Thanks Jack Campin for the information. So 'social Darwinism' is not really relevant to Sharp setting out his approach.

However, I think Darwinism on its own is. He clearly thought that the nations of Europe were inherently different in such a way that nature, if not interfered with by nurture, could produce different national folk musics. He was writing at a time when the history books had stories of how the indo-european tribes had spread, with the dark-haired Celts of Wales, the red-haired Scots and the Scandinavian blonds having their places on the map.

I am not sure how much it matters that he was wrong so long as when reading him we understand that he thought that way.