Across the animal kingdom, males and females rarely live the same length of time and this difference has fascinated scientists for decades. In humans, women consistently outlive men by an average of about five years, a pattern that has remained stable from 18th-century Sweden to modern-day Japan. Yet humans are far from unique. From elephants to moose, from lions to birds, the gap between male and female lifespans stretches across the Tree of Life, but not always in the same direction.
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A Major Global Study On Longevity
A groundbreaking study led by evolution researcher Johanna Staerk and published in Science Advances analyzed sex differences in longevity across hundreds of animal species. It was the most comprehensive research of its kind, examining lifespan data from both mammals and birds living in the wild and in zoos. The results revealed that female mammals generally live longer, and that the differences are far more pronounced in the wild than in captivity.
The Female Advantage In Mammals
Among 528 mammal species studied in zoos, about 72 per cent showed females living longer than males – on average, by around 12 per cent. In the wild, where animals face greater environmental pressures, the difference widened to roughly 19 per cent.
Examples from wild populations illustrate this vividly. Female African elephants often live into their 60s, while males rarely survive past their late 40s. Similarly, female moose typically outlive males by nearly double, reaching 17 to 22 years compared to much shorter male lifespans.
Why Females Outlive Males
Researchers point to several biological and behavioral explanations. One key factor is genetics: in mammals, males carry one X and one Y chromosome, meaning they are more vulnerable to harmful mutations carried on the X chromosome. Hormones also play a role – high levels of testosterone can suppress the immune system and increase risky behavior.
However, the strongest evidence lies in sexual selection. In polygynous species, where males compete for groups of females – like red deer and lions – males grow larger, develop weapons such as antlers or manes, and engage in intense fights for mates. These evolutionary pressures come at a cost to longevity.
When The Pattern Reverses In Birds
Birds often defy this rule. In the same study, 648 avian species were analyzed, and in 68 per cent of them, males lived longer than females. In zoos, males had an average lifespan advantage of 5 per cent, but in the wild, the difference exceeded 25 per cent.
Female birds carry ZW chromosomes (making them the heterogametic sex), which may expose them to more genetic risks. Moreover, egg-laying, incubation, and chick-rearing are energetically demanding tasks that can shorten female lifespans.
There are exceptions, though. Raptors such as eagles and buzzards often show females living longer than males. Interestingly, in species like tawny owls, females live longer in the wild but not in captivity – a pattern scientists still cannot fully explain.
Beyond Birds And Mammals
The trend extends to other animal groups in complex ways. Insects, amphibians, and fish display remarkable variation. Female moths and mayflies, for instance, may live only hours or days after laying eggs, while ant and bee queens in colonies can survive for decades thanks to the protection their social structure provides.
Among frogs, males often die younger due to the strain of calling and competing for mates, whereas in some fish species, such as sticklebacks, males sacrifice their lives guarding nests while females live on to breed again.
Humans Fit The Pattern, Mostly
Human data mirror these broader biological patterns. Women in modern societies live longer than men, with the largest gaps seen in countries like Japan, where the difference exceeds six years. Even among hunter–gatherer groups such as the Hadza in Tanzania, women still outlive men.
However, the human female advantage is smaller than in many other primates. Female chimpanzees and gorillas often outlive males by more than a decade, suggesting that the relatively reduced sexual competition in humans may have narrowed the gap.
What Explains The Differences?
Scientists have proposed two main explanations. The heterogametic sex hypothesis suggests that the sex with two different sex chromosomes – XY in mammals and ZW in birds – tends to live shorter lives. Yet this rule doesn’t fit every species, particularly those with unique evolutionary pressures.
The second theory involves life history and sexual selection trade-offs. Animals that invest heavily in reproduction or competition tend to sacrifice longevity. The new study supports this explanation: in mammals where males are significantly larger and more competitive, females live much longer.
The Cost Of Longevity
Living longer does not always mean living better. Among humans, women tend to spend more years in poor health, often with chronic conditions such as osteoporosis or dementia. Similarly, in other species, females may outlive males but experience reduced fertility or physical strength with age. Longevity, it seems, comes with trade-offs.
The Bigger Picture
The differences in lifespan between males and females are not governed by a single biological law but shaped by a complex web of genetics, hormones, behavior, and environment. Across species, it is a story of evolution balancing the costs of survival with the rewards of reproduction—and one that continues to intrigue scientists searching for the roots of life and longevity.
