Females live longer, usually.

The most comprehensive analysis to date has given us a better grasp of why, on average, women tend to live longer than men.

Average global life expectancy is around 74 years for women and 68 years for men. One popular belief is that women are protected against potentially harmful mutations in the sex-determining chromosomes, but the picture is far from complete.

Mammals with two copies of the X chromosome are genetically female, while a male has two different sex chromosomes X and Y. The theory goes that females are better protected against harmful chromosome mutations because the second copy of the X chromosome acts as a backup.

To delve deeper, researchers at the Max Planck Institute for Anthropology in Germany looked for clues from other animals, analysing data on life expectancy  in 1,176 species – 528 mammals and 648 birds in zoos and in the wild. Among the mammals females lived on average 12 to 13 per cent longer than the males, while for birds among 68 per cent of the species males tended to outlive females by on average some five per cent because male birds have two identical chromosomes (Z).

Mating systems also play a part. Male polygamous mammals with strong competition for mates generally seem to die earlier. This could explain why the male advantage enjoyed by birds is considerably lower than the female advantage among mammals.

The sex investing more in raising offspring also tended to live longer. In primates including humans this probably has an evolutionary advantage as it helps females survive until their offspring are sexually mature.