Research Sheds Light on Why Women Live Longer Than Men—and Why This Pattern Will Likely Continue

Scientists studied hundreds of mammal and bird species to shed light on sex-based lifespan differences

October 15, 2025

A male and female olive baboon Martha Robbins

On average, females live longer than males almost everywhere in the world, and have done so throughout most of history. While stereotypes suggest many possible reasons, a team of researchers employed scientific methods to investigate the evolutionary, biological and environmental causes behind this enduring sex difference in lifespan across hundreds of species worldwide.

They detail their results in a study published earlier this month in Science Advances.

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According to World Bank data, Hong Kong, whose residents can expect to live until around 86, is the longest-lived economy in the world. Monaco takes second, with a life expectancy of 85.

“From a human standpoint, it’s really remarkable that women live longer across almost every country in the world,” Johanna Stärk, lead author of the study and an evolutionary demographer at the Max Planck Institute for Evolutionary Anthropology, tells the Washington Post’s Dino Grandoni. “So we were interested at looking at this from a broader taxonomic perspective.”

To do so, Stärk and her colleagues undertook the most comprehensive analysis of sex differences in mammal and bird lifespans known to date, studying 1,176 species in zoos around the world. Their results revealed that in 72 percent of mammals, females lived longer than males—and females of those species had a 12 percent longer life expectancy, on average. In 68 percent of bird species, however, males lived longer—an average of 5 percent longer than females.

Though there were many exceptions, this data supports the “heterogametic sex hypothesis,” which holds that the sex with matching sex chromosomes lives longest. Among mammals, females have two X chromosomes. Males have one X chromosome and one Y chromosome and are thus the heterogametic sex. In birds, it’s the opposite—females are the heterogametic sex.

Western lowland gorillas, presumably a mother with her baby — Western lowland gorillas in Loango National Park in Gabon Martha Robbins

According to the hypothesis, the heterogametic sex has a survival disadvantage. If a male mammal’s sole X chromosome has a mutation, he has no genetic backup, study co-author Fernando Colchero, an ecologist at the Max Planck Institute for Evolutionary Anthropology, explains to Amarachi Orie at CNN. “Those mutations will eventually be harmful and reduce your longevity,” he adds. Females might benefit because of their additional X chromosome.

Avian sex chromosomes are ZZ for males and ZW for females. This might give male birds the genetic advantage, since they have two of the same sex chromosome.

The study also suggests that mating behaviors are involved in the lifespan gap. In mammal species where males mate with multiple females and thus face strong competition, females live longer than males. In monogamous bird species, however, there’s less competition, and females frequently die before males. Sex differences in lifespan were smallest in monogamous species, whereas polygamous species and those with starkly larger males had generally longer-lived females.

This aligns with the assumption that the striking physical characteristics males develop to mate—be they colorful plumage, weapons or large body size—help them reproduce but shorten their lifespans. Male deer, for example, are polygamous, bigger than females and grow antlers during the breeding period to fight off other males and attract females. Yet they are shorter-lived than female deer. Males face “an evolutionary pressure … to be able to pass to the next generation as many genes as they can,” Colchero tells NPR’s Allison Aubrey. “But that comes at a cost.”

The researchers also found that the sex most involved in raising offspring tends to have a greater lifespan. In longer-lived species, this could be an evolutionary benefit, ensuring that females live long enough for their young to become independent or sexually mature.

According to one theory, environmental risks like predators, disease and difficult climates affect sex-based differences in lifespan. But the researchers found sex differences in longevity even in zoos, where animals are protected from these risks. This is reflected in humans, where medical advances have narrowed the gap in lifespan, but not eliminated it.

The research is “impressive” and “expands our knowledge of the complex interplay of factors that contribute to sex differences in adult lifespan,” Zoe Xirocostas, an ecologist at the University of Technology Sydney in Australia who was not involved in the study, tells CNN.

Overall, the study suggests, evolutionary processes influenced by mating and parental behaviors, along with environmental risks and sex chromosomes, seem to drive sex-based differences in lifespan. As such, the lifespan gap between males and females will probably continue to persist, they write. “At least in terms of sex differences in survival,” they conclude, “our species is not unique.”

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