Urinals..the origin of social networking?

I have always been intrigued and fascinated by the the graffiti in public washrooms. What motivates a person, while standing at a urinal or sitting in a stall, to take a pen or a sharp object and scribble a message on the wall? Then recently, I saw a display on the internet from an artist who photographed grafitti in washrooms. One particular photo of a stall had an extensive discussion going on about abortion. It had, what looked like, hundreds of participants with circles and arrows connecting their message and point of view to previous messages. When I was in Turkey last year, I sat in a public urinal in a colesseum that was built in 300 BC. Evidently, Alexander the Great used it! Anyway, there was grafitti etched in the stone.

It is vary apparent, therefore, that humans have had a strong desire to participate actively in current events and public opinion since before the millenium. What was lacking, in most cases. was the proper medium.

Can it be any wonder then why the recent phenomemon of social networking sites such as Facebook, Twitter, LinkDen, etc have experienced such global acceptance and success? It is also why grafitti (of all kinds), which peaked in the early 90's has been slowly diminishing. About the same time as Facebook and Twitter came on the scene.