Their in-migration, their settlement in India and later movements within the country have led to a high degree of intermingling between the various ethnic and cultural streams.
The ethnic and cultural diversities displayed by Indian population today have thus acquired their distinguishing traits through this process of intermingling. The physical factors of location, accessibility by land and sea and the routes of migration into India have played a key role in defining the complexion of its ethnic links in the past.
The various passes in the Himalayas have offered entry points for the in-migrating streams of people. Their later movements within the country have taken place along the river valley routes leading to a continual process of redistribution of population and ethnic intermixing at every stage. The river valleys and basins were the main areas of attraction because of their fertile soils and availability of water.
The racial groups ousted from these basin after each incursion have moved into the relatively less accessible areas like hilly and forested tracts, which have been un- attractive areas from the point of view of settled agriculture, therefore the indigenous groups inhabiting them have remained comparatively undisturbed.
These areas have also served as refuge areas for displaced ethnic groups from the river basins and open areas. It is in these otherwise isolated regions that the earliest racial groups have survived till today. These areas have the most primitive forms of culture as they did not encourage mixing with other cultures resulting in very limited contact with modern advancement in science and technology.
Early Streams of In-migration:
According to the anthropologist the early man entered India about 4 to 5 lakh years ago. This is inferred from the evidence of the earliest tools left behind by the Palaeolithic (Stone Age) man. The Palaeolithic man entered India from Western passes and moved further along favourable routes of river valleys because these area could meet his basic requirements specially food and water.
This is evident from the excavation sites of Palaeolithic tools in the terraces and basins of rivers like Sohan, Chambal, Sone, Narmada, Sabarmati, Pennar, Godavari and their various tributaries.
It is interesting to note that the main centres of population today like the Ganga Valley and the delta are by and large devoid of any evidence of the existence of the early man. This may be due to unfavorable conditions prevailing in the Ganga valley and delta during the Pleistocene age. The structure of languages and dialects spoken by different ethnic groups in various parts of the country also establish the early ethnic links of our people.