Why Do Single Mothers Give Birth to More Girls Than Boys?

[petrochile]

I have picked up this week's edition of The Economist and they had this article in it, explaining, or should I say trying to figure out why single mothers birth more females, which is the opposite of the world's ratio. Here is the link to it:

http://www.economist.com/science/displaystory.cfm?story_id=3308514