When do you yawn, and why do you think we yawn?

Inspired by: http://www.fluther.com/disc/62611/why-does-my-cat-yawn-when-i-pet-her/

I was wondering when do people find they yawn the most in their day/week and why do they think they yawn at these times. And I was wondering what are people’s views on the “evolution” of yawning.

Personally I seem to yawn a lot in lectures, and I am not sure if many other people do because I don’t go around watching them. I do not feel bored, as I constantly pay attention to what is going on and actively take notes so I do not think this is the reason. I just believe that it is tiredness as all my lectures are in the morning and shortly after I wake up. However it could be that the lack of things going on in a lecture (just a droney voice and slide and after slide of info) could induce a sleepy stupour just like a trance state. I also yawn at night (like loads of people) when tired which I suppose could link to this.

So yeah, discuss. Also mention if you yawn to this thread like I just did now :D