It's simply racial variations. People who come from warmer climates need more pigment to protect them, while people in colder climates do not. There is no advantage to less pigment either- it just happened among Caucasians, and was not selected out. Northern Asians don't have that variation simply because it did not occur in their population.

The mutations you describe turned out to be advantageous for humans who migrated to regions and climates where the angle of the sun was less direct than it was across equatorial Africa (where all humans originated). Humans create Vitamin D by absorbing sunlight through the skin. Lighter skin and lighter eyes absorb more sunlight. This is good when you're in Ireland or Scandanavia, not so good when your family moves back to areas with more sunlight. That's why I have to keep my Irish skin covered with sunblock here in Virginia, to try to avoid skin cancer. Dark pigment protects against skin cancer, and I don't have any. :( The difficulty with this answer is the dark-skinned Arctic peoples (Inuit, Eskimo, Aleut, etc.) The answer there seems to be that they migrated north later than the light-skinned populations did; and possibly, their traditional diet provided enough Vitamin D to make mutation to a lighter skin less needful. Fish is a good source of Vitamin D for populations which can't create it by exposing their own skin to the sun. Vitamin D at Wikipedia http://en.wikipedia.org/wiki/Vitamin_D To my surprise, the article mentions that women in conservative Muslim countries who wear the whole-body veil called the burqa are experiencing Vitamin D deficiency. I had never thought about it, but it makes perfect sense: their skin never gets sunlight, and their traditional diet doesn't include much, if any, fish.

cuse we tend to act out and act against our stereotypes... and I've seen an African Americans with light brown eyes, blue eyes, red eyes (albino) I've seen caucassions with black hair and red hair BTW chinese people are asians and you're neglecting Hispanics, Indians, Native Americans, and Middle-Easterns