How much genetic difference is enough? It is obvious that there is a grouping of features beyond skin color. Where you put the line between races is somewhat arbitrary - and this is the same with all concepts, so it doesn't make sense to think about genetic difference (e.g. in Rwanda Hutu and Tutsi are considered different races, even though genetic difference is almost inexistent http://en.wikipedia.org/wiki/Origins_of_Tutsi_and_Hutu). People have established this concepts because they are/were useful, and will continue to use them.