From The Atlantic Magazine Online
A Burst of Clues to South Asians’ Genetic Ancestry
A tiny ear bone from more than 4,000 years ago is shaping the story of migration and heritage in India.
SARAH ZHANG
September 5, 2019
The climate of South Asia is not kind to ancient DNA. It is hot and it rains. In monsoon season, water seeps into ancient bones in the ground, degrading the old genetic material. So by the time archeologists and geneticists finally got DNA out of a tiny ear bone from a 4,000-plus-year-old skeleton, they had already tried dozens of samples—all from cemeteries of the mysterious Indus Valley civilization, all without any success.
 |
| Burial I6113 was the only one that yielded ancient DNA from the Indus Valley civilization.(VASANT SHINDE) |
The Indus Valley civilization, also known as the Harappan civilization, flourished 4,000 years ago in what is now India and Pakistan. It surpassed its contemporaries, Mesopotamia and ancient Egypt, in size. Its trade routes stretched thousands of miles. It had agriculture and planned cities and sewage systems. And then, it disappeared. “The Indus Valley civilization has been an enigma for South Asians. We read about it in our textbooks,” says Priya Moorjani, a computational biologist at the University of California at Berkeley. “The end of the civilization was quite mysterious.” No one alive today is sure who the people of the Indus Valley civilization were or where they went.
A pair of newly published papers use ancient DNA to shed light on the Indus Valley civilization and the entire history of people in South and Central Asia. The first study is a sweeping collection of 523 genomes—300 to 12,000 years old—from a region spanned by Iran, Russia, and India. By comparing the results with modern South Asians’ genomes, the study showed that South Asians today descended from a mix of local hunter-gatherers, Iranian-related groups, and steppe pastoralists who came by way of Central Asia. It’s the largest number of ancient genomes reported in a single paper, all made possible by an ancient DNA “factory” the geneticist David Reich has built at Harvard. (Moorjani completed her doctorate in Reich’s lab and is a co-author on this paper.)
The second study focuses on just a single genome from the Indus Valley civilization: I6113, a woman who died more than 4,000 years ago. Her skeleton was the only one—out of more than 100 samples the researchers tested from 10 different Indus Valley–civilization sites—that yielded ancient DNA, but even then it was contaminated and of poor quality. “We had to squeeze, squeeze, squeeze the sample really hard, more than we’ve done in any other sample we’ve ever tried,” says Reich, who is also a senior author of the second paper. The team ultimately tried to sequence DNA from I6113’s ear bone more than 100 times, each time yielding a tiny dribble of genetic data. That I6113 gets her own paper is a testament to both the technical difficulty of sequencing her DNA and the importance of the Indus Valley civilization. Even before publication, rumors were swirling in India about what the ancient DNA would show, and how it would play into the politics of the Hindu-nationalist ruling party.
