Why Do Women Outlive Men? Evolution’s Secret Revealed Across 1,000 Species

The study explores the evolutionary origins of the lifespan difference between women and men.

Across the globe, women generally outlive men, a pattern that has persisted throughout history and in nearly every society.

While advances in medicine and improvements in living conditions have narrowed this gap in some parts of the world, researchers suggest the difference is unlikely to disappear anytime soon. The reasons appear to be deeply embedded in evolution and are reflected in many animal species.

A global research team, led by scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig and joined by 15 collaborators from around the world, carried out the most extensive study so far on lifespan differences between males and females in mammals and birds. Their work sheds new light on one of biology’s enduring mysteries: why aging and longevity differ between the sexes.

Longevity: A question of chromosomes?

In most mammal species, females tend to have longer lifespans. For example, among baboons and gorillas, females often outlive their male counterparts.

However, this pattern does not hold true across all animal groups. In many birds, reptiles, and insects, males are actually the ones that live longer. One possible genetic explanation for these differences is known as the heterogametic sex hypothesis, which focuses on variations in sex chromosomes.

In mammals, females possess two X chromosomes, while males have one X and one Y (making them the heterogametic sex). Studies suggest that having two X chromosomes may give females extra protection against harmful mutations, which could contribute to their longer lifespans. In birds, this system works the other way around: females are the heterogametic sex.

Using records from over 1,176 bird and mammal species in zoos worldwide, the researchers found a striking contrast in lifespan, supporting the heterogametic sex hypothesis: in most mammals (72 percent), females lived longer, by an average of twelve percent, while in most bird species (68 percent), males lived longer, overall by an average of five percent. Still, there was remarkable variation with many exceptions.

“Some species showed the opposite of the expected pattern,” says 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.”

Sexual selection and parental care shape lifespan differences

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-standing idea is that environmental pressures—such as predation, pathogens, or harsh climates—drive the observed gaps between males and females. To test this, the researchers turned to zoo populations, where such pressures are largely absent. They found that lifespan gaps persisted even under these protected conditions. Comparing zoo and wild populations showed that the gaps were often smaller in zoos but rarely disappeared—mirroring the human case, where advances in medicine and living conditions have narrowed but not eliminated the lifespan gap.

The findings suggest that sex differences in lifespan are deeply rooted in evolutionary processes—shaped by sexual selection and parental investment, and that genetic differences in the sex determination system may also play a role. Environmental factors influence the extent of the differences, but cannot eliminate them. The differences between the sexes are therefore not only a product of the environment, but part of our evolutionary history – and will most likely continue to exist in the future.

Reference: “Sexual selection drives sex difference in adult life expectancy across mammals and birds” by Johanna Staerk, Dalia A. Conde, Morgane Tidière, Jean-François Lemaître, András Liker, Balázs Vági, Samuel Pavard, Mathieu Giraudeau, Simeon Q. Smeele, Orsolya Vincze, Victor Ronget, Rita da Silva, Zjef Pereboom, Mads F. Bertelsen, Jean-Michel Gaillard, Tamás Székely and Fernando Colchero, 1 October 2025, Science Advances.
DOI: 10.1126/sciadv.ady8433

Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.