In Lennon’s own’s words:
http://www.youtube.com/watch?v=mJCzjF7MvpM
and from http://onenoteahead.blogspot.com/2007_03_01_archive.html:
While Lennon’s deliberate feedback is generally acknowledged to this day as his innovation and the first appearance of such a gimmick on a rock record, the rest of the aforementioned elements were somewhat less original. In George Harrison’s own words, “The guitar riff was actually influenced by a record called ‘Watch Your Step’ by Bobby Parker. But all riffs in that tempo have a similar sound.” [1]
Lennon, who is credited with devising the “I Feel Fine” riff, was more forthright and less defensive than his former bandmate: “’Watch Your Step’ is one of my favorite records. The Beatles have used the lick in various forms. The Allman Brothers used the lick straight as it was.” [1]
Dan Dubelman 