I have very little knowledge regarding these issues, but it is true we are not pure, the Dravidian and Aryan both were invaders, while there were some Chondal and local people before them and we mixed together and now we are Bengali!
I have no interest in finding my roots, these are valueless in my thoughts, also Islam doesn't divide or evaluate a man on his race, color, origin, incapability, rich or poor, these are meaningless as a humankind. But many nations are divided on these valueless arguments to prove themselves better than others, I am really irritated by such talking!