The crude categorization of peoples is done by physical traits such as pigmentation or physiognomy, and we have to acknowledge that these are characteristics that are determined in large part by the expression of genes, which vary between people and populations in ways that we can scrutinize with more depth and accuracy now than at any time in history. Cultural categorizations are mostly derived from ancestry, and this means broadly that people within one group are more similar to each other genetically than they are to people not in that group.
