Seafood Affecting Skin Colour?

Seafood is an interesting factor that also surprisingly affects skin colour. Seafood is an excellent source of vitamin D, so people who have diets rich in seafood are high in vitamin D. This is most commonly seen in people who live in coastal areas, where fish is a primary source of food in their diet. A common case for Eskimos, and people who live in the Arctic regions. Since such high amounts of vitamin D are consumed, the skin doesn't need to reduce pigmentation. A pigmentation reduction would be necessary for those who were not eating a shellfish abundant diet. If these people reduce the amount of seafood they are accustomed to eating, they face the risk of vitamin D deficiency which can lead to osteoporosis.

The Blending of Skin Colours

The distinction between such drastic skin colours was more obvious years ago. Without automobiles, planes, and trains, people didn't move around as much. They mated with people from the same areas passing their traits down from generation to generation. Since they were isolated, most of the skin colours were similar.
As technology increased and travelling became accessible people started mating all over the world. Someone that once lived in Africa could move to the north and mate with a light-skinned individual. Skin pigmentation is passed on as a blend, where a number of different shades could result. When two ethnically diverse individuals have children, the children may not have the exact same coloured skin.

The Effects of the Equator

Variations in human skin colour are due largely to geography and the sun's ultraviolet radiation (UV rays). Depending on where you live in the world, there is usually a common pattern in the colours of skin.  Those that live closest to the equator will have a higher percentage of people with darker skin. Those that live at the poles will have drastically lighter skin. Basically, there is a high occurrence of  dark skin in the tropical areas, and light skin in temperate. The reason behind this is that darker skin is required to avoid vitamin D toxicity. While in equatorial areas, the sun is much stronger and dangerous. As people started moving around the world, natural selection created different shades of skin. Those that continued to be in open areas retained their darker skin for protection. However, people that were in shaded protected areas, or places with less frequent exposure to sunlight developed lighter skin. Light skin colour is necessary outside the tropics to allow for vitamin D synthesis. Since the sun isn't as strong it is much less of a danger, and is ironically necessary. Too much vitamin D can lead to hypercalcemia. The darkest skin is found in the lowest latitudes of the open grasslands of Africa.

Evolution of the Homo genus

If you were to look at the skin of chimpanzees you would see that it is lightly coloured, yet the skin is covered in fur. It is the fur that protects these organisms from the sun. When humans branched off from chimpanzees they retained a few characteristics, light skin being one of them. As the genus Homo started to become more evolved, the body needed to make some adaptations. There was a migration from the forests into open land for the search for food and water. When more efficient hunting and gathering techniques were attained, there was a substantial increase in the metabolic activity of the body. An increase in the number of sweat glands was necessary as a means of cooling down the body. Having fur would be an inconvenience because the sweat would get stuck as the base of the hair follicles, resulting in an insufficient cooling technique. As a result, the body became remarkably more hairless, looking naked from a distance. With this adaptation came a drawback; there was virtually no protection from the UV rays of the sun. Being exposed to the sun for such long periods was of great danger. 

The Basics of Skin

Skin is the outer covering of vertebrates. For humans, it is the largest organ of the integumentary system and functions as an insulator, temperature regulator, and it protects the organs. It can be oily, or dry, and is seen in a vast array of colours. Most of the human skin is covered with hair follicles, but it can also be hairless. Skin acts as a large sensor that keeps the brain in touch with the rest of the body with the use of numerous nerves.
There are three layers: epidermis, dermis, and the subcutis. The epidermis is the outermost layer. Keratinocytes formed from the protein keratin form layers that continually grow outward to replace the dead skin, the stratum corneum. The dermis is made of collagen and elastin fibres, and gives the skin its strength and elasticity. The nerve fibres are situated in this layer as well as the hair follicles. Finally, the subcutis creates a layer of fat cells that acts as a food reserve, and insulation and protection for internal organs.