The Portuguese coined the word "caste" in the 16th century to refer to these four groups. To Hindus, however, the concept of caste has a narrower and more precise meaning, referring to the smaller subgroups defined by subtle distinctions of birth, intermarriage, and occupation. The four main castes comprise more than 2,000 subcastes.
Beneath these castes is a fifth population group—those without any caste, literally, outcastes. This includes the people traditionally known as "untouchables." The Indian constitution of 1950 made "untouchability" illegal. Today these people call themselves dalits ("oppressed"). Also in this fifth group are the "tribals," the 50 million Indians who live in tribal communities that predate the Aryan and Dravidian civilizations. They are members of the "backward" classes.
Caste is a religious and social institution of the Hindu peoples, who comprise about 80 percent of India's population. The rest of India is Muslim, Christian, Sikh, Buddhist, or Jain. Caste is such a deep-rooted and pervasive concept, however, that it has influenced Muslims, Christians, and Sikhs. For example, there are separate churches for dalit and non-dalit Christians. Even the tribals, who are not a part of Hindu society, have started observing "untouchability" toward dalits—who themselves have a caste hierarchy.
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