The fourth chapter of Bonk, "The Upsuck Chronicles" addresses the question of whether or not the female orgasm has anything to do with fertility. A couple of weeks ago, I actually read an article from Popsci that addresses the question of whether or not the female orgasm actually has some sort of purpose in regards to fertility or if it's simply "an evolutionary accident". The article even refers to Kim Wallen, who is one of the scientists that Roach interviews in her book.
Here's a link to the article:
PopSci: What is the Point of the Female Orgasm?