Why are there differentskin colours?
Human skin colour can vary from almost translucent to almost black. The human skin pigmentation is the result of natural selection. The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment called Melanin. Variations in human skin color are adaptive traits that correlate closely with geography and the sun’s ultraviolet (UV) radiation.
The primary reason of varied skin colours is due to presence of the pigment Melanin which is controlled by 6 genes. Both light and dark complexioned people have melanin. However there are two forms of melanin that are produced:
Pheomelanin : It is red to yellow in colour.
Eumelanin : It is dark brown to black in colour.
People with light complexioned skin mostly produce pheomelanin, while those with dark colored skin mostly produce eumelanin. In addition, individuals differ in the number and size of melanin particles. Melanin acts as a protective biological shield against ultraviolet radiation. It helps to prevent sunburn damage that could result in DNA changes and, subsequently, several kinds of malignant skin cancers.
Skin colour is also determined by our ancestry, so we know the people whose ancestry comes from Africa or regions close to the equator tend to have darker skin colour and people further away in higher latitudes will have lighter skin colour. The reason for such differences may have to do with the amount of sunlight in each place. It is something that has been recently identified in terms of which parts of the genome and how much of our DNA is actually involved in determining skin colour. Sunlight helps our bodies to make Vitamin D and can also darken the natural skin colour as a result of tanning. Although sunlight can also be dangerous because of its ultraviolet (UV) light. UV light can destroy folic acid or cause changes (mutations) in the DNA of some skin cells. These mutations can lead to skin cancer. So darker skin is helpful when there is a lot of sunlight. But sunlight isn't all bad.
The other thing to notice is that traits distinguishing human populations evolved a long time ago (between 60,000 and 10,000 years ago, when humans moved out of Africa and colonized North America and Australia), and we can only speculate about selective forces that occurred so long ago. That said, the geographic distribution of UV light hasn’t changed much since then!