Across nearly every culture and historical period, women tend to live longer than men.
While modern medicine and better living conditions have helped reduce this gap in some countries, new research suggests that the difference is rooted deep in evolution—and likely to continue for generations to come.
This pattern is not just seen in humans. It also appears in many animals, which tells scientists that the reasons behind it go far beyond lifestyle and into biology itself.
A large team of scientists from the Max Planck Institute for Evolutionary Anthropology in Germany, along with researchers from 15 other institutions around the world, recently carried out the biggest study ever looking at how male and female lifespans compare in mammals and birds.
They gathered data from over 1,100 animal species kept in zoos worldwide. Their findings help answer a long-standing question in science: why do males and females age differently?
One theory looks at chromosomes. In mammals, females have two X chromosomes, while males have one X and one Y. The idea, called the “heterogametic sex hypothesis,” suggests that having two X chromosomes helps protect females from harmful mutations, which might help them live longer. But in birds, the roles are reversed.
Female birds are the ones with two different sex chromosomes (called Z and W), while males have two Z chromosomes.
In many bird species, it’s the males who live longer. The researchers found support for this idea: in 72% of mammal species, females outlived males by about 12%. Meanwhile, in 68% of bird species, males lived about 5% longer than females.
Still, the researchers say chromosomes are only part of the story. There were many exceptions. For example, in birds of prey, females are often both larger and longer-lived than males. This suggests that other forces, like behavior and reproduction, also influence how long an animal lives.
Another important factor is how animals reproduce. In species where males have to compete for mates—such as in many polygamous mammals—males often have large bodies or special features like antlers or bright colors.
These traits can help them win mates, but they also put stress on the body and can shorten lifespan. In contrast, many bird species are monogamous, and males don’t have to compete as much, so they tend to live longer.
Parental care also matters. In species where one sex spends more time raising the young, that sex often lives longer. In mammals, this is usually the female. For animals like primates, who care for their babies for a long time, it’s a big advantage for females to live longer—at least until their children are grown.
The researchers also wanted to test if outside dangers like predators and disease cause the lifespan gap. To do this, they studied animals in zoos, where such risks are very low.
Even in these safe environments, the lifespan differences between males and females still existed. This shows that the gap is not only caused by the outside world. It comes from deep biological patterns that are hard to erase.
In summary, this study suggests that the differences in lifespan between males and females are deeply rooted in evolution. They are shaped by a mix of genetic factors, mating behavior, and parental care roles.
While the environment can make these differences bigger or smaller, it doesn’t erase them. These patterns have been with us for a long time, and they will likely remain in the future.
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The study is published in Science Advances.
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