While we are bound to see some migration to and from such a large civilization, the people of the region have largely stayed a constant from genealogical evidences. The only mass migration that is detected was from southeast asia.
Do not confuse linguistic patterns with genetic patterns. All the linguistic evidence tells us is that the Sanskrit language came from outside of India. It doesn't tell us how it got there. Sometimes a conquered population adopts the language of the conquerors. Less often, the conquerors adopt the language of the conquered. So Latin and Greek are spoken in much of the former Roman Empire territory, but the ancestors of Romance speakers mostly did not have Latin as their native language. Similarly, most people in the world today who speak English are not native speakers of English. Linguistic and cultural inheritance is not biological inheritance.
So now we have an advanced civilization that trades with other great civilizations of the time period and then magically we see a language full of descriptions of advanced concepts and the only reasonable explanation is that the language didn't develop from the great civilization. This doesn't seem a little off to you?
George, we don't know a lot about what happened in prehistoric times. All we can do is look at evidence and draw inferences based on that. Linguistic evidence is fairly solid on the argument that the original homeland of Proto-Indo-European was not India. There just isn't any real argument on that subject outside of India. It is an old idea that failed to stand up to the linguistic evidence. That suggests historical migrations and/or invasions, but the genetic footprint of those events could well have been overwhelmed by the indigenous gene pool. From what I have read, the IVC collapsed well before the linguistic migration occurred. The collapse more likely happened from some cataclysmic event that wiped out the agricultural and industrial base of that civilization. The Indo-Iranian speakers may have been filling in territories that had become depopulated. They almost certainly brought horses, chariots, and iron. The original Aryans were meat eaters, but the Hindu religion became vegetarian. I suspect that the "great civilization" of the Aryans was something that developed after the IE languages had spread to India. There were a lot of "advanced civilizations" in contact with each other back then. IVC even traded with the Sumerians and Akkadians. They certainly left traditions and traces after the general collapse of their civilization.
But I began this thread to understand more, so perhaps I should ask questions. Why is it not reasonable that some language prior to sanskrit emerged from Afghanistan, Pakistan, India region and spread in chunks throughout Europe, West Asia, and the middle east while continuing to develop and evolve in the IVC region?
The linguistic evidence is quite extensive, but I did give a link earlier to the Wikipedia page that laid out some of it:
Proto-Indo-European Homeland. The argument is based on the common reconstructed vocabulary base of Indo-European languages plus our knowledge of the environments in India, Anatolia, the Russian steppes, and Europe at the time we project a relatively homogeneous ancestor language to have existed. That vocabulary tells us, for example, that the Indo-Europeans had iron, wine, mead, horses, salmon, beech trees, a pantheon of gods, etc. It is not consistent with an origin in the Indian subcontinent. From the article:
The Indigenous Aryans theory, also known as the Out of India theory, proposes an Indian origin for the Indo-European languages. The languages of northern India and Pakistan, including
Hindi and the historically and culturally significant
liturgical language Sanskrit, belong to the
Indo-Aryan branch of the Indo-European language family. The Steppe model, rhetorically presented as an "Aryan invasion," has been opposed by
Hindu revivalists and
Hindu nationalists, who argue that the Aryans were
indigenous to India, and some, such as
Koenraad Elst and
Shrikant Talageri, have proposed that Proto-Indo-European itself originated in northern India, either with or shortly before the
Indus Valley Civilisation. This "Out of India" theory is not regarded as plausible in mainstream scholarship.