Though the overwhelming majority of the population in Bangladesh forms a homogeneous ethnic group today, the racial mix of diverse races occurred in this region over a long time. Broadly speaking, there are two major racial elements in the people of Bengal: (1) the primitive tribes like the Kols, Sabaras, Pulindars, Hadi, Dom, Chandala and others who were designated as the Mlechchas; (ii) the Aryan and Aryanized elements.
The major pre-Aryan racial elements in Bengal were the proto-Austroloids. There is a striking similarity between the language of the aborigines of Bengal and the people in South-East Asia, the archipelago and the aborigines of Australia. The Dravidian languages of South India also belong to proto-Australoid group. Bangladesh, being the frontier of South Asia, also came into contact with the Mongoloid tribes who lived in the adjoining areas. The Mongoloid influence was dominant in the Chittagong Hill Tracts region where Chakmas and other tribes belong to this category. The Mongoloid influence is, however, limited in other areas. Scholars maintain that there is also a substratum of Negroid racial elements in the racial mix in this region.
Thus Bengal was the home of mixed races long before the Aryans came. The Aryan influence in Bengal was primarily limited to upper castes. The gradual stages in the Aryanization of Bengal are not very clear. It appears that the Aryans brought the indigenous people into the framework of Aryan society. This is indicated by the fact that some of the indigenous tribes were classed at Khastriyas (the warrior class). The majority of these pre-Aryan tribes were classified as untouchables. The process of racial mix did not, however, stop with the coming of Aryans. The Semitic traders from the Arab world frequently visited the coastal areas in the Middle Age.