Adapted to their environmental conditions. For instance people near or around killer sun have dark skin, that's not an incredible tan...that's protected skin. Asians have that extra fat on their eyes( they really have round eyes) to protect them from the cold conditions. Even their cute button nose has adapted to those conditions. Basically its from early migrations and evolving.Just 2 examples...toooo much typing :)
Because evolution is real...if creation was real and we actually were all "created in God's image" then we would all look alike! Ex: In Africa the people are taller and darker(it's proven that taller darker people disperse heat better than most people) in China people are shorter and have high cheekbones due millennia of living in the Himalayas with high winds ! Europeans are usually shorter with more muscle mass to protect themselves from extremely cold ice age winters!!
Evolution. Narrow eyes for example are important to avoid "snow blindness" which occurs in snowy environments. Dark skin allows a human to convert most solar energy to heat instead of being absorbed by the skin causing cancer. Some people (more common in South America) can shift their color slightly to lighter or darker depending on depending on sun exposure. Large noses also help with improved breathing in high altitude environments. Sickle cell anemia, which is a blood disorder more common among blacks, is a natural protector against malaria. People who live in higher altitudes also develop a higher red blood cell count that allows them to absorb more oxygen due to thinner air at such altitudes. Such people also have a higher capillary count which "pops" when they move to a lower altitude giving them red cheeks. If you want greater detail, you will need to take a college course. From the answers given here it is obvious who went to college and who didn't.