The four castes of the Ganges civilization still form the backbone of the Indian caste system of today, but they are further subdivided into a total of some 3000 castes.
Some scholars maintain that most of the original population was exterminated by the invaders. The Sudra caste was only fully estabished around 700 BC, so it is possible that its members were supplied by impoverished Aryans rather than the original population.