The caste system is a social hierarchy based on ones birth that is tied to concepts of purity and social status. It has existed in some form in India for at least 3,000 years. The system divides Hindus into four main categories - Brahmins, Kshatriyas, Vaishyas, and the Shudras - with each group occupying a specific place in the complex hierarchy. The main castes were further divided into about 3,000 castes and 25,000 sub-castes, each based on their specific occupation. The caste system is not static, and jatis have changed their position over the centuries of Indian history. However, the jati moves up the social scale as a group and not as individuals. Caste segregation remains prevalent in India, and the suffering of those at the bottom of the caste pyramid, known as Dalits, has continued. The Indian Constitution has outlawed the practice of Untouchability, and the Indian Government has established special quotas in schools and Parliament to aid the lowest jatis. Caste discrimination is not permitted in gaining employment and access to educational and other opportunities.