The Basis of Race

On page 212, Coyne briefly discusses races as "populations of a species that are both geographically seperated and differ genetically in one or more traits". If this is true, what led to the evolution of difference races that we see today around the world ? How has sexual selection also driven the evolution of races? If races merely represent species living in different areas of the globe, should the characterisitics of different races be varied? Connect to natural seleciton and selective advantage in your response.