Parsons Peter A
La Trobe University, Bundoora, Victoria, 3083, Australia.
Biogerontology. 2007 Apr;8(2):225-31. doi: 10.1007/s10522-006-9064-4. Epub 2006 Nov 3.
The primary determinant of survival during aging is the energetic efficiency and metabolic stability required to counter the accumulated internal and external stresses of a lifetime. Hence, genetically stress-resistant individuals should accumulate with age; frailer, less robust, less energetically efficient and less metabolically stable individuals should succumb in parallel. This selection process implies the accumulation of energetically efficient stress-resistant individuals with age to the exclusion of all others. High additive genetic variability for survival is expected under extreme circumstances, however there is limited evidence close to the absolute extremes of life that diversity may fall. At this stage, only a few highly adaptive, oxidative-stress-resistant and presumably somewhat homozygous genotypes should remain. Therefore a fall in variability may occur in these outliers, when frailer individuals are unable to cope and are eliminated at extreme ages. This process could provide an explanation of mortality-rate declines in domesticated (laboratory) and free-living populations of the extremely old. That is, mortality-rate declines may be an expectation from a process of genetic sorting resulting from the accumulated responses to environmental stress over time. Application of an ecological stress theory of aging, which combines the external stresses to which organisms are exposed with internal stresses, appears to be the prerequisite for this conclusion.
衰老过程中生存的主要决定因素是应对一生积累的内外部压力所需的能量效率和代谢稳定性。因此,具有遗传抗逆性的个体应随年龄增长而积累;而体质较弱、不够强健、能量效率较低且代谢稳定性较差的个体则应相应地减少。这种选择过程意味着随着年龄增长,能量效率高且具有抗逆性的个体不断积累,其他个体则被淘汰。在极端情况下,预计生存具有高加性遗传变异性,然而,接近生命绝对极限时,多样性可能下降的证据有限。在这个阶段,可能只剩下少数高度适应性强、抗氧化应激且可能有些纯合的基因型。因此,当体质较弱的个体在极端年龄无法应对并被淘汰时,这些极端个体的变异性可能会下降。这一过程可以解释极老龄家养(实验室)和自由生活种群死亡率下降的现象。也就是说,死亡率下降可能是长期积累的对环境压力的反应导致基因筛选过程的结果。应用结合了生物体所面临的外部压力和内部压力的衰老生态应激理论,似乎是得出这一结论的前提条件。