Source: TW
Overview
Saw some discussions of the origin of “caste” in India, along with some typical ill-informed assertions by mlechCha-s.
Was it Harappan or Indo-Aryan? What we can say based on sociology, history, and genetics is that the historical system emerged through the melding of two probably partly aligned systems of IA and Harappan origin, respectively.+++(4)+++
IE strata
At least the post-Yamanayan Indo-Europeans possessed a certain version of the varNa system with at least three varNa-s. It might have independently broadened to four in different groups.
Conservatively, we see traces of such a varNa stratification among Italics, Germanics, B
altics, Iranics and Indo-Aryans if not more broadly.
Hence, it was at least there in the ancestral Corded Ware-like populations if not earlier.
We suspect some trace goes back to even Proto-Indo-Anatolian (=Indo-Hittite).
This, Indo-European varNa systems broadly had an elite with priestly and governing functions, and separately animal husbandry and servant strata.
Additionally, Indo-Iranians likely possessed some specialized guilds like the rathakAra and the butcher.
Harappan strata
Likewise, the Harappans likely had their own stratification, which included an elite (ruling/priestly), a trading caste, and a highly diversified series of service castes (it might have even been over 10 as recorded in IA late vaidika tradition: e.g., kInAsha, karmAra -> likely Harappan words).
Merging
When the Aryans invaded and conquered Northern India, they absorbed part of the Harappan elite into their brAhmaNa and kShatriya varNa-s. The Harappan traders were likely incorporated into the vaishya-varNa: the vaNijization of the vaishya-varNa. The services castes were let to persist as is, though some of them lost prominence with the deurbanization.
Further, some old as well as newly emergent, predominantly Indo-Aryan guilds were incorporated among these service castes (e.g., rathakAra, ajapAla, hastipAla etc.).
sankara hypothesis
The early Indo-Aryan social theorists of the dharma literature were puzzled by how these service castes might be related to the varNa system. Hence, they came up with a hypothetical (but by no means empirically established) taxonomic system where they tried to explain these service castes as originating via various cross-varNa marriages. Thus, the service-caste-type jAti is likely of large part of Harappan origin both in terms of ancestry and sociology.
shUdra
The term shUdra applied for the 4th varNa has had a shifting sense from the time it first appears to modern times. In the earliest days it was probably applied to the Harappan factions that fought and lost to the dominant Indo-Aryan-Harappan alliances.
Later it came to contain many of the service castes and lost its negative valence. This terminological blurring is unfortunate but once we recognize it, hopefully we can be less animated by it.