An extensive research by David Reich, a geneticist at Harvard University, strongly suggests that there was a migration of AGRICULTURALISTS into northwestern India from what is now Western Iran/Zagros Mountains, around 4000BCE.
This migration was followed two millennia later around 2000BCE, just before the Vedic Age—by a large influx from the area between the Black and Caspian Seas, North of Caucasus Mountains. These newcomers appear to have shared the same ancestry with the populations of the European peninsula/continent.
But who were these earlier, ancient Iranian Agriculturists??? For one, the Neolithic, Iranian Agriculturists shared same ancestry with Old Hittite DNA remains, (the earliest speakers of Indo European Languages,) and with some Assyrian/North Mesopotamian Lineages (See Genetic studies of Damgaard et al. 2018.)
They lived in the Zagros Mountains, where some of the earliest evidence of wine making/production has been discovered. Zagros mountain range begins in northwestern Iran, South of Caucasus, and creates a geographic barrier between the Mesopotamian flat deserts, and the towering Iranian Plateau/Mountains. It has a total length of 1,600 km (990 miles.) The highest point is Mount Dena at an elevation of 4,409 meters (14,465 feet.)
Remnants of the originally widespread oak-dominated woodland can still be found in Zagros Mountains. The ancestors of many familiar foods, including wheat, barley, lentil, almond, walnut, pistachio, apricot, plum, pomegranate and grape can be found growing wild throughout Zagros.
Ancient DNA tests have revealed that the majority of Early Neolithic farmers who colonized Europe belonged to Y-haplogroup G2a. However, the Iranian Agriculturists had a higher frequency of T1a Y-DNA lineages than G haplogroup. Interestingly, during the Copper and Bronze Ages, haplogroup T appears to have been an important paternal lineage among the ruling elites of ancient peoples such as Sumerians, and the Assyrians.
Within Europe the frequency of Y-DNA T lineages is most common in the mountainous parts of the southern Balkans, the central and southern Apennine Mountains in Italy, Auvergne Mountains in France, and mountain pasturelands of southwestern Iberia.
All the aforementioned mountainous regions share many features with Iranian Zagros Mountain Range in Northwestern Iran, South of Caucasus.
The Paternal T lineage is also believed to have been closely associated with maternal HV haplogroup.
HV is the most successful maternal lineage in Europe today. Over half of the female European population descends from a single female, HV lineage progenitor who lived at least 25,000 years ago. Most Europeans belonging to the HV lineage descend from a branch that was renamed haplogroup H.
The modern distribution of mtDNA HV is particularly reminiscent of hotspots for Y-DNA haplogroup T. This strongly suggests that maternal HV and paternal T lineages spread together from a spot in modern day Northwestern Iran, South Caucasus, and Iraqi Kurdistan, to the Fertile Crescent, notably Northern Mesopotamia, as well as to Central and Eastern Europe.
The distribution of HV maternal haplogroup today is as follows:
HV2: found among Zoroastrians, Kurds, and in Slovakia
HV5: found around Lithuania, Belarus and Poland
HV6 : found in Iran, Russia, Slovakia and Britain
HV7 : found in Russia, Ukraine and Sicily
HV8 : found in southern Russia and Slovakia
HV9 : found in Italy, the Czech Republic, Poland, Russia, Scandinavia and Britain
HV10 : found around the Alps
HV11 : found in Italy
HV12 : found in Iran
HV13 : found in Iran
Today, about 20% of Iranian Zoroastrian priests belong to Y-DNA haplgroup T1a, a lineage that goes back to Neolithic Iranian Agriculturists. Also after mtDNA U4, mtDNA HV2 is the most common Zoroastrian maternal lineage.
However, 80% of Iranian Zoroastrian priests belong to Y-DNA lineages I* and I2*. Both I* (I M170) and I2* (I P215) are associated with Cro Magnon/Early European Robust humans, and are exceedingly rare among modern populations.
I* (M170) is the Paleolithic lineage from which all subclades of Y-DNA I derive. I* (I M170) is My Personal Y-DNA marker.
About 86% of the Parsi Zoroastrian Priests belong to R1a1a1 Y-DNA marker, a proto Indo European marker that goes back to ancient Yamnaya culture, and hails from the regions surrounding Dnieper river in modern day Ukraine, and what is now Southern Russia.
Another 14% of Parsi Zoroastrian Priests belong to haplgroup L. According to Dr. Spencer Wells, Haplogroup L-M20 originated in the rugged and mountainous Pamir Knot region in Tajikistan of Central Asia. This haplogroup was found in remains attributed to an elite member of the Hun tribes in Hungary.
In conclusion, I shall add that Pre-historic people in northern Caucasus, Southern Caucasus and Zagros Mountains would have adopted farming and exchanged goods and languages for thousands of years. These Neolithic Iranian Agriculturists of Zagros Mountains soon merged with proto Indo Europeans, and became one people with them.
There is also the great likelihood that the first speakers of an Indo-European language could have hailed from south of the Caucasus Mountains, perhaps in present-day Iran or Armenia.