Why do people living in different parts of the world differ in skin color, physique and others?

Various changes have appeared due to different living conditions of people. People have dark skin due to constant exposure to the sun. With the help of pigments, the body protects the skin from cancer and other diseases. People have narrow eyes due to living in windy deserts. Also, differences may be in height, physique, facial features, and so on. But all people belong to the same species. Representatives of different races can produce healthy offspring. Also, when a person lives for a long time in other conditions, some changes occur and new adaptations appear.