November 06, 2005

More on R1a1 age and haplogroup J2 in upper caste Hindus

A reader has brought to my attention a paper which appeared in 2001 in the Indian Journal of Genetics, and which is quite interesting for the discussion of the origins of haplogroup R1a1, as well as for the problem of the genetic makeup of the Proto-Indo-Europeans.

The Indian researchers have studied the microsatellite diversity of their northern Indian sample, and have estimated the corresponding age of haplogroup R1a1 (referred to as HG3). This age is 5,200 years. However, age is calculated based on assumptions about (i) the mutation rate, i.e., how fast microsatellites mutate, as well as (ii) the generation length. The 2001 paper makes assumptions which lead to an age that is 2.17 times younger than the assumptions of the recent South Siberian study. If we convert these estimates to the younger scale, we obtain ages of 5,193 years for Central Asia and 5,244 years for Eastern Europe. In other words, the age of R1a1 seems to be comparable in the three regions. The discrepancy of the ages in the two papers also underscores how the dating of prehistoric events depends to a great degree to assumptions which vary from researcher to researcher.

More fascinating is the finding that the main haplogroup distinguishing the northern Indian brahmins from the lower castes is J2 (referred to as HG9). I have long argued that haplogroup J2, associated with the early Neolithic expansions was also the PIE lineage par excellence, and this certainly supports this theory. It may very well be that in early times, the Indo-Iranians emerged as J2-bearing Indo-Europeans diffused into the R1a1-bearing east, with the resulting J2/R1a1 then settling on the Iranian plateau and invading India from the north.

The frequency of this haplogroup is highest (23.5%) among the upper-ranked caste Brahmin and is lower (17.1%) among the middle-ranked caste Rajput. It is known that after the entry of the Aryan speakers into India, the Brahmins were the torchbearers and promoters of Aryan rituals (Karve 1961). Therefore it is likely that this group had the highest genetic contact with the Aryan-speaking peoples. This observation is consistent with the high frequency of HG-9 observed among them. This haplogroup may have percolated into the middle-ranked Rajput either through admixture with Brahmins or directly with the Aryan-speaking immigrants. Since historians (Thapar 1975) have noted that some of the Central Asian pastoral nomads are ancestors of Rajputs, it is more likely that this haplogroup (HG-9) was introduced into the Rajputs directly by the Central Asians than indirectly through admixture with the Brahmins. It is noteworthy that HG-9 is absent among the low-ranked caste group, Chamar.

Interestingly though, in Oman the age of R1a1 is 11,400 years or 5,178 equivalent years using the same assumptions about generation length and mutation rate as above. In Iran and Pakistan it is 6,300 and 6,200 years old. Hence, all these ages seem very close to each other, and -given their confidence intervals- we cannot at present determine the point of origin of haplogroup R1a1.


Also of interest is Cordaux's extensive study of Indian Y chromosomes. Interestingly, the odds ratio for an Indian J2 being a caste vs. a tribal is 4 times more likely, whereas for an Indian R1a1 it is only 2.3 times more likely. This further supports the idea that haplogroup J2 significantly differentiates between Hindu caste members and indigenous non-caste populations. Unfortunately, Cordaux does not report differences within the Hindu caste hierarchy; it would be interesting to see whether J2 is even more prevalent among the upper castes within this hierarchy.

Journal of Genetics, 80(3): 125-135

High-resolution analysis of Y-chromosomal polymorphisms reveals signatures of population movements from Central Asia and West Asia into India

N. Mukherjee et al.


Linguistic evidence suggests that West Asia and Central Asia have been the two major geographical sources of genes
in the contemporary Indian gene pool. To test the nature and extent of similarities in the gene pools of these regions we have collected DNA samples from four ethnic populations of northern India, and have screened these samples for a set of 18 Y-chromosome polymorphic markers (12 unique event polymorphisms and six short tandem repeats). These data from Indian populations have been analysed in conjunction with published data from several West Asian and Central Asian populations. Our analyses have revealed traces of population movement from Central Asia and West Asia into India. Two haplogroups, HG-3 and HG-9, which are known to have arisen in the Central Asian region, are found in reasonably high frequencies (41.7% and 14.3% respectively) in the study populations. The ages estimated forthese two haplogroups are less in the Indian populations than those estimated from data on Middle Eastern populations. A neighbour-joining tree based on Y-haplogroup frequencies shows that the North Indians are genetically placed between the West Asian and Central Asian populations. This is consistent with gene flow from West Asia and Central Asia into India.


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