By the end of the fourth millennium B.C. the material culture of Abydos, Ur, or Mohenjo-daro would stand comparison with that of Periclean Athens or … - Vere Gordon Childe

[l]anguage, albeit an abstraction, is yet a more subtle and pervasive criterion of individuality than the culture-group formed by comparing flints and potsherds or the “races” of the skull-measurer. . . . they [the Aryans] must have possessed a certain spiritual unity reflected in and conditioned by their community of speech. To their linguistic heirs they bequeathed, if not skull types and bodily characteristics, at least something of this more subtle and precious, spiritual identity. . . . The Indo-European languages and their presumed parent-speech have been throughout exceptionally delicate and flexible instruments of thought. They were almost unique, for instance, in possessing a substantive verb and at least a rudimentary machinery for building subordinate clauses that might express conceptual relations in a chain of ratiocination. It follows then that the Aryans must have been gifted with exceptional mental endowments, if not in enjoyment of a high material culture. (p. 4)

But as a whole they [Kassites] were not Aryans. Though they adopted the Babylonian language and culture, the local scribes have recorded the Kassite names for god, star, heaven, wind, man, foot, etc. ; not one of these is in the least Indo-European. Moreover, the majority of the personal names of the period ... suggest rather a kinship between the Kassites and the Asianic folk to the north-west. Yet in the names of their kings occur elements recalling Indo-Iranian deities — SuriaS (Sun-god cf . Sans. Surya) IndaS (cf. Sans. Indra)y MaruttaS (cf. Sans. Mantiah, storm-gods) and -bugaS (cf. Iran, baga, god). Moreover, these Kassites introduced the use of the horse for drawing chariots into the Ancient East and its later Babylonian name sitsu seems to be derived from the Indo- Iranian form ^asm (Sans. aim). It is then highly probable that the Kassite invasion was due to the pressure of Aryan tribes on the highlands of Iran, and that its leaders were actually Aryan princes.

These [Mitanni] numerals and divine and personal names are the oldest actual specimens of any Aryan speech which we possess. The forms deserve special attention. They are already quite distinctly Satem forms ; in fact, they are very nearly pure Indic. Certainly they are much more nearly akin to Sanskrit than to any of the Iranian dialects that later constituted the western wing of the Indo-Iranian family. Thus among the deities Nasatya is the Sanskrit form as opposed to the Zend Naonhaitya and all the four gods are prominent in the oldest Veda, while in the Iranian Avesta they have been degraded to secondary rank (Mithra), converted into demons (Indra) or renamed (Varuna =Ahura Mazda). The numerals are distinctively Indic not Iranian ; aika is identical with the Sanskrit eka while ' one ’ in Zend is aeva. So the s is preserved in Satta where it becomes h in Iranian (hapta) and the exact form is found, not indeed in Sanskrit, but in the Prakrits which were supposed to be post-Vedic. Even the personal names look Indic rather than Iranian. Thus Biridaswa has been plausibly compared with the Sanskrit Brhadasva (owning a great horse). If this be right the second element, asva, horse, is in contrast to the Iranian form aspa seen in Old Persian and Zend. ... Finally we know that there existed among the Mitanni at this time a class of warriors styled maryanni which has suggested comparison with the Sanskrit marya young men, heroes.