It is known that IVC was LITERATE. After all thousands of seals show that. But where is the LITERATURE?
The technologies of scrolls and codices ("books") had not been invented yet, because they were built upon the rather sophisticated technology of paper (and its antecedents such as processed papyrus), which had not yet been developed. Therefore, writing had to be done on stone, which is quite durable but very slow work; on clay, which is faster but very fragile; or on other even more ephemeral surfaces such as fabric. Given these constraints, it's miraculous that any significant volume of ancient writing survives at all. Long compositions like poems, letters, journals, etc., would have been written on the least durable surfaces--if anyone had even bothered--and so they would have deteriorated long ago.
Most of the writing we have from contemporary ancient civilizations is preserved on stone tablets and a few clay tablets that managed to survive. These are primarily government and religious documents--work that would have been judged worthy of the effort. What you call "literature," such as poems and stories, had to be passed down orally.
Homer, as we all know, was not the author of
The Odyssey. That legend was passed down orally by tribal storytellers for many generations before modern writing technology became available and Homer wrote it down. The fact that it was a poem provided many checks and balances to ensure that it was not changed too much through the generations. The rhyme and meter had to be retained.
I suggest that the reason no similar literature from the Harappan-era IVC survives is precisely because the Indic people arrived and marginalized the earlier culture. During the long transition from the original language (of which we know nothing, not even its family, we just make the educated guess that it would have been Dravidian), all rhyme and meter would have been lost and the stories would have been re-written as Sanskrit sagas.
It's rather common for a civilization to go into a decline, and then be revitalized by an immigrant culture. The Olmec/Maya civilization was falling apart when the Aztecs wandered down from California, and they renovated it.
On the other hand, as alleged, Aryans were ILLITERATE barbarians, but they left a VERY, very rich body of literature? In fact the richest.
The Indo-European peoples did this all over the regions in which they became dominant. The Greeks were an illiterate people, but they borrowed much of Phoenician civilization from the traders who stopped at their ports regularly. They remodeled the Phoenician abjad (a pseudo-alphabet with no vowels, suitable for all Afro-Asiatic languages like Egyptian, Arabic and Hebrew) into a true alphabet, which was then borrowed and again remodeled by the illiterate Romans. In concert those two barbarian tribes founded the world's dominant civilization.
For centuries, England was the dominant branch of Greco-Roman civilization, and the English are descended from several tribes of Germanic barbarians (Angles, Saxons and Jutes) who muscled in on the civilization the Romans had brought to the Celtic tribes of Britannia when the Romans left. The only Romans who stayed were the priests and they taught the Anglo-Saxons to write.
Original Aryans (Proto-Indo-Iranian speakers) were tribal and nomadic people, possibly from Central Asia.
It's generally acknowledged that the
Urheimat of the Proto-Indo-Europeans was the Pontic Steppe, roughly the region above the Caspian Sea on the (entirely artificial) boundary between Europe and Asia. They did not build cities so, technically, they did not have a civilization. But they had absorbed all of the technologies of their neighboring peoples, including both agriculture (farming and animal husbandry) and bronze metallurgy. It is most likely that they are the people responsible for the domestication of the horse
So even though the Indo-Europeans did not invent any of the world's writing systems, they gave us a technology that revolutionized land transportation as astoundingly as the railroads would several thousand years later. One of the reasons that the Aztecs could not stand up to the European invaders is that there were no large, rideable herbivores in Mesoamerica.
. . . . Celtic and other Indo-European languages replaced most of the the native Vasconic languages in ancient Western Europe . . . .
The Celts occupied all of sub-Scandinavian central and western Europe, and even much of what we now consider eastern Europe. Bohemia, now called the Czech Republic because it's easier to spell and pronounce, is named after the Bohumil, a Celtic tribe.
BTW, it's sheer speculation to assume that prior to the Indo-European invasion, languages related to Basque were widely spoken in Europe. We have only a few fragments of them, not enough to decipher and catalog. There is some evidence suggesting that the Basques are the last surviving descendants of the Cro-Magnon people, and even weaker evidence suggesting that the Cro-Magnon were the original tribe of
Homo sapiens that replaced the Neanderthals, and that these were the people that the Indo-Europeans encountered when they arrived. But at this point these are only hypotheses. There's only so much we can tell from archeology and DNA analysis.
. . . . except for Basque in northern Spain.
And southern France.
Now, now. Aryans were nomadic, that so? So were Mongols, Tatars etc. from Central Asia. They too did foray into other lands, notably China. Could they eliminate Chinese language and culture?
Sometimes nomadic barbarians succeed in overthrowing a more advanced civilization, sometimes they don't. The Germanic tribes sacked Rome, but Rome was already rotting from the inside. The Mongols attacked China during a period of strength, and although they managed to take over the government, within a few generations they assimilated and became Chinese.
Greeks were not nomadic. But Greek invaders hardly influenced Indian language in culture even in the peripheral parts of India.
But the Mughals/Mongols, who
were nomadic barbarians, certainly did. It is because of them that Pakistan exists.