Proto-Euphratean is a hypothetical unclassified language or languages which was considered by some Assyriologists (for example Samuel Noah Kramer), to be the substratum language of the people that introduced farming into Southern Iraq in the Early Ubaid period (5300-4700 BC).
Benno Landsberger and other Assyriologists argued that by examining the structure of Sumerian names of occupations, as well as toponyms and hydronyms, one can suggest that there was once an earlier group of people in the region who spoke an entirely different language, often referred to as Proto-Euphratean. Terms for "farmer", "smith", "carpenter", and "date" (as in the fruit), also do not appear to have a Sumerian or Semitic origin.
Linguists coined a different term, "banana languages," proposed by Igor Dyakonov and Vladislav Ardzinba, based on a characteristic feature of multiple personal names attested in Sumerian texts, namely reduplication of syllables (like in the word banana): Inanna, Zababa, Chuwawa/Humbaba, Bunene etc. The same feature was attested in some other unclassified languages, including Minoan. The same feature is allegedly attested by several names of Hyksos rulers: although Hyksos tribes were Semitic, some of their names, like Bnon, Apophis, etc. were apparently non-Semitic by origin.
Peter Z. Revesz used a computational science data-mining method to analyse the Sumerian vocabulary. A dichotomy of the cognate associations of the Eme?ir and the Emesal dialects was found, "with the former having mostly Dravidian and the later mostly Uralic cognates, indicating that Sumerian arose by the combination of two languages from those language families."
Rubio challenged the substratum hypothesis, arguing that there is evidence of borrowing from more than one language. This theory is now predominant in the field (Piotr Michalowski, Gerd Steiner, etc.).