The original strain of Indica known as Hindu Kush which is said to be lost forever (most likely cross-bred out of existence owing to original Indica's small size), originates from its name sake the Hindu Kush Himalaya, where temperatures drop below freezing point as soon as the sunlight is blocked out by the various mountain peaks.
This is the time when our little Indica friends secrete a waxy resin protecting their flowers from the onset of the unimaginable frost biting cold, a resin laden with THC.
I imagine that the original Hindu Kush would have been more akin to a tiny block of hashish poking out of the ground at a certain point of the night, and probably more potent than anything available by today's stans.