Why do people of different races belong to the same species?

Man is one of the species of the animal world. At the beginning, after the formation of Homo sapiens, as scientists assume, all people were dark-skinned. But it doesn’t really matter. Human races appeared after tens of thousands of years due to different places of residence. Even people who belong to the same race, but live in different places, are different. And this is normal for the wave. Since, for example, in cold places – people are short, more well-fed. In hot places, dark skin is the best protection from the sun.