The Dazzling Diversity and the Fundamental Unity: Peopling and the Genomic Structure of Ethnic India

Abstract

India with a census size of 1.25 billion, harbours more than one-sixth of the world population. Contemporary India has a rich tapestry of cultures and ecologies. However, when we refer to the heritage and the glorious diversity of the land, we are generally referring to the immense diversity of its people. There are about 400 tribal groups and more than 4000 groups of castes and sub-castes, speaking 22 ‘officially’ recognized languages and 461 ‘tongues’ belonging to four major language families. Recent advances in molecular and statistical genetics have enabled the reconstruction of human history by studying living humans. The ability to sequence and study DNA by calibrating the rate of accumulation of changes with evolutionary time has enabled robust inferences about how humans have evolved and retrace their early paths of migration. Modern humans after their origin in Africa about 150,000 years before present, has migrated out-of-Africa to populate the entire globe. It is postulated that one of the earliest of these migration waves passed through India. Subsequently, the Indian sub-continent has occupied the center-stage of many Paleolithic and Neolithic migrations. Waves of migration at different points of time in history have resulted in India being a genetic melting pot. The contemporary social structure of Indian populations is characterized by endogamy with different degrees of porosity. The social structure, possibly coupled with large ecological heterogeneity, has resulted in largescale genetic diversity and local genetic differences within India. In this essay, I provide genetic evidence of how India may have been peopled, the nature and extent of its genetic diversity, and genetic structure among the extant populations of India. Studies of uniparental markers like the mtDNA and Y-chromosome has established the antiquity of the Indian populations. It has also outlined the possible earliest migration routes from out-of-Africa into India. However, for fine-graining the intricacies of migrations and admixture, uniparental markers are not extremely useful. An early effort with genomewide markers modeled the peopling of India as an admixture with only two distinct ancestries. However, recent studies have shown that the peopling in India has a much more complicated history, which has also been reshaped by cultural and demographic events. Evidence shows that populations of mainland India have atleast four distinct genetic ancestries. A distinct ancestry of the populations of Andaman archipelago is also identified and found to be co-ancestral to Oceania populations.