Next to this extraordinary fission and complication of the social body we have to note that the Brahmins, the priests and teachers of the Indian world, unlike so many Western priesthoods, are a reproductive and exclusive class, taking no recruits from any other social stratum. Whatever may have been the original incentive to this extensive fixation of class in India, there can be little doubt of the rôle played by the Brahmins as the custodians of tradition and the only teachers of the people in sustaining it. By some it is supposed that the first three of the four original castes, known also as the “twice born,” were the descendants of the Vedic Aryan conquerors of India, who established these hard-and-fast separations to prevent racial mixing with the conquered Sudras and Pariahs. The Sudras are represented as a previous wave of northern conquerors, and the Pariahs are the original Dravidian inhabitants of India. But those speculations are not universally accepted, and it is, perhaps, rather the case that the uniform conditions of life in the Ganges valley throughout long centuries served to stereotype a difference of classes that have never had the same steadfastness of definition under the more various and variable conditions of the greater world to the west. However caste arose, there can be no doubt of its extraordinary hold upon the Indian mind. In the sixth century B.C. arose Gautama, the great teacher of Buddhism, proclaiming, “As the four streams that flow into the Ganges lose their names as soon as they mingle their waters in the holy river, so all who believe in Buddha cease to be Brahmins, Kshatriyas, Vaisyas, and Sudras.” His teaching prevailed in India for some centuries; it spread over China, Tibet, Japan, Burmah, Ceylon, Turkestan, Manchuria; it is to-day the religion of one-third of the human race, but it was finally defeated and driven out of Indian life by the vitality and persistence of the Brahmins and of their caste ideas.... § 7