I’ve long been fascinated by one of the most stubborn patterns in biology: males and females rarely live the same length of time. In humans, women nearly always outlive men, with an average advantage of about five years worldwide today. This pattern holds across history, from 18th-century Swedes to contemporary Japanese – though the magnitude of this sex-difference can vary considerably.
Humans are not alone in showing such sex biases in longevity. Across the Tree of Life, sex differences in longevity are widespread, but they are neither uniform nor always female-biased.
