“in northern India, rivers in general have early Sanskrit names from the Vedic period, and names derived from the daughter languages of Sanskrit late… - Michael Witzel

So far archaeology and palaeontology, based on multi-variate analysis of skeletal features, have not found a new wave of immigration into the subcontinent after 4500 BCE (a separation between the Neolithic and Chalcolithic populations of Mehrgarh), and up to 800 BCE.

“Right from the beginning, in Ṛgvedic times, elaborate steps were taken to insure the exact reproduction of the words of the ancient poets. As a result, the Ṛgveda still has the exact same wording in such distant regions as Kashmir, Kerala and Orissa, and even the long-extinct musical accents have been preserved. Vedic transmission is thus superior to that of the Hebrew or Greek Bible, or the Greek, Latin and Chinese classics. We can actually regard present-day Ṛgveda recitation as a tape recording of what was composed and recited some 3000 years ago. In addition, unlike the constantly reformulated Epics and Purāṇas, the Vedic texts contain contemporary materials. They can serve as snapshots of the political and cultural situation of the particular period and area in which they were composed. […] as they are contemporary, and faithfully preserved, these texts are equivalent to inscriptions. […] they are immediate and unchanged evidence, a sort of oral history ― and sometimes autobiography ― of the period, frequently fixed and ‘taped’ immediately after the event by poetic formulation. These aspects of the Vedas have never been sufficiently stressed […]” (WITZEL 1995a:91).

“It must be underlined that just like an ancient inscription, these words have not changed since the composition of these hymns c.1500 BCE, as the RV has been transmitted almost without any change […] The modern oral recitation of the RV is a tape recording of c.1700-1200 BCE.” (WITZEL 2000a:§8).