New research examining over 1,000 species reveals that mating strategies and sex chromosomes shape how long males and females live—and why the gap persists.
Women live longer than men in nearly every country on Earth, a pattern so consistent it seems almost inevitable. Now, researchers have traced this disparity back through evolutionary history, finding that the roots of the longevity gap run far deeper than lifestyle or healthcare alone.
An international team led by scientists at the Max Planck Institute for Evolutionary Anthropology analyzed lifespan data from 1,176 mammal and bird species, drawing on zoo records from around the world. Their findings, published this fall, suggest that sex differences in aging are shaped by millions of years of evolution—and that medical advances, while narrowing the gap, may never fully erase it.
The research offers fresh insight into one of biology’s enduring puzzles, revealing that the forces determining how long we live have been at work across the animal kingdom for millennia.
Chromosomes hold part of the answer
The team found that in 72% of mammal species, females live about 12% longer than males. Among birds, the pattern flips: males outlive females by roughly 5% in 68% of species. This reversal offers a clue.
In mammals, females carry two X chromosomes while males have one X and one Y, making them what scientists call the heterogametic sex. Having a backup X chromosome may protect females from harmful genetic mutations, giving them a survival edge. Birds reverse this setup—females are heterogametic—and males tend to live longer as a result.
But chromosomes tell only part of the story. Lead author Johanna Stärk pointed to birds of prey, where females are both larger and longer-lived than males, defying the chromosomal trend. The pattern holds across species, but exceptions abound, suggesting other forces are at play.
Mating strategies drive lifespan
Sexual selection appears to play a bigger role than genetics alone. In species where males compete aggressively for mates—think gorillas or elephant seals—males typically die younger. They invest energy in traits like size, strength, or elaborate displays, all of which boost reproductive success but carry a cost.
Polygamous mammals showed the widest lifespan gaps, with males dying earlier than females. In contrast, monogamous birds, where competition is less intense, saw males living longer. The researchers found that the smallest differences occurred in species where pairs bond for life, suggesting that when males aren’t battling for dominance, they face fewer survival risks.
The pattern extends across diverse species. In baboons and gorillas, where males engage in fierce competition for mates, females consistently outlive their male counterparts by significant margins.
Parental care shapes women’s longevity
Longevity also tracks with parental investment. The sex that does more caregiving tends to live longer, particularly in species where offspring take years to mature. In mammals, females usually shoulder this burden, and in long-lived species like primates, surviving until young reach independence offers a clear evolutionary advantage.
The pattern suggests that evolution favors longevity in the sex responsible for raising the next generation, embedding the disparity into biology itself. This investment in offspring creates selective pressure for extended lifespan, particularly in species where maternal care extends over years or even decades.
Zoo life reveals genetic influence
To separate nature from nurture, the team compared zoo populations with their wild counterparts. Zoos eliminate many environmental threats—predators, disease, starvation—that might explain sex differences in lifespan. Yet even in captivity, the gaps persisted, though they often shrank.
This mirrors the human experience. Advances in medicine and living conditions have reduced the lifespan gap between men and women in many countries, but haven’t eliminated it. The zoo data suggests that while environment matters, genetics and evolutionary pressures set a baseline that protection alone can’t fully override.
The findings paint a picture of lifespan shaped by ancient forces—sexual selection, parental investment, and chromosomal architecture—that continue to influence how long we live today. The gap between the sexes isn’t just a modern phenomenon or a byproduct of social conditions. It’s written into the evolutionary code of countless species, humans included, and will likely endure as long as those forces remain in play.