A team of researchers has found that the contemporary population groups of mainland India are a result of the intermixing of four main types of ancestral lineages. This is in sharp contrast to the conclusion of an earlier major study that all Indian population groups resulted from an admixture of only two ancestral lineages.
The researchers compared genetic data, at 803,570 autosomal SNPs, among 367 individuals drawn from 20 ethnic populations (18 mainland and 2 Andaman and Nicobar Island populations) of India, and also with data on individuals sampled from West Asia, Central-South Asia, and East and South East Asia to trace how humans first arrived in India.
The four ancestral lineages identified in this study are roughly identifiable with the four language families spoken in India – Indo-European (north India), Dravidian (south India), Tibeto-Burman (north-east India) and Austro-Asiatic (highly fragmented language family spoken exclusively by tribal groups inhabiting east and central India).
The team of scientists consisting of Analabha Basu, Neeta Sarkar-Roy, and Partha P. Majumder from the National Institute of Biomedical Genomics also identified a fifth ancestral lineage that are found only among some tribal populations of Andaman & Nicobar islands. Analyzing data that were collected by other researchers, this team also found the same ancestral lineage to be present among the contemporary Pacific island populations.
The researchers have also unearthed the deep imprint of a significant social cultural process in Indian society marked by widespread admixture which ended abruptly 70 generations ago coinciding with the Gupta rule.
They have inferred that this was due to the practice of endogamy which was established almost simultaneously, possibly by decree of the rulers, in upper-caste populations of all geographical regions, ‘during the reign (319–550 CE) of the ardent Hindu Gupta rulers’.
Genetic analysis also revealed that the establishment of endogamy among tribal populations was less uniform.
This study corrects inadequacies of population sampling, such an non-inclusion of tribal groups considered by anthropologists to be indigenous populations, that was a major constraint in some earlier reports. The new study provides a more robust explanation of the genomic diversities and affinities among extant populations of the Indian subcontinent, elucidating in finer detail the peopling of the region.