In my previous post, I suggested a Bronze Age origin for many Indian Y chromosome haplogroups. In this one, I use Ken Nordtvedt's Generations2 program to estimate ages for upper-caste Indians (Brahmins). As Brahmin status is elevated within the Hindu caste system, and is conferred patrilineally, Brahmins are excellent candidates for determining whether or not an exogenous Bronze Age population is responsible for the introduction of Indo-Aryan languages and the establishment of the caste system in India, in accordance with the much-challenged traditional opinion.
I report ages for haplogroups with more than 7 observations:
|N||Generations||Years (25y/gen)||Years (30y/gen)|
|J2a (with DYS388) ||17||214||3350||BC||4420||BC|
|J2a (without DYS388)||17||174||2350||BC||3220||BC|
DYS388 tends to mutate very slowly in most human lineages, but quite fast in haplogroup J, therefore I report results with or without its inclusion.
The three most populous haplogroups (R1a1, R2, J2a) are the best candidates for lineages of exogenous origin, and have Bronze Age coalescence time, in accordance with the traditional theory. However, indigenous lineages (H1 and L1) and others with fewer numbers did enter into the Brahmin gene pool. The majority (64%) does appear to trace its ancestry to the early Indo-Aryans.
Thus, the congruent distribution of haplogroups R1a1 and R2 in India, as well as the limited occurrence of haplogroup J2a mostly in upper castes are easily explained.
An argument against R1a1's Indo-Aryan affiliation is that it is more diverse in tribal Indians. Yet R1a1 occurs at very low frequencies in tribal Indians, who in turn form a very small part of Indian society. A better explanation is that R1a1 in tribals is due to multiple founder effects, and its elevated presence among Indo-European tribals supports this scenario.
The pattern of J2a and R1a1 occurrence and age suggests different roles for these two lineages. J2a seems older, consistent with a larger effective population size, whereas R1a1 is found at a higher frequency and is not limited to Brahmins.
Perhaps, J2a formed the nucleus of the priestly caste, allowing it to diversify for some period of time, with a later founding of a succesful Brahmin lineage by a group of R1a1 males of different caste origin. Such conjectures will have to remain speculative for the time being.