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Joe Shearer
This, for instance, is a more balanced view, but it is not at all clear that people travelled across from Europe; rather, people from a common location may have travelled east and west, more or less in the same time frames, and spread their language and its derivatives into Europe and into India.
I couldn't reply to your post
#61 on the other thread because I do not have sufficient privileges to post there. This debate is extremely old, & in spite of all the evidence that exists for migration, some people continue to reject it either out of sheer stupidity or the foolish belief that acknowledging the differences between population origins leads to disunity. If nations can't be united on a factual basis then they deserve to collapse. The title of that study including the term "European migrants" is meant to recognize affinity between Indo-Iranians & Europeans, it does not imply that Europeans migrated to the Indus. Anyway, the answer you are looking for lies in the Kurgan hypothesis. The Proto-Indo-European tribes resided in the region around the Black Sea. That is their original homeland, & their haplogroup R1a is traced to that particular region too. The Yamna culture for instance provides us with archaeological evidence of their presence within that region. The proto-Indo-European tribes consisted of the proto-Indo-Iranians, the forerunners to the Thracians, the Latins (original Romans), ancient Hellenic tribes (Mycenaeans), etc. Europe already had a population residing there since Paleolithic times, & let's not forget about the R1b haplogroup which is the cousin of the R1a, & today happens to be the most dominant paternal lineage in Western Europe. Many reasons are debated for the migration of proto-Indo-European tribes from their homeland, including the invention of the chariot. Regardless, the PIE tribes migrated both towards the east & the west.
The Mycenaeans for instance arrived in the Greek peninsula & established what would be considered the first Hellenic civilization by dominating as elites over the local populace, & introducing their language, culture, & religion. The Thracians were a mix of PIE tribes & the local Paleolithic population with elements of culture & technology borrowed, absorbed, & learnt from other nations too. The proto-Indo-Iranians went on towards Andronovo giving rise to the Sintashta culture & the greater Andronovo culture itself perhaps. However, as with many groups in Central Asia, the proto-Indo-Iranians would set the standards by migrating towards Afghanistan, the Indus, & the Iranian plateau. Similarly, the Scythians would arrive on a much smaller scale to the Indus Valley many centuries after that. This migration occurred in stages according to sources I have referred to in the past & would have been completed perhaps over the course of a thousand years. The Indo-Iranians called themselves Aryans & dominated the region spreading from the Iranian plateau to the Indus after settling there.
Their cultural, political, & military dominance led to the spread of their language & culture to even those ethnic groups that currently speak an Indo-Aryan language but do not descend primarily from the Aryans. There may have been slight mixture here & there but it was by no means enough to greatly change the phenotype of the indigenous. However, regions where the Indo-Iranians settled primarily, such as the Indus, Afghanistan, & northwestern India still retain the Aryan appearance among many ethnic groups such as the Kashmiris, Pasthuns, etc. Of course, over time, slight mixture with non-Indo-Iranians would have somewhat corrupted their appearance too. The presence of the R1a haplogroup confirms that this migration occurred, & another point to note is that languages & cultures did not spread back then without contact with its originators. Religious similarities such as the "sky father" exist in Vedic, Hellenic, & Latin mythology alongside many other similarities testifying to the relations between these ancient people. Another interesting point to note is that the PIE tribes must have dominated as elites in all the regions they traveled to including R1b dominant Western Europe. That's how speakers of Indo-European languages came to exist in Western Europe in spite of the absence or extremely minimal presence of R1a (the PIE marker). The haplogroup R1a is more dominant in Eastern Europe. Anyway, I typed this post out in a hurry so there could be a few errors present, as is the case with most if not all lengthy documents without proof reading.