I would not care, eg, if the IA-s could be shown to emerge from the proto-Masai culture of E-Africa. - Michael Witzel

"In Europe, river names were found to reflect the languages spoken before the influx of Indo-European speaking populations. They are thus older than c. 4500-2500 B.C. (depending on the date of the spread of Indo-European languages in various parts of Europe)... “in northern India rivers in general have early Sanskrit names from the Vedic period, and names derived from the daughter languages of Sanskrit later on" (WITZEL 1995a:104-105).

“River names in northern India are thus principally Sanskrit, with few indications of Dravidian, MuNDa or Tibeto-Burmese names. However, Kosala, with its uncharacteristic -s- after -o- may be Tibeto-Burmese (Sanskrit rules would demand KoSala or KoSala, a corrected form that is indeed adopted in the Epics).” ... To sum up, what does the evidence of hydronomy tell us? Clearly there has been an almost complete Indo-Aryanisation in northern India; this has progressed much less in southern India and in the often inaccessible parts of central India. In the northwest there are only a few exceptions, such as the names of the rivers GangA, SutudrI and perhaps KubhA.” (p 106-7)

Other evidence, from Mitanni and neo-Hittite sources, indicates that the names of Mitanni kings were traditionally Indo-Aryan, even though the Mitanni belonged to the Hurrian-speaking peoples. We therefore surmise that the Mitanni once lived close to an early Indo-Aryan group, that had perhaps taken a dominant position over the pre-Mitanni population, and then became quickly acculturated as Hurrian speakers.