A new study has found that a mixture in the Indian population between Ancestral North Indians (ANI) and Ancestral South Indians (ASI) occurred 1900 years to 4200 years ago.
An international collaboration between Harvard Medical School (HMS) at Boston and CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, identified 73 groups across India and studied one million genetic variations based on which they estimated whether or not the population had close affinity. The study has revealed that 100% of the mixture is consistent with having occurred in a subset of groups during this period.
"These results show that India experienced a demographic transformation several thousand years ago, from a region in which major population mixture was common to one in which mixture even between closely related groups became rare because of a shift to endogamy," read the paper.
Essentially, scientists isolated DNA from blood samples, looked at changes in the DNA and compared it with different populations to estimate the age of the ANI-ASI mixture.
While ANI related to the people of Central Asia, the Middle East, the Caucasus, and Europe, ASI were distantly related to indigenous Andaman Islanders, but not any group outside India.
According to co-first author Dr Kumarasamy Thangaraj, there are disadvantages for the populations, who follow rigid endogamy. "Deleterious mutations introduced in the genome of small endogamous populations can increase substantially in the population and lead to population-specific diseases since there is no new gene pool from other populations that can dilute or reduce the frequency of the mutation," said Thangaraj.
In an email interview to HT, co-first author and HMS graduate student at Priya Moorjani said insights from this study will help improve our understanding of the present day population structure in India.
"While these dates correlate with major changes in India such as the arrival of Indo-European languages and de-urbanisation of the Indus valley civilisation, a date of mixture is very different from the date of migration," said Moorjani.