Women tend to live longer than men. There are traditional explanations: Men smoke more. They drink more. They tend to engage in riskier behavior.
But the fact that this lifespan gap holds true regardless of country or century indicates something deeper is also at play. A growing body of evidence suggests that women’s relative longevity may derive, in part, from having double X chromosomes, a redundancy that protects them against harmful mutations.
That theory was further bolstered Wednesday with the publication of the most sweeping analysis to date of the lifespan differences between males and females in more than 1,000 mammal and bird species.
“From a human standpoint, it’s really remarkable that women live longer across almost every country in the world,” said Johanna Staerk, an evolutionary demographer at the Max Planck Institute for Evolutionary Anthropology in Germany. “So we were interested at looking at this from a broader taxonomic perspective.”
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The “heterogametic sex hypothesis” holds that if something goes haywire with a gene on one of a woman’s X chromosomes, her cells have a spare to rely on. But men, with only a single X chromosome, have no such reinforcements. The same sort of problem may happen with a male’s unpaired Y chromosome.
In men, “if there’s any deleterious mutations or any mutations that will reduce the lifespan, you don’t have a backup,” said Fernando Colchero, who is also with the Max Planck Institute.
Colchero and Staerk cautioned that chromosomes don’t tell the whole story. Scientists don’t know exactly which genes on the X and Y chromosomes are important for longevity, they said.
Read the full story: Why do women outlive men? A study of 1,176 species points to an answer. (WaPo)
