Women tend to live longer than men in most parts of the world, a new study reviewing the mortality rates of both sexes has revealed.
The study examined mortality rates over the past 250 years and found that women tend to outlive men when famine or disease strikes.
Researchers from Duke University and the University of Southern Denmark analysed data from seven populations who had an average life expectancy of less than 20 years.
The populations included slaves in Trinidad and the United States in the 1800s, famine victims in Ireland and Ukraine, and Icelanders affected by two measles epidemics in 1846 and 1882.
They found that in all populations "women had lower mortality across almost all ages, and, with the exception of one slave population, they lived longer on average than men."
Girls living in Ukraine during the 1933 famine had a mortality rate of 10.85, while the boys lived to the average age of 7.3.
After the Irish potato famine, life expectancy for both sexes dropped from the average 38 years to 18.17 for men and 22.4 for women.
"Most of the female advantage was due to differences in mortality among infants: baby girls were able to survive harsh conditions better than baby boys," the study, led by Professor Virginia Zarulli and Professor James Vaupel, concluded.
They said that women's maternal instincts could be considered life-saving, noting that many mothers had taken extreme measures to save their children.
Biological differences between the two sexes also played a role, the researchers suggested. They pointed out that the female sex hormone oestrogen has anti-inflammatory qualities and has been shown to enhance the immune system's ability to ward off infections. Testosterone has been linked to an increased risk in heart failure, the study noted.
"Our results add another piece to the puzzle of gender differences in survival," the researchers said. The findings were published in the January edition of the Proceedings of the National Academy of Sciences on 8 January.