Ann Althouse has a theory which she blogs about from time to time, that any scientific studies which show a difference between men and women, must show women in a positive light. Here is another data point to help prove her theory:

For years, researchers have observed that when women are faced with periods of economic or environmental distress, the number of male babies born, in comparison to females, declines. But why this happens is not known.

Now, researchers think they have figured it out - and they say it has more to do with the promise of the future than the stressful realities of the day.
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In 2003, he compared the number of male live birth rates in East and West German hospitals from 1946 to 1999.
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Under normal circumstances the sex ratio should be just above or just below 100.

According to Catalano, the East German dip was the probable result of the country's 1991 economic collapse. West Germany, which didn't experience the collapse, didn't show a corresponding anomaly.
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Researchers have long known that males tend to be weaker than females, as fetuses, embryos, children and adults. Indeed, it's not until people reach their 90s that men start outliving females, Catalano said.

It's also been shown that more male fetuses and embryos are spontaneously aborted than females. This becomes particularly apparent after six weeks of gestation.

So this is saying that men are "weaker" at all stages of life than women, and therefore more likely to be spontaneously aborted during gestation. All stages of life? Really? Where is that coming from? Imagine the outcry that would occur if anyone were to dare suggest the opposite though. It is certainly an interesting topic though. Maybe women just have a genetic disposition to giving birth to girls, and are subconsciously murdering their boy babies in utero!