Correct, the article is flat wrong on this. Indian sources that even predate the Greeks also speak in detail about the societal arrangement.
> Second, what the data shows is not a record of social structure. It shows that modern Indian castes have practiced endogamy -- mating within the group, with negligible inflow from other groups
Yes, but they are still sampled, albeit in varying proportions, from the same source populations, referred to in the literature as ASI and ANI, which are themselves composite groups.
Sure, but that was several thousand years ago. Again, most people are perfectly happy to describe unmixed ancestry for the last 2400 years as being "pure", and the castes go back farther than that.
Just because "most people" are willing to draw that line at 2400 years doesn't make it a valid argument.
At most you could say that there is genetic evidence to support the hypothesis that the castes have practiced endogamy for a long time, evidenced by their characteristic genetic admixtures from their shared source populations, and that the caste hierarchy is roughly correlated with ANI admixture rate. That doesn't equate to the word "pure" at all.
People are willing to make all sorts of claims about their and others' identities to suit their personal agendas, and it's their right to do so, but they aren't doing science.
What about the many millennia that elapsed between the last major shared human population bottleneck and 2400 years ago?
https://en.m.wikipedia.org/wiki/Purusha_Sukta
It's interpretation is varied and controversial to say the least.
But one shouldn't confuse the theoretical model presented in the liturgical texts (referred to with the term "varna", meaning "color" or "tone") with the concrete manifestation of traditional endogamous divisions in society (referred to with the term "jati", meaning "station of birth').
The ground reality is more oriented around the complexities of class, tribe, language and occupation, and even physical phenotype, which were then rationalized through the theoretical 4-fold system of caste.
There are parts of India (the southern and eastern parts) where the actual social structure doesn't map as cleanly to the 4-fold system, except among the higher castes. However endogamy and strong caste hierarchy is still just as common in these regions.
In terms of population genetics of South Asia specifically, here is a good place to start:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2702070/#__sec2...
It is obvious, and the same data shows that groups can be very pure indeed. From this very article:
> Genetics also show that India’s caste system, previously thought to have developed under colonial rule, was in place thousands of years earlier.
First, "previously thought to have developed under colonial rule" is just false. The ancient Greeks wrote about India's caste system, thousands of years ago.
Second, what the data shows is not a record of social structure. It shows that modern Indian castes have practiced endogamy -- mating within the group, with negligible inflow from other groups -- for thousands of years.
Most people would be happy to describe this state of affairs as "pure" ancestry.