MsEVP, I know you are not strictly talking about Buddhism - although your little t�te-�-t�te with Whicker identified some of it - but as I understand it, the notion of the transmigration of the soul does not exist in Buddhism. The common misunderstanding with reincarnation is that a person has led countless previous lives, usually as an animal, but somehow in this life they are born as a human being and in the next life will be reborn as an animal, depending on the kind of life they have lived.
The Buddha taught according to the mental and spiritual capacity of each individual. For the simple village folks living during the time of the Buddha, the doctrine of reincarnation was a powerful moral lesson. Fear of birth into the animal world would have frightened many people from acting like animals in this life, hence the ten realms of being taught within Buddhism.
One might ask what realm you are in now. Buddhism would say that if you are hungry for power, love, and self-recognition, then you live in the Preta world. If you are motivated only by thirsts of the human organism, you are existing in the world of the beast. Man (or woman) is characteristically placed at the midpoint of the ten stages; he (or she) can either lower themselves abruptly or gradually into hell, or, through discipline, cultivation and the awakening of faith rise to the enlightened state of the Buddha, the highest level of being. This we are always human, always achieving perfection, ultimately aiming to be the best we can be.
If we take this teaching literally today we become confused because we cannot understand it rationally. If someone believes the philosophy that by not being our �best� our soul regresses to try again and again in a different shell each time, then one might assume that this is probably quite a good, true and moral life to lead.