Wednesday, 21 September 2011

The so-called lower castes and tribals are genetically closer to one another than to people belonging to upper castes

By Syed Akbar
Hyderabad:  The so-called lower castes and tribals are genetically 
closer to one another than to people belonging to upper castes.
An original research study by the city-based Centre for Cellular and 
Molecular Biology reveals that lower caste populations in India are closer to 
tribal populations because of the tribal origin of the lower castes.
According to CCMB senior scientist Kumarasamy Thangaraj, the origin of 
the caste system in India has been a subject of debate with many linguists and 
anthropologists suggesting that it began with the arrival of Indo-European 
speakers from Central Asia about 3500 years ago. Previous genetic studies 
based on Indian populations failed to achieve a consensus in this regard.
In the present study the CCMB scientists analysed the Y-chromosome and 
mitochondrial DNA of three tribal populations of southern India and 
compared the results with available data from the Indian subcontinent in an 
attempt to reconstruct the evolutionary history of Indian caste and tribal 
populations. 
The scientists did not find any significant difference in the mitochondrial 
DNA between Indian tribal and caste populations, except for the presence of 
a higher frequency of west Eurasian-specific haplogroups in the higher 
castes, mostly in the north western part of India. On the other hand, the study 
of the Indian Y lineage revealed distinct distribution patterns among caste 
and tribal populations.
"The paternal lineage of Indian lower castes showed significantly closer 
affinity to the tribal populations than to the upper castes. The frequencies of 
deep-rooted Y haplogroups such as M89, M52, and M95 were higher in the 
lower castes and tribes, compared to the upper castes," says Dr Thangaraj. 
The study suggested that the vast majority (more than 98 per cent) of the 
Indian maternal gene pool, consisting of Indo-European and Dravidian 
speakers, is genetically more or less uniform, suggesting that invasions after 
the late Pleistocene settlement might have been mostly male-mediated.
However, Y-SNP data provided compelling genetic evidence for a tribal 
origin of the lower caste populations in the subcontinent. Lower caste groups 
might have originated with the hierarchical divisions that arose within the 
tribal groups with the spread of Neolithic agriculturists, much earlier than the 
arrival of Aryan speakers.
The Indo-Europeans established themselves as upper castes among this 
already developed caste-like class structure within the tribes. The Indian 
society and culture might have been affected by multiple waves of migration 
and gene flow that occurred in the historic and prehistoric times.
The first among this is the ancient Palaeolithic migration by the modern 
humans during their initial colonisation of Eurasia. This is followed by the 
early Neolithic migration, probably of proto-Dravidian speakers, 
from the eastern horn of the Fertile Crescent. The Indo-European speakers, 
who might have arrived about 3,500 years ago, are the third potential source 
of Indian gene pool.
"Indian tribal and caste populations derived largely from the same genetic 
heritage of Pleistocene southern and western Asians, receiving limited gene 
flow from external regions since Holocene. The paternal lineage of Indian 
castes are more closely related to the Central Asians than to the Indian tribal 
groups, thereby supporting the view that Indian caste groups are primarily the 
descendants of the Indo-European migrants," Dr Thangaraj points out.
The newly defined Indian-specific mitochondrial sub-clad, M41, was found 
in about five per cent of the Pardhan samples. This lineage was previously 
reported as an undefined M lineage found at a very low frequency in caste 
(Brahmin, Yadava and Mala) and tribal (Koya and Lambadi) populations of 
AP, but not anywhere else in India.
Indian populations were founded by a rather small number of females, 
possibly arriving on one of the early waves of out-of-Africa migration of 
modern humans; ethnic differentiation occurred subsequently, through 
demographic expansions.
The results suggest that the Indian subcontinent was settled soon after the 
initial out-of-Africa expedition, and that there had been no complete 
extinction or replacement of the initial settlers; rather it might have been 
restructured in situ by the major demographic episodes of the past, and by the 
relatively minor gene flow due to the recent invasions from both the West 
and the East.
The lower caste shows more similarity with the tribal groups than with the 
upper caste populations (4.72 per cent difference between the upper 
and lower castes). This is suggestive of a tribal origin for the Indian lower 
castes. Geography does not seem to have affected this association of the 
tribal groups with the lower castes. At the same time, significant variation 
(6.17 per cent) was observed between upper castes and tribal groups. 
However, variation of Dravidian tribal groups with Dravidian higher castes 
was found to be lower (4.4 per cent) than that with Indo-European speaking 
north Indian higher castes (8.1 per cent).

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