 Earlier theories held that these similarities suggest a common racial origin for the various Celtic peoples, but more recent theories hold that they reflect a common cultural and language heritage more than a genetic one.Celtic cultures seem to have been widely diverse, with the use of a Celtic language being the main thing they had in common.Today, the term Celtic generally refers to the languages and respective cultures of Ireland, Scotland, Wales, Cornwall, the Isle of Man, and Brittany, also known as the Celtic nations.