As race is a social construct, whoever was generally deemed to be of one race was usually treated as a member of that race. However, in legal matters where the question of race was taken to court the government ultimately decided what race you are. A popular example of this is the [ame="http://en.wikipedia.org/wiki/One_drop_rule"]one drop rule[/ame], which was one of the ways that the American legal system attempted to define and delineate between races. What this meant is that you could be socially believed to be white, when in reality you were legally defined as black. That was the point I was making, but I think you missed it.So people weren't attacked on their physical traits and skin color? When someone tried to enter a bathroom they were asked for a government ID card designating their race because people couldn't tell race by looking at each other since physical differences between races don't actually exist?
Of course there are. As I said, there are physical differences that evolved geographically as humans dispersed across the globe. However, the delineation of humans into separate races is impossible as whatever dividing line that is made between these physical characteristics is completely arbitrary.So there are no physical differences between the two below individuals that is noticeable to everyone?
The most obvious difference between the two people in your photograph is skin color, but there is no way to scientifically delineate between "black" and "white" based on skin pigmentation due to melanoma levels. Of course, we are just referring to two racial categories; some have come up with as many as dozens of different races. And then we could also include ethnicity, which would further complicate the matter. How many races do you think humans can be classified into, and what is your scientific basis for doing so?
You, also, cannot define what is "black" and what is "white" based on physical characteristics. Over the past 300 years many have tried, but none have been able to stand up to scrutiny in the scientific community.