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Updated: May 15, 2017 11:08 IST

About 4000 years ago the Narmada valley emerged as the melting pot of India. Three waves of migrating populations, spreading northwards from the Hyderabad region, westward from north Orissa and southwards from Kabul burst upon each other in central India, a new study published on Thursday, found.

“We wanted to find out how people move and where will these people meet?” Mayank N. Vahia at the Tata Institute of Fundamental Research (TIFR), who led the study, said. “It turns out they would meet in the Narmada Valley.”

The researchers traced the migrations of people within the Indian subcontinent starting about 10,000 years ago. It is believed that the first migrations into the subcontinent happened about 60,000 to 30,000 years ago.

Some potential migration routes of various population groups entering the South Asian subcontinent more than 30,000 years ago. Red indicates the path of the earliest migrants along the coastal route; Yellow denotes entrants from the Khyber Pass and green indicates the path taken by migrants from Iran via the Bolan Pass. ( Courtesy: Tata Institute of Fundamental Research )

With over 1.2 billion people and an estimated 4,600 ethnic groups, there is a great cultural diversity in India today but in terms of genetic diversity, Indians come from only four major pools. These are the Ancestral North Indians (ANI), Ancestral South Indians (ASI), Austro-Asian Indians (AAI) and the Tibeto-Burman. The ANI, ASI and AAI account for 90% of the population and among these the ANI and ASI are dominant. The Tibeto-Burmans are relatively small and were not included in the study. Almost everybody in India is a mix of ANI and ASI.

Even when their respective migrations brought them into contact with each other, people from these three major groups never really mixed. Most of the tribes were endogamous and not inclined to intermarry even if they lived in close proximity. This aversion to mixing meant distinctive genetic identities persisted making it easier to trace origins. It also explains why there is no monolithic Indian genetic identity.

The group at TIFR simulated the movement of the groups and then checked it against genetic data available from the Centre for Cellular and Molecular and Biology in Hyderabad. They chose three geographical locations as the most likely sources of these migrations 10,000 years ago: Hyderabad area for ASI, Kabul for ANI and Bhubaneshwar for AAI.

During the prehistoric period, India was sparsely populated, unlike today. The groups under consideration in the study are believed to have arrived independently about 60 000 to 40 000 years ago to the Indian subcontinent when the region was completely uninhabited.

For thousands of years, they lived in the localised geographic regions where they landed without feeling the need to migrate. There were both push and pull factors responsible for the movement, the study notes. If adjacent areas to their current habitations were found to be habitable, determined mostly by the availability of resources, the groups moved.

Habitability of locations in the South Asian subcontinent. The red regions indicate highly habitable places; white zones denote regions that lie more than 4,000 metres above sea level and are, therefore, deemed uninhabitable. ( Courtesy: Tata Institute of Fundamental Research )

The researchers extended the simulation to arrive at conclusions about the present population of India and find that it agrees with the pattern of current population distribution in India. “The map of India’s population about 4000 years ago is more or less the way the distribution is now,” Dr Vahia explained. “There are large concentrations of people in the Indus river valley and in the Ganga basin.”