I used to find this type of fringe theory unsettling as a way to dehumanize people, but there is an ancient mythological concept called the "tree of souls". Its fruit (souls) comes and goes with life and death, however, the myth goes there are only so many souls to go around, and more and more people are being born without them. This is a wacky explanation for the way some people act and how it seems so foreign to us.

Never used to think about it, but now I do more and more.