About 15,000 B.C. increasing population pressure throughout Turkestan and Iran occasioned the first really extensive Andite movement toward India, slowly moving southward into the Deccan. 
As the Salem missionaries penetrated southward into the Dravidian Deccan, they encountered an increasing caste system, the scheme of the Aryans to prevent loss of racial identity in the face of a rising tide of the secondary Sangik peoples. 
The Aryans made very little racial impression on India except in the northern provinces. In the Deccan their influence was cultural and religious more than racial.  Hinduism became contaminated with a flood of degrading and debilitating cults and creeds from the Deccan.  Dravidian culture has survived in Deccan to modern times.