Given two different Earths -
(a) an Earth on which morality was the result of cultural evolution, to the extent that all but two percent of humans had the same general concept of right and wrong, the remaining two percent being clinically sociopathic, and
(b) an Earth on which a God had instilled identical moral laws in all humans, but had also instilled the potential for rejecting those laws, and in which two percent of humans had taken advantage of that potential,
- how would an external observer tell the difference?
But that wouldn't be morality, rather, it would just be social convention.