Copyright law and the most famous 6 seconds of contemporary music

I'm working on some research regarding copyright laws in the music industry, with a focus on genres when they are emerging (i.e., considered underground). Copyright laws are all about providing incentives for creative development and productive research. One of the big questions about copyright laws, particularly in the arts, is whether they have any retroactive power regarding things created (and not copyrighted) in the past that are being currently adopted and used (often without remuneration).

One of the people I'm working with on this sent me the video below regarding what is likely the most famous 6 second drum break in contemporary music. Its originally by a band called the Winstons and was written in 1969. This 6 seconds made its way through rap and hip-hop, helped found drum & bass and jungle music, and has made its way into advertising.