Freakonomics Calendar, May 21

"In countries like China, India, and Pakistan, there are millions more men than women. What is to blame: selective abortion, infanticide, bride-burning, and other forms of misogyny? The economist Emily Oster argues that, while all these factors are in part responsible, the problem is also due to a virus: when a pregnant woman has Hepatitis B, she is far more likely to have a baby boy than a baby girl."