Okay, this is now a phenomenon, in the Hegelian sense that for something to happen, it has to happen twice. The last two classes in which I've taught Darwin have provoked strong reactions. Students have walked out. I can only conclude that this is to do with some perceived threat to their view.
The first instances were in my survey class in Spring 2009. So few people came to the Darwin classes (it was the only hard copy set text, everything else was online), that I guessed it could only mean one thing. The new cases are from my Literature and the Environment classes (podcasts now on iTunes U). I saw people actually getting up and leaving in the middle of the lecture. There must have been about three of them. Then there were the people who didn't show up, and the people who dropped.
Wow. A two hundred year old guy still knows how to clear a room.