Let's make it simple just for you and cut the debate short until you gather some knowledge and at least provide a little resistance. Your example stops your debate there and then. Of course there's genetic differences between humans, but not in the clear cut definition of race. There's more genetic variety within Africa than there is anywhere else on the earth, so are you going to label people in Africa as different races, if so, you tell me what they are?
So to make it easier for you to understand, two individuals from Africa may be more genetically different from each other than you are