[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, sent flying to the refuge of the hills a large contingent of Hindus of mingled Dravidian and Aryan stocks, but stamped with the culture of the Ganges basin.  These occupied the richer valleys and the more accessible plateaus of the highlands, driving the primitive Gonds and Bhils back into the remoter recesses of the mountains.[1394] Dravidians and aboriginal Kolarians survive in their purity in the wilder and more inaccessible regions, but in the lower valleys their upper classes show signs of mixtures with the Rajput invaders, while the lower classes betray little Aryan blood.[1395]

[Sidenote:  Diversity of peoples and dialects.]

Afghanistan, of disordered relief, set as a transit region between the plains of Mesopotamia, the Oxus and the Indus, has a confused ethnology in keeping with the tangle of dissected plateaus and mountain systems which constitute its surface.  Here we find three distinct branches of the Indo-European race, divided up into various peoples of diverse tongues and subdivided further into countless tribes; and two branches of Mongol-Tartars scattered, as if out of a pepper box, from the Helmund to the Oxus, tossed in among diverse peoples of Iranic and Galcha origin in hopeless confusion.  The various Afghan tribes, separated from each other by natural barriers and