ABSTRACT
Considerations of natural selection suggest that life span maximization is not a significant evolutionary priority.
Animals in the wild must survive at least long enough to reproduce in a highly competitive environment. Survival hinges on the ability to fight or escape from predators, recover from physical trauma, tolerate toxins in food, subdue infectious microbes, and optimize energy storage and expenditure to endure long periods of starvation. The need to allocate energy resources to these various challenges diverts at least some resources from maintenance functions. Among important maintenance functions is the prevention of, and recovery from, chronic, inevitable damage. Such damage can arise from a variety of nonphysiologic reactions in tissues, including reactions of macromolecules with reducing sugars (glycation) and other aldehydes, oxidants, alkylation by methylating agents, and spontaneous hydrolytic processes. Even if some of the products of these reactions are transient, they can exert adverse effects on organisms. Incomplete repair of damaged macromolecules could well lead to the cumulative effects that characterize aging. No single damage mechanism like oxidative damage is likely to fully explain the aging phenomenon — an “understanding” of aging may prove to comprise a ranking of the various damage (and incomplete repair) processes that characterize life.
