I'm no literary historian, but I can't see how poetry can have come before prose (Benjamin, above, quoting Rousseau). Surely prose is simply the standard use of written language as a communication medium, which would have followed on from pictorial representations, while poetry requires innovations like rhythm, couplets, division into stanzas etc.

Rousseau may have been right that "feelings speak before reason". But since when has feeling required, exclusively, poetry for its expression? You stub your toe, you'll vent your feelings in the most expressive way, but it's hardly going to be poetry.

Mind you, Rousseau spouted a lot of nonsense anyway.