A distinctive feature of Southeast Asia is its cultural diversity. Of the six thousand languages spoken in the world today, an estimated thousand are found in Southeast Asia. Archeological evidence dates human habitation of Southeast Asia to around a million years ago, but migration into the region also has a long history. In early times tribal groups from southern China moved into the interior areas of the mainland via the long river systems. Linguistically, the mainland is divided into three important families, the Austro-Asiatic (like Cambodian and Vietnamese), Tai (like Thai and Lao), and the Tibeto-Burmese (including highland languages as well as Burmese). Languages belonging to these families can also be found in northeastern India and southwestern China.