lie near or
across natural highways of human migration. As a tide of humanity sweeps
around or across the mountains, a branch stream turns into a side
valley, where it is caught and held. There it remains unaltered,
crystallizing in its seclusion, subjected for ages to few modifying
influences from without. Its people keep their own language and customs,
little affected by a totally different race stock similarly placed in a
neighboring alcove of the mountains. Lack of communication engenders an
endless multiplication of dialects, as we find them in the Alps, the
Caucasus, in Kafirstan of the Hindu Kush and in Nepal. Diversity of
speech, itself a product of isolation, reacts upon that political and
social aloofness of mountain folk, to emphasize and fix it.

[Sidenote: Survival of primitive races in mountains.]

From this principle it follows that the same highland region shows
strong differentiation and marked social individuality from one district
to another, and from one valley to the next, despite a prevailing
similarity of local geographic conditions. In fact, the very similarity
of those conditions, strong in their power to isolate, present the
conditions for inevitable variation. A mountain region gets its
population from diverse sources, or, which is quite as important, at
different times from the same source. For instance, Nepal received
contingents of Rajput conquerors, dislodged from the Punjab, in the
seventh century, the eleventh, and finally the dominant Gurkhas at the
end of the eighteenth. To-day these represent different degrees of
amalgamation with the local Tibetan stock of Nepal. They are
distinguished from each other by a diversity of languages, and a
multiplicity of dialects, while the whole piedmont of the country shows
a yet different blend with the Aryan Hindus of the Ganges valley, who
have seeped into the Terai and been drawn up, as if by capillary
attraction, into the hill valleys of the outer range. The Vindhyan Range
and its associated highlands, long before the dawn of Indian history,
caught and held in their careful embrace some of the fragile aboriginal
tribes like the Kolarian Ho, Santals and Korkus. Centuries later the
Dravidian Bhils and Gonds sought refuge here before the advancing
Indo-Aryans, and found asylums in the secluded valleys.[1393] Finally
those same northern plains whence the Dravidians had come, after the
Mohammedan conquest of central India in the sixteenth century, se