The highest life expectancy recorded for women anywhere in the world has risen by a year every four years since 1840. This inexorable advance in longevity is, arguably, the most important of all the changes to human life in the past two centuries.

These gains in health are also widely shared: “India today has a higher life expectancy than Scotland in 1945 — in spite of a per-capita income that Britain had achieved as early as 1860.” This remark comes from a wonderful book, The Great Escape: Health, Wealth, and the Origins of Inequality, by Princeton University’s Angus Deaton, published last year, which documents the revolution in both health and wealth since the early 19th century. Of the two, the former is the more important. Who would not give up many material comforts if, in return, they could avoid the agony of watching their children die or enjoy the company of their loved ones in old age?

No blessing is unmixed. Prolonged survival “sans teeth, sans eyes, sans taste, sans everything” is to be neither envied nor desired. Yet the revolution in health is still a blessing. As Professor Deaton notes: “Of all the things that make life worth living, extra years of life are surely among the most precious.” Someone whose standard of living is twice as high and expects to live twice as long as someone else could even be deemed to be four times better off.