*A note from the Author*
We all know that the issue of race is a delicate subject and one that is unavoidably linked to skin color. This post will not focus on the subject of race, but rather on why we see differences in the color of human skin. Race is a social construct, not a biological one. The color of our skin is not determined by our race, social standing or ethnicity, but rather by the environmental stressors our ancestors were subject to.
Skin color could be humanity’s most visible characteristic. Coming in a gradient of colors, it provides us with a billboard of information regarding an individual’s health, age, and ancestry. However, skin is more than just a walking advertisement. It is the vanguard of our bodies, protecting our delicate innards from many forms of physical, chemical or microbial harm (23). Skin also provides critical information about the ambient environment and any objects touched. Additionally, it helps regulate body temperature by sweating or by either increasing/decreasing blood flow within the blood vessels located in skin layers.
The skin is divided into two main groups of layers: the dermis and the epidermis. The dermis consists of a thicker inner layer of skin, whereas the epidermis consists of a thinner outer layer of skin. Within the epidermis are four layers of skin. The most important of these layers, in regards to skin color, are the melanocytes layers since they host melanin, the primary pigment found in the body (24).
Melanin are cytoplasmic organelles called melanosomes. They come in two different forms: eumelanin and pheomelanin. Eumelanin consists of the brown and black pigments, whereas pheomelanin consists of the red and yellow pigments. As a result, if an individual has more eumelanin they will exhibit darker skin color compared to someone with more pheomelanin. Additionally, within skin color, there are also two skin types that react differently. The first is constitutive skin color which consists of your genetically predetermined skin color in absence of any external stimuli, like sunlight (24). Simply put, this is the skin color you were born with, the original #nofilter, #no makeup look. The second is known as facultative skin color which develops when exposed to any external stimuli, like sunlight. So, that killer tan you got when you went to Bali? That’s your facultative skin hard at work!
Generally, an individual with more eumelanin will exhibit a higher degree of facultative skin color and be descendant from individuals who resided in either the poles or close to the equator. As a direct opposite, individuals with more pheomelanin will exhibit a lesser degree of facultative skin color, and be descendant from individuals who resided below the poles and away from the equator. This strong latitudinal signal is thought to be directly associated with exposure to high degrees of sunlight (23).
Both the poles and the equator present higher more intense degrees of sunlight and UV radiation. As a result, individuals living in these kinds of environments would have had to adapt to more intense and longer periods of sun exposure. It has been proven scientifically that darker skin holds significant benefits towards prolonged and intense sun exposure. Eumelanin prevents more UV radiation from entering the body than pheomelanin. Facultative skin is also more resistant to sunburns, allowing individuals with a higher amount of facultative skin to be exposed to sunlight for longer periods of time. Compared to darker colored individuals, lighter colored individuals tend to reside away from areas of increased sunlight. As a result of not having as much sun exposure, their skin color will adaptively shift to a light color to allow for maximum absorption of solar rays. This allows them to exploit as much sunlight as possible which in certain doses can be helpful for the body and mind. Who doesn’t love a good cat nap in the sun?
Like all tetrapod’s our skin is made to protect us from harm and is the initial locus for the synthesis of vitamin D (9). Vitamin D is an important micronutrient needed to maintain overall body function and maintenance. It manages calcium in the blood, gut, and brain and helps to provide communication between cells (23&9). Like vitamin C, vitamin D is not produced within the body but instead is primarily absorbed from sunlight. However, if too much UV penetrates the body, damage such as sunburns and cancers can form. So, a balance must be made between the amount of UV penetration and vitamin D synthesis.
Since individuals with darker skin color have increased protection against UV radiation, they are unable to absorb vitamin D as effectively as individuals with lighter skin color. Still, individuals with darker skin are able to obtain enough vitamin D, but only if they reside in environments with adequate sunlight. And, since there is a higher amount and intensity of sunlight located in the poles and equator, individuals with darker skin are still able to receive enough vitamin D. On the other hand, lighter skin colored individuals have decreased protection against UV radiation but are able to better absorb vitamin D. But, if lighter skin colored individuals find themselves in areas with higher and more intense rates of sunlight they have an increased risk of obtaining diseases like skin cancer from increased UV absorption. If dark-skinned individuals reside in areas where there is not enough sunlight, they run the risk of not obtaining enough vitamin D. This can lead to serious deficiencies such as rickets, if not remedied.
As society further develops, it becomes easier for individuals to reside in environments for which their skin might not be best adapted. Darker skinned individuals residing in environments with restricted sunlight may overcome vitamin D deficiency by consuming vitamin D fortified foods, such as milk, multivitamins or vitamin D tablets. Lighter skinned individuals residing in environments with high exposure to sunlight may overcome over absorption of solar radiation by wearing either sunscreen or clothing, thus reducing the surface area exposed directly to sunlight. So, whether you can absorb vitamin D like a boss or thwart UV radiation with a flick of your wrist, each and every one of us shows amazing amounts variability. No wonder we’re able to inhabit most of the globe. Go Homo sapiens, go!
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