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Caste System and Genes in India

Health In Focus   - G J E 4
  • Genetic studies were performed to study the caste system and its origins
  • Majority of the studied mitochondrial DNA were of Indian origin
  • A considerable minority belonged to West European origins
  • The lower castes consisted of proto-Asian mitochondrial DNA
  • West European mitochondrial DNA was found concentrated mostly in the upper castes
  • Caste system was formed 1900 years ago with the development of 4,635 unique genetics groups based on religion, tribal and linguistic differences
The Centre for Cellular and Molecular Biology, Hyderabad along with The Harvard University, conducted a study on the origins of the Indian caste system based on the mitochondrial DNA. This study that was published in The American Journal of Human Genetics is the first comprehensive study on the genetic basis of caste.

The Use of Mitochondrial DNA for Mapping Heredity

This study and most other heredity mapping studies use mitochondrial DNA to understand the origin of study populations. The nuclear DNA is a combination of the DNA of the mother as well as the father while the mitochondrial DNA is inherited only from the mother because the mitochondrial DNA from the sperms don't enter the egg.
Caste System and Genes in India
Caste System and Genes in India
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A child's nuclear DNA, when assessed across 4 generations, is a combination of nuclear DNA from 7 men and 7 women. However, mitochondrial DNA is inherited from only one woman.

Genetic Analysis

Dr. Kumarasamy Thangaraj, who is the principal author of the study, took samples from nearly 571 people from across India, including the Andamans. The samples were used to carefully analyze the mitochondrial DNA and to understand the genetic patterns of the various populations.

‘The rampant intermingling of populations within India that existed more than 2000 years ago makes divisions based on caste, religion or linguistic differences insignificant.’
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"Only a few thousand years ago, the Indian population structure was vastly different from today," said professor of genetics at Harvard Medical School Dr. David Reich, who is also a co-senior author in the study. "The caste system has been around for a long time, but not forever."

Genetic Hotspot

The current study shows that India was a genetic hotspot where there was an intermingling of populations, with DNA mixing across India. This is evidence that intermarriages were common as there was no seclusion from any part of the society.

Earlier it was believed that there was a North Indian population that had a genetic association with West Europeans and a South Indian or Dravidian population with ancestors associated with people from the Andamans. However, genetic studies have shown that there was rampant intermingling, across the country, that lead to DNA traces present throughout the population.

This population intermingling came to a halt about 1,900 years ago, when stratification of the population based on caste took place.

Support from the Rig Veda

The Rig Veda mentions the existence of caste in its texts, which was not present in the earlier Vedic texts. Moreover, Manusmriti, which dictates the stratification of society based on caste was initiated during the same period. The genetic studies find coherence with the ancient Hindu texts.

Significance of the Study

The study shows that there was no mixing of populations over 4,000 years from now, but during the period between that and 1,900 years ago, it was common to intermarry within the Indian population or, less often, even between European descendants. However, from about 2,000 years ago, stratifications within the Indian population led to distinct genetic groups, which strengthened over time.

This led to high genetic as well as social imprints that aided in promoting the interest, craft, ideologies and skills associated with certain groups but resulted in deeply entrenched implications that continue to sweep Indian society.

The Bane of the Caste System as Envisioned from a Genetic Aspect:
  • Genetic Exclusion: The caste system created certain specific groups of populations that were secluded from the populations.
  • Genetic Diseases: Intermarriage between closely related population leads to the rise in genetic diseases. Even recessive diseases, or diseases that require two copies of similarly mutated genes to give rise to the disease condition, increase in number when marriage is restricted to only within the community. The severity of the diseases ranges from being mild to even life threatening like Klinefelter's syndrome and pycnodysostosis. The rise in multifactorial diseases like diabetes may also be associated with such genetic seclusions as mild aberrations in genes continue to be inherited and magnified across generations.
  • A Single Mixed Population: The evidence that people from across India share a genetic similarity, makes it unnecessary to have divisions based on religion or linguistic disparities.
This hallmark study brings to the fore that man-made divisions within society are irrelevant when the underlying genetic data signifies unions that existed for more than 2000 years prior to the groups in society. The last 2000 years have limited intermixing due to the enforcement of castes, creating restrictions in the genetic pool, harboring diseases and divisions within the society.

The clashes between different castes in India prompt the principal researcher to comment thus "Look, we were all brothers and sisters 2,000 years back," Thangaraj says "why are you fighting now?"

References:
  1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC311057/
  2. http://www.pbs.org/wgbh/nova/neanderthals/mtdna.html
  3. Source: Medindia
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