Turkish is a member of the Turkish, or Western, subgroup of the Oghuz languages, which includes Gagauz and Azeri. The Oghuz languages form the Southwestern subgroup of the Turkic languages, a language family comprising some 30 living languages spoken across Eastern Europe, Central Asia. and Siberia. Some linguists believe the Turkic languages to be a part of a larger Altaic language family. About 40% of Turkic language speakers are Turkish speakers. The characteristic features of Turkish, such as vowel harmony, agglutination, and lack of grammatical gender, are universal within the Turkic family and the Altaic languages. There is a high degree of mutual intelligibility between Turkish and the other Oghuz languages, including Azeri, Turkmen, Qashqai, Gagauz, and Balkan Gagauz Turkish.