DNA indicates how ancient migrations shaped South Asian languages and farming

A new DNA study of unprecedented size has unveiled ancient human movements that shaped the genetic makeup of present-day South Asians in complex ways. Those long-ago treks across vast grasslands and through mountain valleys may even have determined the types of languages still spoken in a region that includes what’s now India and Pakistan. 

The investigation addresses two controversial issues. First, who brought farming to South Asia? Genetic comparisons indicate that farming was either invented locally by South Asian hunter-gatherers or launched via borrowing of knowledge from other cultures, rather than brought by Near Eastern farmers from what’s now Turkey. No DNA signs were found of those farmers, who earlier studies suggested had brought farming to Europe. Second, where did local languages originate? New DNA evidence supports the idea that mobile herders from Eurasian steppe grasslands, not Near Eastern farmers, brought Indo-European languages to South Asia.

Ancient DNA had already suggested that Indo-European speaking Eurasian herders called the Yamnaya reached parts of early Bronze Age Europe by around 5,000 years ago (SN: 11/15/17). Yamnaya-related ancestry appeared among South Asians between around 3,900 and 3,500 years ago, an international team reports in the Sept. 6 Science.

“By the early Bronze Age, human movements were stirring the genetic pot throughout Asia,” says archaeologist Michael Frachetti of Washington University in St. Louis. He led the massive project along with Harvard Medical School geneticists David Reich and Vagheesh Narasimhan and archaeologist Ron Pinhasi of the University of Vienna.

What stands out, Frachetti adds, is that Eurasian herders entered South Asia urban centers in relatively small numbers. Thus, a South Asian transition to speaking Indo-European tongues need not have resulted from a large wave of herders rapidly migrating into the region. Scientific scenarios of language change have often been predicated on movements of entire populations that transformed how people spoke elsewhere. 

The research team analyzed DNA extracted from the skeletons of 523 people excavated in Central Asia and northern parts of South Asia. These finds date from around 14,000 to 2,000 years ago. Comparisons were made to previously published examples of ancient DNA from across Eurasia and to present-day Eurasians’ DNA.

Genetic evidence indicates that Near Eastern farmers moved north through Asian mountain valleys into what’s now Iran, along with archaeological evidence of farming tools, by around 5,000 years ago, the researchers say. At the same time, DNA indicates that steppe herders moved south through the same mountain corridors to reach the same area.

Near Eastern farmers appear to have traveled no farther east than Iran, roughly 1,500 kilometers from South Asia’s western outskirts. No genetic trace of Near Eastern farmers appeared in 11 individuals who lived just west of South Asia, in eastern Iran and Turkmenistan, between around 5,300 and 4,000 years ago. Instead, their ancestry came from ancient Iranians and Southeast Asian hunter-gatherers. That genetic mix resembled that of a 4,000- to 5,000-year-old individual buried in northern India who belonged to the Indus Valley Civilization, also called the Harappan civilization. A genetic analysis of that skeleton, by Reich, archaeologist Vasant Shinde of Deccan College Post Graduate and Research Institute in Pune, India, and their colleagues appears September 5 in Cell. This genetic match led researchers to categorize all 12 of these people as Harappans. Members of the Indus Valley Civilization provided the largest source of ancestry for South Asians today, the team says.

Harappan DNA contains no contributions from farming groups, leading the scientists to suggest that locals either invented or borrowed farming techniques.

Yamnaya herders also migrated into South Asia. DNA indicates that they mated with farmers in northern Europe before journeying to northern parts of South Asia between 4,000 and 3,000 years ago, the researchers find. Herder DNA accounts for a minority of present-day South Asians’ ancestry.  

Relatively small numbers of Indo-European speaking migrants may have moved into South Asian communities for a variety of reasons, such as marriage or to pursue a craft such as metalwork, Frachetti says. By providing vital contributions to their new societies, newcomers could have influenced the development of new forms of Indo-European speech, he suggests.

These Europe-to-South Asia Yamnaya travelers may also explain why some current Indo-European languages in Europe and South Asia share linguistic features, the scientists contend. Yamnaya ancestry in South Asians today is disproportionately high in members of groups that consider themselves of priestly status, they add. Those groups include Brahmins, the traditional caretakers of religious texts written in the early Indo-European language Sanskrit. 

Findings in the new Science study do indicate that some mobile herders trekked from Europe to what’s now India shortly after 4,000 years ago, influencing South Asian ancestry and languages, says Kristian Kristiansen, an archaeologist at the University of Gothenburg in Sweden who did not participate in the new studies.

But the origins and spread of Indo-European languages remain controversial. Yamnaya herders contributed much less DNA to ancient South Asians than they did to Europeans, says linguist Paul Heggarty of the Max Planck Institute for the Science of Human History in Jena, Germany. The Yamnaya may have carried Indo-European languages to Europe, Heggarty says, but the new findings suggest that ancient Iranians, estimated to have spoken Indo-European tongues roughly 6,000 to 7,000 years ago, brought those languages to South Asia.