Monday, 12 January 2009

Social hierarchy has genetic basis too

By Syed Akbar
Hyderabad: The Indian caste and social hierarchy has genetic basis too. The genetic make-up of people belonging to upper castes is similar and closely related among themselves as compared with the people hailing from the so-called lower castes.
Brahmins, who occupy the topmost position in the Indian Varna system, are genetically more closer to the next immediate group Kshatriyas, than they are to people belonging to "lower" castes. The genetic distance between Kshatriyas and the third Varna group Vysyas is closer than the genetic distance between Vysyas and Brahmins. The so-called lower social hierarchical Muslim groups like Dudekula and Shaik also closely resemble in genetic make-up to other lower rung groups in society.
However, people of Andhra Pradesh, irrespective of their caste or socio-economic hierarchy are genetically related among themselves. For instance, Brahmins from Andhra Pradesh are genetically closer to people of other castes and social hierarchy in the State as compared with Brahmins of say, north India.
These interesting genetic statistics came to light during a research study on "genetic stratification versus social stratification" of people in Andhra Pradesh conducted by the Biological Anthropology Unit of Indian Statistical Institute in collaboration with the Centre for Cellular and Molecular Biology. The study was published in the "Human Biology" magazine, USA.
As part of the study, DNA samples of 948 individuals belonging to 27 caste populations from Andhra Pradesh were analysed. The nature and extent of genomic diversity within and between these populations have been examined with reference to socio-economic and geographic affiliations.
Andhra Pradesh has people with several endogamous castes, tribes and religious groups presenting enormous variety in its populations, socio-cultural patterns and organisation. Several anthropological investigations suggest that the (caste) populations of Andhra Pradesh that practice close consanguineous marriages prefer village endogamy and restrict marriage contacts to small distances and hence are highly inbred. This has probably led to a reduction in effective population size, creating breeding isolates within apparently single endogamous castes and sub-castes.
The castes or socio-economic categories studied as part of the research project (in decreasing order of hierarchy) were: Brahmins, Kshatriya, Vysya, Akuthota, Kamma, Kapu, Pokanati, Panta, Vanne, Balija, Ekila, Kurava, Thogata, Yadava, Ediga, Gangla, Jangam, Chakali, Mangali, Vaddi, Madiga, Mala, Erukala, Sugali and Yanadi. Two Muslim groups, Dudekula and Shaik, were also included in the study.
"Compared to other Indian and world populations, the populations of Andhra Pradesh form a distinct cluster clearly separated from the rest. The other populations in the tree seem to be aligned on broad geographic, ethnic, or linguistic affiliations. For example, Asian populations from north-eastern India form a distinct cluster, as do the other Asian populations from sub-Himalayan India and East Asia. Populations from Western India, Central India and North India also form distinct subclades (sub-group of people with common ancestor), although geographic contiguity is apparent with their placement as neighbouring clades," observes project leader Prof B Mohan Reddy of Indian Statistical Institute.
According to him, some of the population from south India that have European physical features (Iyenger, Lingayat, Gowda and Muslims), however, form a subclade along with the three American groups (US whites, US Hispanics and African Americans).
Although genetic distance tended to increase with increasing difference in the social hierarchy, the differences were not statistically significant. Even this meek trend disappears when the DA (genetic) distance is considered or when average distances for different pairs of populations between different hierarchical groups is computed.
Furthermore, the average distance between populations of the same socio-economic group is not significantly different from or lower than the average distance between the populations of different groups. However, each of these hierarchical groups shows the largest genetic distance with the tribes compared to the mutual distances among them, suggesting genetic isolation and differentiation of the tribes and castes.
According to Mohan Reddy, Akuthota Kapu, Vanne Kapu and Pokanati (the three sub-groups of the Reddy caste) appear as relatively more distinct outliers above the theoretical regression line, suggesting that external gene flow played a role in their differentiation. The Gandla, Yanadi, Mangali and Kapu appear as outliers below the theoretical regression line, indicating that isolation and stochastic processes played a role in sculpting their genetic composition. The rest of the populations are scattered above and below but in the vicinity of the regression line, in conformity to the model and suggesting a uniform degree of gene flow among them.
"When we computed the distances for the hierarchical caste groups, treating the three Varna categories in the upper castes (Brahmins, Kshatriyas and Vysyas) separately, no particular pattern of genetic distances, adhering to the implicit hierarchy, emerged between them. This suggests a lack of strong genetic signatures consistent with the traditional Varna system (constituting only Brahmins, Kshatriyas, Vysyas and Sudra categories), although a semblance of genetic stratification was evident with respect to socio-economic hierarchy (upper, middle and lower castes)," he pointed out.

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