Evolution may explain why women live longer than men

The significant lifespan differences between men and women have intrigued scientists for ages. Recent comprehensive research sheds light on why, on average, women enjoy longer lives than men. This analysis, the most extensive of its kind, evaluates lifespan disparities across various mammal and bird species.

Current global averages reveal that women live roughly 74 years, while men average around 68 years. Several theories have been proposed to explain this trend: young men frequently suffer untimely deaths from accidents or violence, and women may possess a genetic advantage against detrimental mutations due to their XX chromosome makeup, but the reasons remain convoluted.

To explore these discrepancies further, Johanna Stärk and her team at the Max Planck Institute for Evolutionary Anthropology analyzed life expectancy data from 1,176 species—528 mammals and 648 birds—found in both wildlife and zoos.

Findings indicate that in 72% of mammal species, females outlive males by an average of 12 to 13%. Conversely, in 68% of bird species, males have a longer lifespan, living approximately 5% longer than females. These patterns suggest a correlation between genetic factors and longevity.

In mammals, possessing two X chromosomes results in a female phenotype, while males carry an X and a Y chromosome. The presence of a second X chromosome may shield females from harmful genetic mutations, functioning as a protective backup. In contrast, birds display a different genetic model: females have one Z and one W chromosome, while males have two Z chromosomes. This difference further supports the hypothesis that the sex with different chromosomes faces a longevity challenge.

Researchers uncovered some intriguing exceptions. Fernando Colchero, another team member from Max Planck Institute, emphasizes the importance of examining evolutionary factors influencing these disparities. The mating systems of various species are crucial; for instance, in species such as baboons, gorillas, and chimpanzees, where polygamous behaviors prevail, males often die sooner due to heightened competition for mates.

Nicole Riddle from the University of Alabama at Birmingham notes that males in these scenarios frequently develop traits selected by sexual selection—such as larger body size or ornamentation—which are energetically expensive and often lead to risks in male-male competition, detracting from personal survival investments.

This phenomenon affects both mammals and polygamous bird species. Given the role of sexual selection in shaping these characteristics, it appears to clarify why males have a less pronounced lifespan over females in avian populations compared to mammals. Here, both genetic advantages and associated costs of mating behaviors interplay to determine survival outcomes.

Interestingly, Stärk’s research reveals that the sex responsible for greater offspring investment generally enjoys longer lifespans. In mammals, this often favors females who benefit from surviving sufficiently long to nurture and rear offspring until maturity.

However, not all birds conform to established patterns—certain predatory species see larger females engage in territorial defense yet enjoy longer lives. This anomaly presents a fascinating puzzle yet to be solved.

Researchers found that lifespan differences between sexes diminish in captive environments, compared to their wild counterparts, as controlled conditions reduce risks like predation and disease. Such differences might explain the gradual reduction of lifespan gaps among men and women in human populations, although foundational genetic and physiological distinctions between the sexes are likely to persist.

“Despite advancements in medical science, we don’t anticipate complete resolution of these inherent disparities,” states Colchero. “There remain deeply-rooted genetic and physiological variances between genders.”