近日,刊登在新一期美国《国家科学院院刊》上的一项新研究表明,人类死亡率的显著下降仅仅发生在4代人身上,而且之前世代的幼年死亡率比现在的死亡率高了约200倍。
目前,随着低死亡率国家在避免人类死亡方面取得持续的进展,大部分国家人民的预期寿命在增长,很多地方甚至已经超过了80岁。迄今为止,卫生和经济等因素对死亡率下降的影响已经得到广泛的关注,但是对人类死亡率延展性的观察还未被放置在一个广泛的进化背景中进行。
德国马克斯·普朗克人口统计学研究所的Oskar Burger及其同事们试图通过对比各种人类种族死亡率进化剖面图来定量死亡率下降的速度和数量,他们使用现代狩猎—采集者——他们的生命史能够反映出过去世代的生命史——的死亡率数据,把近年来人类死亡率的下降放到了一个更广泛的进化背景中来研究。
研究结果显示,30岁的狩猎—采集者与72岁的日本人的死亡概率相同——这让72岁成为了新的30岁。此外,与一些生活在工业化国家的人们的死亡率相比,狩猎—采集者的平均死亡率更接近人类活着的最近亲属——黑猩猩。
然后,这组研究人员把人类的这种寿命的延长与在选择性繁殖成更长寿命的果蝇的寿命延长进行了比较。他们发现,人类长寿的能力是空前的。同时,研究人员指出,这些结果还提示死亡率的下降可能不是来源于基因的修改,而是来源于环境。
并且,这种死亡率下降的情况大部分发生在1900年以后,只经历了大约4代人。
这些发现挑战了现有的衰老理论,现有理论假定有害而可能致命的突变导致了生育年龄之后人类的死亡率的加速。而这组研究人员表示,还需要额外的研究来理解是什么让人类死亡率具有如此的可塑性,并且检验这种可塑性的限度。(生物谷Bioon.com)
doi:10.1073/pnas.1215627109
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Human mortality improvement in evolutionary context
Oskar Burgera,1, Annette Baudischa, and James W. Vaupel
Life expectancy is increasing in most countries and has exceeded 80 in several, as low-mortality nations continue to make progress in averting deaths. The health and economic implications of mortality reduction have been given substantial attention, but the observed malleability of human mortality has not been placed in a broad evolutionary context. We quantify the rate and amount of mortality reduction by comparing a variety of human populations to the evolved human mortality profile, here estimated as the average mortality pattern for ethnographically observed hunter-gatherers. We show that human mortality has decreased so substantially that the difference between hunter-gatherers and today’s lowest mortality populations is greater than the difference between hunter-gatherers and wild chimpanzees. The bulk of this mortality reduction has occurred since 1900 and has been experienced by only about 4 of the roughly 8,000 human generations that have ever lived. Moreover, mortality improvement in humans is on par with or greater than the reductions in mortality in other species achieved by laboratory selection experiments and endocrine pathway mutations. This observed plasticity in age-specific risk of death is at odds with conventional theories of aging.