A real quote, from the introduction to a real paper, submitted and accepted in a real graduate degree program at a university whose name has been concealed to protect the innocent: "In the course of this dissertation, I will demonstrate that the great body of folkloric musical material that is regarded as indigenous, which is to say, fundamentally created within the context of the musical/cultural milieu, spanning the temporal and geographical limits that are through custom and common practice regarded to comprise the British Isles, can, in most cases, be demonstrated to have originated within those same strictures, with the exception of similar materials that have been established to come from either adjecent or remote geographical locations, and that have subsequently been integrated into the common canon."

if you missed that, I'll summarize-- he found that nearly all British Isles songs are from the British Isles, unless they are from somewhere else.