The above are Y chromosomes from ancient samples in the steppe, Iran/Turan, and South Asia. The time periods are obvious. EMBA = “Early Middle Bronze Age”, MLBA = “Middle Late Bronze Age” and LBA = “Late Bronze Age.” IA = “Iron Age.” H = “Historical.” And the other periods are Neolithic or Copper Age. This is from Narasimhan et al. (click the image above for the supplements).
The Forest/Steppe samples are most from what Sintashta archaeological sites. One thing that is evident in early Indo-European pastoral people is that they seem to be highly patrilocal and patrilineal. One particular genetic lineage group of males seems to dominate different early groups. The data from Narasimhan et al. show us that:
R1a is overwhelming in the Sintashta.
R2 & L is found in pre-Indo-European Iran.
Q & N is in Sintashta too.
H1 is mostly found in South Asian populations.
You can see the distribution in modern populations on Wikipedia, but data from a paper is illustrative:
The numbers don’t add up to 100% because I deleted some columns. Brahmins have a lot of R1a. We knew this. But please note that they have lots of other Y chromosomal lineages as well.
We need to be cautious here about not overreading these data. But please notice that Punjabi Brahmins have more IVC-derived Y chromosomes than R1a. R2, J2, and L are all likely related to eastern Iranian farmers. In contrast, UP and Bihar Brahmins have more R1a, and less the of the Iranian farmer Y chromosomal groups. Finally, observe that UP Brahmins have a substantial minority of H1, which is quite plausibly from the AASI.
Here is a hypothesis that I will present which explains the origin of Brahmins, and to some extent Indic civilization as we understand it. The high fraction of IVC Y chromosomes in Punjabi is a function that this region was the center of a more complex society when the Indo-Aryans began filtering into the region. The “Brahmins” was created from an amalgamation of the Aryan priestly class with IVC priests. Many of the things unique to Brahmin culture are from the IVC.
Second, Narasimhan et al. report that IVC ancestry declines as one goes east in the Gangetic plain, AASI goes up, but “West Eurasian” ancestry stays more constant because Indo-Aryan ancestry is high in groups like Brahmins in Bihar. I believe that the Gangetic plain was liminal and more open to Indo-Aryan expansion than the core Punjab, where Aryans assimilated a much larger group of IVC people. Rather, in the Gangetic plain Indo-Aryans assimilated more “jungle people.” Perhaps some hunter-gatherers, but also slash and burn agriculturalists of predominantly AASI origin. The fraction of H1 in UP Brahmins indicates that this was the case even in core Aryan tribes.
The emergence of Brahmanism, and later Hinduism, was a complex multivalent synthesis. There wasn’t one single mixture, one single invasion, but rather multiple peoples interacting and integrating. Though Brahmins are enriched for Indo-Aryan, Narasimhan et al. could not define them as a lineage with common descent. That means parallel cultural processes created multiple founding Brahmin lineages, rather than a single process creating a single lineage.