The ED period is the first for which it is possible to say something about the ethnic composition of the population of Lower Mesopotamia. This is due to the fact that texts from this period contained sufficient phonetic signs to distinguish separate languages. They also contained personal names, which can potentially be linked to an ethnic identity. The textual evidence suggested that Lower Mesopotamia during the ED period was largely dominated by Sumer and primarily occupied by the Sumerian people, who spoke a non-Semitic language isolate (Sumerian). It is debated whether Sumerian was already in use during the Uruk period.