NO ONE HAS IT HARDER THAN THEIR FATHER DID:

[I]ncome is not the only important measure of human well-being and life chances. Consider two global revolutions that are improving the human condition and making it more equal.

The first is how long people live. In 1751, according to the Human Mortality Database, Sweden's overall life expectancy at birth was barely 38 years. But this was an arithmetic average for a population within which survival prospects were wildly, brutally disparate. Roughly a fifth of all Swedes died in their first year of life; by age 5 only 70 Swedes were still alive of every 100 born. But about half of those who made it to age 5 lived to 60 and beyond.

This dispersion of lifespans means that the distribution of survival was correspondingly unequal. When measuring disparities in income distribution, economists conventionally use the "Gini coefficient." This index runs from 0 (perfect equality) to 1.0 (representing perfect inequality when a single person possesses everything). If we use this metric to assess inequality in Sweden's lifespans in 1751, we get a Gini index of 0.46.

By comparison, the World Bank says the Gini index for income in Mexico in 2010 was 0.47. Lifespans in 18th-century Sweden, in short, were distributed about as unequally as incomes are in Mexico today.

Flash forward to 2011. Sweden's life expectancy at birth was nearly 82 years. The risk of dying in infancy in Sweden today is about 100 times lower than in 1751--and the risk of dying in early childhood is more than 100-fold lower. Today 90% of Swedes can expect to survive to age 65, and more contemporary Swedes live to 86 than to any other particular age. The estimated Gini index for Sweden's inequality in age at death has plummeted to 0.08. Lifespans have never been so long--or so equally distributed--as they are now.

The trend in Sweden holds for the rest of the world. In the early 1870s Italy's life expectancy was under 30 years and the odds of death before age 5 nearly 45%. The estimated Gini index for age at death was 0.56. Today (2009) Italy's life expectancy at birth is about 82 years, and the Gini index for the distribution of national lifespans is as low as Sweden's.

And the U.S.? Life expectancy rose from about 61 years in 1933 to about 79 in 2010. Over those same decades the Gini index for lifespan inequality was cut in half--from 0.22 to 0.11. Despite the ethnic, income and other differences that characterize our society, Americans of all backgrounds have never enjoyed such equality in length of life as we know today.

Detailed, reliable, long-term mortality for most of the world is unavailable. However, the broad pattern for every national population is essentially the same: the higher the life expectancy at birth, the lower the inequality in age at death.

Demographers suggest that life expectancy at birth for the world in 1900 was about 30 years. Today, according to the World Health Organization, the U.N. Population Division and the U.S. Census Bureau, it is about 70.

Given the close correspondence between life expectancy and the Gini index for age at death, we can be confident that the world-wide explosion in life expectancy over the past century has been accompanied by a monumental narrowing of world-wide differences in length of life. When a population's life expectancy rises from 30 to 70, the Gini index drops by almost two-thirds--from well over 0.5 to well under 0.2.

This survival revolution--and the narrowing of inequalities in humanity's life chances--is an epochal advance in the human condition. 

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