Woah! Finally a thread for me
Well, my imagination is endless at this point. I think life is a mission. I partially agree with Scatty, our "soul" normally exist on a non-physical plane living in somekinda society. At each rebirth you are given(or choose) a mission to be fulfilled in your "life" on earth. For example you can born a poor child in africa than you struggle for your life, if you succeed, you get respect on the soul-plane, you can of course choose easy life(rich parents, good lookin etc) but you won't be respected if you do that...
Some people say everybody is on earth ON PURPOSE. Like everybody has a mission. I think it might look like this. After your life ends, you go back to the soul-plane to review your archivements, goods and bads. Then if you wish you can start another "mission" and live again. Of course you won't remeber the soul plane or your mission, you will just have an instinct to do stuff randomly but that is you mission nontheless. After you die, you get back your memories as well, so you can summarise your efforts. This works like kredits I think, so if one life you struggled like hell to even survive, you are revarded an easier life for next time. OF course the "boss" decides who gets what. I think there might be somekinda superior power on the soul-plane too, a higher being or somekinda "senate" or something that judges your deeds each time you get back and reward you accordingly...
And of course you can be anything not just human

If you want to you can become an elephant or ant, or even a amoeba

it all depends on your archivements

k:
Sssso... whaddya think?