According to Zimmer, Yoga philosophy is reckoned to be part of the non-Vedic system, which also includes the Samkhya school of Hindu philosophy, Jainism and Buddhism:[46] "[Jainism] does not derive from Brahman-Aryan sources, but reflects the cosmology and anthropology of a much older pre-Aryan upper class of northeastern India [Bihar] – being rooted in the same subsoil of archaic metaphysical speculation as Yoga, Sankhya, and Buddhism, the other non-Vedic Indian systems."[61][note 6]
A yoga system that predated the Buddhist school is Jain yoga. But since Jain sources postdate Buddhist ones, it is difficult to distinguish between the nature of the early Jain school and elements derived from other schools.[89] Most of the other contemporary yoga systems alluded in the Upanishads and some Buddhist texts are lost to time.[90][91][note 12]