After the Harappans, large influx brought steppe DNA into South Asia: Geneticist Vagheesh Narasimhan

In early September, the journals Cell and Science published two long-awaited papers based on the science of ancient DNA. The papers confirmed and expanded on what has been reported in the recent past about human settlement in South Asia. The study in Cell is based on the DNA from a single sample, a female, from a 4,500-year-old burial site in the Harappan city of Rakhigarhi. A summary of the results includes three key findings: the individual was from a population that is the largest source of ancestry for South Asians; Iranian-related ancestry in South Asia split from the Iranian-plateau lineages more than twelve thousand years ago; and the first farmers of the Fertile Crescent—a region that was the cradle of the Egyptian, Phoenician, Assyrian and Mesopotamian civilisations—contributed little to no ancestry to later South Asians. This indicates that not only were that the greater part of most South Asians’ genome is derived from the Harappan people, but also that farming may well have an independent origin in the region. Most South Asians carry some ancestry derived from steppe pastoralists, ranging from less than ten percent to a little over twenty percent. This ancestry is entirely absent in the Harappan genome, suggesting that the steppe pastoralists migrated to the subcontinent in substantial numbers after the decline of the Harappan civilisation. Both papers clearly spell out the likelihood that the steppe pastoralists brought the Indo-European languages to the subcontinent.

Hartosh Singh Bal, the political editor of The Caravan, spoke to Vagheesh Narasimhan, the lead author of the Science paper. Narasimhan is a post-doctoral fellow at the Reich Laboratory, at Harvard Medical School. His research is focused on using ancient DNA to understand human migration and evolution. They discussed the research methodologies that led to the laboratory’s findings, possible correlations between languages and genetics, and what the results say about when the steppe pastoralists arrived in India. The geneticists’ work so far, Narasimhan said, maps the settling of the subcontinent till 1000 BC. But a similar study of more recent samples is necessary to answer questions central to an understanding of Indian society today, including the origins and the evolution of the caste system.