Spiritual bodies and depraved humanity

I was recently asked to elaborate on a statement I had made in a spiritual talk. The question arose about the source of the Augustinian/Calvinist teaching that "mankind is totally depraved." Sometimes this doctrine is expressed as "essentially depraved." I had responded that the teaching arose from early Gnosticism.
Indeed, within the dualistic ideas of Gnosticism, we find the notion that the "divine spark," the "spiritual body" is trapped in a physical, material body. Since the material world was considered to be the malevolent creation of a god who was either stupid, wicked or both, the human being was completely evil because he was in a material, bodily form. His salvation consists, the Gnostic system teaches, in his inner "subtle body" or "divine spark" being liberated from the body. While this teaching was "Christianized" by eliminating the idea that the world was created by a malevolent deity, it retained the idea that the fallen man was totally depraved and could not even desire what was good without the intervention of a special species of created grace.
At least one of these Gnostic sects, the Sethians, also believe that Adam and Eve had "spiritual bodies" in Eden, and would never have procreated, and certainly not have had a sexuality, had it not been for the fall into a material, physical body. They held that when God said to "multiply," He was speaking only of some form of "spiritual multiplication" not actual child bearing. Of course, the idea of sexuality is physical, and the production of children would only entrap more "divine sparks" in a material body. Some modern Christians agree with the Sethian Gnostics that marriage is essentially a "venial sin," (one of Augustine of Hippo's heretical teachings also) and that sexual relations in marriage are "suspect" at best, wicked more likely. Sexual procreation, then, is contrary to God's will, since he would have provided for a non-physical form of procreation had man not fallen. Of course, in that case, cloning and in vitrio fertilisation should be "sacraments" because they give man a way of fulfilling what Gnostics believe to be God's original will.
We will say more about this later.