From the mystical doctrines of the Upanishads, one current of thought may be traced to the mysticism of Persian Sufism, to the mystic, theosophic log… - Moriz Winternitz

As Maurice Winternitz ... notes about the Vajrasûchî, a text attributed to the Brahmin-born monk Ashvaghosha: 'This work refutes the Brahmanical caste system very cuttingly. The author (...) seeks to prove from the Brahmanical texts themselves, by quotations from the Veda, the Mahâbhârata and the law book of Manu, how frail the claims of the Brahman caste are.'

Almost a century ago, Winternitz ( 1962) was refreshingly forthright about the lack of agreement regarding even the approximate date of the Veda: "It is a fact, and a fact which it is truly painful to admit, that the opinions of the best scholars differ, not to the extent of centuries, but to the extent of thousands of years, with regard to the age of the Rg Veda. Some lay down the year 1000 B.C. as the earliest limit for the Rg Vedic hymns, while others consider them to have originated between 3000 and 2500 B.C." (253).

...We shall probably have to date the beginning of this development to about 2000 or 2500 BC