In the near future the ancient DNA group led by David Reich will publish a bunch of stuff, and one paper will note that the variation in steppe ancestry in the Bronze Age Greeks did not have class implications. In other words, the ancient Greeks did not have a caste system as you might find in India, despite the way the Spartans treated the helots or Messinians. Of course, the Indo-Europeans did have a ‘tripartite’ caste system of rulers and warriors, priests and commoners. In the Indian varna system, this was translated into Kshatriyas, Brahmins and Vaishyas. But it is found elsewhere, including among the German Saxons. But to my knowledge nothing like the Indian caste system has been found genetically in these ancient populations; some individuals have more “farmer” ancestry in initial generations, but this is all smoothed away by admixture.
India is different. It has jati-varna, with varna being caste as you would understand, but jati being one of thousands of endogamous “communities” in the subcontinent. At first, like many, I assumed this had something to do with the Indo-Aryan migration into the subcontinent, but I noticed a few things early on. First, there are apparent genetic differences between groups in Non-Aryan South India that are not Brahmin. For example, between Nadars and Dalits. These differences correlated to global biographic fraction differences. Dalits have more AASI (Ancient Ancestral South Indian). Mind you, I believe South Indian “Dravidians” were strongly shaped by the Indo-Aryans, so that’s not dispositive. Nevertheless, Non-Aryan cultural regions have this institution, and, jati is peculiarly India, even if varna is not.
But, what has shifted my view is looking at admixture variation in “Indus Valley Periphery” samples in samples dated from 3000-2000 BC. There’s a wide range of AASI. Why? Well, admixture in structured populations takes time. But there’s something suspicious to me about this variation combined with India’s later endogamy and the mystery of how the Indus Valley Civilization organized itself. There seems to have been very little stratification in a way we would understand it from Egypt or Mesopatamia. Were they anarchists? I doubt it. The early emergence of jati may explain the IVC sociopolitical system. The Indo-Aryans, when they arrived, were simply integrated into the framework.
Ancient DNA will prove me right or wrong. But I’m putting my cards on the table.