theorized that untouchability originated as class stratification in urban areas of the Indus Valley civilisation. According to this theory, the poorer workers involved in 'unclean' occupations such as sweeping or leather work were historically segregated and banished outside the city limits. Over time, personal cleanliness came to be identified with "purity", and the concept of untouchability eventually spread to rural areas as well. After the decline of the Indus Valley towns, these untouchables probably spread to other parts of India. Scholars such as Suvira Jaiswal reject this theory, arguing that it lacks evidence, and does not explain why the concept of untouchability is more pronounced in rural areas. American scholar George L. Hart, based on his interpretation of Old Tamil texts such as Purananuru, traced the origin of untouchability to ancient Tamil society. According to him, in this society, certain occupational groups were thought to be involved in controlling the malevolent supernatural forces; as an example, Hart mentions the Paraiyars, who played the drums during battles and solemn events such as births and deaths. People from these occupational groups came to be avoided by others, who believed that they were "dangerous and had the power to pollute the others". Jaiswal dismisses the evidence produced by Hart as "extremely weak" and contradictory. Jaiswal points out that the authors of the ancient Tamil texts included several Brahmanas (a fact accepted by Hart); thus, the society described in these texts was already under Brahmanical influence, and could have borrowed the concept of untouchability from them. British anthropologist John Henry Hutton traced the origin of untouchability to the taboo on accepting food cooked by a person from a different caste. This taboo presumably originated because of cleanliness concerns, and ultimately, led to other prejudices such as the taboo on marrying outside one's caste. Jaiswal argues that this theory cannot explain how various social groups were isolated as untouchable or accorded a social rank. Jaiswal also notes that several passages from the ancient Vedic texts indicate that there was no taboo against accepting food from people belonging to a different varna or tribe. For example, some Shrauta Sutras mandate that a performer of the Vishvajit sacrifice must live with the Nishadas (a tribe regarded as untouchable in later period) for three days, in their village, and eat their food. Scholars such as Suvira Jaiswal, R. S. Sharma, and Vivekanand Jha characterize untouchability as a relatively