Roughly 8.6 per cent of India's population is made up of "Scheduled Tribes" (STs), traditional tribal communities. In India those who are not Christians, Muslims, Jews, Sikhs, Buddhists, or Zoroastrians are identified as Hindus. The reason being varied beliefs and practices allowed in Hindusim and according of Hindusim as a geographical identity than merely Religious ones. Though, many of the Scheduled Tribes have modes of worship not typical to mainstream Hindusim but ontologically form part of the cultural practices of the land, as Nature or ancestral worship, with varying degrees of syncretism.
According to the 2011 census of India, about 7.9 million out of 1.21 billion people did not adhere to any of the subcontinent's main religious communities of Hinduism, Islam, Christianity, Sikhism, Buddhism, or Jainism. The census listed atheists, Zoroastrians, Jews, and various specified and unspecified tribal religions separately under the header "Other Religions and Persuasions".[1]
Of these religious census groupings, the most numerous are Sarna (4.9 million respondents), Gondi (1 million), Sari Dharam (506,000), Donyi-Poloism (331,000); Sanamahi (222,000) and Khasi (139,000), with all other religions numbering less than 100,000 respondents, including 18,000 for "tribal religion", 5,600 for "nature religion", and 4,100 "animists".[1]
The tribal people observe their festivals, which have no direct conflict with any religion, and they conduct marriage among them according to their tribal custom. They have their own way of life to maintain all privileges in matters connected with marriage and succession, according to their customary tribal faith. In keeping with the nature of Indian religion generally, these particular religions often involve traditions of ancestor worship or worship of spirits of natural features.[2]
The various tribes can be categorised into different major linguistic groupings, such as Indo-Aryan, Dravidian, Austroasiatic, Tibeto-Burman, and Andamanese.[3]
About 25% of the Munda people and Oraon people, and 60% of the Kharia people of Bihar (population about 130,000), are Christian. Altogether, 43% of Kharia population is Hindu while 46% is Christian. However, almost two-thirds (63%) of the Santhal, over 40% of Munda and Ho tribal population are Hindus. Tribal groups in the Himalayas were similarly affected by both Hinduism and Buddhism in the late 20th century. The small hunting-and-gathering groups in the union territory of the Andaman and Nicobar Islands have been under severe pressure of cultural assimilation.[4]
According to the Indian legal system, all the native or indigenous religions of India fall broadly under Hinduism, since the constitution does not classify only Vedic religions as Hinduism as used in the colloquial norm. The term "Hindu" is derived from Persian meaning "Indo" (or Indian), hence the official word "Hinduism" broadly refers to all the native cultures of the Indian subcontinent. The 1955 Hindu Marriage Act "[defines] as Hindus anyone who is not a Christian, Muslim, or Jew".