Don, thank you for your most informative post. There's a discussion in another thread (Music and the Brain) as to whether or not music is "necessary for human survival", in light of the mounting evidence that our brains have areas specifically designed for recognizing/remembering musical tones and that these areas are linked to both emotion and memory. I think your post resolves those questions.
IMO the educational roles played by the bards and troubadours in ancient times - using music and rhyme, as you described - were indeed "necessary for human survival". That is, for the evolution of what is unique to our species - our language, culture, religion, philosophy and search for knowledge. Without the 'mnemonic devices" of music and rhyme, human knowledge and history could not have been preserved. And we'd probably still be swingin' thru the trees.
Not that that's a bad idea, some days!