The belief is thought to have been an necessity among primitive peoples. Certainly long before ancient Egypt peoples believed in transmigration of the soul. If they were not sophisticated enough to understand the concept of a soul, then they may have simply called it life. An individual or object which moved had life, and the one which did not, did not have life. This is analogous to the belief of animism.Gradually the concept of a soul developed with a further realization that the soul departed the body at death and entered the body at birth. Soon it was thought the soul leaving a dead body would seek another body to enter, or enter an animal of a lower life form. It was also thought the soul left the body during sleep. This soul was pictured as vapours that entered and left through the nostrils and mouth.
Later grew the notion the soul transmigrated to an infant of one of dead person's kin. This helped to explain family resemblances.
The terms reincarnation and transformation of the soul, especially when applied to humans, are about synonymous. However reincarnation is not accurately synonymous with either metamorphosis or resurrection. Metamorphosis is roughly the changing of one life form into another life form. Resurrection, in the Christian sense, means the rising again of the body after death.
About the first definition of soul transmigration came from Pythagoras, the Greek philosopher and mathematician, who taught that the soul was immortal and merely resides in the body; therefore, it survived bodily death. His further teachings held the soul goes through a series of rebirths. Between death and rebirth the soul rests and is purified in the Underworld. After the soul has completed this series of rebirths is becomes so purified that it can leave the transmigration or reincarnation cycle. Plato, another Greek philosopher, shared similar views as Pythagoras in that the soul of man was eternal, pre-existence, and wholly spiritual.
In Plato's view of the transmigration of the soul from body to body, however, there is a difference. Plato claimed the soul tends to become impure during these bodily inhabitations although a minimal former life knowledge remains. However, if through its transmigrations the soul continues doing good and eliminates the bodily impurities it will eventually return to its pre-existence state. But, if the soul continually deteriorates through its bodily inhabitations it will end up in Tartarus, a place of eternal damnation. This appears to be an origination of both the concept of karma and the Christian concept of hell.
It was around the first century AD that both the Greek and Roman writers were surprised by the fact that the Druids, a priestly caste of the Celts believed in reincarnation. The Greek writer Diordus Siculus (c. 60 BC - 30 AD) noted that the Druids believed "the souls of men are immortal, and that after a definite number of years they live a second life when the soul passes to another body." The Greek philosopher Strabo (c. 63 BC - 21 AD) observed the Druids believed that "men's souls and the universe are indestructible, although at times fire and water may prevail." (Source: The Mystica)
