I've heard that Northern India was populated by migrations coming out of Central Asia. But where and how did the South Indian population come to be?

There are some on r/India who believe that Dravidians never existed, but were merely tribal lineages who broke away from the Aryan migrations. But how then would one explain the completely distinct Dravidian language family?

Is there evidence in Vedic texts or otherwise that points to a separate Dravidian population?