My experience on this forum so far suggests people peddle opinions as facts and very rarely indulge in academic courtesies like citing references for their claims.....
However In the other thread someone had claimed that only brahmins are considered as Dvija(or twice born). Well this may not be entirely true. Brahmins today undergo the Samskara of Upanayana, following which the person undergoing the ceremony is believed to be the have undergone a second, and superior, spiritual birth. To mark this initiation the individual wears a girdle.
Prof P. V Kane, in his magnum opus - History of the Dharmasastras, opined that Upanayana may have emerged as a singular institution during the period of the Dharmasastras. In the Apastamba Dharma sutra, Apastamba provides indication that all members of the first three varnas under went the rite. Apastamba suggest that, like brahmanas, the Kshatriya wear a sacret girdle made from a 'jna' used as a bowstring(vysyas a rope used in the plough)
Upanayana was, in old days, a prelude to the Brahmacarya stage (learning). While Brahmacarya would have been important for all the three varnas, at least during the period when institution of state was in its infancy and agriculture was yet to expand and attain sophistication. However around the time of the beginning of the common era, sophisticated state institution had emerged, the realm of these states had expanded and with it more lands were now available for agriculture.
With the emergence of new states and sophisticated farming, traditional form of education would have become inadequate to help the Kshatriyas and vysyas cope with the new challenges. Thus the two varnas may have begun looking within their groups for training and education and may have completely abandoned traditional mores of education. With this also disappeared traditional forms of initiation like Upanayana.
