Most historians have suggested that Sumer was first permanently settled between c. 5500 and 4000 BC by a West Asian people who spoke the Sumerian language (pointing to the names of cities, rivers, basic occupations, etc., as evidence), a non-Semitic and non-Indo-European agglutinative language isolate. In contrast to its Semitic neighbours, it was not an inflected language.
Others have suggested that the Sumerians were a North African people who migrated