history of doubt

Since I'm on a plane every weekend, I listen to podcasts, music, books on tape, etc, a lot. One radio show I like is Speaking of Faith. I thought the episode entitled "A History of Doubt" was both intriguing and educational. The author is not religious. She describes famous doubters such as Aristotle, etc. One thing that I thought was interesting was her discussion on cynics, epherists (sp?), skeptics, and the such. I was not aware, before, for instance, that the source of the word cynic comes from dog-like.