True human race?

Interesting thoughts, however, I would challenge two things:

1. All humans descended from the same parents, thus, their gene pool was rich enough to provide for all of the variation (which some call races) we see today. It was not until Moses that prohibitions against marrying within the immediate family were established. Cain and Seth, then, would have been required to marry sisters, and their offspring married siblings and cousins. The gene pool at that point was rich enough to support such behavior without negative consequences. Incidentally, there is no such thing as "race" in zoological classifications. It is a arbitrary concept used to explain differences people groups, which the Bible calls "tribes". An interesting parallel is the Canine. Great danes, peckinese, and Daschaund all all dogs, just different breeds, forcibly created by man through selective breeding. If left to themselves, they will all breed into muts. Correspondingly, with the integration of the world, mass travel, changing social stabdards, etc, it is likely that the so called races will get harder to differentiate because of interbreeding.

2. Actually, sin is in our flesh, since our flesh is corruptible, and cannot inherit the Kingdom. 1 Cor 15 provides a great explanation of this. When Adam and Eve ate the fruit, it is possible that the fruit, once ingested caused a mutation in the DNA, which led to death. Once this passed through their body, and got into the ground and then the plants, the corruption passed to all living things. While this theory is conjecture, scripture is plain that all creation is corrupted, and is waiting for the redemption (Rom 8:22)