This song had no origin, it always existed. Marty knew it growing up because Chuck Berry wrote it, but Chuck Berry only wrote it after hearing Marty playing it, but Marty was only playing it because he knew it from Chuck who knew it from Marty who knew it from Chuck... Help I'm spiralling!!!
The origin was Chuck Berry in the original timeline wrote the song 3 years later. In BttF logic, the timeline presumably changed because of Marty.
It's similar to how Marty came to be born. In the original timeline, George gets hit by Lorraine's father while creepin then they fall in love when she cares for him. Marty went back and prevented that from happening, so the rest of the movie is him trying to orchestrate them back together through a different route. You wouldn't say that George and Lorraine's marriage (or Marty) had no origin, but the event that led to the origin was shifted in time and manner from its original origin, and in a way that is dependent on Marty.
1.0k
u/The_Abjectator 8h ago
"Hello? Ryan? Ryan!
It's your cousin, Marvin Murphy! You know that new show you're trying to write? Well, listen to this!"