I am not sure if anyone can pinpoint where it all started, but personally i'm not voting for The Real World although that definitely was groundbreaking and served as a model for many to follow it (as well as create a superpower production team). If you want to track genre roots you can look at An American Family which was first broadcast on PBS on January 11, 1973 (and of course arguments can be made for Candid Camera which premiered in 1949) but i think the current "Realitymanianeurosis" began/morphed with shows like Donahue, Oprah, Jenny Jones, Jerry Springer (his early days as well as his latter days), Sally Jesse Raphael, etc.
An American Family, in case you've never heard of it, and many haven't, was televisions very first reality show and it was shot documentary style (yes a reality tv show all the way back in 1973--i was only seven years old--were you even alive?--much of the MTV generation wasn't) The show was twelve episodes long and chronicled seven months in the life of the Loud family: Bill and Pat; and their five children: Lance; Kevin; Grant; Delilah; and Michele. The program was widely criticized as it challenged conventions of the day; the oldest son, Lance, was openly gay; and marital tension (and perhaps the stress of being filmed?) eventually led to marital dissolution. This was true reality.
Anyway, I remember, back in the day, over a decade ago, before this whole thing exploded i was expounded (and i do expound/ramble so well--as i'm sure you've noticed) on a walk (back in my fore-mentioned careless days) home from work with a friend about the (then) current seeming trend of people WANTING to air ALL of their dirty laundry on the talk shows, or in the case of Jerry Springer duke it out. I philosophied in my oh so elegant (in my own mind) some kind of secular form of confession and think i might of even formed some kind of linkage back to Madonna in her early days and catholic background.
(and isn't it just a bit ironic that i'm here now rambling on about this theory on a public blog...)
soon there will be so many people on reality t.v. there won't be anyone left to watch...