Maybe there's only one soul. Like in The Egg. It's just one soul reincarnating into one life after the next, jumping forwards and backwards in space and time. Eventually after passing through the lifetimes of every sentient being that is, was, or ever shall be, the path of reincarnation loops back upon itself. There is only one soul, only one consciousness in the cosmos. One infinite endless circling wheel of experience, all bound in a universe finite in both space and time.