Shahrestani Parvin, Mueller Laurence D, Rose Michael R
Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697-2525, USA.
Curr Aging Sci. 2009 Mar;2(1):3-11. doi: 10.2174/1874609810902010003.
Human mortality data show stabilization in mortality rates at very late ages. But human mortality data are difficult to interpret because they are affected by changing medical practices and other historically variable causes of death. However, in the 1990s, data from a variety of labs showed that the mortality rates of medflies, fruit flies, wasps, yeasts, and nematodes also stabilize at very late ages. These reproducible "mortality-rate plateaus" forced biologists to develop theories for their existence. There are two main theories of this kind. "Lifelong heterogeneity" theories suppose that highly robust subcohorts are more abundant at later ages because less robust subcohorts have mostly died off. On this type of theory, aging does not stop; aging continues inexorably in all individuals. In contrast, in evolutionary theories for mortality-rate plateaus, based on the eventual plateaus in Hamilton's Forces of Natural Selection at late ages, aging does indeed stop. A variety of experiments have cast doubt on lifelong heterogeneity theories as explanations of mortality-rate plateaus. A few experiments have corroborated the Hamiltonian theory. This has the important corollary that it appears to be possible for aging to stop, at sufficiently late ages, at least among some populations. The implications of this result for aging research are profound. Most importantly, it suggests the possibility that the physiology of adults undergoing aging may be substantially different from the physiology of life after aging.
人类死亡率数据显示，在高龄阶段死亡率趋于稳定。但人类死亡率数据难以解读，因为它们受到医疗实践变化及其他历史上可变的死亡原因影响。然而，在20世纪90年代，来自多个实验室的数据表明，地中海果蝇、果蝇、黄蜂、酵母和线虫的死亡率在高龄阶段也会稳定下来。这些可重复的“死亡率平台期”促使生物学家为其存在提出理论。这类理论主要有两种。“终生异质性”理论认为，高度强健的亚群体在晚年更为丰富，因为较弱健的亚群体大多已经死亡。在这类理论中，衰老不会停止；衰老在所有个体中无情地持续。相比之下，在死亡率平台期的进化理论中，基于汉密尔顿自然选择力在晚年最终达到平台期，衰老确实会停止。一系列实验对将终生异质性理论作为死亡率平台期的解释提出了质疑。一些实验证实了哈密顿理论。这有一个重要的推论，即至少在某些群体中，衰老在足够晚的年龄似乎有可能停止。这一结果对衰老研究的影响意义深远。最重要的是，它表明正在衰老的成年人的生理学可能与衰老后的生命生理学有很大不同。
