I was just curious, does anyone know why people of diffirent races have physical diffirences? Is there some evolutionary advantage to diffirent skin tones, ect? I know that Eskimos are adapted in various ways to colder temperatures (I believe The Man Himself covered this in one of his columns), but what about the others?
Two points:
First: to answer your factual question, the melanin that makes skin darker helps protect against exposure to the sun. Hence a tendency toward high melanin levels in populations that live in sunnier climes.
Second: you’re kind of putting the cart before the horse. These differences don’t occur “in different races”; rather the races are defined, arbitrarily, based on these differences. A race, like a species, is an artificial construct, and has no real meaning in nature.
Well, according to Marvin Harris, the white “race” developed for a very practical reason – the need for calcium. According to Harris, before humans moved into the cooler climes of Europe, there were no white people. People obtained dietary calcium from green, leafy plants, such as spinach. Also, there were few people who, as adults, were lactose tolerant.
However, such vegetation was not so readily available in Europe at the time. That’s when consumption of cow’s milk became an important part of the European diet. There were two problems, however. One was that most adults were lactase deficient. The other was that in order to efficiently make use of the calcium in milk, one must have Vitamin D.
Of course, the easiest source of Vitamin D is from sunlight. Our bodies produce it when sunlight hits our skin. After that it was evolution. The lighter one’s skin, the greater the quantity of Vitamin D that can be produced. Evolution favored those who remained lactase sufficient (because people with severe intestinal problems and brittle bones were less likely to reproduce) into adulthood and those with lighter skin (stronger bones). The result was white people.
The trade-off, of course, is that light skin is much more susceptible to skin cancer. That’s an advantage of dark skin.
Simulpost – lissener has it dead on. “Race” is not a scientific concept. It’s very difficult to categorize humans on the basis of physical characteristics.
Thank you for your clarification and information.
The skin color/sun exposure/vitamin situation is a little more complicated than it first appears. For instance, there is an argument that dark skin in the tropics is not so much to protect against skin cancer (which typically occurs after the person reproduces, thus possibly evading Darwinian weeding-out) but to protect against kidney damage from an overabundance of vitamin-D caused by sun exposure. And the Inuit of North American are a relatively dark-skinned group for being so far north - but then, their diet has an abundance of vitamin D from eating vast quantities of fish, seal, and whale, so perhaps there wasn’t any push towards lighter skin.
Moving away from external differences, various populations (as opposed to “races”) have internal differences as well.
For example, abnormal hemoglobin is found not just among sub-saharan Africans (i.e. “blacks”) but also around the Medditerrean and through the Indian sub-continent in people of quite varying hue. These variation do have the rather important characteristic of making one less likely to die of malaria. Which might explain their prevelance in areas with historical heavy malaria infestations.
Less well proven, but an interesting theory, is that being a cystic fibrosis carrier protects one to some degree against diarrhea diseases, some of which have a high mortality rate, especially among the young. This trait is found almost exclusively among those of European descent.
So sometimes the reasons for differences among groups of people have to do with disease resistance.
Remember the real point is not Vitamin D, it’s calcium. The Eskimos get sufficient calcium from fish bones and other sources. They never began drinking milk for a major source of calcium. No milk, no light skin. Interesting to note that pinneped (seals, etc.) milk does not contain lactase. Again, that has to do with other calcium sources in the diet.
Then kindly explain the herding pastoralists of East Africa (Masai, among others) who are among the darkest-skinned people of the world and yet who also retain the ability to digest milk throughout adulthood and derieve a significant portion of their protein and calcium from the consumption of cow’s milk?
Nor do all light-skinned people retain lactase through adulthood. Many of the northern agriculturalists of Asia are lighter-skinned than their neighbors, but can not tolerate milk as adults.
I would say that living at a high latitude leads to an environment where a light skin may become an advantage, but not necessarily so - the native Tasmanians, for instance, lived very far south yet had very dark skins. Nor (according to what records we have) did they eat seafood, having neither fishhooks nor nets with which to catch them.
Likewise, although there is some overlap between eating dairy and light skin, there are quite a few dark-skinned milk drinkers.
So my conclusion is that there is more than one factor at work here, and the result as far as the human body goes is a compromise between these factors and what traits evolution has to work on. We have some people who have the ability to digest milk all thier lives, for instance, but there are no humans who can digest grass as cattle do - that’s just not within the range of possible adaptions for us, at least not anytime soon.
Hmmmm…What about CHOCOLATE milk? 
Just thought I’d post this link to edwino’s Race and Genetics FAQ.
The answer is simple: there doesn’t have to be a reason. If dark-skin is neutral and is not linked to anything deleterious, then it will not be selected against. It doesn’t have to serve a purpose–just like nipples on men don’t serve a purpose. If a people have inherited a trait from an ancestor and it doesn’t confer bad qualities or take up too much maintenance “energy”, it will tend to remain in the population notwithstanding the occurence of favorable mutations and/or genetic drift.
But I think you’re missing another crucial point. There are multiple environmental factors that determine the adaptive qualities of a certain trait. Just because East Africans may not need dark skin for the absorption of calcium does not mean that they don’t need it for protection against UV radiation. Additionally, culture may play a role. Dark skin may be considered more attractive in sexual partners than light skin, or maybe there’s so much gene flow between East Africans and other dark-skinned peoples that selection against dark skin is constantly thwarted. So you see, evolution is very complicated.