With the tragic killing of George Floyd on May 25, the issue of America's trouble racial past is front-and-center once again. Simple differences in skin color have led to the brutal treatment of African Americans for centuries. But in this discussion, there is one aspect that has been left out: why? Why do humans have different skin colors? The answer has to do with a number of factors, but it largely comes down to climate, namely solar radiation. And such an incidental environmental factor causing so much repression and brutality makes the division caused by racism all the more tragic.
First, let's look at the human variation of skin color. Human skin color varies around the world. It ranges from a very dark brown among some Africans, Aborigines of Australia, and Melanesians, to a pinkish hue among Northern Europeans.
The variation of skin color has to do with a pigment called melanin. All humans have it, but its level is controlled by at least six genes. Two forms of it are produced: pheomelanin and eumelanin. Light-complexioned people produce mostly pheomelanin; those with darker skin produce mostly eumelanin.
Melanin is produced in the outer skin layer, the epidermis by specialized cells called melanocytes. They have photosensitive receptors that detect UV radiation from the Sun. After a few hours of exposure, they produce melanin, leading to skin darkening.
Those with darker skin historically thrived in tropical latitudes due to the intensity of solar ultraviolet radiation. Darker skin favored such climates because melanin acted as a biological shield against UV rays, preventing sunburn damage and possible skin cancers. They were at a lower risk of melanoma and other diseases.
All people darken from prolonged exposure to the sun, although the effect is more pronounced on light-complexioned people (some Northern Europeans cannot even tan and experience burning and peeling instead).
But overall, Sun exposure is good for you. The body produces Vitam D when a certain amount of UV radiation penetrates the outer skin layer. In fact, 90 percent of Vitamin D comes from the body reacting to the Sun; only 10% comes from nutrition.
That is why those in northern latitudes adapted over the centuries to have less shielding pigmentation. When UV radiation is weak, dark skin prevents the production of Vitam D, which can lead to rickets disease in children and osteoporosis in adults.
Exceptions exist. The Inuit peoples of Canada have heavy skin pigmentation for those who historically dwelt in far northern latitudes, but they ate enough fish and sea mammal blubber to compensate for Vitamin D.
Before the beginnings of mass human migrations five centuries ago, those with dark skin were largely concentrated in the Southern Hemisphere. As one went further north or south, light color progressively increased. Most with lighter pigmentation lived north of 20º latitude, where ultraviolet radiation is much less intense.
Constantin Wilhelm Lambert Gloger, a 19th-century German zoologist, first made the argument for Sun exposure affecting skin pigmentation. In 1833, he observed that heavily pigmented animals are found mostly in hot climates with intense sunshine. In contrast, those closer to the poles commonly have light pigmentation.
All that to say, our skin tone differences ultimately come from the Sun, not any other reason due to biology or culture. And as science shows us, the differences between people of different races truly only is skin deep.
At GoSun, we believe in harnessing the power of the Sun, but most of all, we believe in working together for a better future.
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