Yoga is a group of physical, mental, and spiritual practices or disciplines which originated in ancient India. There is a broad variety of yoga schools, practices, and goals[2] in Hinduism, Buddhism, and Jainism.[3][4][5] Among the most well-known types of yoga are Hatha yoga and Rāja yoga.[6] The origins of yoga have been speculated to date back to pre-Vedic Indian traditions; it is mentioned in the Rigveda,[note 1] but most likely developed around the sixth and fifth centuries BCE,[8] in ancient India's ascetic and śramaṇa movements.[9][note 2] The chronology of earliest texts describing yoga-practices is unclear, varyingly credited to Hindu Upanishads.[10] The Yoga Sutras of Patanjali date from the first half of the 1st millennium CE,[11][12] but only gained prominence in the West in the 20th century.[13] Hatha yoga texts emerged around the 11th century with origins in tantra.[14][15] Yoga gurus from India later introduced yoga to the west,[16] following the success of Swami Vivekananda in the late 19th and early 20th century.[16] In the 1980s, yoga became popular as a system of physical exercise across the Western world.[15] Yoga in Indian traditions, however, is more than physical exercise; it has a meditative and spiritual core.[17] One of the six major orthodox schools of Hinduism is also called Yoga, which has its own epistemology and metaphysics, and is closely related to Hindu Samkhya philosophy.[18] Many studies have tried to determine the effectiveness of yoga as a complementary intervention for cancer, schizophrenia, asthma, and heart disease.[19][20] The results of these studies have been mixed and inconclusive, with cancer studies suggesting none to unclear effectiveness, and others suggesting yoga may reduce risk factors and aid in a patient's psychological healing process.[19][20] On December 1, 2016, yoga was listed by UNESCO as an Intangible cultural heritage.[21]