In his first book, The Birth of Tragedy out of the Spirit of Music, Nietzsche claims that tragic drama, as a practice, emerged from an originally solely-musical chorus. First people sang story-songs, especially dithyrambs, and then later came dialog and characters as the subjects of the songs.
(There's also a lot about Apollinian and Dionysian cultures, and the role of aesthetics in justifying the existence of the world, and so on, but I don't want to get into any of that.)
How has this purely historical thesis held up? Is there any kind of modern consensus on how early tragedy evolved?