the shudra, states marvin davis, are not required to learn the vedas. they were not "twice born" ("dvija"), and their occupational sphere stated as service ("seva") of the other three varna. the word "dvija" is neither found in any vedas and upanishads, nor is it found in any vedanga literature such as the shrauta-sutras or grihya-sutras. the word is almost entirely missing, in any context, from ancient sanskrit literature composed before the last centuries of the 1st millennium bce, and it scarcely appears in dharmasutras literature. increasing mentions of it appear in dharmasastras texts of mid to late 1st millennium ce. the presence of the word "dvija" is a marker that the text is likely a medieval era indian text.