The collapse of infant and child mortality

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The single largest component of the modern life expectancy gain, and the reason the headline number moved so far. In pre-transition populations something on the order of a quarter to a third of children died before age five; globally the under-five death rate is now below four percent and in the highest-income countries below half a percent. Because a death at age one removes some seventy or eighty years from the cohort mean and a death at age eighty removes only a few, shifting a death from infancy to old age moves life expectancy at birth enormously while moving the maximum age at death not at all. This is the arithmetic that makes almost every popular longevity claim ambiguous: the same headline supports both "we live much longer" and "old age has barely changed", and both are true of different quantities.