Frederik Kortlandt

"Indo-European is a branch of Indo-Uralic which was radically transformed under the influence of a North Caucasian substratum when its speakers moved from the area north of the Caspian Sea to the area north of the Black Sea (…). As a result, Indo-European developed a minimal vowel system combined with a large consonant inventory including glottalized stops, also grammatical gender and adjectival agreement, an ergative construction which was lost again but has left its traces in the grammatical system (...)."