Ancient genetic imprint unites the tribes of India
·11:19 11 September 2008
·NewScientist.com news service
The first humans to arrive on the Indian subcontinent from Africa about 65,000 years ago left a genetic imprint that can still be found in the tribes of India.
Anthropologists have long argued over thegenetic makeup of the country's population, because of its complex history of migrations and movement.
The first humans to people the sub-continent came from Africa, following the so-calledsouthern route, along the tropical coast of the Indian Ocean.
"Whether the original inhabitants of India were replaced by more modern immigrants or contributed to the contemporary gene pool has been debated," saysMichael Bamshadof the University of Washington in Seattle, who has studied the genetic diversity of India.
One way researchers have used to figure this out is to use linguistic groups.
The tribes speaking Indo-European languages, for instance, are known to be descendants of the people who migrated into India relatively recently from Central Asia and the Caucasus. It was also thought that the Austro-Asiatic speakers were direct descendants of the original settlers.
Mothers of India
To determine which groups can trace their ancestry to the founding population of India, Vadlamudi Raghavendra Rao of theAnthropological Survey of Indiain Kolkata and his colleagues analysed 2768 samples of mitochondrial DNA taken from 24 tribes all over India.
Mitochondrial DNA is inherited from the mother, so can be used to trace the maternal lineage of a population.
The researchers looked for a particular set of mutations in the mitochondrial genome called the M2 haplogroup. This set of genetic markers is unique to India and is a sub-lineage of the M haplogroup that identifies the first humans who arrived in India from Africa 65,000 years ago.
The analysis showed that the M2 lineage began in India about 50,000 years ago, about 15,000 years after modern humans arrived.
The team also found that the M2 lineage and its branches made up nearly 10% of the mitochondrial DNA of the studied tribes.
"We found these 'footprints' in all the tribal populations," says Rao.
"We analysed the most primitive tribes, spread over the south, central and east India and found the signatures of earliest antiquity."
Significantly, the M2 lineage cuts across major linguistic barriers. The new study shows that both the Dravidian and Austro-Asiatic language groups share these same genetic markers.
According to team member Satish Kumar, the M2 haplogroup can also be found, albeit with reduced frequency, among members of the so-calledhigher castes of India, such as the Brahmins (priests) and the Kshatriyas (warriors).
Upper castes are thought to be the outcome of the arrival over time of a more technologically advanced people that marginalised the indigenous population, starting about 10,000 years ago.
Even these new migrants assimilated into India and to some extent mixed with the population, as the presence of M2 genes in the group attests.
"The early settler component is not restricted to one particular language family, or one particular population," says Kumar.
Rao agrees. "Biologically, there are no castes and tribes, there are only communities," he says.