Theories of Ageing

Most people will live to experience ageing. Up until ten years ago, maximum life span (the maximum biological limit of life in an ideal environment) was not thought to be subject to change; it was set in the 1960’s by Hayflick at around 115 years. Life span is considered the key to the intrinsic biological causes of ageing, as these factors ensure an individual’s survival to a certain point until biological ageing eventually causes death. 

There are many theories about the mechanisms of age related changes, and they are not mutually exclusive. Gershon and Gershon (2000) have split them in two main groups:
1. Genetic programming (biological clocks) – a built-in programme in the genome is activated at a certain stage of an organism’s life cycle, and leads to death via a self-destruct mechanism. There are two major lines of research in genetic theories.
 The Hayflick limit: Cells divide for a set number of times, and then become senescent.
 Telomere loss and ageing: These are repeat sequences of DNA and protein which protect the ends of chromosomes from degradation and fusion with one another (Zakian 1995)
2. Stochastic events, random damage and errors of repair (wear and tear) – random damage accumulates throughout the lifespan and this damage gradually causes a reduction in the efficiency of the overall function of the organism and eventually results in its demise. In 1956, Denham Harman proposed the theory that ageing is caused by an accumulation of molecular damage caused by "oxidative stress", the action of reactive forms of oxygen, such as superoxide, on cells. Although the theory dominated the field of ageing research for over fifty years, it still leaves gaps in that field of research (Beckham and Ames 1998).

Most evidence for ageing mechanisms is related to a reduced ability to repair and maintain the cell, however, Gershon and Gershon (2000) note that often there is poor distinction and confusion made between primary causes of ageing and secondary age-associated phenomena. Experimentation is also laboratory-based negating environmental influences on the subject, affecting the experiment outcome. It is still uncertain to what extent the mechanisms governing ageing are genetically determined.

The mechanism of the actual ageing process remains elusive. The current theories show ageing to be a multi-factorial process governed by a multitude of parallel and often interacting processes. Many are controlled jointly by a combination of genetic and environmental factors.