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India, Thailand Have Shared Cultures. Now, a Genetic Study Unravels a Timeline.

India, Thailand Have Shared Cultures. Now, a Genetic Study Unravels a Timeline.

A group of Thai traditional dancers at a Songkran festival in Bangkok, April 2019. Photo: PEAK99/Wikimedia Commons, CC BY 3.0

  • In a new study, researchers from the Czech Republic have tried to pin down the precise patterns of historical migration between India and Thailand.
  • “Our results suggest that there may have been multiple waves of diverse South Asian populations that migrated to Southeast Asia in the past,” one of the researchers said.
  • The study’s novel contributions are about when the intermixing happened and the Indian population groups that contributed to this intermixing.
  • The genetic ancestry of the Mon, the Khmer, the Kuy and the Nyahkur populations overlapped with the genetic ancestry of the Irula and the Mala communities of Southern India.
  • They also reported that the genetic ancestry of several Southeast Asian populations matched those of the Adi Dravidar, the Bhumihar and the Coorghi communities, among others.

Hyderabad: In the third century BC, Emperor Ashoka sent Buddhist monks from the Indian subcontinent to nine regions of South and Southeast Asia to spread Buddhist thought. One of their destinations was modern-day Thailand. Since then, Buddhism has been the most popular religion in Thailand, counting some 94% of its people as followers.

In the 13th and 14th centuries, Indian Brahmins and traders moved to and settled in Thailand, as did more merchants and others from the 14th to the 19th centuries.

The results of this movement are visible in the many cultural similarities between the two countries. The great Thai epic Ramakien is a version of the Hindu epic Ramayana. A form of shadow puppetry in Thailand, called ‘Nang Talung’, is very similar to ‘Bommalattam’ in South India. And the Thai New Year, Songkran, is derived from the Sanskrit word ‘Sankranti’.

In a new study, researchers, led by Piya Changmai of the University of Ostrava in the Czech Republic, have tried to pin down the precise patterns of migration between the two countries. The study was published in the journal PLoS Genetics on February 17.

“Our results suggest that there may have been multiple waves of diverse South Asian populations that migrated to Southeast Asia in the past. These people subsequently intermarried with the local Southeast Asians,” Changmai told The Wire Science.

“The movement of a substantial number of people from South Asia to Southeast Asia in the past may have been responsible for the spread of Indian culture to the region.”

The researchers also reported genetic intermixing between the speakers of two major linguistic families in Southeast Asia: Kra-Dai and Austronesian. This finding supports a previously proposed idea – that these languages are derived from a common ancestral tongue.

Studying genetic ancestry

A musician of the Tai Lue ethnic group at Wat Nong Bua, Nan Province. Photo: Takeaway/Wikimedia Commons, CC BY-SA 3.0

For the study, Changmai and his colleagues collected saliva samples from members of 10 ethnolinguistic groups in Thailand:

  • From the Khmer, the Kuy, the Lawa, the Maniq, the Mon and the Nyahkur – who speak Austroasiatic languages
  • From the Hmong – a group that belongs to the Hmong-Mien ethnolinguistic group
  • From the Tai Lue – who speak Kra-Dai languages, and
  • From the Akha and the Sgaw Karen – who speak Sino-Tibetan languages

The Austronesian languages are spoken mainly in Taiwan, Maritime Southeast Asia (Brunei, East Timor, Indonesia, Malaysia, Papua New Guinea, the Philippines and Singapore), the Pacific Islands and Madagascar.

The Austroasiatic languages are spoken in Mainland Southeast Asia (Cambodia, Laos, Myanmar, Thailand, Vietnam and Malaysia) and South Asia (Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan and Sri Lanka).

Together, these make up the Austric languages.

The Hmong-Mien, the Kra-Dai and the Sino-Tibetan are separate linguistic families.

Changmai said one of the hurdles to their study was on the very first step: collecting the saliva samples. “Some groups reside in the forest or remote areas, which are difficult to approach,” he explained. “It was difficult to obtain saliva samples from some ethnic groups due to their beliefs.”

Once they had the samples they needed, the researchers isolated human DNA from them and identified certain parts called nucleotide polymorphisms (SNPs).

DNA is made of four nitrogenous bases: adenine (A), guanine (G), thymine (T) and cytosine (C). They come together with additional compounds to form nucleotides. Nucleotides come together to form the DNA.

An SNP occurs when a particular nucleotide in a specific position of the DNA is changed to a different nucleotide. Most people in a population may have A in a nucleotide at a particular position. But a small number of people may have a C instead of an A at that point. This would be an SNP.

Tracking SNPs in populations helps geneticists get a sense of the relationships between these populations. For example, a geneticist might find that in a population, most people have A at a particular position in their DNA but a minority has C at the same position.

The geneticist might then observe that the C-variant of the SNP is dominant in another population. Based on these observations, the geneticist could consider if there was some intermixing between the two populations.

After collecting SNP data from present-day populations, the researchers, led by Changmai, combined their findings with existing data about ancient and current populations.

At this point, they used admixture analysis, also called biogeographical ancestry analysis. That is, they used a population’s genetic ancestry to unravel its geographical ancestry. Specifically, the researchers compared a set of SNPs from the target population with a set of SNPs from different geographical regions to build clusters based on the levels of similarity.

All this provides a spatial sense of the populations’ movement. To get a sense of the time in which these movements happened, the team turned to haplotype-based population genetics methods.

Haplotypes are a set of SNPs that are so close to each other that they are inherited together. Tracking how haplotypes change between populations over time can allow researchers to understand their geographical and temporal ancestry at once.

A single nucleotide polymorphism (SNP) is a change of a nucleotide at a single base-pair location on DNA. Created using OpenSCAD v2021.01 and Inkscape v1.0.2. Author: David Eccles/Wikimedia Commons, CC BY 4.0

Indian ancestry in Southeast Asia

From their analysis, the researchers found that the genetic ancestry of the Mon, the Khmer, the Kuy and the Nyahkur populations overlapped with the genetic ancestry of the Irula and the Mala communities of Southern India. This is an indication that these populations intermixed sometime in the past.

The researchers also found overlaps between South Asian genetic ancestry and populations speaking the Austroasiatic (Khmer, Kuy, Mon and Nyahkur), the Austronesian (Cham, Ede and Giarai from Vietnam, and Malay from Malaysia) and the Sino-Tibetan languages (Burmese from Myanmar).

Third, the researchers also checked the genetic ancestry of the people from China, Vietnam and Thailand (Tai Lue) who spoke Kra-Dai. They found that most of the Kra-Dai-speaking groups had Tibetan and Atayal ancestry. (The Atayal is an indigenous community from Taiwan and speaks Austronesian languages).

So the team concluded that the populations of the speakers of the Austronesian and the Kra-Dai languages mixed. This supports a hypothesis that researchers proposed in 2006 that the two groups are connected by their language.

According to this idea, the Kra-Dai and the Austronesian families emerged from a common ancestor, called Proto-Austro-Tai.

The idea continues that the Kra-Dai family is actually a subgroup of the Austronesian family of languages – that it developed into a separate family when Austronesian speakers from Taiwan settled in the Guangdong coast of South China and interacted intimately with the local population there some 4,000 years ago.

Next, the haplotype analysis revealed that several Southeast Asian populations that the study investigated (Burmese, Khmer, Cham, Ede, Giarai, Kuy, Malay, Nyahkur and Mon) had genetic ancestry that matched seven Indian ‘sources’: Adi Dravidar, Bhumihar, Coorghi, Dhobi, Cochin Jews and people from SC communities in Karnataka, as well as Gujaratis and Bangladeshis.

According to political theorist and anti-caste activist Kancha Ilaiah Shepherd, the term ‘Adi Dravidar’ refers to marginalised caste groups in Tamil Nadu who, through a self-respect movement, asserted themselves to be the original (i.e. ‘adi’) inhabitants of Tamil Nadu (‘dravida’).

The anti-caste activist and leader Iyothee Thass introduced the term 'Adi Dravidar'.
The anti-caste activist and leader Iyothee Thass introduced the term ‘Adi Dravidar’. Source: YouTube

Shepherd also told The Wire Science that while ‘Bhumihar’ refers to land-owning caste groups in North India, particularly Bihar, ‘Coorghi’ refers to marginalised caste groups in the Coorg region of Karnataka. ‘Dhobi’ refers to people from marginalised caste communities distributed around India and traditionally engaged in laundry-work, he added.

As for ‘Cochin Jews’ – Shepherd said the label refers to people who emigrated from Israel and settled in Cochin, even if many of these groups have now moved back to Israel.

Changmai cautioned that the aforementioned present-day populations, which the haplotype analysis identified, are “just proxies for the actual sources”. That is, there’s a possibility that the genetics of the ancient South Asian populations that intermixed with ancient Southeast Asian populations may be different from today’s populations.

Novel findings

This said, Ranajit Das, a population geneticist at the Yenepoya Research Centre, Mangaluru, the study belabours already well-known information about the ancestry of Southeast Asian populations.

“Except for generating some novel genotype data of some Thai populations, they did not find anything super-interesting in the article,” he told The Wire Science. “The fact that there was cultural (and thus genetic) intermixing between South Asian countries such as Thailand and India is quite well-known.”

However, Gyaneshwar Chaubey, a professor of zoology in Banaras Hindu University who works on human population genetics of South and Southeast Asia, was more upbeat in his reading of the paper’s importance.

According to him, the timeline – of when the intermixing happened and the disaggregation of the Indian populations that contributed to this intermixing – are the study’s two novel contributions.

The researchers reported that the Khmer and the South Asian populations intermixed more than 1,000 years ago – while the Nyahkur, the Ede and the South Asian populations did so around 1,000 years ago.

The Burmese populations seem to show the most recent intermixing with South Asian populations – around 400 years ago.

The researchers also checked if the Akha, the Lawa, the Manig and the Hmong populations had a South Asian ancestry. They didn’t. The researchers attribute this to the possibility that most of these populations are located in remote regions and could thus have escaped Indian influence.

King Suryavarman II of the Khmer empire depicted in a bas-relief at Angkor Wat, the world’s largest religious complex, in Cambodia. It was built at his behest and dedicated to the Hindu god Vishnu. Photo: Maharaja45/Wikimedia Commons, CC BY-SA 4.0

Consequences of genetic history

Overall, the study sheds a lot of light on the genetic ancestry of many Southeast Asian population groups.

According to Changmai, population genetics research can complement findings from other disciplines, like anthropology and archaeology, and that together they can help us understand the complex history of Southeast Asia.

Chaubey, however, said the contributions of such ancestry-mapping exercises through population genetics goes beyond understanding history. According to him, findings like those of the Changmai et al. study can help reveal their disease biology and thus inform clinical decisions.

As an example, he referred to a series of papers from his own group where they reported the different vulnerability of different Indian populations to COVID-19. In the same vein, Chaubey also referred to drug development.

Once we understand which gene(s) modulate a certain disease, he explained, we can check which populations these genes are derived from in the target group. This can then help clinicians prefer some medical treatments over others.

“If we know that a drug is working in population X and not in population Y, and the target population is closer to population X, then one can directly test the drug in the target population,” he told The Wire Science.

Changmai himself said he would like to analyse more genetic data from Southeast Asia – both from present populations and ancient samples.

“There is very little genetic data from populations in Laos, Cambodia and Myanmar,” he said. “Moreover, DNA preservation is not easy in tropical climates, which may have contributed to the limited data until now.”

Sayantan Datta (they/them) are a queer-trans science writer, communicator and journalist. They currently work with the feminist multimedia science collective, and tweet at @queersprings.

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