This is the most common mitochondrial DNA (mtDNA) Haplogroup in India. Almost 60 per cent of the Indian population carries this Haplogroup, which is why in our tests a Bengali and a Maharashtrian show the same results. The M haplogroup is an indicator of the earliest migration of humans outside Africa.
The matrilineal line for all humans goes back to a single woman living in Africa between 150,000 to 170,000 years ago, often termed Eve by geneticists. She was by no means one of the first humans to have walked in Africa, in fact humans had been around for some 30,000 years at this point, but every human alive today is descended from her, an indication that the other lines of descent have died down at some point.
Eventually her descendants split into two groups marked by the change labelled either L0 or L1 in the mtDNA, and both groups are still found in hunter-gatherer groups in Africa. A few thousand years later, another change occurred on the mtDNA of L1 individuals, the change termed as L2 and still found in Central sub-Saharan Africa.
We start getting more precise dates at this point. Some 80,000 years ago, an additional change marked L3 individuals, who spread to North Africa and were the first humans to move out of the continent sometime around 60,000 years ago. While the exact path of migration is debatable, it is believed they followed the coastal route along the Gulf and down to India, surviving on a diet rich in shellfish.
(The map is based on the National Geographic version of the migration of the Haplogroup. The text updates this version based on recent research and offers a differing version.)
The group kept moving and seems to have first halted and settled in the Subcontinent. While this haplogroup is rarely found in people living west of the Indus Valley, it is found in over 30 per cent of the population in the northwest and reaches a high of about 80 per cent in Bengal. The wide distribution and greater genetic diversity in much of the Subcontinent suggests M*-bearing individuals are direct descendants of the first inhabitants of southwestern Asia.
This leads us to the conclusion that the vast majority of the maternal lines in the Subcontinent are of great antiquity, dating back to some of the earliest settlers of the Subcontinent. Subsequent migrations into the Subcontinent seem to have been largely composed of males who married women already settled in the Subcontinent. The preponderance of M in the Subcontinent seems to exist across castes and religion, clearly indicating that these distinctions seem to have appeared at a later date and do not reflect differences of biology. According to Dr Pitchappan, “The female lineages of the two women studied from Bengal and Maharashtra show they are descendants of an early migrant to India. The women were drawn from a local—autochthonous [indigenous] expansion.”