If females and males are in the same environment, in general, females will live longer. It’s a common theme throughout the animal kingdom. Scientists have tested whether it is the X chromosome or the ovary that is important. Using a genetic trick, they created mice with one or two Xs, with either ovaries or testes.9 Those with a double dose of the X lived longer, even if they had testes and especially if they didn’t, thus proving once and for all that female is the stronger sex.
