Race is a social construct. The incontrovertible evidence has only been uncovered recently, as DNA analysis became more a mature technology – but the theoretical explanation has been out there at least since I was an undergraduate in the sixties.
White skin color is pretty much an accident, requiring the correct set of genes, and cereal based agriculture to make my pale skin better for soaking up sunlight in the northern latitudes and producing vitamin D. Some northern dwellers didn’t turn pale – their food sources were rich in vitamin D. Somewhere around 7,000 years ago, northern European grain farmers started getting pale. It appears to have taken about 1.500 years to become a social thing.
The DNA evidence comes from a technology I haven’t mastered. It’s kind of like fingerprints – we accept the expert’s testimony, largely on faith. I’ve sat on graduate committees where the work was done with DNA manipulation. I’ve extracted DNA. Still I lack the knowledge to replicate the research . . . so I take it on faith. Faith in the scientists who do have the knowledge. Faith that it matches the hypothesis I learned half a century ago. Faith that skin color is such an insignificant difference between humans. The knowledge that “race” as we know it is the product of a graduate student’s research about 250 years ago.
This brief video covers the development of white skin color in under ten minutes.
A longer, more complete explanation:
Both are worth watching.
Trego's Mountain Ear 