Hard times are especially hard on pregnant women. Miscarriages go up, as do premature births. The result: fewer baby boys. Economist Ralph Catalano, professor at the School of Public Health at the University of California, Berkeley, showed that for the first time in a 2003 paper in the journal Human Reproduction.

Researchers have known, based on studies going back to the 1970s, that war and environmental disasters can affect the sex ratio, which normally sees to it that about half the babies born are boys and half girls. In times of environmental disaster, women are under stress, which can increase early release of hormones, including cortisol, thought to trigger labor.

Male fetuses are more likely to be miscarried or born prematurely than females, Catalano says, and premature babies are at higher risk of death. So more male fetuses don't make it through pregnancy or die shortly after premature birth.

Stress affects men's reproductive systems, too. Some experts believe stress can slow down sperm motility. That, in turn, might result in fewer Y-chromosome-carrying sperm — normally the faster swimmers that create male babies — reaching the egg.

Catalano wanted to see if bad economic times were like earthquakes, leading to a similar sex ratio imbalance. He looked at the sex ratio in East and West Germany from 1946 to 1999. The two Germanys reunited in 1990, but he found that in 1991, after the collapse of the economy of the former East Germany, fewer boys than normal were born there; the natural balance held in the former West Germany.

"Gestation is very sensitive to the environment," Catalano says. "Fewer males are born." And the effects on reproduction go further than that, he adds. "Coitus is less frequent. One of the principal consequences of economic decline is lowered libido."