Why Women Outlive Men Across Species, Reasons Found

A major international study has shown that biological sex differences, not just social or environmental factors, explain why women generally live longer than men. Researchers compared lifespans across over 1,100 mammal and bird species. Female mammals lived roughly 12% longer than males, while in birds, males live about 5% longer. These trends held true even in controlled zoo populations, pointing to an underlying biological cause rather than outside factors like predation or climate.

Chromosomes: The Lifespan Link

The key factor is the chromosomal setup. In mammals, females have two X chromosomes; males have one X and one Y. The extra X allows for compensation if harmful mutations appear, reducing risk for females. In birds, the system is flipped: females are "ZW" and males "ZZ". Here, the ZZ males are slightly longer lived, supporting the overall idea that having a matched pair of sex chromosomes provides a genetic buffer.

Survival also depends on reproductive behavior. In mammals, especially those with high competition for mates, males often invest in growth, aggression, or elaborate displays to attract females. This investment shortens their average lifespan. In birds, where monogamy is more common and both sexes often share parenting, the survival gap between males and females is reduced. When a sex takes on heavier parental care, longevity can increase for that sex, as seen in long-lived birds and primates.

What This Means for Humans

Medical advances have shrunk the life expectancy gap in modern societies, but the divide has not disappeared. The research suggests the underlying genetic and evolutionary factors will continue to influence longevity differences. Scientists hope these findings will help craft better, sex-specific strategies for healthcare and aging interventions in the future.