When were you first made aware of people being treated differently because of their race or ethnicity?

Race is a recent concept that arose in the 18th and 19th centuries. If you look at the terms Ariayan and Semite, they were only coined once the proto-indo-european language had been discovered. Ideas about differences in race are socially constructed. Now, some people have different cultures, and sometimes in modern society, these cultures break down in terms of 'race', but races themselves are not different. they are artificial inventions.