DJ Food's Strictly Kev, from Britain, performed a radio show in 2004 that traced the history of Mashups (or Cut-Ups as they call them on the other side of the pond).
Here's part of the summary:
"On January 18th 2004, Strictly Kev premiered the original 'Raiding The 20th Century' on XFM's 'The Remix' show in London. It was a 40 minute attempt to catalogue the history of cut up music - be it avant garde tape manipulation, turntable megamixes or bastard pop mash ups. "
Click here to go to Ubu.com and download the mp3 of the show.