My model of the Indo-Aryan caste society envisages a situation where the IE languages were brought in by the nomadic bands of R1a1 people to north-western India from Central Asia/Eastern Europe migrating in search of the greener pastures and who were superimposed by Aryan priestly families belonging to J2a and G2 lineages from West Asia. Instead of Semitic introgression theory, I could have called it Aryan Intrgoression Theory (AIT) for priestly family migrations and Steppe migrations for IE migrations. But I'll stick with Semitic Introgression Theory for the overall development of the caste Indian society.
As I argued before, the priesthood most likely was created in West Asia with its earliest literate civilizations. This is the reason we find R1a1 across the castes and erstwhile outcasts in North India but J2a is more restricted to Brahmins.
However, I also commented that this model need not be completely true in the case of the South India as there could be earlier J2a migrations from West Asia which could be seen in tribes like Toda.
Curiously, it appears we have another earlier migration from West Asia to North India too. A village in Himachala Pradesh called Malana is where you find this isolated community. According to a recent paper by Rajiv Giroti and Indu Talwar (2010), nearly 60% of this population belong to J2a. The community speak a Tibeto-Burman language (probably, we can get better idea if their matrilineages are tested).
But the interesting part is Wikipedia article on them;
People in Malana consider all non-Malani to be inferior and consequently untouchable. Visitors to Malana town must pay particular attention to stick to the prescribed paths and not to touch any of the walls, houses or people there. If this does occur, visitors are expected to pay a forfeit sum, that will cover the sacrificial slaughter of a lamb in order purify the object that has been made impure. Malani people may touch impure people or houses as long as they follow the prescribed purification ritual before they enter their house or before they eat. Malanis may never accept food cooked by a non-Malani person, unless they are out of the valley (in which case their Devi can't see them). Malanis may offer visitors food but all utensils will have to undergo a strict purification ritual before they can be used again.I have already argued that purity-pollution rules were ritualized in West Asia and the core Brahmin Varna belonged to that society. Now, we have a population in India which though not part of the Varna system has all the ritualized purity system and patrilineally closer to West Asia ((Iran) in its orientation.
One more proof that, the caste system was basically a creation of West Asian priestly class and not Shamanic IE people from Central Asia/Eastern Europe.
The Most Ancient Democracy in the World is a Genetic Isolate: An Autosomal and Y Chromosome Study of the Hermit Village Malana (Himachal Pradesh, India)
RAJIV GIROTI AND INDU TALWAR