I've never understood how one can have "moral facts" that cannot be observed scientifically.

Given the fact that the 'scientizing' paradigm is as much open to criticism as anything in the OP, it's hard to see what, if any, relevance this has.

But it does not matter, I am not being normative, but merely descriptive. If moral values did not ultimatey arise from natural selections, where did they arise from?

This is just equivocation of physical human impulses and moral imperatives.The two don't have anything to do with each other, aside from the possibility of being conterminous.