In 1920, at the end of the last major pandemic, global life expectancy was just over 40 years. Today, in many parts of the world, human beings can expect to live twice as long. How many of those extra years came from vaccines, the decrease in famines, or widespread use of seatbelts? Looking deeper into the science and statistics, Steven Johnson tells an inspiring story of brilliant thinkers bolstered by strong systems of public support, and of activists fighting for meaningful reform.