Did Buddhism Pre-Exist the Historical Buddha?

Evidence for a type of Buddhism ‘pre-existing’ the birth of the historical Buddha, however, might exist in the Brahmanic teachings of the Upanishads. In the Kathakopanisad, a doctrine is critically described that does not accept the concept of a central and eternal ‘atma’, but which instead advocates a theory of ‘separate elements’ (prthag-dharman pasyati).