Cielingcat wrote:
In Hinduism, at least, all souls are part of Brahman or something like that, and so the amount of souls is functionally limitless. You can decrease the amount of souls by becoming enlightened, which lets you stop being reincarnated.
It's much more complicated than that, but that's the lowdown.
In Riverworld, souls (called Wathan) also react something like this, but the reincarnation is not automatic: Someone needs to recreate the body like it was just before death and the Wathan reattachs to it. Being enlightened enough will result in your Wathan merging with God after death, in fact becoming a part of God.
And the book is being about an old alien race reincarnating all the humanity for a few hundred years to allow them a second chance to reach Enlightement.
Also, the Wathan are not initially part of God, but created by a generator buried in the Earth, technology which was initially accidently discovered by another alien race (even older). Before Wathans existed, people could live but had no sense of self-identity, like ants.
So, in this universe, the soul is the heart of personnal identity, but not required to live. (And some animals even have a soul, if a rudimentary one)
In the last book, which was not initially part of the serie, the explaination changes for the enlightened Wathans: they don't merge with God, they are just put aside until the end of the experiment, being considered to be worthy of being permanently reincarnated with access to the alien technology.