第七章：人类寿命
Thus far, our examination of aging and longevity has focused on basic biological mechanisms observed in simple eukaryotic organisms. We have been able to construct, with a fair degree of consistency, a hypothesis predicting that longevity evolved in animals and plants, whereas aging reflects a random, or stochastic, phenomenon. Longevity evolved through genes selected for survival to reproductive age. However, the declining force of natural selection with age discourages the fixing of genes that convey an “aging” genotype and phenotype.
As we turn our attention to our own species, we must address a fundamental question: With respect to aging and longevity, have humans followed a pattern of 进化ary development similar to that observed in other, nonhuman populations? It is possible that the 环境, the primary driving force behind Darwin‘s theory of natural selection, has not affected adaptation in humans to the same degree as in other species. Homo sapiens is the only species, with the possible exception of a few nonhuman primates and marine mammals, that has a brain large enough to confer the ability to alter the 环境 to the species' advantage. Altering the 环境 can have a huge impact on survival. The construction of houses and fences or walls provides shelter and keeps out enemies; the making and wearing of clothing provides protection from harsh weather; and the development and use of agriculture prevents starvation. Thus, the possibility exists that because of our manipulation of the 环境, 环境al factors have influenced the origins of our longevity differently than for other species.
This chapter focuses exclusively on human longevity. We begin with an exploration of the origins of human longevity and discuss the theoretical basis for the life span that Homo sapiens has today. Note the use of the phrase “origins of human longevity” rather than “进化 of human longevity.” This is done intentionally, to distinguish Homo sapiens from other species in the archaic Homo genus, such as Homo heidelbergensis and Homo neanderthalensis. Although the genes resulting from 进化ary selection for longevity were carried forward into H. sapiens, our superior intelligence most likely established life-spaand mortality trajectories that differ significantly from those of our Homo predecessors. These trajectories continue to evolve. The second section of the chapter presents some historical and recent observations that test the theoretical basis for the origins of human longevity and life span.
