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Untouchability, in its literal sense is the practice of ostracising a minority group by segregating them from the mainstream by social custom or legal mandate. The term is most commonly associated with treatment of the Dalit communities in Indian subcontinent who were considered "polluting" , but the term has been used for other groups as well, such as the Burakumin of Japan, Cagots in Europe, or the Al-Akhdam in Yemen. Traditionally, the groups characterized as untouchable were those whose occupations and habits of life involved ritually polluting activities such as fishermen, manual scavengers, sweepers and washermen.
Untouchability has been outlawed in both India and Pakistan post their independence. However, "Untouchability" hasn't been legally defined till date. The origin of Untouchability and it's historicity are still debated, but it is believed to have existed at least as far back as 400 AD. According to 2011 Census of India more than 70% population reportedly did not indulge in the practice of Untouchability anymore. 
Exact origins of Untouchability are unknown. Although the historicity of untouchability is debated due to lack of consensus on what "Untouchability" is, it is believed to have been born around 400 AD due to the struggle for supremacy between Buddhism and Brahmanism (an ancient term for Brahmanical Hinduism).
According to Sarah Pinto, an anthropologist, untouchability in India applies to people whose work relates to "death, bodies, meat, and bodily fluids". In the name of untouchability, Dalits have faced work and descent-based discrimination at the hands of the dominant castes. Based on the punishments prescribed in The Untouchability (Offences) Act, 1955 the following practices could be understood to have been associated with Untouchability in India:
- Prohibition from eating with other members
- Provision of separate cups in village tea stalls
- Separate seating arrangements and utensils in restaurants
- Segregation in seating and food arrangements in village functions and festivals
- Prohibition from entering into places of public worship
- Prohibition from wearing sandals or holding umbrellas in front of higher caste members
- Prohibition from entering other caste homes
- Prohibition from using common village path
- Separate burial grounds
- Prohibition from accessing common/public properties and resources (wells, ponds, temples, etc.)
- Segregation (separate seating area) of children in schools
- Bonded labour
- Social boycotts by other castes for refusing to perform their "duties"
Government action in India
During the time of Indian independence, Dalit activists began calling for separate electorates for untouchables in India to allow for fair representation. Officially labeled the Minorities Act, it would guarantee representation for Sikhs, Muslims, Christian, and Untouchables in the newly formed Indian government. The Act was supported by British representatives such as Ramsay MacDonald. According to the textbook,"Religions in the Modern World", B.R. Ambedkar who was also a supporter of the act, was considered to be the “untouchable leader” who made great efforts to eliminate caste system privileges that included participation in public festivals, access to temples, and wedding rituals. In 1932, Ambedkar proposed that the untouchables create a separate electorate that ultimately led Gandhi to fast until it was rejected.
A separation within Hindu society was opposed by national leaders at the time such as Mohandas Karamchand Gandhi, although he took no exception with the demands of the other minorities. He began a hunger strike to protest this type of affirmative action, citing that it would create an unhealthy divide within the religion. At the Round Table Conferences, he provided this explanation for his reasoning:
I don't mind untouchables if they so desire, being converted to Islam or Christianity. I should tolerate that, but I cannot possibly tolerate what is in store for Hinduism if there are two divisions set forth in the villages. Those who speak of the political rights of the untouchables don't know their India, don't know how Indian society is today constituted and therefore I want to say with all the emphasis that I can command that if I was the only person to resist this thing that I would resist it with my life.
Mohandas Karamchand Gandhi achieved some success through his hunger strike. Dalit activists faced pressure from the Hindu population at large to end his protest at the risk of his ailing health. The two sides eventually came to a compromise where the number of guaranteed seats for Untouchables would be reduced, but not totally eliminated.
The 1950 national constitution of India legally abolished the practice of untouchability and provided measures for positive discrimination in both educational institutions and public services for Dalits and other social groups who lie within the caste system. These are supplemented by official bodies such as the National Commission for Scheduled Castes and Scheduled Tribes.
Despite this, instances of prejudice against Dalits still occur in some rural areas, as evidenced by events such as the Kherlanji massacre.
Japan: Burakumin jobs were those designated as "unclean" by Buddhist and Shinto standards. They worked as butchers, tanners, and executioners. The Buraku people were forced to live in segregated neighborhoods, and could not mingle with any of the higher classes of people. The buraku was universally looked down upon, and their children were denied an education.
Nigeria and Cameroon: Osus
Others: * Tanka (danhu) ("boat people") in Guangdong, Fuzhou Tanka in Fujian, Si-min (small people) and Mianhu in Jiangsu, Gaibu and Duomin (To min) 惰民 duò mín ("idle/lazy/fallen/indolent people") in Shijiazhuang, jinxing yum-in 九姓魚民 jiǔxìng yúmín ("nine name fishermen") in the Yangtze River region, yon-hoe ("music people") in Shani in China
- "Untouchable - Encyclopaedia Britannica".
- "AIR 1958 Kant 84".
- Dr. Babasaheb Ambedkar, Writings and Speeches, Volume 7.
- "The Continuing Practice of Untouchability in India: Patterns and Mitigating Influences" (PDF). India Human Development Survey.
- Some Recent Theories Of The Origin Of Untouchability https://www.jstor.org/stable/44139355?read-now=1&seq=1#page_scan_tab_contents
- "Untouchability - The Origin Of Untouchability".
- Pinto, Sarah (2013). Where There Is No Midwife: Birth and Loss in Rural India. Berghahn Books. p. 47. ISBN 978-0-85745-448-5.
- "THE UNTOUCHABILITY (OFFENCES) ACT, 1955".
- Smith, David (2016). Woodhead, Linda; Partridge, Christopher; Kawanami, Hiroko, eds. Hinduism. New York: Routledge. p. 38-40.
- Kumar, Ravinder. "Gandhi, Ambedkar and the Poona pact, 1932." South Asia: Journal of South Asian Studies 8.1-2 (1985): 87-101.