Women have an average life expectancy that’s about 4 years longer than men’s – regardless of culture or geography. Even among animal species, females outlive males.

Why females have an advantage in the longevity department hadn’t been well understood. In the past, some had assumed it had to do with lifestyle. But scientists say there may be a genetic mechanism underlying this age-old phenomenon. In a new study, researchers found that mice with two X chromosomes lived longer, regardless of