Spiritual and Religious Theories on Past Lives Reincarnation (Samsara): Central to Hinduism, Buddhism, and Jainism, this theory posits that an eternal soul cycles through birth, death, and rebirth, shaped by the moral weight of actions (karma) until achieving liberation. Metempsychosis: Taught by ancient Greek philosophers like Pythagoras and Orphic mystery cults, this view involves the transmigration of the soul into new human or animal bodies as part of a cosmic cycle. Non-Linear Reincarnation: Some metaphysical beliefs suggest souls are not bound by linear time, meaning a consciousness could theoretically incarnate in a historical period prior to a previous life.