Relationship between Metabolic Rate, Free Radicals, Differentiation and Aging: A Unified Theory

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Abstract
There is presently no single, widely accepted, unifying theory of aging that is applicable to a wide spectrum of organisms. This fact has led many gerontologists to believe that mechanisms of aging may differ in various phylogenetic groups, albeit no compelling evidence or a priori reason has been forwarded to support this view. Given the basic similarity of molecular and cellular processes in living systems, it is indeed more probable that the contrary may be true, and that the underlying causal mechanisms of aging are essentially similar in all organisms. Conceptually, theories of aging can be assigned to two fundamentally different schools. One view regards aging as a continuation of the process of differentiation involving a programmed “shutdown” of genomic activity or a sequential activation of specific genes whose products have deleterious effects on cellular functions. Alternatively, aging is postulated to be a direct or indirect product of metabolic damage arising from the inadequacy of protective and reparative mechanisms.