Newborn girls are
hardier than newborn boys during famines, epidemics
Duke University
Women today tend to
live longer than men almost everywhere worldwide -- in some countries by more
than a decade.
Now, three centuries
of historical records show that women don't just outlive men in normal times:
They're more likely to survive even in the worst of circumstances, such as
famines and epidemics, researchers report.
Most of the life
expectancy gender gap was due to a female survival advantage in infancy rather
than adulthood, the researchers found. In times of adversity, newborn girls are
more likely to survive.
The fact that women
have an edge in infancy, when behavioral differences between the sexes are
minimal, supports the idea that explanation is at least partly biological, the
researchers say.
Led by Virginia Zarulli, an assistant professor at the University of Southern Denmark, and James Vaupel, a research professor at Duke University, the team analyzed 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
United States 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.
In Liberia, for
example, freed American slaves who relocated to the West African country in the
1800s experienced the highest mortality rates ever recorded. More than 40
percent died during their first year, presumably wiped out by tropical diseases
they had little resistance to. Babies born during that time rarely made it past
their second birthday.
Another group of
people living in Ireland in the 1840s famously starved when a potato blight
caused widespread crop failure. Life expectancy plummeted by more than 15
years.
Overall 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 percent difference.
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 suggest
that the life expectancy gender gap can't be fully explained by behavioral 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 defenses against infectious disease.
"Our results add
another piece to the puzzle of gender differences in survival," the
researchers said.
The findings were
published Jan. 8, 2018, in the early online edition of Proceedings of the
National Academy of Sciences.
