There are different theories about the establishment of the caste system. There are religious-mystical theories. There are biological theories. And there are socio-historical theories.
The religious theories explain how the four Varnas were founded, but they do not explain how the Jats in each Varna or the untouchables were founded. According the Rig Veda, the ancient Hindu book, the primal man - Purush - destroyed himself to create a human society. The different Varnas were created from different parts of his body. The Brahmans were created from his head; the Kshatrias from his hands; the Vaishias from his thighs and the Sudras from his feet. The Varna hierarchy is determined by the descending order of the different organs from which the Varnas were created. Other religious theory claims that the Varnas were created from the body organs of Brahma, who is the creator of the world.
The biological theory claims that all existing things, animated and inanimated, inherent three qualities in different apportionment. Sattva qualities include wisdom, intelligence, honesty, goodness and other positive qualities. Rajas include qualities like passion, pride, valour and other passionate qualities. Tamas qualities include dullness, stupidity, lack of creativity and other negative qualities. People with different doses of these inherent qualities adopted different types of occupation.
According to this theory the Brahmans inherent Sattva qualities. Kshatrias and Vaisias inherent Rajas qualities. And the Sudras inherent Tamas qualities.
Like human beings, food also inherents different dosage of these qualities and it affects its eater's intelligence. The Brahmans and the Vaisias have Sattvic diet which includes fruits, milk, honey, roots and vegetables. Most of the meats are considered to have Tamasic qualities. Many Sudra communities eat different kinds of meat (but not beef) and other Tamasic food. But the Kshatrias who had Rajasic diet eat some kinds of meat like deer meat which is considered to have Rajasic qualities. Many Marathas who claim to be Kshatrias eat mutton. The drawback of this theory is that in different parts of India the same food was sometimes qualified to have different dosage of inherent qualities. For example there were Brahmans who eat meat which is considered Tamasic food.
The social historical theory explains the creation of the Varnas, Jats and of the untouchables. According to this theory, the caste system began with the arrival of the Aryans in India. The Aryans arrived in India around 1500 BC. The fair skinned Aryans arrived in India from south Europe and north Asia. Before the Aryans there were other communities in India of other origins. Among them Negrito, Mongoloid, Austroloid and Dravidian. The Negrito have physical features similar to people of Africa. The Mongoloid have Chinese features. The Austroloids have features similar the aboriginals of Australia. The Dravidians originate from the Mediterranean and they were the largest community in India. When the Aryans arrived in India their main contact was with the Dravidians and the Austroloids. The Aryans disregarded the local cultures. They began conquering and taking control over regions in north India and at the same time pushed the local people southwards or towards the jungles and mountains in north India.
The Aryans organized among themselves in three groups. The first group was of the warriors and they were called Rajayana, later they changed their name Rajayana to Kshatria. The second group was of the priests and they were called Brahmans. These two groups struggled politically for leadership among the Aryans. In this struggle the Brahmans got to be the leaders of the Aryan society. The third group was of the farmers and craftsmen and they were called Vaisia. The Aryans who conquered and took control over parts of north India subdued the locals and made them their servants. In this process the Vaisias who were the farmers and the craftsmen became the landlords and the businessmen of the society and the locals became the peasants and the craftsmen of the society.
In order to secure their status the Aryans resolved some social and religious rules which, allowed only them to be the priests, warriors and the businesmen of the society. For example take Maharashtra. Maharashtra is in west India. This region is known by this name for hundreds of years. Many think that the meaning of the name Maharashtra is in its name, Great Land. But there are some who claim that the name, Maharashtra, is derived from the Jat called Mahar who are considered to be the original people of this region. In the caste hierarchy the dark skinned Mahars were outcasts. The skin color was an important factor in the caste system. The meaning of the word "Varna" is not class or status but skin color.
Between the outcasts and the three Aryan Varnas there is the Sudra Varna who are the simple workers of the society. The Sudras consisted of two communities. One community was of the locals who were subdued by the Aryans and the other were the descendants of Aryans with locals. In Hindu religious stories there are many wars between the good Aryans and the dark skinned demons and devils. The different Gods also have dark skinned slaves. There are stories of demon women trying to seduce good Aryan men in deceptive ways. There were also marriages between Aryan heroes and demon women. Many believe that these incidences really occurred in which, the gods and the positive heroes were people of Aryan origin. And the demons, the devils and the dark skinned slaves were in fact the original residence of India whom the Aryans coined as monsters, devil, demons and slaves.
As in most of the societies of the world, so in India, the son inherited his father's profession. And so in India there developed families, who professed the same family profession for generation in which, the son continued his father's profession. Later on as these families became larger, they were seen as communities or as they are called in Indian languages, Jat. Different families who professed the same profession developed social relations between them and organized as a common community, meaning Jat.
Later on the Aryans who created the caste system, added to their system non-Aryans. Different Jats who professed different professions were integrated in different Varnas according to their profession. Other foreign invaders of ancient India - Greeks, Huns, Scythains and others - who conquered parts of India and created kingdoms were integrated in the Kshatria Varna (warrior castes). But probably the Aryan policy was not to integrate original Indian communities within them and therefore many aristocratic and warrior communities that were in India before the Aryans did not get the Kshatria status.
Most of the communities that were in India before the arrival of the Aryans were integrated in the Sudra Varna or were made outcast depending on the professions of these communities. Communities who professed non-polluting jobs were integrated in Sudra Varna. And communities who professed polluting professions were made outcasts. The Brahmans are very strict about cleanliness. In the past people believed that diseases can also spread also through air and not only through physical touch. Perhaps because of this reason the untouchables were not only disallowed to touch the high caste communities but they also had to stand at a certain distance from the high castes.
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