Is it hard to digest that there could be two schools of language, one developing in South and one in North, why does one need to push that Arayans or someone else brought in the language in north, when south can have specific langauage developed same could be possible in north too.
As far as fair skin is concerned its the proximity to equator that made the difference in evolution, one doesnt need europeans dna in north to get fair skin.
Ramanyana has some good description of south and given that Bali, Sugriv, Hanuman who where kind of apes where able to have communication means there was ample interaction of north indian language in south india atleast at top levels. At ground level there are good chances of having a mother tongue which might be very specific to dravidan region. This also brings in a situation which shows south was still evolving and there was big region where human beings were like apes. And presence of Ravana (a brahmin by caste) shows that there was interaction at society level and some brahmins and kshtriya's took control over developing human race in south. Chances are that some of the language parts where passed by them, rest where locally developed and hence there is so much difference yet some connectivity.