Ageing thesis

The actual time of death or total longevity of an organism is determined either by the innate rate of physiological decline or by the rate of ageing and also by the severity of the extrinsic challenges destabilizing its homeostatic balance. Ageing is a highly complex phenomenon whose proper understanding involves the elucidation of many processes besides those involved in debilitation during the post reproductive phase (Sohal, 1985). According to the view of Rockstein and Miquei (1973), the lifespan of all metazoan animals can be subdivided in to four major stages; viz successful fertilization and embryonic development, growth, maturation and senescence. They defined senescence as the sum total of all those changes in structure and function which are deleterious and degradative in nature. It ultimately results failure of the individual to survive and thereby in the death.