Analyses of whole-genome sequence data of urban Sinhalese and two indigenous Adivasi clans in Sri Lanka, which live in geographically separated regions in the country, shed light on the migratory history of these populations and their genetic relationship to each other and to many Indian populations. The study published recently in the journal Current Biology found that Sinhalese and Adivasi are genetically closest to each other and to South Indians, but, at a regional and fine-scale level, the two Adivasi clans are genetically distinct.
For the study, whole genomes of 35 urban Sinhalese individuals and 19 individuals from two indigenous Adivasi clans were sequenced. Of the 19 genomes of Adivasi clans that were sequenced, five were from Interior Adivasi and 14 were from Coastal Adivasi. The sampling and data generation became possible due to the outreach efforts of Sri Lankan collaborator, Dr. Ruwandi Ranasinghe from the University of Colombo. In addition, the whole genome data of 35 Sri Lankan Tamils sampled in the UK, which were already sequenced as part of the 1,000 Genomes Project, were included in the analyses.
Sinhalese chronicles and previous genetic studies had proposed that Sinhalese had migrated from northern or northwest India around 500 BCE, though their exact origins and migratory history are still debated. That Sinhalese speak an Indo-European language, Sinhala, whose present-day distribution lies primarily in northern India further supports the idea of their migration from northern India. But the current study contradicts the findings of the previous studies from a genetic perspective. “The genetic ancestries and their proportions in the Adivasi and Sinhalese are most similar to Dravidian speaking populations who live in Southern India today,” says Dr. Niraj Rai from Birbal Sahni Institute of Palaeosciences (BSIP), Lucknow and one of the corresponding authors of the paper.
Also Read | Genome study: 180 million genetic variants found in 9,772 individuals
“Even among South Indian populations, we find that the Sinhalese are genetically closest to those communities that have higher proportions of the so-called ASI or Ancestral South Indian ancestry. In contrast to many North Indians, these populations generally have lower levels of a genetic ancestry related to ancient groups from the Eurasian Steppe, proposed to have carried Indo-European languages into South Asia and that are today spoken widely in northern regions of India,” says Dr. Maanasa Raghavan, Assistant Professor at the University of Chicago and a corresponding author of the study. But how does one reconcile the fact that Sinhalese speak a language that is classified as Indo-European, which today is spoken mostly in North India?
The authors explain that genes do not reflect linguistic affinities, and biological and cultural evolution can have different trajectories. They speculate that this genetic-linguistic discordance may have been caused by the Sinhalese population having migrated from somewhere in North India geographically, but genetically speaking, the migration may have come from a group that resembles more South Indian Dravidian speakers today.
An alternative explanation is that a small group of Sinhalese, perhaps representing the elite, might have migrated to Sri Lanka and transmitted the language but not genes. “If the Sinhalese were derived from a North Indian genetic cluster with higher Steppe-related ancestry, mixing had to have happened with ASI populations to dilute their genetic ancestries and pull them genetically closer to South Indian populations in our analyses. More anthropological studies are needed to fully understand these differing genetic and cultural affinities of the Sinhalese,” Dr. Raghavan says.
The time of formation of the Sinhalese genetic pool was dated in the study to about 3,000 years ago, falling within the range of dates displayed broadly by Indian and other Sri Lankan populations and around the time of the proposed migration date of the Sinhalese in the chronicles (500 BCE). “The date our analysis reveals is interesting. It implies that the Sinhalese ancestors migrated to Sri Lanka fairly close in time to the dynamic genetic mixing events that were occurring about 2,000-4,000 years ago in India that created the ANI-ASI genetic spectrum we see in today’s populations,” Dr. Rai explains.
Sinhalese chronicles also say that when Sinhalese migrated from India to Sri Lanka about 3,000 years ago, Adivasi were already existing in Sri Lanka. This is also supported by anthropological studies that propose that Adivasi are descended from early hunter-gatherers in the region. The Adivasi are, in fact, traditionally hunter-gatherers and the Indigenous peoples of Sri Lanka.
“At a broad scale, Adivasi today look genetically very similar to the Sinhalese and Sri Lankan Tamil. This must mean that the Sinhalese, Sri Lankan Tamils, or other groups migrating from South India must have met the Adivasi, mixed with them heavily, and contributed to what is the present-day genetic structure of the Adivasi,” Dr. Raghavan says.
Sinhalese and Adivasi are close to each other and share broad-level genetic similarities, but on a fine-scale demographic resolution, the study found that the two Adivasi clans are a bit different from the Sinhalese. The Adivasi have slightly higher levels of ancient hunter-gatherer ancestry than the Sinhalese and Sri Lankan Tamils, and have maintained smaller population sizes over the course of their history, both of which support their traditional hunting and gathering lifestyle. The Adivasi genomes also display signatures of endogamy, which appear as long stretches of DNA inherited from a common ancestor. The study further reports that a consequence of the low population size and endogamy is that the genetic diversity in the Adivasi is lower than the urban populations, which may have an impact on their health and disease status.
While both Adivasi clans maintained lower population sizes compared to the Sinhalese and Sri Lankan Tamils, the authors found that the Interior Adivasi clan seemed to have undergone a stronger reduction in their population size compared to the Coastal Adivasi, leading to a greater loss of their genetic diversity. “We find the two Adivasi clans — the Coastal Adivasi and the Interior Adivasi — also have some differences in their genetic ancestry arising due to distinct geographic separation between them,” says Dr. Rai.
This, according to Dr. Raghavan, indicates that the Interior Adivasi clan must have undergone stronger pressures, perhaps societal or environmental, to keep the population size lower compared to their Coastal counterparts. Explaining how the two Adivasi clans are more similar to each other, but still have genetic differences at a fine scale, she says that this basically means that at some point in time, due to geographic separation, the genetic and lifestyle attributes of the two clans started to drift apart.
In fact, the fragmented nature of the Adivasi clans also impacted the study sampling strategy. While 35 individuals representing the two large groups — Sinhalese and Sri Lankan Tamils — have been included in the analyses, the numbers for the two Adivasi populations are small — five for interior Adivasi and 14 for coastal Adivasi.
Though it would be ideal to keep matched sample sizes of different populations for genetic analyses, the reason for including only small numbers for the two Adivasi clans was because the Adivasi communities today are very fragmented. “Historical, anthropological, as well as our genetic results all suggest that these communities live in small sizes and practice endogamy,” says Dr. Raghavan. “Because of endogamy, a lot of these individuals tend to be quite related to one another. Having really high relatedness in a group impacts the genetic analyses because then everybody’s going to look like each other. So that’s why our sample sizes were lower for the two Adivasi clans.”
Despite the number of individuals representing the two Adivasi clans being small, the researchers were able to recapture the entire population history of these two groups. The study was able to address the questions that the researchers set out to do despite the Adivasi sample sizes being small, says Dr. Raghavan. “Since every individual’s genome is a mosaic of their ancestor’s genomes, even a small number of individuals can represent their population’s genetic histories. Moreover, we didn’t find any genetic outliers within the Adivasi clans. So, all the sampled individuals fit into the model that we propose,” clarifies Dr. Rai.
“This is the first time that high-resolution genome data have been sequenced from multiple populations in Sri Lanka, including the Indigenous Adivasi and urban Sinhalese, to understand the deeply rooted ancestries and their population histories,” says Dr. Rai. Broadly, the study has important implications for how humans moved across South Asia and highlights the high degree of interconnectedness between India and Sri Lanka over millennia.
Published – July 01, 2025 04:25 pm IST
