So I decided to go back to the horse's mouth and look up the notes from the Folkways Pete Seeger box set (notes by Guy Logsdon and Jeff Place). And the answer is - Pete doesn't know either.

"The origin of this American folksong remains unknown; however, Pete speculated that, 'Like many an American song, this seems to have been built out of a fragment of an old English ballad or sea song.' Later, he indicated that he believed that it might have 'been influenced by or passed through West Indian musical idioms.' It is an easily remembered and sung song. Guthrie T. Meade believed that it was related to 'The Sailor Boy' (Laws K12)."

Forever a mystery, I guess. But we tried.

Dan