Oh I'm sure Buddhist...ermm... churches, have their explanation but I'm very interested in knowing it and how strong their argument is.
It could be very weak (ie. my "souls dwell nowadays more in humans than in animals") or then it might make sense. Maybe now and then there will born new souls? But how exactly that would happen, won't it go against core pillars of buddhist worldview etc. etc.
Also, I'm talking about Buddhism in its original, "pure" form which is much more like philosophy than religion. Without ghosts, monsters, heaven, hell and "stuff".