Dear Dr. Elst,
I am not an authority on these historical matters. But, simple science tells us that the so called 'Arya" people entered the Indian sub-continent from outside, most probably through ancient Persia. Whether they came armed to the teeth as warriors or just moved in as nomadic tribes may be open to conjecture. But the proto-Sanskrit speaking, fair skinned, Aryas certainly came from outside the Indian sub-continent.
Now, some folks are saying that the Indus Civilization was the birth place of Aryans!
The Aryans were never autochthonous to the Indian subcontinent. The primordial residents of South Asian were brown or dark skinned people. Human beings living in tropical countries tend to be dark skinned, as we all know, because they possess a high degree of melanin under the skin to protect them from the ultra violet effects of the warm sun. Hence, people living in tropical and equatorial locations are usually dark skinned. They never turn white or fair under such climatic conditions. On the contrary, light skinned people living in tropical conditions may in generations turn brownish due to the need to protect themselves from the sun's energy.
It seems to me, this simple scientific fact is sufficient to show that the original home land of the Aryas was outside the Indian Sub-Continent of India - most probably the steppe-lands of the Asian Continent, if not some other cold or temperate location in Eurasia.
Hope this helps!
With regards,
RV