As from the point of view of religious belief, so also from that of social organization no clear line of demarcation can be drawn between Brahmanism and Hinduism. Though it was not till later times that the network of class divisions and subdivisions attained anything like the degree of intricacy which it shows in these latter days, still in its origin the caste-system is undoubtedly coincident with the rise of Brahmanism, and may even be said to be of the very essence of it.[3] The cardinal principle which underlies the system of caste is the preservation of purity of descent, and purity of religious belief and ceremonial usage. Now, that same principle had been operative from the very dawn of the history of Aryanized India. The social organism of the Aryan tribe did not probably differ essentially from that of most communities at that primitive stage of civilization; whilst the body of the people--the _Vis_ (or aggregate of _Vaisyas_)--would be mainly occupied with agricultural and pastoral pursuits, two professional classes--those of the warrior and the priest--had already made good their claim to social distinction. As yet, however, the tribal community would still feel one in race and traditional usage. But when the fair-coloured Aryan immigrants first came in contact with, and drove back or subdued the dark-skinned race that occupied the northern plains--doubtless the ancestors of the modern Dravidian people--the preservation of their racial type and traditionary order of things would naturally become to them a matter of serious concern. In the extreme north-western districts--the Punjab and Rajputana, judging from the fairly uniform physical features of the present population of these parts--they seem to have been signally successful in their endeavour to preserve their racial purity, probably by being able to clear a sufficiently extensive area of the original occupants for themselves with their wives and children to settle upon. The case was, however, very different in the adjoining valley of the Jumna and Ganges, the sacred _Madhyadesa_ or Middle-land of classical India. Here the Aryan immigrants were not allowed to establish themselves without undergoing a considerable admixture of foreign blood. It must remain uncertain whether it was that the thickly-populated character of the land scarcely admitted of complete occupation, but only of a conquest by an army of fighting men, starting from the Aryanized region--who might, however, subsequently draw women of their own kin after them--or whether, as has been suggested, a second Aryan invasion of India took place at that time through the mountainous tracts of the upper Indus and northern Kashmir, where the nature of the road would render it impracticable for the invading bands to be accompanied by women and children. Be this as it may, the physical appearance of the population of this central region of northern India--Hindustan and Behar--clearly points to an intermixture