Are the Nicobar Islands the place where the allegedly Stone Age aboriginals live?
I don't know
A recent discovery has it that the broad masses of Bengladesh, India, Sri Lanka and Pakistan share two major lineages ~ Persian and the group ancestral to the Andaman islanders. In doing numerous DNA studies the researchers found that ALL Indian subcontinent people have those two lineages, with no others of any note. The general appearance of individuals has nothing whatsoever to do with the percentage of either lineage in the background.
In short Indians are very mixed.
Yes and I don't think "allegedly" is required in this case. The Andaman and Nicobar island chains, shown in #12, had had several tribes of aboriginals, the rest of which have which have been contacted and generally not fared well. The Andaman's had been used for penal colonies by the Brits and one native appeared in a Sherlock Holmes story because of that. The population on North Sentinel Island (not named on the map at #12, but it's the little island just below the last "a" in "Herbertabad") has vigorously resisted contact in hardcore stone age 2nd amendment fashion. I think there finally has been at least one brief non-lethal contact made, but for the most part knowledge of them is from a safe distance.
Well, up until now.