Download When the caste die was cast - National Institute of Biomedical

When the caste die was cast
G.S. Mudur
New Delhi, Jan. 25: A genetic study has traced the emergence of a strict caste system in India to about
1,575 years ago, indicating that the Gupta dynasty imposed social strictures on populations that had until then
mixed and mated largely unfettered.
The study, by scientists at the National Institute of Biomedical Genomics at Kalyani in Bengal, has also shown
that five ancestral populations -- not two as inferred earlier --- spawned the tapestry of India's present-day
population diversity.
Earlier studies by Indian and US scientists had indicated that people across the country mated without
concern for class, caste or ethnic barriers for over 2,000 years before the advent of the caste system.
Those studies had also suggested that most present-day mainland Indians have descended from two ancient
groups called the ancestral North Indians (ANI) and the ancestral South Indians (ASI).
"We've now identified a sharp window of time that marks a consolidation of the caste system," Partha
Majumder, the director of the Kalyani institute who led the new study, told The Telegraph.
The findings were published today in the Proceedings of the National Academy of Sciences, a research
journal.
Majumder and his colleagues Analabha Basu and Neeta Sarkar Roy analysed the genetic makeup of 367
people from 20 populations chosen to represent the diversity of India's population.
They picked Khatris from northern India, Brahmins from Bengal and Gujarat, Iyers and other Dravidian
speakers from southern India, Marathas from Maharashtra and several tribes from central and southern India
and the Andaman and Nicobar Islands, among others.
Their research aimed at reconstructing India's population history by studying subtle differences in genomic
makeup that can reveal information about individuals' ancestry, their genetic distance from others, and
signatures of endogamy --- marriage only within one's community --- in populations.
Their study shows that most populations on mainland India owe their ancestry to four groups: the ANI, the ASI
and two others -- an ancestral Tibeto-Burman (ATB) group, and an ancestral Austro-Asiatic (AAA) group.
The Jarawas and the Onges share their ancestry with present-day Pacific islanders, implying a distinct
ancestral population for these Andaman and Nicobar tribes.
The genetic evidence also suggests that almost all upper-caste populations began to practise endogamy
about 70 generations ago after a long period of unrestricted mixing.
"The gene flow across these populations came to an abrupt end about 1,575 years ago, assuming an
average of 22 years for each generation," Majumder said.
"We went back to history books and found that this period coincides with the reign of the Gupta emperors."
The scientists say their findings suggest that the Gupta rulers -- possibly Chandragupta II or Kumaragupta I -used the state machinery of a developing political economy to enforce social and moral strictures leading to
strict and widespread endogamy.
"I don't have a dispute with this suggestion," said Shatrughna Sharan Singh, professor of ancient Indian
history at Patna University.
"An early version of the caste system may have emerged during the Vedic times, perhaps as far back as
1,200 BC, but it is possible that the caste system based on micro-division of labour consolidated itself during
the reign of the Guptas."
The scientists say that endogamy wasn't adopted quickly everywhere. "Low levels of gene flow continued to
occur between certain populations. We can see signatures of such gene flow in present-day people," Basu
said.
The study, for instance, suggests that across eastern and northeastern India, Bengal's Brahmins continued to
admix with Tibeto-Burman populations until the emergence of the Buddhist Pala dynasty in the eighth century.
"This is an important (research) paper," said David Reich, professor of genetics at the Harvard Medical
School, who had seven years ago led an independent effort to reconstruct India's population history that had
pointed to two ancestral groups: ANI and ASI.
"We had excluded the Austro-Asiatic and Tibeto-Burman speakers from our analysis as we wanted to
understand the gradient of ancestry seen mainly in Indo-European and Dravidian speakers," Reich told this
newspaper.
"The history of Tibeto-Burman speakers and Austro-Asiatic speakers and the Andaman and Nicobar tribals is
very important even though these groups comprise a small fraction of the present-day population."
Majumder and his colleagues say their genetic study also suggests that the census counts of the AustroAsiatic and Tibeto-Burman speakers in India are "gross underestimates" of the extent of the AAA and ATB
genetic components in present-day populations.
Many present-day Indians who speak Indo-European languages or even Dravidian languages may thus have
genetic components they inherited from AAA or ATB groups.
"Languages evolve much faster than genes," Majumder said. "The evolution of language has masked the
genetic backgrounds of some populations."
ARYANS, DRAVIDIANS AND, NOW, TWO MORE
Bangalore Mirror Bureau | Jan 26, 2016, 04.00 AM IST
By: Mihika Basu
A new study has found that Indians also descended from Tibeto-Burman (North-East) and
Austro-Asiatic (East and Central India). It has also identified a fifth ancestral lineage dominant
among Negrito tribals of Andaman and Nicobar Islands
Contrary to the current understanding that India's population has descended from two ethnolinguistic groups, a new study has discovered that there were actually four. The study, which has
been published in the prestigious Proceedings of the National Academy of Sciences (PNAS) after
over 20 years of research work, explores the genetic history of present-day Indians and the
peopling of the Indian subcontinent. Researchers previously suggested that mainland India's
current population largely descended from Indo-European or Aryans (North India) and
Dravidians (South India) groups. The two additional groups now are Tibeto-Burman (North-East
India) and Austro-Asiatic (fragmented in East and Central India).
"India, with more than one-sixth of the world population, has been under-represented in
genome-wide studies of variation," director of the West-Bengal based National Institute of
Biomedical Genomics (NIBMG), Prof Partha P Majumder, told Bangalore Mirror.
"The present study, using judiciously selected populations who provide a more complete
representation of Indians resident in diverse geo-cultural ecosystems of the country, and also
using about double the number of DNA variants per individual than a previous major study, has
been able to provide robust evidence that four — not two — ancestral stocks contributed to the
genetic diversity of present-day Indians. These ancestral stocks are roughly identifiable with the
four language families in India - Indo-European (North India), Dravidian (South India), TibetoBurman (north-east India) and Austro-Asiatic (fragmented in east and central India, spoken
exclusively by the tribals)."
The NIBMG is an autonomous institution under the Union department of biotechnology.
Majumder and his colleagues explored DNA variation in about 400 unrelated Indians belonging
to 20 ethnic groups. Two of these groups are Negrito tribals who reside in the Andaman &
Nicobar Islands. The remaining 18 groups - both tribal and caste groups - are from mainland
India.
They also reviewed data from the Human Genome Diversity Panel (HGDP), a repository of
genomic data representing hundreds of people worldwide.
While studies have been conducted in the past by various researchers, including the authors of
this article, this is the largest DNA variation study conducted in India, taking into account both
the number of ethnic groups (20 groups) and the number of DNA variants (over one million
variants) examined on each individual. "It is a significant finding and a much more complete
profile of the ancestral lineage. Suitable technology was not available earlier, so getting a
foolproof answer was difficult. But the technology currently available have enabled is to assess a
large number of markers in human genome," said Majumder.
The authors also said they have shown there is a distinctive ancestry of the Andaman & Nicobar
Islands populations. Accordingly, the Andaman archipelago (island group or chain) was peopled
by members of a distinct, fifth ancestry, says the paper titled "Genomic reconstruction of the
history of extant populations of India reveals five distinct ancestral components and a complex
structure".
"A fifth ancestral lineage that is dominant among the Negrito tribals (Jarawa and Onge) of
Andaman & Nicobar Islands was also identified. Using publicly-available HGDP data, we found
evidence that this lineage is also ancestral to the present-day Pacific Islanders. Although presentday Indians largely group themselves in relatively-isolated social groups, with negligible
proportion of marriages taking place between individuals belonging to different social groups,
this situation did not prevail in the past. Gene exchange was widespread among the four
ancestral groups of the present-day Indians, our study has revealed. That is, difference in social
position was not a major bar to marriage," he said.
WHEN MARRIAGE RESTRICTIONS CAME
The paper says inter-marriage, without major restriction, was replaced by the formulation and
declaration of social norms, leading to the formation of endogamous groups - groups whose
members married only within their groups and not outside.
"This study, using DNA data, estimated that the transition in India from free intermarriage to
endogamy took place about 70 generations ago; that is, about 1,600 years ago. Leafing through
the pages of Indian history, one finds that during this time the Gupta empire, founded by
Maharaja Sri Gupta, covered much of the Indian sub-continent, with Pataliputra (near Patna) as
the capital of the empire. A lot of social transformation took place during the Gupta period.
Notable among these was the enforcement of social strictures against marriage between castes, as
enshrined in the Dharmasastra. This reveals that some social norms leave imprints on the DNA
of people, which can be reconstructed by careful genetic studies," the finding reveals.
EARLIER STUDIES PLAYED DOWN
The researchers have argued in their paper that previous studies on the number of ancestral
components in the populations of India may have been underestimated because of lack of
inclusion of tribal populations, inadequate representation of the geo-cultural diversity of India in
the set of sampled populations, and selective removal of some populations based on deviance of
their genomic profiles.
The path-breaking study further said: "Our study has corrected this deficiency and has provided a
more robust explanation of the genomic diversities and affinities among extant populations of the
Indian subcontinent, elucidating in finer detail the peopling of the region."
Map of India showing
approximate locations of
sampling of the populations
included in this study.
Populations shown in 'grey'
are populations from the
Andaman and Nicober
archipelago. Populations
shown in 'red' are Dravidian
speaking tribal populations
from the Nilgiri Hills in
Southern India. Populations
shown in 'cyan' are AustroAsiatic speaking tribal
populations from the East and
Central India. Populations
shown in 'green' are caste
populations primarily
speaking the Indo-European language. Populations shown in 'blue' are Tibeto-Burman
speaking populations of North-East India and are predominantly tribes, except the Manipuri
Brahmins.
National Institute of Biomedical Genomics (NIBMG)
* The conclusion of an earlier major study that sought to reconstruct population history of India
using DNA data was that the present-day Indians are derived from two ancestral stocks of people,
one of whom is ancestral to all north Indians and the other ancestral to all south Indians. That
study was published in 2009 in Nature journal, jointly by scientists of the Broad Institute in the
USA and the Centre for Cellular and Molecular Biology, Hyderabad.
* In the current study, the authors have inferred that at least four distinct ancestral
components—not two, as estimated earlier—have contributed to the gene pools of existing
populations of mainland India. The authors have also shown there is a distinctive ancestry of the
Andaman & Nicobar Islands populations, which is likely ancestral also to Oceanic populations.