They are different classes into which the Hindoos have been divided from the earliest times.
Four; the Brahmins or priests, who sprung from the head of Brahma; the Warrior caste, which issued from his arms; the Agriculturists and Traders, who came from his thighs, and lastly, the Sudras, or laborers, who sprung from his feet.
They cannot under any circumstances intermarry; nor can a member of a lower caste ever pass to a higher. Only, if he lead a good life, he may console himself with the hope of being born in a higher caste the next time.
No regular caste, but there exists a most unhappy race called Pariahs, who are treated with the utmost contempt, and employed only in the vilest offices. They cannot enter the house of any one belonging to a pure caste, and they are not only unclean themselves, but are supposed to contaminate everything they touch. Different accounts are given as to the origin of these Pariahs.
The three higher castes are forbidden it altogether. The Sudras may eat every kind but beef, but the Pariahs are under no restriction whatever. The idea seems to be that they are so vile that no kind of food could pollute them.
So much so, that it is impossible to say when they were first established. The Pariahs are being gradually raised from their degradation by the efforts of Christian missionaries.