It depends on what you mean by "original." Do they have to have the same basic identity, same genetics, same language? How much change is permitted? After all, even descent societies in the same basic area for 10,000-20,000 years (I'm thinking of a few Khoesan groups, and possibly their fusion neighbors) experienced enormous change in language, lifeways, and biology.

There's an implicit politics in the question, which may not be your intent, but it's worth mentioning: the idea that you can't redress wrongs connected to settler colonialism, because the people the current ascendant class took land from weren't the first either. I reject this case, primarily because the most recent dispossession was very often blatantly and demonstrably illegal or treaty-violating, or else the result of military conflict that can be shown as manufactured for that express purpose. The restitution model (not the practice, which is often quite another beast, and one that moves slowly and injudiciously to put it mildly) in South Africa, for that reason, cuts off direct restitution at the enactment date of the 1913 Natives Land Act--the first firm race-based measure across South Africa, despite its temporary abeyance in the Cape Province--but claimants from older communities, and against other claimants, are eligible for "redistribution," that is, land elsewhere. Only those dispossessed after June 1913 are to receive direct awards. In practice everything's gone rather haywire, and it cuts out a number of blatant cases from before 1913, but the basic concept is at least defensible.

To answer the question itself, I'm not aware of any certain cases. It couldn't be in Africa, because we've had waves of human evolution throughout--and elsewhere outside of Africa, many waves of migration and re-colonization, fusion and fission, not all of which we can accurately map. The only clear case I can think of is Antarctica, where national research stations have remained in the same basic hands since their establishment, and "new lands" like volcanic islands (maybe Iceland falls under this header?). We could probably add some of the Pacific Islands to this list, especially from the second wave of Austronesian/Polynesian expansion (if we permit limited fusion), and perhaps Madagascar and some areas in Australia as well (ditto), but I'm not sure which ones. Of course, that just involves the largest of group collectives; the possession or occupancy by lineages, or subgroups, obviously is much more complicated even within those societies.

There is an isolated island on the Indian Ocean.

Well, Estonians think of themselves as "European aboriginals", since this nation groups has lived in the same territory for at least 10 000 years or so, ever since the place was cleared from the remnants of the last ice age. I'm not sure how well this would stand up to any criteria, but this is at least taught to Estonian children.