I know that I am arguing the what can't be proven; but I could accept culture shift for rise of Celtic culture in Britian except for the appearance of Celtic languages. I can see adopting a better farming method, or a type of decoration that you find attractive, but a whole language? Why? What purpose would it serve? Who would you communicate with? It seems to me that there had to be an influx of various celtic tribes, even if there wasn't an invasion. Also; regarding bagpipes, you know they may have been invented in the middle east, but they are used in the common music of all of the Celtic cultures that remain. Although for some reason, they mostly vanished from the common music of the Celtic peoples that migrated to the new world.