I've heard several different things.

The Newtonian outlook is that they are portions of the Creator's energy somehow granted an individuated status.  Each one is then nurtured by advanced "nursery" souls and brought forward to a level that enables them to create on their own.  Analogous to our raising of children.

Another wise woman told me that all souls were created at the same time and, like people, some got it really quickly, some less quickly and some are just hanging out, while others can't quite figure it out. 

Outside of that, I don't know.

So it safe to say that it's unknown? 

But first they join hands with all the rest of Creation to sing and dance around this enormous sparkling diamond in the sky....

I Am Dude wrote on Feb 19^th, 2010 at 11:35pm:

No, Beau, everyone is a chip off the old diamond....