Current distinctions among groups within the Indian subcontinent are ancient, and strong inbreeding must have shaped marriage patterns in India for thousands of years, according to a study of genetic variation in Indian populations published in Nature. The study also reveals that the 'caste' system in India has existed for thousands of years, contradicting the view of some historians that 'caste' in modern India is an 'invention' of colonialism in the sense that it became more rigid under colonial rule.
David Reich and colleagues looked at single nucleotide polymorphisms in people representative of 25 diverse groups from around India. Their results reveal that there are two ancient, genetically divergent, populations that are ancestral to most Indians today. Traditionally upper caste and Indo-European speakers are descended from a group that is genetically close to Middle Easterners, Central Asians, and Europeans. The other group is not close to any group outside the subcontinent.
As well as the historical significance, the research also has medical implications for Indian populations. Recessive hereditary diseases - single gene disorders that occur only when an individual carries two malfunctioning copies of the relevant gene - are likely to be common in populations descended from so few 'founder' individuals. Mapping the causal genes will help to address this problem, but the authors caution that false-positive disease associations may occur if researchers do not take into account ancestry differences between cases and controls.
David Reich (Harvard Medical School, Boston, MA, USA)
(C) Nature press release.
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