“The Indus Valley Civilization has been an enigma for a long time,” says Priya Moorjani, a population geneticist at the University of California, Berkeley, who wasn’t involved with the study. “So it’s very exciting to … learn about [its] ancestry and history.”
The Indus Valley Civilization emerged sometime around 3000 B.C.E. and had collapsed by about 1700 B.C.E. During its height, it stretched across much of what is today northwestern India and parts of eastern Pakistan. It is alternatively known as the Harappan civilization, after the first of its sites to be excavated in Punjab province in Pakistan beginning in the 1820s. Along with ancient Egypt and Mesopotamia, it was among the world’s first large-scale urban agricultural societies, boasting somewhere between 1 million and 5 million inhabitants across five central cities.
Although hundreds of skeletons from the Indus Valley have been uncovered, the region’s hot climate rapidly destroys the genetic material that has been instrumental in tracing the history of other early civilizations.
In recent years, however, scientists have learned that the petrous bone of the inner ear contains an unusually high quantity of DNA, allowing them to locate usable genetic material even in otherwise degraded skeletons. A team led by geneticist David Reich at Harvard University and archaeologist Vasant Shinde at Deccan College in Pune, India, decided to try the promising technique with Indus specimens. They sampled more than 60 skeletal pieces, including numerous petrous bones, before they were able to extract ancient DNA from one. Then they had to sequence the sample more than 100 times to piece together a relatively complete genome.
“There’s no doubt this is the most intensive effort we’ve ever made to get ancient DNA from a single sample,” Reich says.
The sampled individual, most likely a woman based on her DNA, was buried among dozens of ceramic bowls and vases in an Indus site known as Rakhigarhi, about 150 kilometers northwest of modern-day Delhi. Archaeological evidence suggests she lived sometime between 2800 and 2300 B.C.E. Her genome closely matched DNA from 11 other individuals who had been found at sites in Iran and Turkmenistan, where conditions favor better DNA preservation. (Those individuals belong to a set of 523 ancient DNA sequences used to chart the population history of South Asians and published today in Science.)
Knowing that the Indus civilization traded with those regions, and that those 11 individuals had little in common genetically with others buried in their regions, Reich and colleagues concluded they were likely Harappan migrants….[ ]