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Women not only outlive men in normal times, but also during the worst of circumstances, such as famines and epidemics, according to a study which challenges the notion that females are the weaker sex. This advantage in times of crisis may be largely due to biological factors such as genetics or hormones, researchers said. Most of the life expectancy gender gap was due to a female survival advantage in infancy rather than adulthood, they said. In times of adversity, newborn girls are more likely to survive, the researchers found. The fact that women have an edge in infancy, when behavioural differences between the sexes are minimal, supports the idea that explanation is at least partly biological, they said. Led by researchers at the University of Southern Denmark and Duke University in the US, the team analysed mortality data going back roughly 250 years for people whose lives were cut short by famine, disease or other misfortunes. The data spanned seven populations in which the life expectancy for one or both sexes was a dismal 20 years or less. Among them were working and former slaves in Trinidad and the US in the early 1800s, famine victims in Sweden, Ireland and the Ukraine in the 18th, 19th and 20th centuries, and Icelanders affected by the 1846 and 1882 measles epidemics. The researchers discovered that, even when mortality was very high for both sexes, women still lived longer than men by six months to almost four years on average. Girls born during the famine that struck Ukraine in 1933, for example, lived to 10.85, and boys to 7.3 - a 50 per cent difference, researchers said. When the researchers broke the results down by age group, they found that most of the female survival advantage comes from differences in infant mortality.
Newborn girls are hardier than newborn boys. The results, published in the journal PNAS, suggest that the life expectancy gender gap can not be fully explained by behavioural and social differences between the sexes, such as risk-taking or violence. Instead, the female advantage in times of crisis may be largely due to biological factors such as genetics or hormones. Estrogens, for example, have been shown to enhance the body's immune defences against infectious disease. "Our results add another piece to the puzzle of gender differences in survival," the researchers said.
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