I knew someone would come back the multiple organism transfer. The problem here is that at any given point in history there will never be the same number of organisms on the planet. Extinctions are a good example of this. Where do those consciousnesses go while there are fewer creatures in the system? Humans have been steadily executing life on the planet, breaking down systems. There are less and less of those creatures that make up the majority: insects. Can you even imagine the chaos of insect reincarnation? They live for very brief periods.
The biggest problem lies in the early explosion of complex organisms. Where did the extra souls come from?
Souls, Reincarnation, and Heaven are all machinations of the hopeful wish to persist. They have no data to support them.