Across almost every country on Earth, women outlive men. But the reason may not be what you think.
For years, scientists believed the difference came from genetics. Men have one X and one Y chromosome, while women have two Xs. That extra copy was thought to protect women from harmful mutations. But a massive new study published in Science Advances in October 2025 reveals a deeper story that spans 1,176 species and millions of years of evolution.
Fast Facts
- Study: Conducted by the Max Planck Institute for Evolutionary Anthropology, published in Science Advances (2025).
- Scope: Analyzed over 1,100 species of mammals and birds to uncover lifespan patterns between sexes.
- Key Finding: Female mammals live around 13% longer than males, while male birds live about 5% longer than females.
- Main Driver: Sexual selection and mating behavior play a larger role in lifespan than chromosomes alone.
- Takeaway: Evolution favors endurance and care over competition, shaping how long different sexes live.
What Scientists Found About Lifespan Differences
An international team led by the Max Planck Institute for Evolutionary Anthropology studied more than 1,100 mammal and bird species using data from both zoos and wild populations. They wanted to know if the male–female lifespan gap seen in humans also appeared across the animal kingdom. The results were striking.
Among mammals, including humans, females lived on average 13 percent longer than males. Among birds, however, males lived about five percent longer than females. Even in zoo conditions, where animals are safe from predators and harsh weather, the pattern persisted. That meant the cause was not just danger or disease but built into biology and behavior.
“Lifespan differences between males and females stretch across species, driven by genes, mating strategies, and parenting roles,” explained the research team from the Max Planck Institute for Evolutionary Anthropology. “Even without environmental stress, biology keeps the gap alive.”
Researchers found the key lies in sexual selection, how animals compete for mates. In species where males battle or show off to win partners, they often die younger. Males that invest in muscle, bright colors, or weapons like horns pay a price in energy, stress, and injury. Females, who often focus more on survival and care, tend to live longer.
Not Just Chromosomes, It’s Behavior Too
For decades, scientists pointed to the “heterogametic sex hypothesis.” It said the sex with two different chromosomes, XY in male mammals and ZW in female birds, should live shorter lives. But this study found that only partly true.
Some species break the rule completely. In many birds of prey, for example, females are both larger and longer-lived than males. That means chromosomes alone cannot explain the full story. Behavior, body size, and how each sex invests in reproduction also play major roles.
Lead author Johanna Stärk noted, “Some species showed the opposite of the expected pattern. 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.”
Species with strong male competition, like deer, lions, and seals, show the widest lifespan gaps. In contrast, animals that form lifelong pairs, such as many songbirds and humans, show much smaller differences.
In simple terms, fighting for love shortens life. Evolution rewards risk-takers with mates but not always with time.
What This Means for Humans
Humans follow the same pattern found in most mammals. In nearly every country, from Sri Lanka to Japan to Sweden, women live longer than men. Globally, the gap is about five years.
Our closest relatives, chimpanzees and gorillas, show the same trend. Female apes usually outlive males, especially in the wild. Interestingly, the difference is smaller in humans. Scientists think that is because over time, human societies reduced dangerous male competition and improved maternal health and child care.
These patterns began long before modern medicine. They come from ancient trade-offs between competition and survival, choices written into our biology by evolution.
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Read the Full StoryWhy It Matters
This research reshapes how we understand aging. It shows that lifespan differences are not fixed by DNA alone. They depend on how each sex spends energy, whether fighting rivals or raising families.
When males compete aggressively, they burn energy faster and face more risks. In species where both parents share care equally, lifespans are more balanced. Among humans, better healthcare and gender equality can narrow the gap even further.
Evolution set the foundation, but culture and environment still shape the outcome.
Lessons from the Animal Kingdom
The study uncovered fascinating exceptions. Some species flip the pattern completely. Female eagles and hawks, for example, live longer even though they are larger and more dominant. That shows that size is not the only factor. Hormones, diet, and parenting styles matter too.
Even within a single species, conditions can change the results. Animals in zoos live longer overall, but the difference between males and females becomes smaller. With safety, steady food, and less stress, the biological cost of competition fades but never disappears.
How Evolution Still Shapes Our Health
While this study looks at animals, it connects deeply to human life. Men today still face higher risks from heart disease, stress, and risky behavior. These tendencies trace back to ancient instincts that once helped ancestors compete for mates and status.
Women, meanwhile, often benefit from stronger immune systems and social networks that improve survival. Yet modern life is shifting these patterns. Health systems, education, and changing gender roles are helping men live longer. Biology explains how the gap started, but society determines how it continues.
The Bigger Evolutionary Picture
Evolution does not aim for long life, it aims for successful reproduction. For many species, that means males evolved to take risks to pass on their genes, even if that costs them years. Females evolved to protect offspring until they could survive alone, so longevity became an advantage.
“Pre-copulatory sexual selection seems to play a fundamental role in shaping sex differences in life expectancy in mammals and birds,” said Stärk. “It’s not only about who survives longer, but why certain reproductive strategies come at a biological cost.”
As lead researcher Johanna Stärk explains, “Sexual selection doesn’t end with reproduction, it shapes how long we live.” The struggle for mates, it turns out, leaves lasting marks on survival.
What We Can Learn
Human longevity is part of a story far older than civilization. The balance between risk and care still guides how we live. By understanding that link, societies can close lifespan gaps through better health, reduced stress, and shared caregiving.
Nature’s lesson is simple: the fight to impress may win attention, but cooperation helps species endure.
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Read the Full StoryEvolution’s Quiet Message
Women’s longer lives are not luck, they are evolution’s reward for endurance. This study reminds us that every life carries traces of ancient choices. Long before hospitals and technology, nature had already written the rules of survival. Those who balance strength with care live the longest.
Source:
Staerk, J., Conde, D. A., Tidière, M., Lemaître, J.-F., Liker, A., Vági, B., Pavard, S., Giraudeau, M., Smeele, S. Q., Vincze, O., Ronget, V., da Silva, R., Pereboom, Z., Bertelsen, M. F., Gaillard, J.-M., Székely, T., Colchero, F. (2025). Sexual selection drives sex difference in adult life expectancy across mammals and birds. Science Advances, 11(40). DOI: 10.1126/sciadv.ady8433.