On the Sankhya were based the two heterodox religious systems of Buddhism and Jainism, which denied the authority of the Veda, and opposed the Brahman caste system and ceremonial. Still more heterodox was the Materialist philosophy of Charvaka, which went further and denied even the fundamental doctrines common to all other schools of Indian thought, orthodox and unorthodox, the belief in transmigration dependent on retribution, and the belief in salvation or release from transmigration. The theory that every individual passes after death into a series of new existences in heavens or hells, or in the bodies of men and animals, or in plants on earth, where it is rewarded or punished for all deeds committed in a former life, was already so firmly established in the sixth century B.C., that Buddha received it without question into his religious system; and it has dominated the belief of the Indian people from those early times down to the present day. There is, perhaps, no more remarkable fact in the history of the human mind than that this strange doctrine, never philosophically demonstrated, should have been regarded as self-evident for 2500 years by every philosophical school or religious sect in India, excepting only the Materialists. By the acceptance of this doctrine the Vedic optimism, which looked forward to a life of eternal happiness in heaven, was transformed into the gloomy prospect of an interminable series of miserable existences leading from one death to another. The transition to the developed view of the Upanishads is to be found in the Çatapatha Brahmana (above, p. 223).