Indo-Iranian (proto-Aryan) and ancient Iranic (Aryan) languages were ERGATIVE languages. Other Indo-European languages are NOT ERGATIVE at all. Ergativity among language of the (proto-)Aryans evolved somewhere on the Iranian Plateau or Caucasus, period! And NOT at places where ERGATIVITY doesn't exist.
You're completely wrong here. The oldest Indo-Iranian languages that we know, Vedic Sanskrit and Avestan (the language of Zoroastrianism, the ancient religion of Persia), show no signs of ergativity. The split-ergativity that you can find in modern Hindi-Urdu must be late innovation, not an original feature. You're also forgetting about the
Nuristani languages (which, as you may know, form a third branch of the Indo-Iranic languages, alongside of Indic and Iranic), which likewise show no sign of ergativity. In my opinion, the Hindukush region is much more suitable than the Iranian plateau for a Proto-Indo-Iranic homeland. You also have the case of the
Burushaski language which appears to have had early Indo-European contact.
More in favor of the hypothesis of Gamkrelidze and Ivanov.
The Indus Valley Civilization was like Maykop Civilization a Bronze Age civilization and both civilizations were highly influenced by West Asian Sumer Civilization. Sumer predates all of them! And Maykop Civilization in turn Indo Europized the Yamna Horizon.
There're many parallels between the Maykop and Indus Valley civilizations, like bull and the SUN worshipping. But the first known Sun and bull worshippers were the Sumerians.
Possible migration of S224, ancestral to both Z283 in East Europe and Z93 in SouthCentral Asia!
The problem with Gamkrelidze's and Ivanov's scenario is that they somehow assume that Armenian is particularly representative of Proto-Indo-European whereas in reality there's no particular reason to assume so, on the contrary: Armenian has a Hurro-Urartian substrate (meaning that Hurro-Urartian was one of the languages spoken there before speakers of Proto-Armenian arrived there, and I would also like to point out that the Biblical name "
Ararat" is very probably derived from "
Urartu"), and there is no evidence for Indo-European/Hurro-Urartian contact in the other branches.
Aside from Whittaker's claims (which are far out, in my opinion), there's no evidence that Proto-Indo-Europeans had early contact with speakers of Sumerian. In my opinion, the only language families that can be safely assumed to have had very early contact with Proto-Indo-European speakers are Kartvelic (ie. Georgian) and Uralic.