What makes races look the way thay are?

This question is not in any way meant to be offensive I am just curious. So, how come people from Asia or of Asian decent seem do have faces that are a little more (not trying to be racist) flat? The same with people of hispanic and african decent, how come they have darker skin than caucasians? It seems that all other species of animal look the same in one region but as you diversify to other regions they change, e.g. bears. In North America there are grizzlys and black bears but in the arctic the polar bears are white because of the white snow. Does the same rule apply to humans?