Genetic evidence on the origins of Indian caste populations

The origins and affinities of the similar to1 billion people living on the subcontinent of India have long been contested. This is owing, in part, to the many different waves of immigrants that have influenced the genetic str ucture of India. in the most recent of these waves, Indo-European-speaking people from West Eurasia entered India from the Northwest and diffused thro ughout the subcontinent. They purportedly admired with or displaced indigen ous Dravidic-speaking populations. Subsequently they may have established t he Hindu caste system and placed themselves primarily in castes of higher r ank. To explore the impact of West Eurasians on contemporary Indian caste p opulations, we compared mtDNA (400 bp of hypervariable region 1 and 14 rest riction site polymorphisms) and Y-chromosome (20 biallelic polymorphisms an d 5 short tandem repeats) variation in similar to 265 males from eight cast es of different rank to similar to 750 Africans, Asians, Europeans, and oth er Indians. For maternally inherited mtDNA, each caste is most similar to A sians. However, 20%-30% of Indian mtDNA haplotypes belong to West Eurasian haplogroups, and the frequency of these haplotypes is proportional to caste rank, the highest frequency of West Eurasian haplotypes being found in the upper castes. In contrast, for paternally inherited Y-chromosome variation each caste is more similar to Europeans than to Asians. Moreover, the affi nity to Europeans is proportionate to caste rank, the upper castes being mo st similar to Europeans, particularly East Europeans. These findings are co nsistent with greater West Eurasian male admixture with castes of higher ra nk. Nevertheless, the mitochondrial genome and the Y chromosome each repres ents only a single haploid locus and is more susceptible to large stochasti c variation, bottlenecks, and selective sweeps. Thus, to increase the power of our analysis, we assayed 40 independent, biparentally inherited autosom al loci (1 LINE-1 and 39 Alu elements) in all of the caste and continental populations (similar to 600 individuals). Analysis of these data demonstrat ed that the upper castes have a higher affinity to Europeans than to Asians , and the upper castes are significantly more similar to Europeans than are the lower castes. Collectively, all five datasets show a trend toward uppe r castes being more similar to Europeans, whereas lower castes are more sim ilar to Asians. We conclude that Indian castes are most likely to be of pro to-Asian origin with West Eurasian admixture resulting in rank-related and sex-specific differences in the genetic affinities of castes to Asians and Europeans.