Human beings are first known to have appeared on the African continent about 100,000 years ago. From there, they moved to different parts of the world over a long period of time. It is commonly understood that humans preferred certain locations over others while deciding to make their settlements. The proximity to water bodies was one of the important factors, along with altitude and slope of the land, in deciding this preference. As people sought newer places, due to population pressure or in search of better access to food and water, populations diffused away from their previous locations. This is how new settlements and habitations were built which slowly evolved into villages, towns, cities and countries over a period of time.
We understand fairly well the reasons for early human beings to choose a particular location for settling down. We are not sure, however, about the routes they took to reach these places from their previous locations. For example, we are not very certain about the route human beings took to arrive in India from Africa. One of the main reasons for this was the lack of availability of relevant databases and simulation models. Historically, we have traced these travels along a source of water, and this is not an unreasonable assumption to make. But for the first time now, we have attempted to carve a detailed path that early human beings most likely took to arrive in the Indian subcontinent and disperse within it.
Thanks to very high-resolution maps of the earth released by NASA recently, and with some basic assumptions about the motivations for migration of human beings, we have prepared a mathematical simulation of the paths that these early humans would have taken to reach India and settle down.
To be sure, we have not traced this path from the origin. We have looked only at migration within the Indian subcontinent after the human beings had arrived on its borders, from the south and east, and the northwest. The first group of people to have come to India arrived by sea and settled in south India some 60,000 years ago. About 10,000 years later came the Austro-Asians, again along the coastline. The last of the great migrations in India happened a further 10,000 years later, this time through Afghanistan and Khyber pass. These people came from Europe and formed the population in north India. The three groups had distinct genetic makeups.
For our simulation, we considered that these three groups first settled in areas around current Hyderabad and Bhubaneswar and started moving inwards from there. The last batch of migrants moved in from the northwest, the areas around current Afghanistan and Pakistan.
We divided the land into small grids of 8 km by 8 km, using the NASA data, and looked at the “habitability” of each of these grids. For our purpose, we used three criteria to assess the habitability of the grid — proximity to a reliable and sufficient source of water, the incline of the plane, and the altitude. A place with an altitude of over 5,000 m, for example, was considered not comfortable for living and we assumed that the people would have avoided these places. Another relatively safe assumption we made was that food, the kind of which humans used to eat at that time, was available in all the habitable grids in one form or the other.
Having so divided the land surface, we placed humans in one grid and then checked for their likely mobility in the neighbouring grids depending on whether they were more habitable or less. By moving along this way, we traced the likely paths that these early human beings would have taken to reach the major settlements of their time.
As people move, their genetic composition shows changes to adapt to newer environment and climate. Genetic changes also occur due to intermingling of different gene pools. Current technology has enabled the creation of a rich repository of genetic resources of human beings across the world and the way it has evolved over time. When we matched genetic data with our simulation, it gave results that were in agreement with the migratory paths that were being suggested.
For example, from our study we expected that as we move from the east to the west in India, the contribution of European genes would increase as compared to Austro-Asian genes. That is exactly what studies on genetic data also revealed. We extended our simulation to the present day and the results matched the population density of current settlements and the genetic composition of the people living there.
The route map that we have come up with can be very useful in determining whether a particular site is likely to have any archaeological significance even before any elementary exploration is done. In fact, the map does suggest that there are likely to be some places of archaeological interest that have not yet been examined.