From ancient civilizations to modern societies, nearly every country and historical era shows women living longer than men. Medical progress and better standards of living have narrowed this gender gap in some regions, but recent research confirms the difference is deeply embedded in evolution.
Scientists from the Max Planck Institute for Evolutionary Anthropology—in collaboration with a global team—have conducted the most extensive analysis on sex-based lifespan differences in mammals and birds, drawing fresh conclusions about the biological roots and ongoing persistence of this phenomenon.
Chromosomal Clues: How Genetics Shape Lifespan
The “heterogametic sex hypothesis” offers a compelling genetic explanation for why longevity varies between males and females. In mammals, females possess two X chromosomes which provide a backup against harmful mutations, while males have one X and one Y chromosome, making them the heterogametic sex more vulnerable to genetic flaws. Among birds, the situation reverses: male birds have two Z chromosomes and females have Z and W, making female birds typically less resilient genetically.
This chromosomal distinction, confirmed by studying more than 1,176 species in zoos worldwide, appears to play a significant role in determining which sex lives longer. Researchers found that roughly 72% of mammal species had longer-lived females, averaging 12% more lifespan, whereas in 68% of bird species, males lived 5% longer on average.
The Limits of Chromosomal Theory: Not All Species Fit the Mold
While the chromosome hypothesis fits many cases, notable exceptions challenge this simplistic view. Some birds of prey, for example, have females that are both larger and longer-lived than males. The pattern also shifts depending on other biological and social factors, indicating that while chromosomes matter, they form only part of the story. Sex-based differences in longevity emerge from complex connections between genetics and interaction with the environment.
Mating Systems, Sexual Selection, and Lifespan
Mating strategies strongly impact how long each sex lives. In mammals, males in polygamous systems face intense competition, often evolving larger size, more prominent weaponry, or colorful signaling to attract mates. These evolutionary pressures raise the risk of injury, disease, and early death, contributing to shorter lifespans. By contrast, many birds form monogamous pairs, reducing competition and enabling male birds to live longer. Across species, the study found that lifespan differences are smallest in monogamous animals and most marked where polygamy and pronounced sexual dimorphism exist.
The Lifesaving Role of Parental Care
Parental care patterns also influence sex-based longevity. The sex that invests more in raising offspring, traditionally females in many mammalian species, tends to gain extra years of life. In long-lived species such as primates and elephants, females commonly survive to ensure their young reach independence or sexual maturity, creating a biological incentive for extended lifespan. Yet, in animal groups where males play a larger role in nurturing young—like some monkeys and birds—male longevity can surpass female lifespan, illustrating the adaptive nature of parental investment.
Evidence From Zoos Versus The Wild
Environmental hazards such as predators, disease, and harsh climates have long been proposed as reasons why male longevity lags behind. By analyzing zoo populations, where external threats are minimal, researchers found that the longevity gap persists, though it narrows in captivity. This mirrors human experience, where improved living conditions shrink but don’t erase lifespan differences between men and women. Even under optimal circumstances, biology keeps lifespan gaps intact.
Evolution: The Fundamental Driver Behind Lifespan Differences
These diverse findings converge on one key insight: sex-based longevity gaps are woven into evolutionary history. Genetics, sexual selection, and parental care intertwine to shape life expectancy, with the environment acting mostly to magnify or minimize the gap rather than erase it. Some animal species invert the expected pattern—for example, female raptors—showing how adaptation, ecological context, and ancient evolutionary pressures all play a role.
The Future: Longevity Gaps Set To Persist
Most scientists agree that while advances in healthcare and social conditions can shrink sex-based gaps in longevity, evolutionary forces make it unlikely these differences will disappear entirely. Ongoing research continues to unravel the complex interplay between genetics, behavior, environment, and lifespan in humans and other animals. As our understanding of aging advances, so does appreciation for the intricate biological legacy determining how long men and women, and their animal counterparts, are likely to live.
