- Mammals vs. birds: Of the 1,176 species analyzed, female mammals lived an average of 13 percent longer than males. In contrast, among birds, males lived about five percent longer than females.
- Mating strategies matter: In species where competition for mates is intense — as is true for most mammals — males tend to die younger. In species that form monogamous pairs, such as many birds, males often outlive females.
- Zoo comparisons: The gap between male and female lifespans is greater in wild populations than in zoo environments. This pattern indicates that both genetics and external conditions influence how long each sex lives.
Across nearly every country and historical era, women tend to live longer than men. While medical advances and improved living standards have reduced this gap in some places, new findings suggest the difference is deeply rooted in evolution and unlikely to vanish. Similar patterns appear across many animal species, hinting that the roots of longevity go far beyond modern life.
A team of scientists led by the Max Planck Institute for Evolutionary Anthropology in Leipzig, working with 15 collaborators around the world, carried out the largest and most detailed analysis ever of lifespan differences between male and female mammals and birds. Their results offer fresh insight into one of biology’s most enduring questions: why do the sexes age at different rates?
Longevity: A question of chromosomes?
In most mammal species, females live longer — for example, female baboons and gorillas often surpass males in age. But this pattern reverses in other groups. In many birds, reptiles, and insects, it is the males that have longer lifespans. One possible explanation, known as the heterogametic sex hypothesis, links these differences to sex chromosomes. Mammalian females possess two X chromosomes, while males have one X and one Y (making them the heterogametic sex). Having a pair of X chromosomes may shield females from harmful mutations and extend their lifespan. In birds, the system is reversed: females are the heterogametic sex.
Using data from more than 1,176 mammal and bird species in zoos around the world, researchers observed a striking contrast that supported this hypothesis. In most mammals (72 percent), females lived longer, by an average of twelve percent. In most bird species (68 percent), males were the longer-lived sex, averaging five percent longer lifespans. Yet the pattern was far from universal. “Some species showed the opposite of the expected pattern,” explained lead author Johanna Stärk. “For example, in many birds of prey, females are both larger and longer-lived than males. So sex chromosomes can only be part of the story.”
How mating and parenting shape longevity
In addition to genetics, reproductive strategies also play a role. Through sexual selection, males in particular develop conspicuous characteristics such as colorful plumage, weapons, or large body size, which increase reproductive success but can shorten lifespan. The new study supports this assumption: In polygamous mammals with strong competition, males generally die earlier than females. Many birds, on the other hand, are monogamous, which means that competitive pressure is lower and males often live longer. Overall, the differences were smallest in monogamous species, while polygamy and pronounced size differences were associated with a more pronounced advantage for females.
Parental care also plays a role. The researchers found evidence that the sex that invests more in raising offspring — in mammals, this is often the females — tends to live longer. In long-lived species such as primates, this is likely to be a selective advantage: females survive until their offspring are independent or sexually mature.
Zoo life reduces — but does not erase — lifespan gaps
A long-held idea suggests that environmental pressures, such as predators, disease, and harsh weather, drive differences in male and female lifespan. To test this, the scientists turned to zoo populations, where such risks are minimal. Even in these safe conditions, lifespan gaps persisted. Comparing zoo and wild data showed that while the differences were smaller in captivity, they rarely disappeared altogether. This pattern mirrors the human experience: better healthcare and living conditions may shrink the gap between men and women, but do not erase it.
Taken together, the findings indicate that lifespan differences between males and females are deeply embedded in evolution. They are shaped by sexual selection, parental care, and genetic factors linked to sex determination. The environment influences how large these gaps become but cannot remove them entirely. These contrasts between the sexes are not simply a product of circumstance — they are woven into our evolutionary past and are likely to persist far into the future.
