Why do races have different bone structures?

Sometimes mother nature just likes to mix the pot up a little bit. The earth as we all know has many different climates. and thriving effectively in all of these different climates showed some traits to be more beneficial then others. And through a Process of natural selection, certain traits became more frequent because of the ability of the individual to survive with these traits. Bone structure would be the same. All humans are about 99.8 % the same.