It's a known fact that women, on average, live longer than men do by about 5.4 years.
A team of researchers writing for Science Advance explained the phenomenon. "Both scientists and the general public have long been intrigued by the relatively large and consistent differences in survival between women and men," they wrote.
The October 2025 study is called: "Sexual selection drives sex difference in adult life expectancy across mammals and birds."
- "Across human cultures and historical periods, women, on average, live longer than men, a pattern best understood from a comparative evolutionary perspective," they wrote.
- "Like humans, 72% of mammals exhibited a female life expectancy advantage, while 68% of birds showed a male advantage, as expected from the harmful effects of sex chromosomes described by the heterogametic sex hypothesis."
- "Although the magnitude varies, the direction of this effect is nearly universal in human populations regardless of historical, cultural, or social context."
But why?
The Researchers Found an Answer for the Question: Why Do Women Live Longer Than Men, on Average?
The researchers analyzed "adult life expectancy in 528 mammal and 648 bird species in zoos."
According to Psychology Today, the researchers found, "In 381 out of 528 mammalian species (72%), male animals died younger than female animals."
From this research, the experts were able to tease out an explanation for the gender disparity. "The factor that explained most of the result pattern was whether a species was monogamous or non-monogamous," wrote Psychology Today.
In species that were not monogamous, the female death age advantage was high, whereas in monogamous species it was limited.
Thus, the findings indicate that the "males may show risky behavior that may endanger survival (e.g., fighting with other males) to mate with females," according to Psychology Today.
The Experts Studied the 'Sexual Selection Hypothesis' to Explain Gender Differences in Life Expectancy
According to the study, the findings strengthen what is called the "sexual selection hypothesis."
"The sexual selection hypothesis posits that individuals (often males) may prioritize competition for mating or fertilization opportunities over survival, either through investing in sexually selected traits like ornaments or larger body size (i.e., precopulatory competition) or through the production of high quantity and quality ejaculates (i.e., postcopulatory competition)," the study says.
"The intensity of sexual selection is expected to be lower in socially monogamous than in polygynous species, where the costs of monopolizing access to mating opportunities can greatly reduce survival."
Before the current research, "evidence of the direct effect of sexual selection on sex differences in life expectancy from studies in the wild remains inconclusive," the study found.
There were some exceptions to the results. One involved lemurs.
(Photo by Rasid Necati Aslim/Anadolu via Getty Images)
"Lemurs, despite being predominantly nonmonogamous, showed negligible ALE (average life expectancy) differences, confirming observations in wild populations. Lemurs appear to be exceptional among primates, exhibiting balanced sex ratios, a lack of SSD, female social dominance, and genital masculinization," the study concluded.
"Of the two hypotheses we tested, we found that the social mating system, typified as social monogamy versus nonmonogamy (i.e., polygynandrous, polyandrous, promiscuous, or polygynous mating systems), was the most consistent correlate of ALE differences across both mammals and birds," the researchers wrote.
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