Fieldtrip Conversations

This past week I went on a geology fieldtrip for a class I didn't take. It was five days of driving, hiking/rock stops, and eating out. There was one professor (M), three students who took the class (D, C, S) one of who is another girl, and me. All of us knew each other before. Probably the least degree of previous association was me and the professor.
We had quite a few conversations (not surprisingly) and I was struck by who talked when. The topic seemed like it had a lot more to do with who talked rather then the situation (hiking, driving, or eating).
Below I list the five most common topics and then the order in which it felt like we participated in the conversation.

Rocks (specifically granites)
M, S, C, D, R
History (mostly war)
M, C, R, D, S
Religion (we are all LDS)
R, M, C, D, S
Movies/books (predominately classics)
M, D, R, C, S
Music
D, M, C, S, R

It is unsurprising that our professor talked the most about the rocks, he was teaching us stuff, and it is also unsurprising that he was one of the most frequent conversationalists in general, because he did drive the whole time and thus even if some of the rest of us were napping if there was a conversation he was generally a part of it.
The rest of us talked, it appears, roughly in order of knowledge about the subject. Hence, I spoke least about rocks and music and most about religion and books/history.
Anyway, some random thoughts. I'm sure other things affected it too (natural talkativeness, position in the car, etc). But it was intriguing.