We are able to follow skin colour changes during human migration northward towards Eastern Asia, across the Bering Strait and south towards the equator on the American continent. Here, skin colour has not yet become completely dark. The 15,—20, years that the American Indians have been there is too short a time. Eskimos stopped along the way, but kept some of their dark skin colour because they ate Vitamin D-rich seafood. Their diet made completely white skin unnecessary for them to survive.
About , years ago the Neanderthals came to Asia and Europe and endured for more than , years. They were strong and had large brains, but they died out during the Last Ice Age.
Evidence of cranial deformation has been found, and this suggests Vitamin D deficiency. They ate little fish, which is unwise if one needs to protect oneself from cold and wind and one gets too little sunlight.
Their light skin was perhaps not enough help. Our forefathers, the Cro Magnons, survived, possibly because they ate more fish. A similar hypothesis has been suggested to explain why Erik the Red's descendants disappeared from Greenland during a cold spell, and this is partially supported by examinations of bones excavated at Herjolfsnes [Herjolf's Point] and by the fact that little fish was eaten.
There is a high degree of uncertainty, however, and more research is necessary. The agricultural revolution came from the Middle East about 11, years ago and brought with it a diet of grain and meat at the expense of fish, and, as a matter of fact, our Indo-European language.
It is probable that our skin became lighter extra quickly so that we would get enough sun and Vitamin D, since we had a low intake of this through diet. In an evolutionary perspective, women may be more important to keep healthy than men. This likely explains why women in most populations are lighter skinned than men.
Solar radiation darkens the skin in at least two ways. As soon as we get out into the sun, the melanin in the skin begins to darken, but it becomes lighter again when we go indoors.
The darkening is a result of UVA, or ultraviolet radiation that is nearly violet in colour, and our newest theory is that the purpose is to protect against the breakdown of substances in the blood. And the story of skin pigmentation is complex. She writes:. But in the far north—where low light levels would favor pale skin—the team found a different picture in hunter-gatherers: Seven people from the year-old Motala archaeological site in southern Sweden had both light skin gene variants, SLC24A5 and SLC45A2.
Thus ancient hunter-gatherers of the far north were already pale and blue-eyed, but those of central and southern Europe had darker skin. But other factors might be at work, a new study suggests. From the varying effects of frostbite to the sexual preferences of early men, a host of theories have been reviewed.
Vitamin D plays an important role in bone growth and the body's natural protection against certain diseases, and the inability to absorb enough in areas of less-powerful sunlight would have decreased life expectancies in our African ancestors. The further north they trekked, the more vitamin D they needed and the lighter they got over the generations, due to natural selection.
This explanation accounts for the world's gradients of skin color traveling south to north, the prevalence of vitamin D deficiency among African immigrants to higher latitudes, as well as the relatively darker skin of Canada's Inuit peoples, who have good levels of vitamin D despite living in the Arctic, due to their diet rich in oily fish.
So our ancestors had to develop a better cooling system. The answer was sweat, which dissipates heat through evaporation. Early humans probably had few sweat glands, like chimpanzees, and those were mainly located on the palms of their hands and the bottoms of their feet.
Occasionally, however, individuals were born with more glands than usual. The more they could sweat, the longer they could forage before the heat forced them back into the shade. The more they could forage, the better their chances of having healthy offspring and of passing on their sweat glands to future generations. A million years of natural selection later, each human has about 2 million sweat glands spread across his or her body. Human skin, being less hairy than chimpanzee skin, "dries much quicker," says Adrienne Zihlman, an anthropologist at the University of California at Santa Cruz.
Hairless skin, however, is particularly vulnerable to damage from sunlight. Scientists long assumed that humans evolved melanin, the main determinant of skin color, to absorb or disperse ultraviolet light. But what is it about ultraviolet light that melanin protects against? Some researchers pointed to the threat of skin cancer.
But cancer usually develops late in life, after a person has already reproduced. Others suggested that sunburned nipples would have hampered breast-feeding. But a slight tan is enough to protect mothers against that problem. During her preparation for the lecture in Australia, Jablonski found a study that examined the effects of ultraviolet light on folate, a member of the vitamin B complex.
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