I start from the sociological perspective – race is a social construct. Years ago, in one class or another, I learned that “There is more difference within a race than between races.” As I recollect, about 250 years ago, a grad student, working on his dissertation, examined and classified 60 skulls and moved the concept of race from ethnicity to physical anthropology, and folks have been looking in the wrong direction ever since. Never have had much respect for Johann Friedrich Blumenbach’s research methodology, and I figure his conclusions kind of suck – but I wasn’t on his committee. Can you believe looking at 60 skulls and coming up with 5 races?
Ibn Khaldun pretty much wiped out the idea of basing race on skin color about 7 centuries back. He was pretty much the world’s first sociologist, but it took a while to get his work translated into French, and later English. His arguments weren’t perfect, but were a whole lot better than Blumenbach’s.
Another nail in the coffin of racial definition is genetic diversity. If I remember my own lectures correctly, and I bloody well do, there is more genetic diversity in chimpanzees separated by one river than in the entire human race (Donelly, at Oxford, was the principal author of the study).
Darwin kind of summed it all up in Descent of Man: “Man has been studied more carefully than any other animal, and yet there is the greatest possible diversity amongst capable judges whether he should be classed as a single species or race, or as two (Virey), as three (Jacquinot), as four (Kant), five (Blumenbach), six (Buffon), seven (Hunter), eight (Agassiz), eleven (Pickering), fifteen (Bory St. Vincent), sixteen (Desmoulins), twenty-two (Morton), sixty (Crawfurd), or as sixty-three, according to Burke. This diversity of judgment does not prove that the races ought not to be ranked as species, but it shows that they graduate into each other, and that it is hardly possible to discover clear distinctive characters between them.”
If you want the paper on when Europeans unconsciously made the decision to be more white, this article provides the modern explanation from the physical anthropologists. Please note, the discussion is on white skin, not race.