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Before medical surgery, a patient in Tamil Nadu /Andhra Pradesh and Telangana is asked a few questions regarding allergies to medication and so on. He/she may well be asked about his/ her caste, too. Doctors want to ensure they don’t belong to the Arya Vaishya Chetty caste group as researchers found out ten years ago that people from Arya Vaishya Chetty (in Tamil Nadu)/ Vysya (in Andhra Pradesh and Telangana) caste group cannot be given the anesthetic drug, suxamethonium or scoline. They suffer from a genetic defect of pseudocholinesterase deficiency, which means their bodies don’t have enzymes to metabolize scoline. Administering scoline is fatal for the patients from the Arya Vaishya Chetty clan and anesthetists will try a combination of other anesthetic drugs for them.

Medical research carried out in Tamil Nadu has found that patients from Arya Vaishya Chetty have pseudocholinesterase deficiency. Such patients end up on the ventilator because scoline, the muscle relaxant, paralyzes lung function during anesthesia. Since people of the caste group Arya Vaishya Chetty don’t have butyrylcholinesterase in their blood plasma that can metabolize scoline, they don’t revive easily from anesthetic effects. Such pseudocholinesterase deficiency is found among specific communities in the world.

Research in population genetics has been throwing up increasingly interesting and useful findings such as the above. Population genetics is the study of the genetic composition of populations. The stream of study tries to understand how and why the frequencies of gene forms change over time within and between populations. It provides an insight into the mechanism of evolution.

In Europe, and the US, for instance, population groups are studied for their genetic makeup to provide appropriate healthcare. Some demographic groups including nationalities have been found to be susceptible to certain types of diseases.

For instance, sickle cell disease, a type of anemia, is common among African, Afro Americans and people from the Mediterranean region. Similarly, Tay-Sachs disease is common among Ashkenazi Jews or people from French Canadian ancestry. It doesn’t mean others won’t get these diseases but some are more vulnerable due to gene defects.

Population genetics is the study of the genetic composition of populations. The stream of study tries to understand how and why the frequencies of gene forms change over time within and between populations. It provides an insight into the mechanism of evolution

In the West, genetic counselling is done to couples ahead of marriage to tell them what the chances of their children contracting those diseases are. Ashkenazi Jewish children are screened for gene profiling and are counseled when they grow up and get ready for marriage, say researchers.

For almost a century, Dravidian ideology has been centered on the hypothesis of invading Aryans and domicile Dravidians who were chased to the south of the Subcontinent. The theory of Aryan invasion was put forward by colonial scholars. German Indologist Max Muller put forward this theory of Aryan invasion in the year 1853. Ever since, the Aryan Invasion Theory (AIT) has been challenged by several researchers.

Kumarasamy Thangaraj from Centre for Cellular and Molecular Biology (CCMB), who is presently the Director of Centre for DNA Fingerprinting and Diagnostics (CDFD), Hyderabad says that there is nothing like Aryans invading India. Genetically, there is no evidence for such an invasion. “In prehistoric India, there were two ancestral populations; ancestral south Indians and ancestral north Indians, and both the groups have mixed,” he said.

The admixture of populations

The landmark research paper ‘Genetic Evidence for Recent Population Mixture in India’ published in the American Journal of Human Genetics, 2019, states that most Indian groups descend from a mixture of two genetically divergent populations namely Ancestral North Indians and Ancestral South Indians.

While the Ancestral North Indians are related to Central Asians, Middle Easterners, Caucasians and Europeans, the Ancestral South Indians are not so closely related to groups outside the subcontinent but distantly related to indigenous Andaman Islanders. The evidence for the mixture was initially documented based on the analysis of Y chromosomes and mitochondrial DNA. It has been further confirmed and extended through whole genome studies.

One of the authors of this paper, Kumarasamy Thangaraj said that the first human arrived in India from Africa 65,000 years back. Arriving through the south sea coast, they migrated further and settled in Andaman Islands. The ones who stayed back in South India became Ancestral South Indians.

Meanwhile, another group from Africa migrated to the North – bifurcating into Europe and Middle East – and the group which migrated to the Middle East arrived in India. This group is termed Ancestral North Indians. Four thousand years ago, these two groups mixed to form many other groups. This admixture made India an ethnic museum. India has 4,635 well defined groups, including 532 tribes and 72 primitive tribes. Another wave of migration came as Steppes pastoralists (politically referred to as Aryans) around 1500 BC.

The admixture which happened from 4,000 years ago continued another 2000 years. But around 2,000 years ago this admixture stopped. The groups got into an endogamous system – marrying within the community. “The system of endogamy is older than the caste system,” says Thangaraj.

One of the authors of this paper, Kumarasamy Thangaraj said that the first human arrived in India from Africa 65,000 years back. Arriving through the south sea coast, they migrated further and settled in Andaman Islands. The ones who stayed back in South India became Ancestral South Indians.

Thangaraj says that there are otherwise no genetic bases for caste groups, saying anthropology and sociology deal with those questions. He adds that brahmins in Tamil Nadu have not been systematically tested for Steppes pastoralist genome but a few may have it.

Marriage within family

Endogamy stopped inter-group marriage and increased consanguineous relations where close relatives started marrying within the community. Such consanguineous marriages helped to safeguard family assets and nurture close bonds.

But endogamy and consanguineous marriages resulted in increasing the frequency of genetic mutations. The genetic defect which is in heterozygous (recessive mutation) condition in parents would turn homozygous (the gene from both father and mother are similar and mutation chances are compounded) due to endogamy and consanguineous marriages. Such genetic defects cause diseases ranging from hearing defects to breast cancers across the world, particularly in South Asia where endogamy and consanguineous marriages are most common.

Arya Vaisya Chettys are unlikely to have picked up the defective genes from other communities. Consanguineous marriages are common among them.

The research paper ‘Pseudocholinesterase Deficiency: A Comprehensive Review of Genetic, Acquired, and Drug Influences’ published in American Association of Nurse Anesthesiology states that population of European and American descent is homozygous for the deficiency in the ratio of 1 to 1,00,000 while individuals from Vyasa community in India has the frequency rate of 4%.

Given the extensive consanguineous and intra-caste marriages, genetically counselling may well be important for marrying couples for the health of their prospective children.


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