Natural selection? Nah, rather God's Plan and Providence.
I don't think God planned on the Fall, and the selection was done naturally as a result, rather than a deliberate separation (well Babel, maybe it was the result of that, but the process was natural)
God is all-knowing. He knew the Fall would happen. God plans and sustains everything at every moment. Anything that happens naturally, it happens because God made it to do that of it's nature.
Venerable Anne Catherine is quoted as saying that black skin was the result of sin.
That could be ignorance ;) Skin colour means little. Would albino "black" people be sinless?
Or it just proves that separation (for example, death) is the consequence of original sin. Is there any doubt that the separation of soul from body is the result of sin? Why not in some sense also the separation of human persons? I'm not saying these physical differences are
sin, but possibly a consequence.
Yes, the genetic code is very complex and mostly unknown. It is possible to remove certain things from the code in certain organisms though.
Yes, but in doing so, is it not a different organism? A bio-engineered strawberry with a fish gene, is no longer just a strawberry but also part fish.
Like a male can not carry an X linked trait without expressing it, whereas females can, so males that don't have that trait, don't have it in them at all.
Yes, the trait (ie the expression). But the genes are still there. If they weren't, then males could not give female offspring at all. But we know that Eve was formed from Adam, hence Adam's body must have hold the information to express such traits, even if it's impossible to express them. That's just my opinion though.