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Caste in the genes

Biologist Kumarasamy Thangaraj finds himself treading the turf of historians. A scientist at the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad, Thangaraj has been using genetic material from ethnic and caste communities from across India to piece together the social and migratory history of its people. The findings, as he is discovering for himself, may at times be revelatory and at times provocative enough to stir a debate.

Thangaraj’s latest study has bolstered genetic evidence to support an alternative theory for the origins of India’s ancient, controversial and enduring caste system that hasn’t quite seeped into popular notions of caste origins yet.

It’s an idea thrown up more than 45 years ago by Damodar Dharmananda Kosambi, a Harvard-educated Indian mathematician who was, again, not a trained historian.

Conventional ideas fashioned by history lessons have linked the caste system to the period of the Aryans who began to arrive in the subcontinent from central Asia only after 1500 BC. But research by Thangaraj and his colleagues now suggests that the caste system may have roots that go much further back in time — several thousands of years before the arrival of the central Asians.

Shift in way of life

The new study, which compared selected genetic sequences from members of different caste groups in the country, suggests that the caste system may have emerged some 8,000 years ago. “Maybe it was a response to a shift in the way of life — from hunting-gathering to rudimentary farming and the establishment of the first settlements,” says Thangaraj, a geneticist speculating ancient events.

But a bit of scientific speculation backed by genetic studies may be excused because what prompted ancient Indians to introduce sharply defined hierarchical divisions within their society remains unknown. “The origins of the caste system — like many other things in history — remain a mystery,” says Lalji Singh, director of CCMB who leads a team trying to discover history through genes. For deoxyribonucleic acid (DNA) sequences can tell tales of the past.

Researchers have been focusing on segments of the Y-chromosome — acquired only from fathers — as well as mitochondrial DNA — inherited only from mothers. Over hundreds and thousands of years, mutations — subtle alterations in the genetic sequences — build up and tend to cluster within communities that are either geographically or genetically separated. By comparing genetic sequences from individuals from different communities, scientists can build a complex ‘family tree’ of human communities and tell how closely related certain ethnic groups or communities are to each other.

Anthropologists believe that today’s tribal communities of India are the descendants of the earliest immigrants from Africa 45,000 years ago

The CCMB team is among groups of scientists in India, Europe and the US racing to unearth the past through population genetics because India’s human family tree is widely expected to be complex as well as rewarding. The high diversity of ethnic communities and population groups in India is the result of multiple waves of human migrations over thousands of years.

“Population genetics in India is expected to provide insights not just into our own history, but also the history of early modern humans,” says Singh. A CCMB team led by Thangaraj and Singh last year used DNA studies to show that two tribes in the Andamans — the Onges and the Great Andamanese — are the direct descendants of the earliest modern humans who moved out of Africa about 70,000 years ago.

Some genetic studies suggest that modern humans on their march out of Africa had arrived in India about 45,000 years ago. Anthropologists have long believed that today’s tribal communities of India, particularly those in central and southern India, may be the descendants of these earliest migrations into India. However, the influx continued even after that first entry of modern humans. Archaeological and linguistic evidence suggests that people who spoke a language that preceded the Dravidian language arrived about 9,000 years ago. The Indo-Europeans, or Aryans, arrived about 3,500 years ago.

The first major insight into how genetic studies may help decipher caste origins came in 2001 when Michael Bamshad, a University of Utah researcher, and his colleagues in the US and India showed that the Indo-Europeans who arrived in India about 3,500 years ago selectively inserted themselves into high ranking positions in India’s caste system.

The study revealed significantly differing proportions of Eurasian genes in people belonging to high-ranking and low-ranking castes in India. Their results indicated that upper castes are genetically closer to Europeans, while the lower castes are more similar to Asians.

Diverse views

But two years later, an independent study by Estonian geneticist Toomas Kivisild indicated that Indian tribal communities and caste populations both come from the same genetic heritage of people from western Asia associated with the earliest farming practices. But complicating matters further, US-based researcher Richard Cordaux showed a year later that India’s castes are closer to central Asians than to its tribes.

The CCMB scientists have been analysing genetic sequences of people from a number of caste groups from across India over the past five years. They have picked upper, middle and lower castes — Brahmins from Andhra Pradesh, Kashmir and Uttar Pradesh, upper caste Rajputs from UP, and the lower caste Saharia, Yadava, Kor, Keer and Kobi from Madhya Pradesh, among others.

In their new study, the researchers compared genetic sequences of three tribes in Andhra Pradesh — Andh, Pradhan, and Nagkoil — with previously published genetic data from a number of other communities from across India.

“We find that there is greater genetic similarity between the lower castes and tribes than between the lower castes and upper castes,” says Thangaraj. The CCMB researchers have published their findings in a recent issue of the journal BMC Genetics.

The Y-chromosome data from 374 people belonging to the lower castes from different geographic regions of India and speaking different languages show only one per cent variation with the south Indian tribal groups. The difference between the lower castes and upper castes was 4.7 per cent. “Our findings point to a tribal origin of the lower castes,” says Thangaraj.

This is an idea that Kosambi had proposed in his 1964 classic, The Culture and Civilisation of Ancient India, where he analysed history through social and economic perspectives rather than merely chronicling events and episodes. Kosambi had suggested that as cultivation and farming established itself on the subcontinent, the emergence of new knowledge and occupations associated with food production and permanent settlements may have given way to hierarchical divisions within tribal societies.

A rudimentary version of the caste system may have thus emerged with the shift towards cultivation and settlements. “It’s possible that when the Aryans arrived, the divisions became sharper, more well-defined, and the caste divisions intensified,” said Thangaraj.

CCMB director Singh says the results appear provocative. He, however, cautions that they are only indicative and not conclusive. “We’ll need a much larger study to verify these results,” he adds. Singh estimates that the establishment of connections between castes with a reasonable level of certainty would involve a mammoth task. India has more than 4,600 ethnic groups and communities. Taking at least 100 samples from members of each of the communities would mean isolating genetic fragments from nearly 480,000 people. The largest studies so far have involved only about 10,000 samples.

“But it’s an effort worth undertaking,” says Singh. “This is a different kind of history. It will have potential medical applications.” Many researchers believe that a new kind of “personalised” medicine will emerge in the next 10 to 15 years. For certain conditions, an individual’s genetic identity may be used to select the best possible treatment, Singh says. “When that happens, your affinities to the tribes and the caste groups may determine which medicine will best suit you.”

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