This article came out a year and a half ago (January 2007) and unfortunately for me, I was able to read just today. I suggest you read the entirety of the article. It may sound sexist, but actually, no. Well, at least I don't find it that way. Basic idea is women do not need to be funny whilst men need to have that ability in order to be in the evolutionary contest.
Hitchens : Why Women Aren't Funny
April 2008, Alessandra Stanley had a counter article. In this article, what Stanley basically says is that women are and can be funny.
Who Says Women Aren’t Funny?
So what does Hitchens do? Make a rebuttal video!