The sexual selectionFor the Europeans, which are generally unaccustomed to seeing people of other races, Asians and Blacks look all the same at first. This is due to the fact that, amongst Europeans, there is a huge variation inside the same population when it comes to eye/hair/skin color, while they see just black haired brown eyed people in other races.
There are some tens of mutations that induced these variation amongst Europeans, explaining so many hues of hair, eye and skin color, but till now, scientists we're not able to tell for sure, based just on the DNA, the eye or hair color of a European individual.
A team at Decode Genetics led by Kari Stefansson analyzed the DNA coming from about 7 000 Icelandic and Dutch individuals, finding 60 different mutations behind such colorful variation in a human type. But no single mutation or cluster of mutations can forecast if an individual has brown, blue or green eyes; brown, blond or red hair or fair/freckled skin. But the newly found genes involved in pigmentation represent clues for investigating conditions connected with a specific coloring. "It has long been thought that before the migrations that first brought our species out of Africa some 60 000 years ago, ancestral human populations had characteristically dark skin, eyes and hair", the researchers mentioned.
Europeans evolved high variations in skin, eye and hair color, but - interestingly enough - all European human types colonizing Europe after the Ice Age came from Asia. Even the blond blue-eyed Indo-Europeans are believed to have come from Central Asia or Caucasus area.
Skin and hair tends to be darker in races evolved near the equator, enhancing the idea that human pigmentation is linked with the defense against sun's radiation. Not only Europeans, but many northern Asian types have lighter skin than the southern groups. "The most obvious functional advantage of lighter skin pigmentation in northerly latitudes is that it facilitates the synthesis of vitamin D3 in spite of low levels of ultraviolet radiation exposure," the researchers explained.
But the high variations in eye and hair color among Europeans goes even further. Natural selection is by far not the only factor that could explain these mutations; a sexual selection is also involved: those traits were appreciated in sexual partners (viewed as beautiful) and this way these people could have had increased sexual fitness, translated in more offspring. In fact, studies showed that inside all races, lighter skinned individuals are seen as more attractive. In the North, this is the result. Imagine 15,000-20,000 years ago how all the women of the group preferred the blond blue-eyed hunk: he would have practically fathered a whole generation. "The 60 (mutation are) clustered in different genomic regions along five different chromosomes (6, 12, 14, 15 and 16)," wrote the researchers.
Most mutations just encode a tendency to display, let's say, green versus blue eyes or brown versus blue eyes, but they do not lead to a specific trait alone. "A mutatuon on chromosome 6p25 is associated with an increased likelihood of freckles and skin sensitivity to sunlight, as well as to brown hair", the researchers added.
Decode Genetics also mentioned that the discoveries could help "forensic geneticists, and studies of diseases of the skin and eyes that are known to be correlated with such traits."