THE Rigveda, a collection of Sanskrit hymns written around 3500 years ago, doesn’t contain much genetics. It does, however, have the first mention of India’s caste system, and now a genetics study reveals that inbreeding going back thousands of years has led to marked genetic differences between castes. It also shows that India’s many distinct peoples spring from just two ancient populations.
India’s caste system stretches back thousands of years and was not largely a creation of colonial rule, as some historians claim, a genetic study has shown. Researchers analysed the DNA of 132 individuals with wide-ranging backgrounds from 25 diverse groups around India.
They found evidence of strong inbreeding leading to genetic groups that had been isolated from each other for thousands of years. Most people had a mixture of genes from two ancient populations representing traditionally upper-caste individuals and everyone else.
The first was genetically close to people from the Middle East, Central Asia and Europe, while the second had an ‘Ancestral South Indian’ lineage confined to the subcontinent. The research challenges the notion that India’s notorious rigid caste system, with its priestly Brahmans and low-status ‘untouchables’, was largely manufactured by the British.
Some historians claim that while a caste system of sorts had existed since ancient times, in its original form it was not hereditary or inflexible and allowed people to move up and down the social ladder. It was the British who cemented the caste system into Indian society and culture by using it as a basis of a ”divide and rule” policy, it is alleged. The caste system was a convenient means of keeping society under control.
The new findings published in the journal Nature indicate that, genetically at least, Indians had been divided long before the British arrived.
The scientists analysed more than 500,000 genetic markers from people representing 13 states, all six language families in India, traditionally ”upper” and ”lower” castes, and tribal groups.
One group of Andaman islanders was, unusually, related exclusively to the Ancestral South Indian lineage. Co-author Dr Nick Patterson, from the Harvard University/MIT Broad Institute in Massachusetts, US, said: ”The Andamanese are unique. Understanding their origins provides a window onto the history of the Ancestral South Indians, and the period tens of thousands of years ago when they diverged from other Eurasians.”
The research has important health implications for Indians. Other genetically isolated groups such as Ashkenazi Jews are well known to suffer from an increased incidence of genetic diseases. The same may be true for many groups in India, the scientists believe.
“The finding that a large proportion of modern Indians descend from founder events means that India is genetically not a single large population, but instead is best described as many smaller isolated populations,” said Dr Lalji Singh, one of the study leaders from the Centre for Cellular and Molecular Biology in Hyderabad, India.
24 Sep 2009, The Telepgraph
A new genetic study has provided glimpses of India’s population patterns from deeper in the past than before, revealing the existence of two distinct, ancestral populations in the country about 45,000 years ago. Indian and US scientists have used human genes to explore a largely uncharted domain of prehistoric populations and shown that nearly all Indians are descendants in varying genetic proportions of these two distinct populations.
The researchers also found that after the ancient admixture, endogamy has shaped marriage patterns in India for thousands of years, predating the caste system. They analysed more than 560,000 genetic markers from the genomes of 132 Indians representing 25 population groups, six language families and several castes and tribes. The findings will appear in the journal Nature on Thursday.
The study has suggested two ancient populations — ancestral North Indians and ancestral South Indians — that had diverged from older population groups, derived from the earliest modern humans who trudged out of Africa some 70,000 years ago.
“They appear to be progenitor populations — nearly all the groups we studied have descended from mixtures of the two,” said Kumarasamy Thangaraj, a co-author and senior scientist at the Centre for Cellular and Molecular Biology (CCMB), Hyderabad.
Thangaraj and Lalji Singh from the CCMB collaborated with scientists at the Broad Institute of Harvard and the Massachusetts Institute of Technology to study variations of a large number of genetic markers in individuals from different population groups. The patterns of variation can provide information about genetic distances between the groups and their history.
The genetic patterns suggest that most present-day Indian population groups have inherited 39 per cent to 71 per cent of their ancestry from the ancestral North Indians who are genetically close to central Asians or Eurasians.
The balance comes from ancestral South Indians who do not appear to share genetic proximity with any group outside India. “The ancestral South Indians may have diverged from the earliest of modern humans to arrive in India,” Thangaraj said.
The new study was not designed to explore how far back in time the distinct populations arrived, or when they began to mix. But the new data combined with earlier research would put the ancestral South Indians in India about 65,000 years ago and the ancestral North Indians about 20,000 years later.
Although there is abundant archaeological evidence — rock shelters, stone tools and wooden spears — for prehistoric human settlements in India, population patterns and movements of the earliest modern humans in India remain unclear.
“It seems to me that attempts to postulate a population pattern so far back in history, going back to before 10,000 BC, would have many uncertainties,” said Romila Thapar, emeritus professor of ancient Indian history at Jawaharlal Nehru University, Delhi. “Our data on population groups for such early periods is limited,” Thapar told The Telegraph.
Genetic studies by other research teams have indicated that modern humans began walking out of Africa into West Asia, central Asia and South Asia, about 70,000 years ago. The new study has also confirmed earlier findings from the CCMB that the Onges in the Andamans are the descendants of the first modern humans who moved out of Africa, but have remained isolated on the islands.
The Onges appear exclusively related to the ancestral South Indians.
“Understanding the origins of the Andamanese (tribes) could provide a window into the history of ancestral South Indians,” Nick Patterson, a mathematician and a team member from the Broad Institute, said in a statement.
The CCMB-Broad Institute study has shown that genetic contribution of ancestral North Indians is high in upper caste and Indo-European language speakers on the subcontinent — such as the Pathans from Pakistan or the Kashmiri Pandits, Vaish, Srivastava groups from India.
But some tribal and lower caste groups appear closer to the ancestral South Indians.
The study also indicated that four groups — the Onges from Andamans, the Siddhis from Karnataka, and the Nyshi and Ao Naga from the Northeast — have genetic proximity to populations outside India and do not have detectable contributions from either the ancestral North Indians or ancestral South Indians.
New Delhi, Sept. 23, 2009
http://www.nature.com/nature/journal/v461/n7263/full/nature08365.html
