Caste meaning Varna or colour to the Aryans was the logical distinction between the conquerors (Aryans) and the conquered (Dasas and Panis). It was in about 1,000 B.C. that the Aryans settled between the Indus and Gangetic regions; it was here that they learnt the art of cultivation. With the coming of agriculture, greater division of labour came into existence and thereby different occupations.
Once the Aryans settled as agriculturists and experienced the consequential developments mentioned above, the Aryan society also developed into grouping known as the four-fold caste system. Those who took to the occupation of fighting were know as Kshatriyas; those who took to cultivation were known as the four-fold caste system. Those who took to the occupation of fighting were known as Kshatriyas; those who took to cultivation were known as Sudra; and as there was an opportunity to contemplate because of the leisure engendered by agricultural occupation, the priestly community elevated themselves to the status of brahmins. Significantly, as the Aryans began to cultivate land, the earlier word "gavasthi" meaning search for cows came to mean 'to fight', because fights between the various tribes of Aryans for fertile land and herds of cattle were common.
Soon, by 600 B.C. a new grouping emerged in the Aryan community, Whenever a community takes to agriculture, some agriculturists produce surpluses or accumulate capital. Such an activity naturally brings to the forefront a group of people dealing with trade and commerce. That is how vaishyas came into existence, since the emergence of this community is rooted in the surpluses generated by agriculture, the erstwhile sudra community moved up to form this new grouping, while the non-Aryans and mixed-Aryan became sudras. About this time the concept of pollution also figured. It is definite that pollution was a known idea at this time because those who undertook unclean occupations like cleaning of carcases, fishing and other occupations came into existence. It was this aspect of unclean occupations associated with pollution that later on grew into untouchability.
From sixth century B.C. onwards there is historical evidence to show that the Sudras were primarily drawn from non-Aryans and mixed-Aryans, as for example, Ashoka enslaving one and-half lakh people after the kalinga war and bringing them to the Gangetic region to cut forests and cultivate land. We can, therefore, say that the four-fold caste division based on occupations was as good as established by the time the Mauryan empire was established. It is also significant to note that there are references in the inscriptions of Ashoka that bird-catchers, fishermen and butchers came to be treated as people beyond the pale of the then social structure. This stigma, in all probability, was confirmed because of the growing belief in the non-slaughter of animals, both on the part of the Buddhists like Ashoka and those of the Aryan community gradually discarding sacrifices.
Apart from these developments by the sixth century B.C., Brahmanism grew obscurantist because of its rituals and sacrifices. The Aryan rituals and festivals were over-emphasised by the priestly community because of the compulsion for making themselves indispensable in those time. As the Aryans took to agriculture, the priestly community realized that they had no meaningful occupation to perform apart from catering to some of the medical needs of people. Furthermore, looking at the way in which the Kshatriya warrior community was thrusting itself ahead, the brahmins or priestly community brought out a coup de grace by building mythologies to beguile the Kshatriya community. Historical evidence shows that it was during the Aryan stay in the Saraswati region that the legend of manu was created - all kings were adjudged as descendants of the ninth Manu, while the first Manu was created by Brahma. At this stage, the priestly or brahmanical community laid more emphasis on rituals and festivals supporting it by interpretation of the Rig Veda so that their own importance would not be ignored. Thus, in this process brahmins overshot their worm by making religion obscure to the average man.
Challenged by these desertions of common people as well as royalty, the Aryans, in particular the Brahminical community, brought about another coup de grace in the four centuries preceding the Christian era. Sanskrit language was rejuvenated by Panini. Coupled with this linguistic victory Brahmins wrote a number of dharma shastras including that of Manu. The Work of Manu is of a colossal magnitude. It relates both to secular and sacredotal fields of life. They also supplemented these with grihya dharma, rajya dharma, sreni-darma, ashrama-darma, silpi-shastra and so on. The purpose of all these writing was to regulate and discipline the whole life of man, whatever his calling or situation in life.
Also, in the same period, there were many more developments. With the influx of foreigners, a place was to be found for all of them. To achieve the objective the priestly order of India evolved the concept of jati-dharma, it is the dharma to be followed by each sub-caste or grouping within the four Walls of caste system. From now onwards, the four-fold division lost its usefulness and increasingly became a metaphysical concept. The real sacred lay in the jati-dharma or the dharma of the sub-caste; while the concept of chatur-varna stayed as an abstraction. What exactly any individual belonging to a jati a or a sub-group should do was minutely laid down covering all facets of life, like taboos relating to dinning, the items of consumption, the pantheon of gods to be worshiped, contraction of marriage, and the reverence to be shown to other jatis as well as the substraction of four-fold caste system as ad when the occasion called for. Since every individual was born into a jati and as the dharma of jati comes to be treated as an immutable truth, each individual was born in some kind of subjection.