Study shows stress results in stronger boys

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) – Populations of boys born in
stressful times enjoy an advantage their whole lives, living
longer, on average, than males born in times of peace and
prosperity, U.S. researchers reported on Monday.

The study adds to earlier findings that pregnant women are
more likely to miscarry male fetuses than females fetuses
during times of stress.

It shows that this tendency to miscarry males has a culling
effect, said Ralph Catalano of the School of Public Health at
the University of California, Berkeley, who led the study.

“The populations are hardier because they lost the weak
ones earlier,” Catalano said in a telephone interview.

“No individuals got stronger — it’s just that the weak
ones aren’t there.”

The findings, published in the Proceedings of the National
Academy of Sciences, also solidify what biologists have long
known — that males are the weaker sex.

“That’s one thing I can say,” Catalano said.

“Statistically, it is clearly true. Compared to men,
(women) are biological fortresses.”

Catalano and colleague Tim Bruckner were following up on
the earlier studies that showed fewer boys are born during
times of stress, such as economic recessions or depressions and
natural disasters.

They used data from Sweden, which has a database of birth,
life and death information dating back to 1751. Demographers
have certified that the database can be extrapolated to the
global population in absence of more precise information from
other regions.

EVEN RATIO

On average, around the world, about 105 boys are born for
every 100 girls. But males are more likely to die young in
general, and by the time couples are courting the ratio is
fairly even.

Except after hard times.

There are two competing theories as to why, Catalano said.
One was that a stressed pregnant woman produces more of a
hormone called cortisol, which in turn damages fetuses.

Damaged fetuses are frequently miscarried. “Because male
fetuses are more fragile than female fetuses, they are more
likely to be damaged,” Catalano said.

Cortisol often makes a male fetus kick and squirm, and a
second theory holds that a mother’s body will miscarry a male
fetus that does not kick or wiggle strongly enough and which
is, presumably, weak.

“It’s not in her evolutionary interest to have a weak son
in times of stress,” Catalano said. “He may not survive or may
not be competitive for females.”

Both theories predict that fewer boys would be born, but
they would have different long-term outcomes, Catalano said.
Either all the male fetuses are damaged a little, and the boys
who are born are weakened, or the miscarriage process culls the
weak fetuses and leaves the strong ones.

So they looked at the data. In Sweden, after the most
stressful times such as a famine, men’s lives were four months
longer than in happier times.

“The weak boys got culled out and those boys that survived
are hardier on average. They live longer,” Catalano said.

For an individual, this might be a small difference but
over a population it is significant, Catalano said.

Catalano said he has seen the same effects in action today.

“In California after 9-11 we reported that the sex ratio in
California went down,” he said. “Many more males than you would
expect died after September 11 in utero.”

Similar effects were seen after the collapse of East
Germany in 1991, he said, when unemployment soared in the
former socialist state.