Waheguru ji ka Khalsa, Waheguru ji ki Fateh ji
That is a very important question. I believe that earlier souls were freely flowing in the Universe. Possibly not staying at one place for long. But in some ancient mix of water, chemicals and energy flow, first basic microorganisms were formed. And souls of that time found some sort of resting place in the barely there definitions of first life forms. And they became attached. They were attached to the bodies, to the life forms. When the life forms evolved and began dividing (cell mitosis). It caused souls to split yet stick with new life forms. Over years, souls kept on sticking to their life forms, yet they evolved. And souls forgot Waheguru. And this is the best story I could cook up for now :| but the important part is, to know where you have to go. Where you have to be. With Waheguru. Have His Darshan. Guru's Darshan. And then there is no birth and life, friends or foes. Just Guru. Waheguru.