Stu, I think you hit the nail on the head. The way I figure, 30,000 years ago or so, one loan human being was quite a tasty treat for a sabre-tooth tiger. But a whole messload of human beings in a group meant even the mighty wooly mammoth had to be afraid. In other words, there's safety in numbers and to be exiled from a group literally meant death. The need to be part of a group has carried over into our behavior today. We take joy in being accepted by a group, but despair if we are an outcast.
However, pack mentality is why I've always been uncomfortable in groups.....the larger the group I'm in, the more I lose my identity as a person and just become one fraction of a group. While the feeling of acceptance and just losing the ability to think for yourself can be a quite pleasant feeling, I still find it to also be an uncomortable feeling to lose my individuality and so I try and stay away from them (I rarely hang out with more then one or two people at a time.)
On the other hand, I think that's why so many people root for sports teams. When you cheer for a team, you automatically become part of a large group who will automatically accept you and the feeling of acceptance and comraderie is a great feeling...until you meet someone who cheers for another team.
I do follow my favorite (American) football team (from home, never been to see them in a stadium) but my lousy brain always mucks things up for me. Whenever "we" lose, I'm always mildly upset, but when "we" win, there's always that nagging voice in the back of my brain that says "why are you happy? you didn't win any money or fame or gold medals by gum, you are just some sap watching people slam into each other on TV." Damned brain...spoiling my fun.
But I digress.
Other notes. Aerial, the same phenomona happens when you are in traffic. You'll always be in the lane that's stopped while another lane is moving. As soon as you switch lanes, the new lane stops and your old lane starts moving...
Oh, about sports fans being fat....well...that's why they are fans and not actual participants.
I figure people enjoy watching sports for the same reason they enjoy watching action movies. You get to vicariously live the actions of a "hero" doing things you can/will never do. Sporting events can have the same elements of a movie...you have the good guy(s) (your team), the bad guy(s) (the other team), drama, action, suspense, etc. I suppose people find it as easy to associate with watching men kick a ball around as with men shooting giant bugs from Klendathu (bonus points to whomever knows what I just referenced)
Ok, enough rambling, I have to pretend I'm working now.