Mark Henderson, Times (London), Sept. 24, 2009
Genetic profiling shows that the structure of Indian society today reflects early social groupings, not just colonialism India’s caste system is not a relic of colonialism but has existed in some form for thousands of years, the most comprehensive study yet of the genetic diversity of the sub-continent has suggested.
The genetic profiles typical of modern castes are indistinguishable from those of much older tribal groups, Indian and American scientists have found. This suggests that they emerged from populations of shared ancestry who have married among themselves for many generations.
The researchers wrote in the journal Nature: “Some historians have argued that caste in modern India is an ‘invention’ of colonialism, in the sense that it became more rigid under colonial rule. However, our results indicate that many current distinctions among groups are ancient and that strong endogamy [marriage within a group] must have shaped marriage patterns in India for thousands of years.”
Kumarasamy Thangaraj, of the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad, and a leader of the study, said: “It is impossible to distinguish castes from tribes using the data. The genetics proves that they are not systematically different. This supports the view that castes grew directly out of tribal-like organisations during the formation of Indian society.”
Researchers analysed more than 500,000 genetic markers from 132 people from 25 different groups.
The research established that modern Indians of all castes are descended from two ancestral groups.
Indians can trace between 39 per cent and 71 per cent of their ancestry to a population known as the Ancestral Northern Indians (ANI), who are quite closely related to Europeans and Asians. Those with a higher ancestral contribution from the ANI group are more likely to belong to higher castes, and to speak Indo-European languages such as Hindi and Bengali.
The other ancient population are the Ancestral Southern Indians (ASI), who are not genetically close to any group outside the sub-continent. People with a higher ASI ancestry are more likely to belong to lower castes, and to speak non Indo-European languages such as Tamil.
The research, by scientists from CCMB in India and Harvard University and the Massachusetts Institute of Technology (MIT) in the United States, has also established that Indians are much more genetically diverse than Europeans.
This result indicates that many modern Indian groups are descended from a small number of “founding individuals”, whose descendants interbred among themselves to create genetically isolated populations.
Lalji Singh, director of CCMB, said: “India is genetically not a single large population, but instead is best described as many smaller isolated populations.”
This insight has important medical implications for people of Indian origin, because groups that are descended from small founding populations often have a high incidence of inherited diseases. Ashkenazi Jews, for example, have a high risk of Tay-Sachs disease.
This may explain why several genetic conditions are more common in India than elsewhere: a mutation in a gene called MYBPC3, which raises the risk of heart failure sevenfold, is found in 4 per cent of Indians but is exceptionally rare elsewhere.
The only ethnic group who do not have this shared ancestry is the indigenous population of the Andaman Islands in the Indian Ocean, who appear to be of exclusively ASI descent.
Nick Patterson, of the Broad Institute of Harvard and MIT, said: “The Andamanese are unique. Understanding their origins provides a window on to the history of the Ancestral South Indians, and the period tens of thousands of years ago when they diverged from other Eurasians.”
Mr Singh added: “Our project to sample the disappearing tribes of the Andaman Islands has been more successful than we could have hoped, as the Andamanese are the only surviving remnant of the ancient colonisers of South Asia.”
Aravinda Chakravarti, of Johns Hopkins School of Medicine in Baltimore, Maryland, wrote in a commentary for Nature: “Greater ANI ancestry is significantly associated with Indo-European speakers and with traditionally ‘higher’ caste membership. This provides a model of how diversity within India came about. As such, its details are imperfect and will surely be contested, revised and improved.
“Caste and custom may be strong barriers between groups, perhaps even today. But the common shared ancestry and rampant ANI/ASI mixture may be the strong, invisible thread that binds all Indians.”