India has served as a major corridor for the dispersal of human beings that started from Africa about 100,000 years. Though the date of entry of modern humans into India remains uncertain, evidence from archaeological studies suggest that by the middle paleolithic period (50,000-20,000 years before present (ybp), humans appear to have spread to many parts of India. Molecular genetic evidence also supports the fact that a major population expansion of modern humans took place within India. The time of this demographic expansion has been speculated to be about 60,000-85,000 ybp (Mountain et al. 1995). Contemporarily, there is an extensive social, cultural, linguistic and biological diversity in the Indian population, nurtured to a large extent by the varied topography of the country. The vast majority of the people of India (~80%) belong to the Hindu religious fold. Hindus are hierarchically arranged into 4 socio-cultural clusters of groups (castes) and there are set rules governing marriage within the Hindu religious fold. About 8% of the population is constituted by tribals, who are ancestor worshippers and are largely endogamous. The remaining belongs to other religious groups, including Muslims, Christians, Buddhists, Jews, etc. Primarily, marriages occur within the religious groups. In addition, language and geographical location of habitat, serve as barriers to free gene flow. These factors have resulted in the formation of a several thousand endogamous groups in India. Indian population, comprising of more than a billion people, consists of 4693 communities with several thousands of endogamous groups, 325 functioning languages and 25 scripts.

In some geographical regions of India, inbreeding is practiced. The population inbreeding coefficient in India varies from 0.00-0.20. Besides, different waves of migration have led to admixture of different ethnic groups, cultures and languages, with the native population, thereby contributing significantly to the present day gene pool of the subcontinent. With the exception of Africa, such an extent of genetic diversity is not observed in comparable global regions. Indian population can be, to a large extent, substructured on the basis of their ethnic origin as well as linguistic lineages. All the four major morphological types- Caucasoid, Mongoloid, Australoid and Negrito, are present in the Indian population (Malhotra 1978). The "Caucasoid" and "Mongoloid" populations are mainly concentrated in the north and northeastern parts of the country. The "Australoids" are mostly confined to the central, western and southern India, while the "Negritos" are restricted only to the Andaman Islands (See Morpho Map) Linguistically, Indian populations belong to four major language families: Indo-European, Dravidian, Tibeto-Burman and Austro-Asiatic. The Indo-European and Dravidian languages are spoken in the northern and southern parts of the subcontinent, respectively (See Linguistic Map). The Tibeto-Burman speakers are supposedly immigrants to India from Tibet and Burma (now, Myanmar) and are concentrated in the northeastern parts of the country. The Austro-Asiatic speakers are exclusively tribals and are dispersed mostly in the central and eastern parts of the country. Molecular diversity studies have revealed that the Austro-Asiatic speakers are likely to have been the most ancient inhabitants of India.

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