Realize, we live in a magical universe where anything can happen and does happen. The psychic explorer is advised to exercise a great deal of caution and always resort to sound judgment. All creatures on the wheel of life evolve gradually, as do the souls which inhabit these forms. Take for example the monarch butterfly - there are thousands in existence, yet they collectively possess one soul. When a specie dies and is considered extinct, that collective soul forms the basis for a new specie.
Theories regarding divergent lifelines and parallel universes are all very true.
The human soul can not as yet declare it's unique existence, for it enjoys simultaneous multiple existences in these various dimensions. Also, the physical body is very frail with a limited cranial capacity compared with evolution on a universal grand scale. Therefore, the daemon lends only part of his essence to a human incarnation, otherwise the concentration of prana would be too great, akin to overloading an electrical appliance. It must be stressed that, as a race, these ancient souls come infrequently and they are not fighting a turf war in heaven as our primitive mythologies suggest. Joan of Arc was an incarnated daemon, as were Christ and Buddha.