In Vedic literature it cannot be found any reference regarding the restrictions in diet, drink and inter-marriage. Therefore, the varnas appear to be open classes. They were based on individual qualities rather than on birth and descent. Therefore, it has been assumed by some sociologist that the original parts of the Vedas do not know the system of caste. In the Rig Vedic literature the occupations assigned to different varnas are not well defined.
In India, there was a class division of occupations amongst the four varnas. According to Manu, "Among the several duties, the most commendable are teaching the Veda for the Brahmin, protecting the people for the Kashtriya and trading for vaishya". But there are certain relaxations regarding the prescribed occupations of the four varnas in times of distress and adversity. A Brahmana who is unable to maintain himself by his own occupation may adopt the occupation of Kshatriya similarly the Kshatriya may adopt the occupation of a Vaishya. Further a Vaishya who is unable to subsist by his own occupation may adopt the Shudra`s mode of living.
