Linguists realised from the 17th century onwards that the language spoken by these people, the Goidelic languages, was a branch of the Celtic languages. This is usually explained as a result of invasions by Celts from the continent. However, other research has postulated that the culture developed gradually and continuously, and that the introduction of Celtic language and elements of Celtic culture may have been a result of cultural exchange with Celtic groups in southwest continental Europe from the Neolithic to the Bronze Age.[12][13]