where did the original concept of reincarnation come from?

India with Hinduism. As well as Buddhism. They have roots in reincarnation beliefs.

[wolfgaze]

"The concept of reincarnation and karma is the cornerstone of many Asian religions—Hinduism, Buddhism, Jainism, Sikhism, Zoroastrianism, the Tibetan Vajrayana, Japanese Shintoism, and Chinese Taoism. Similar ideas can be found in such historically, geographically, and culturally diverse groups as various African tribes, American Indians, Pre-Columbian cultures, Polynesian kahunas, practitioners of the Brazilian umbanda, the Gauls, and the Druids. In ancient Greece, several important schools of thought subscribed to this doctrine, among them the Pythagoreans, the Orphics, and the Platonists. The concept of reincarnation was adopted by the Essenes, the Pharisees, the Karaites, and other Jewish and semi-Jewish groups. It also formed an important part of the cabalistic theology of medieval Jewry. This list would not be complete without mentioning the Neoplatonists and Gnostics and in modern times the Theosophists, Anthroposophists, and certain spiritualists." ~ Stanislav Grof M.D.