Last year marked the 350th anniversary of the modern concept of life expectancy, which grew out of a correspondence between two brothers in 1669. Not only did life expectancy emerge as the first important nongambling application of the then new doctrine of chances, the correspondence also contained a probability‐based distinction between the median value of a random variable and its expected value, and it set the stage for the first correct formulation of pensions and life annuities. After 350 years, life expectancy remains a gauge of long‐term progress of a country, of subpopulations within a country, and as an international measure of development. On this round anniversary, it is worth remembering the original correspondence and its value today because of the importance of the concept of life expectancy itself and because of the mathematical structure that was used to define it.

中文翻译：

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预期寿命是350岁

去年是现代预期寿命概念诞生350周年，该概念源于两个兄弟在1669年的对应关系。预期寿命不仅成为当时新的机会主义的第一个重要的非赌博性应用，而且还包含基于概率的随机变量中位数与其预期值之间的区别，这为首次正确制定养老金和人寿年金奠定了基础。在350年之后，预期寿命仍然是衡量一个国家长期进步，衡量一个国家内部人口以及衡量发展的国际标准。在这周年纪念日