correction retroflexes

[Rajarshi Banerjee]

Sorry: I made an absent minded error earlier here is a correction:

It was pointed out in an earlier mail that there is a retroflexion gradient
from the morthwest to the south, gujarati having very weak retroflexion and
tamil and malayalam being strongly retroflexed.

Words like badA(big) or gaNesh require some retroflexion. All Indian
languages are retroflexed to some degree. I have found punjabi speakers
using retroflexes in words like nAl where. the l is pretty strongly
retroflexed.

Everyone must have noticed that retroflexes are used all over south asia
bangladesh to pak and afghanistan, but dissappear rather abruptly once we
leave south asia.

People from western and central asia, russia and most of europe( excluding
english, german and the like) dont use retroflexes either. I am no linguist
but
I would think that this is a pretty significant divide and an important
marker in determining language drift or evolution. Is there any popular
explanation for this?