I don't have all the answers. I'm continually trying to piece these things together.
C.S. Lewis held that homo sapiens evolved into a spiritually-minded species when God willed it, but that early humans turned away.
Origen held that the fall occurred before the universe was. In the preexistence, we fell, by turning away from God. The purpose of the universe, he held, was to rectify this. In this way, the Lamb was slain before the founding of the world. I have heard some say that clothing Adam and Even with skins was symbolic for giving fallen souls fleshly bodies.
One thing I think many can attest to: We are born fallen. None of us can claim perfection. We all make moral mistakes. We all have a wrestling with our more animalistic impulses. Many of us feel a spiritual need and desire a relationship with God. Christianity provides a frame of reference for some to pursue this.
Currently, I am trying to keep an open mind and a listening ear. I gravitated from being a Witness, flirted with agnosticism, but after reading Crisis of Conscience, I began to gravitate toward Christianity again and this has provided a good sense of direction that I was lacking in the interim.
As Paul said, "For at present we see in hazy outline by means of a metal mirror, but then it will be face to face. At present I know partially, but then I shall know accurately even as I am accurately known." I believe only when we will all see God face to face will we have a more complete understanding.