Why female mammals live longer than males but female birds die first
Male and female Eurasian bullfinch (Pyrrhula pyrrhula). The inheritance mechanism in birds is the opposite of the mammal one. It’s the female who is ‘heterogametic’ — she has both a W and a Z chromosome. Male birds with their second Z, therefore, are less prone to suffer mutation damage than females. And so they live longer.
‘For no man at all can be living for ever, and we must be satisfied’ — Maurya in
The heroine of JM Synge’s 1896 play, set in Inishmaan, has lost her husband and five sons to the sea. News arrives that a body has been washed up in Donegal. The clothing shows it’s that of Michael, another son. Bartley, the last of Maurya’s boys, is sailing to Connemara to sell a horse. He too perishes; a ghost-rider has been seen. "They’re all gone now," says the grief-stricken mother, "and there isn’t anything more the sea can do to me".
Synge depicts a semi-pagan hunter-gatherer world — "It’s little he (the priest) knows about the sea" etc.
Michael’s and Bartley’s lives are cut short, but Cathleen and Nora, their ‘gatherer’ sisters, live on. Not just in Aran, but everywhere else, women live longer than men.
Nor are such difference confined to humans... wild creatures also exhibit variations in lifespan between the sexes. The social insects provide spectacular examples. Female wasps and bees survive the winter but males don’t. Honeybee drones die after participating in a nuptial flight but their mother, the queen, can live on for up to seven years.
But stressful lifestyles can’t always be held responsible; the trials and tribulations of the boardroom and bedroom hardly compare to those faced by Michael and Bartley. Something more fundamental is going on.
Why women live longer than men. A new study @ScienceAdvances by an intl. research team led by Johanna Stärk and Fernando Colchero @MPI_EVA_Leipzig traces the evolutionary roots of the #lifespan gap between women and men. https://t.co/SKVVM3ROZm & https://t.co/uHwqarWtXc pic.twitter.com/Rg0H9RdnQw
— MPI-EVA Leipzig (@MPI_EVA_Leipzig) October 2, 2025
Scientists at Leipzig’s Max Planck Institute have been studying longevity. Lead author Johanna Stärk says that differences in survival between the sexes "are deeply rooted in evolutionary history" and "can be observed in many animal species".
Lifestyle and environment are important, but genes also play a part.
The Max Planck team measured the lifespans of 1,176 wild creatures. Female mammals, the analysis showed, live 13% longer on average than males. The reverse, however, is the case with birds; males last 5% longer.
To control for environmental factors, the researchers compared the longevities of animals in zoos with those of creatures fending for themselves in the wild. Pampered zoo inmates, fed and found, lead relatively stress-free lives. Their wild cousins’ existence, by contrast, is often ‘poor, nasty, brutish, and short’.
Not surprisingly, zoo-dwellers tend to live longest. However, differences in life expectancy between the sexes were less pronounced in zoos than in the wild.
An individual’s gender is determined by the sex chromosomes.
A male mammal possesses both an X chromosome and a Y, whereas a female has two Xs.
Without a second X copy, the male bird is more vulnerable to damage by genetic mutations. The female is less exposed. If one of her Xs becomes impaired; she has the second copy as backup and harm is less likely to occur.
This argument is supported by the bird findings. The inheritance mechanism in birds is the opposite of the mammal one. It’s the female who is ‘heterogametic’ — she has both a W and a Z chromosome. Male birds with their second Z, therefore, are less prone to suffer mutation damage than females. And so they live longer.
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