LEIPZIG — Across human societies and throughout the animal kingdom, a persistent pattern emerges: females and males age at different rates. Now, the most comprehensive analysis to date reveals the evolutionary roots of this phenomenon, tracing why female mammals typically outlive their male counterparts while the reverse proves true among birds.
An international research team led by scientists from the Max Planck Institute for Evolutionary Anthropology has uncovered compelling evidence that lifespan differences between the sexes are deeply embedded in our evolutionary past. Their study, published in 2025, analyzed data from 1,176 mammal and bird species worldwide.
Key Findings from the Research:
Chromosomal Influence: The "heterogametic sex hypothesis" received significant support. In mammals, where females have two X chromosomes and males are XY, females lived longer in 72% of species studied, with an average 12% lifespan advantage. In birds, where females are the heterogametic sex (ZW chromosomes), males lived longer in 68% of species, averaging 5% longer lifespans.
Mating Strategy Impact: Species with intense male competition for mates showed pronounced male lifespan disadvantages. Polygamous mammals with significant size dimorphism displayed the largest gaps, while monogamous species showed minimal differences.
Parental Care Connection: The sex investing more in offspring rearing—typically female mammals—tends to live longer, particularly in long-lived species like primates where survival until offspring maturity provides evolutionary advantage.
Environmental Effects: When comparing wild populations to protected zoo environments, lifespan gaps persisted but diminished, indicating that both genetic and external factors influence longevity differences.
"The pattern we observed across hundreds of species demonstrates that sex differences in lifespan aren't simply products of modern human behavior," explained lead author Johanna Stärk. "They're woven into the fabric of evolution through complex interactions between genetics, reproductive strategies, and environmental pressures."
The research confirms that while improved living conditions and healthcare may reduce lifespan disparities between men and women, the underlying evolutionary mechanisms ensure these differences are unlikely to disappear entirely.