If you remember, this season we saw Jacob and the man in black's childhood. during that episode, you see that there was a shipwreck of people a looooooong time ago and they made a society on the island. I believe they were the first.
Well...Jacob's and Black's stepmother said that she was from her mother, so that means that there were people before her. (not clear if they all (those before her) were protecting the light from other people or not, but it doesn't even matters much).
We do know the Egyptians had been to the island with all the statues and hieroglyphic engravings everywhere. This may well be where 'Mother' comes from for all we know.
Also there is cuneiform language seen on the cork stone in the Source. This is also a language more ancient than the Romans.
It's likely that humans have populated the island for as long as they've had ships capable of travelling long distances. (ie a few thousand years). Before that? Who knows!
