The limit to human longevity: an approach through a stress theory of ageing

Survival to old age is enhanced by high vitality and resilience associated with substantial physiological and morphological homeostasis. This is underlain by genes for stress resistance, which confer high metabolic efficiency and hence adaptation to the energy costs of the stresses to which free-living populations are exposed. Under the stress theory of ageing, selection for genes for stress resistance is primary, and achieved life-span is secondary. In some human populations of the modern era, selection for stress resistance is less intense than in earlier times, because of adequate nutrition and reduced exposure to environmental stresses. Such relaxed selection should permit the accumulation of deleterious mutants that are likely to be stress sensitive. Accordingly, increased maximum life-span in future human populations would appear difficult to achieve.