THE Rigveda, a collection of Sanskrit hymns written around 3500 years ago, doesn鈥檛 contain much genetics. It does, however, have the first mention of India鈥檚 caste system, and now a genetics study reveals that inbreeding going back thousands of years has led to marked genetic differences between castes. It also shows that India鈥檚 many distinct peoples spring from just two ancient populations.
Nick Patterson of the Broad Institute in Cambridge, Massachusetts, and colleagues examined fragments of DNA from 25 groups across India. They included castes and hunter-gatherer tribes, or 鈥渟cheduled populations鈥�. Each of these groups was genetically distinct, but the profiling indicated that all Indians spring from one of two populations: Ancestral North Indians (ANI), who are genetically close to Europeans, and Ancestral South Indians, who are distinct from both east Asians and ANI (Nature, ).
鈥淚f you鈥檙e trying to understand disease and distribution between south and north India, there could be environmental or lifestyle issues,鈥� says Patterson, 鈥渂ut genetics could also offer a perfectly possible explanation.鈥�
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The analysis showed that castes are descended from a small pool of ancestors and that an initial lack of genetic variability has been reinforced by marriages within the group. The current caste system has resulted in limited gene flow for thousands of years, says Patterson.
