South Asians Admixed With Cambodians About a Millennium Earlier Than Previously Thought: DNA Analysis

New Delhi: Ancient DNA from protohistoric period Cambodia indicates that South Asians admixed with local populations of Southeast Asia as early as 1st-3rd centuries CE, according to a new study published in Nature. This Study has implications for the nature and depth of contact between South Asia and Southeast Asia.

The study is based on a radiocarbon-dated individual from Cambodia (expected to have been alive between 78–234 CE) and was published on December 29, 2022. It showed that South Asian admixture is present in various present-day Mainland Southeast Asia (MSEA) populations, especially those heavily influenced by Indian culture. It says that Indian influence “may have stimulated early state formation in the region.”

Previous aDNA studies did not detect South Asian admixture in ancient individuals across MSEA. The authors say that their study “shows that the South Asian gene flow to Cambodia started about a millennium earlier than indicated by previous published results of genetic dating relying on present-day populations. Plausible proxies for the South Asian ancestry source in this individual are present-day populations in Southern India, and the individual shares more genetic drift with present-day Cambodians than with most present-day East and Southeast Asian populations.” The ancient individual from Cambodia studied, “harbours an approximately three times higher proportion of South Asian ancestry as compared to the present-day Cambodians.”

The study says that its results “suggest that some South Asians migrated to MSEA and intermarried with local people before or at the early stage of state formation. These South Asians may have influenced the expansion of Indian culture and the establishment of Indian-style states (also known as Indianized states).” But as “aDNA data from MSEA are scarce… further data collection is necessary to trace the incorporation of South Asian ancestry into the populations of this region.”

The work of Harvard University geneticist, professor David Reich, one of the co-authors of this study, has been in the spotlight, especially over the past few years. As Tony Joseph, author of Early Indians wrote in 2020, Reich’s work, among other things, helped answer “the thorniest, most fought-over question in Indian history: if Indo-European language speakers, who called themselves Aryans, stream into India sometime around 2,000 BC – 1,500 BC when the Indus Valley civilisation came to an end, bringing with them Sanskrit and a distinctive set of cultural practices? Genetic research based on an avalanche of new DNA evidence is making scientists around the world converge on an unambiguous answer: yes, they did.”

Reich, the author of Who We Are and How We Got Here, was part of two older papers that were published in 2019, ‘The Formation of Human Populations in South and Central Asia’ (Vageesh Narasimhan et al) and ‘An Ancient Harappan Genome Lacks Ancestry from Steppe Pastoralists or Iranian Farmers’ (Vasant Shinde et al) that established that migration from the Steppe to India was between 3,500-4,000 years ago.

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