I have this theory that goes something like this:

Humans, like other animals and plants come from the ground in the form of minerals, vitamins, basic elements etc.
For example, yo Mama eats a banana and the minerals, vitamins, elements etc go into making yo self.
So you can say as such, in such that what I said, you are made of stuff that comes from bananas and other fruits, veges, meaty things or whatever, which basically originated from the soil. And to elaborate and be more exact, bits and pieces also come from the sun as in vitamin D.
Vis a vis, physically, we pretty much come from dirt and a bit of sun.
So mentally our whole psyche, soul, personality, what have you, must also be made up of bits of something.
Yes! Our whole mental existence is made up of lots of tiny bits of mental components from ages before.
And when we leave this present existence our body melts down thanks to the wonders of bacteria and virus machinations so that our components can be recycled for other purposes not only human in form.
But what of our soul?
Well I have a theory for this also you see.
Our soul is also broken down into tiny little bits which float around in soul space until by purely random selection is used for new existence, human or otherwise.
I suppose you might say this is called reincarnation.
The whole concept of life and beyond the deathy thing is a whole mystery to most but I see it clearly in a way. First of all there is no pearly gate syndrome...what a load of cobblers! We mearly stop existing. Hard to accept menatlly but it is the truth Hubert.
We then after some long and random process reform along with many other soul bits into a completely new and fantastic form of life be it Nematode, Moss, Plankton, Cassowary or what have you.
So, to say that we are reincarnated from one life to another as human only is a load of noogies. And to say that our soul is preserved completely is also noogie territory.
We are unique and will never exist again as the whole we are now.
And our chance of being human again is slim, for you see there are millions of forms of nitrogen based life forms on this here planet Earth, and the human form is but one little insignificant poo.
But what is the big deal about being human anyway, eh Jane?
Not to mention that we shed thousands of skin cells a day...something to muse over there.
Farkney!

So forget your worries and enjoy a cup of Kilimanjaro.