I believe in reincarnation/energy transfer--whatever you wanna call it.
Your soul is like a big ball of energy. Once you die, your body isn't able to store that energy any more, so that energy has to find a new host in order for you to be reincarnated. For example:
Say I die, right? Well then my soul must move on to start a new life. So, it travels the earth looking for a new life to assume. Hey, look a baby tree! (Trees are living creatures too) It enters the plant and starts it's new life as a tree. Once that tree dies, who knows where that soul/energy will go? It's up to fate to decide that soul's destiny.
At least that's what I believe.