David Reich's study in population genomics is interesting enough in itself and I can concede, comparative studies of paleogenomics with modern population groups may provide hitherto unknown insight into the origin of modern human social groups.
But the conclusion he has drawn in his paper on Indian social groups, and its impact on history, is quite problematic and times contradictory. To begin with their conclusion is not even original. Studies in linguistics of Indo-European languages have long established that some sort of migration of language has taken place between distant geographies, indirectly implying that people who spoke those languages migrated and intermingled. This is the basic premise of the linguistic model of the dispersal of the Indo-European language. In this model, although there is a broad consensus that migration happened, but there is divergence of opinions among experts on the general direction of the migration and on any starting point of the migration.
Its not just that there are contending models on the dispersal of language groups, thus also its speakers, there are also contending archaeological models on dispersal of the culture that these language groups carried. While we today we have several linguistic and archaeological models that are in variance with competing models within their own discipline, the matter of fact is even these linguistic and archaeological models cannot be reconciled with one another.
So now genetic science, more specifically population genetics, had jumped into the gray and is picking sides. Archaeogenetics cannot reconcile, with any reasonable certainty, the lack of archaeological Data to support the many linguistic theories on the dispersal of the Indo-European languages.
Coming specifically to this paper, David Reich has put us in a bit of a philosophical bind.. One hand he claims that the admixture, of ANI genetics with west eurasian gene sample, only indicates close relationship between these two gene groups and makes no claim on their potential migration from one place to another or one group was the dominant contributor into another. Having set this argument , he unnecessarily delves into the archeological and the linguistic model on dispersal of cultures, whose very premise is Migration. Why this apparent contradiction. If he has decided to pick sides, that Indo-European language migrated into India at the end of the bronze age, let him state it clearly, provide irrefutable proof for this conclusion, as much his field allows, and help reconcile the contradictory archaeological and linguistic evidence. Otherwise he should have just stated the evidence of genetic admixture and left it at that.
The other issue I have with is the apparent dating of admixture of ANI and the ASI groups. The paper says that the admixture happened over a long period of time, between 4000 - 2000 years
ago (meaning 2000 BCE to the beginning of the common era). This is too vast a period and flies against the face of textual evidence, where we have that hereditary caste system coupled with endogamous social interact tions came into existence within few centuries of composing of the early Vedas.
There is also the statement that all social groups in modern India have admixture of West eurasians, steppe pastoralist, ANI and ASI. What this implies is that ANI and the ASI groups lived side by side without co-mingling (perhaps even the west eurasians is and steppe pastoralist loved side by side without any social interaction) for centuries to devolop their distinct genetic marker, then co-mingled so profusely that every succeeding social group carried both the genetic marker and then spread out through the length and breadth of the Indian subcontinent and then mysteriously developed a system of endogamy that created a large number of isolated, but in close cohabitation, social groups that morphed into the modern social Caste groups.
The above pictures is problematic in more than one way. The sample size is too small to draw such sweeping and grand conclusion. What socio-cultural forces shaped such dramatic alternating phases of isolation - admixture - isolation, and in such a short period of time, is still unexplained.
Thanks for your thoughts. Nicely written.
The data does provide genetic evidence of directional drift.
Both towards India and within India.
He does postulate convincing theories for maternal versus paternal DNA.
I do not deny that he has picked a side, or belonged to the side going in.
But the science has been laid out for scrutiny. The inferences for debate.
The ANI and ASI being resident for a long time side by side is more to do with internal sociipolitical narratives than real science. He has said it as much in his piece. It's not even couched or ambiguous.
The early isolation now out of the way, the admixture followed by endogamous isolation is explained clearly by the narrative of the injection of a foreign way of life and theology in a position of social if not militirastic dominance into a long resident native population group and belief and linguistic system.
It's churn.
Then co-existence in an amalgam with a brand new social hierarchical order.
Sanskrit and Tamil.
Vedic Hinduism and resident dieties and belief system.
The eventual peripheralisation of Vedic God's to a minor role.
Fire for Water.
All of this is well discussed. As you have correctly said.
But the genetics now points to the same.
Cheers, Doc
@S. A. T. A