Any scientific explaination for geographic distribution of various human skin colours across the world?

Certainly. Skin tones of humans are related to the climate to which their ancestors adapted, many thousands of years ago. In areas of heavy, dircect UV rays from the sun, i.e., the savannahs of Africa, Southern India, the darkest pigmentation (melanin, a skin protein) is found. Lighter pigmentation is found in more northerly climes,...as in Europe. Many Asian peoples are darker than Europeans, though they are just as far north. But their ancestors were adapted to vast open steppes,...less UV rays than Africa, but more than Europe. Europeans adapted to a vast, northern, forested environment, where sunlight was much less. Sunlight provides an important ingredient to human growth and health,..Vitamin D, which is produced in the skin under the influence of sunlight. Where sunlight is less, lighter skin is an advantage. It allows for more absorption of vitamin D. You must remember, though, that these adaptations occurred when humans had much less control over their environments than today. And there has been much migration since the earliest humans appeared. So, the geographical location and skin colour of modern peoples may bear no relation to the location of their ancient ancestors. With the advances in human skills, diet, etc,...there is little need or likelihood for further adaptations. People of European ancestry are unlikely to become darker because they live in South Africa or Australia. Africans or Indians are unlikely to become lighter skinned because they live in Europe or North America.

Any scientific explaination for geographic distribution of various human skin colours across the world?
There are two basic reasons. Your body need melanin to protect against too much UV radiation. There are enzymes that can repair some damage but will be overwhelmed if the dosage is too high and the skin will be burned. You need enough to prevent burning. The other consideration is the proper amount of ergosterol being converted to vitamin D. Light skin is an adaptation that allows a greater amount of UV light to penetrate and increases the amount of vitamin D which is vital for calcium absorption. In higher latitudes where the amount of UV is much less, lighter skinned individuals are selected over darker ones because they can produce enough vitamin D.
Reply:I believe it is because of adaptation that we have different skin colors. In temperate countries where the sun's rays are not so intense, human's skin will naturally be fairer as opposed to that of human's skins in tropical countries which is darker because of melanin which protects us from ultraviolet rays. If you are asking why there are dark skinned indivbiduals in the temperate countries and vice versa, well it can be explained by interracial marriages.
Reply:The answers are good BUT the Aborigine and the guys in New Guina, the Amazon indians, are in tropical areas. I wonder also.
Reply:evolutionary-- based on exposure to sunlight.
Reply:The answers that most of the folks have, about skin color being related to the amount of sunlight in that part of the world is the "traditional" interpretation.





However, the famous biologist, Jared Diamond has proposed that it's sexual selection. In other words, in different areas, certain groups have specific beauty ideals that are different from other groups.





He points out that when you look in different parts of the world (not just the Euro/African skin color distribution) you can find lots of light skinned/light haired people (like the Melanesians) at the equator, while you can go to places like Northern China (very little sun exposure) and find some very dark people.





No one has designed any experiments or models to test either of those hypotheses, but Jared Diamond has a great way of looking at things outside of the traditional interpretations.