From larger chromosomes to bigger intenstines, the reasons why women outlive men

Time of India

08-07-2025

Social media is full of memes showing men doing reckless stunts with captions like, 'This is why women live longer than men.' While entertaining, these memes barely scratch the surface of the real reasons behind the gender longevity gap.
According to a new book - 'The Stronger Sex: What Science Tells Us About the Power of the Female Body' of Starre Vartan - the truth is far more scientific—and fascinating.
In an article on CNN, Starre citing numerous studies said that women tend to outlive men, even under extreme conditions like famines, epidemics, and slavery. As per Starre, this trend persists across history and geography, suggesting deep-rooted biological advantages. Genetics, hormones, and even the structure of the female body all contribute to this survival edge.
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She cited a 2018 study published in PNAS, which examined data from seven historical populations affected by crises like the Irish Potato Famine, Icelandic measles outbreaks, and slavery in Trinidad. The study found that women consistently lived longer than men—sometimes even as newborns—under brutal conditions.
So, what gives women this edge?
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The Genetic and Hormonal Advantage
A key factor lies in the
XX chromosome
pairing. Unlike males, who inherit one X and one Y chromosome, females have two Xs. The X chromosome is much larger and carries nearly 10 times more genes, many of which play critical roles in immune function. This genetic surplus provides women with a stronger and more adaptable immune system.
Dr. Sharon Moalem, neurogeneticist and author of The Better Half, notes that this double-X setup allows women to 'out-mutate' men immunologically, giving them an edge in the fight against constantly evolving viruses and bacteria. Estrogen, a hormone found in higher levels in women, also plays a role in enhancing immune responses.
Stronger Immune Responses
Female bodies generally exhibit stronger immune responses—both in the innate system (the first line of defense) and the adaptive system (which targets specific pathogens). Women have higher levels of neutrophils (infection-fighting white blood cells) and more robust B cell activity, allowing them to produce more targeted antibodies and retain immunological memory longer. This makes them better equipped to handle repeat infections and vaccinations.
However, this powerful immunity comes at a cost: women are more prone to autoimmune diseases and are more likely to live with chronic illnesses after surviving conditions that could be fatal to men.
Testosterone: A Risky Trade-Off
On the other hand, testosterone—present in higher levels in males—appears to weaken immune function. Animal studies show that removing testosterone improves immunity, while adding it suppresses it. Evolutionarily, this might be a trade-off: testosterone may boost competitiveness and reproductive success, but it also increases the risk of infections and disease.
Lifestyle Factors Also Matter
Men, on average, are more likely to engage in high-risk behaviors—smoking, heavy drinking, and dangerous activities—and hold more physically hazardous jobs. However, even in populations where men and women live similar lifestyles, women still tend to outlive men, suggesting biology plays the dominant role.
Anatomy Plays a Part, Too
Recent research led by microbial ecologist Erin McKenney and anthropologist Amanda Hale at North Carolina State University uncovered another surprising difference: women's small intestines are significantly longer than men's. Published in PeerJ in 2023, the study found this anatomical trait allows women to extract more nutrients from food—a possible evolutionary adaptation to support pregnancy and breastfeeding.