Genome wide ancient DNA from 523 ancient individuals sheds light on genetic exchanges between the Steppe, Iran and South Asia, and highlights the parallel demographic histories of two subcontinents: Europe and South Asia.. The Formation of Human Populations in South and Central Asia

By sequencing 523 ancient humans, we show that the primary source of ancestry in South Asians is an ancient population we detect at sites in cultural contact with the Indus Valley Civilization (IVC) that we show formed a genetic gradient between early hunter-gatherers of Iran as well as hunter-gatherers of South Asia (with a negligible contribution from Central Asia). Following the IVC’s decline, people from this population mixed with groups primarily descended from southern Asian hunter-gatherers to form one of the two main sources of South Asian variation, the “Ancestral South Indians” (ASI) whose direct descendants live today in southern India. Around 4000-3500 years ago, people from this same population mixed with descendants of Steppe pastoralists who spread via Central Asia to form the “Ancestral North Indians” (ANI). The Steppe ancestry in the ANI is distinctively similar to that in Bronze Age Eastern Europe, suggesting that it is tracking a movement of people that affected both regions and that likely spread the unique features shared between Indo-Iranian and Balto-Slavic languages. Our results suggest that a language ancestral to Indo-Iranian was spoken on the Steppe ~4000 years before present.