The theory is that white people came around as a result of the Ice Age and a vitamin D deficiency in their blood that produced a look that simply stayed. I think if you put say ,10.000 black people in a place like Greenland and allowed them to live there for thousands of years undisturbed, then the end result would be a caucasian race of some description. However, white people in a hot climate would just succumb to skin cancer thus they would always be covering up. In the latter case only if black people were interbred with the white group would the dark complexion return. Just a theory mind.