The Genomic Formation of South and Central Asia

Abstract

119 The genetic formation of Central and South Asian populations has been unclear because of an 120 absence of ancient DNA. To address this gap, we generated genome-wide data from 362 ancient 121 individuals, including the first from eastern Iran, Turan (Uzbekistan, Turkmenistan, and 122 Tajikistan), Bronze Age Kazakhstan, and South Asia. Our data reveal a complex set of genetic 123 sources that ultimately combined to form the ancestry of South Asians today. We document a 124 southward spread of genetic ancestry from the Eurasian Steppe, correlating with the 125 archaeologically known expansion of pastoralist sites from the Steppe to Turan in the Middle 126 Bronze Age (2300-1500 BCE). These Steppe communities mixed genetically with peoples of the 127 Bactria Margiana Archaeological Complex (BMAC) whom they encountered in Turan (primarily 128 descendants of earlier agriculturalists of Iran), but there is no evidence that the main 129 BMAC population contributed genetically to later South Asians. Instead, Steppe communities 130 integrated farther south throughout the 2nd millennium BCE, and we show that they mixed with 131 a more southern population that we document at multiple sites as outlier individuals exhibiting a 132 distinctive mixture of ancestry related to Iranian agriculturalists and South Asian hunter-gathers. 133 We call this group Indus Periphery because they were found at sites in cultural contact with the 134 Indus Valley Civilization (IVC) and along its northern fringe, and also because they were 135 genetically similar to post-IVC groups in the Swat Valley of Pakistan. By co-analyzing ancient 136 DNA and genomic data from diverse present-day South Asians, we show that Indus Periphery- 137 related people are the single most important source of ancestry in South Asia—consistent with 138 the idea that the Indus Periphery individuals are providing us with the first direct look at the 139 ancestry of peoples of the IVC—and we develop a model for the formation of present-day South 140 Asians in terms of the temporally and geographically proximate sources of Indus Periphery- 141 related, Steppe, and local South Asian hunter-gatherer-related ancestry. Our results show how 142 ancestry from the Steppe genetically linked Europe and South Asia in the Bronze Age, and 143 identifies the populations that almost certainly were responsible for spreading Indo-European 144 languages across much of Eurasia. …