Traditional aging theories: which ones are useful?

Many theories have been proposed for answering two questions on aging: “Why do we age?” and “How do we age?” Among them, evolutionary theories are made for interpreting the evolutionary advantage of aging, and “saving resources for group benefit” is thought to be the purpose of aging. However for saving resources, a more economic strategy should be to make the individuals over reproduction age undergo a rapid death rather than undergo aging. Biological theories are made for identifying the causes and the biological processes of aging. However, some of them including cell senescence/telomere theory, gene-controlling theory, and developmental theory, have unfortunately ignored the influence of damage on aging. Free-radical theory suggests that free radicals by causing intrinsic damage are the main cause of aging. However, even if intracellular free radicals can cause injuries, they may be only associated with some but not all of the aging changes. Damage (fault)-accumulation theory predicts that the intrinsic faults as damage can accumulate and lead to aging. But the reality is that, an unrepaired fault cannot possibly remain in a living organism, since it can destroy the structural integrity of a tissue and cause a rapid failure of the organism. Therefore, these theories are untenable on interpreting aging. Nevertheless, among them, the developmental theory and the damage (fault)-accumulation theory are more useful than others, because they emphasize the importance of damage and body-development in aging. Some physical theories are also useful by pointing out common characteristics of aging process, such as loss of complexity, increase of entropy, and failure of information-transmission. An advanced aging theory should be a theory that can include all of the useful ideas in these traditional theories.