T-Rex: One day Jack died and was reincarnated... as a new baby!

T-Rex: "Oh sweet I guess death isn't the end," thought Jack.

T-Rex: "Oh weird hold on a second, if people are reincarnated where do new people come from, which are required as our planet's population has been growing for hundreds of years?" thought Jack.
Dromiceiomimus: "Maybe animal souls can get 'promoted' to dinosaur souls," thought Jack.

Utahraptor: "But hold on, that still doesn't solve it because no way the number of living things on Earth has been static," thought Jack.

T-Rex: "And if we're giving souls to things like bacteria, are we also giving them to viruses, which are really just infectious agents of other cells, but still have DNA?" thought Jack.
Utahraptor: "Or plants? This is getting very complicated."

T-Rex: Then Jack forgot everything about that AND his past life - until 80 years later when he died and was reincarnated again, at which point he remembered it all once more.
T-Rex: "Oh dang, figuring this out is going to take a while," thought Jack.