"The global doubling of human life expectancy between 1850 and 1950 is arguably one of the most consequential developments in human history, undergirding massive improvements in human life and lifestyles. In 1850, Americans died at an average age of 30. Today, the average is almost 80. This story is typically told as a series of medical breakthroughs - Jenner and vaccination, Lister and antisepsis, Snow and germ theory, Fleming and penicillin - but...