Myth of the Aryan Invasion
It has often been pointed out that the complete absence of the horse among the animals so prominently featured on the Indus seals is good evidence for the Non-Aryan character of the Indus Civilization. Parpola quotes from a fairly up to date and authoritative report by Richard Meadow that there is as yet no convincing evidence for horse remains from archaeological sites in South Asia before the end of the second millennium BC. Many claims have been made, but few have been documented for independent verification. The wild relatives of the horse and donkey are not native to South Asia, and the domesticated animals were brought into the region from the west and north.
Parpola points out why the 'horse argument' is so central to the issue. The Proto-Aryan words for the horse and the various technical terms associated with the war chariot can all be solidly reconstructed to Proto-Indo-European. This is good linguistic evidence that the Vedic horse and chariotry are firmly rooted in the Proto-Indo-European heritage. The evidence strongly suggests that the Indus culture was non-Aryan.
The Dravidian Hypothesis
The survival of Brahui, a Dravidian language, spoken even today by large numbers of people in Baluchistan and the adjoining areas in Afghanistan and Iran, is an important factor in the identification of the Indus Civilization as Dravidian. Brahui belongs linguistically to the North Dravidian group with several shared innovations with Kurukh and Malto; no dialectal features connect it with the South or Central Dravidian languages. Hence Parpola concludes that Brahui represents the remnants of the Dravidian language spoken in the area by the descendants of the Harappan population.
The pervasive substratum influence of Dravidian on Old Indo-Aryan is also an important clue to the presence of Dravidian in the northwestern region from the earliest times. The presence of a few Dravidian loan-words in the Rigveda is now well recognized. The Rigveda has also phonological and syntactical features borrowed from Dravidian. Among the features listed by Parpola are the retroflex sounds, gerund, quotative and onomatopoeic constructions. The Prakrit dialects too underwent a radical simplification of the Indo-Aryan syllabic structure through assimilation of consonants and intrusive vowels, features which are best explained, as Parpola points out, as adjustment to the phonology of a Dravidian substratum.
Survival of place-names is generally a good indicator of the linguistic pre-history of a region. Parpola points out several place-names in the northwestern region like nagara, palli, pattana and kotta with good Dravidian etymologies. I am not however convinced by his attempt to derive Meluhha (the name of the land of the Indus in the [Mesopotamian] cuneiform texts) from Dravidian mel-akam, 'High country', not actually attested, as Parpola himself points out, in any of the Dravidian languages.
Parpola also points out that syntactical analysis of the Indus inscriptions has revealed Dravidian-like typological characteristics, especially the attribute preceding the headword. The cumulative weight of evidence makes Dravidian the most likely language to have been spoken by the Harappans.