If we are all descendants of Prophet Nuh A.S., why are we so many races?

As we are all descendants of Prophet Adam A.S., I understood the explanation of Hawa A.S. giving birth to various sets of twins of different race and thereafter the marrying of the males to females of a different set to produce various race. However, i then learned we are all descended from Prophet Nuh A.S and that all other lineages had perished *(which is mentioned in this answer )*. **Question:** If we are all descendants of Prophet Nuh A.S., why are we so many races?