of memories also becomes less efficient. Aging not only manifests in the intact organism as a whole, but also it affects the whole gamut of molecules (DNA, proteins, lipids, carbohydrates etc) to cells and to tissues (sarcopenia or diminution of muscle mass, for example).
Some gerontologists argue that homeostenosis is the most important key mechanism for aging. Homeostenosis refers to diminution (=stenosis/bottleneck) in body reserves. An elderly person who is apparently healthy and can carry out normal day to day activities, becomes unduly sick and frail, when faced with challenges such as a simple common cold, as he is homeostenosed.
What causes aging is not known for sure and many hypotheses have been proposed. They fall into two broad categories, programmed or intrinsic and wear and tear or extrinsic (stochastic). By definition, it is clear that programmed aging occurs from within the person's own make-up, whereas wear and tear aging is the result of the combination of a variety of environmental factors. Factors such as chemical toxins, radiation injury (X Ray, UV Ray etc), free radicals and other factors are some examples of extrinsic/environmental culprits.
Some people tend to go into old ages without suffering any major illnesses. This is healthy aging and is predominantly genetically determined. It is thus aptly said that healthy aging begins with the fetus.
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