*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 does 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.
Have you ever found yourself in the paint aisle, staring wordlessly at the seemingly endless array of color fusion? I always find myself staring at those swatches and wondering how on earth there can be hundreds of variations of yellow. Perhaps, I’m just an unrefined savage when it comes to understanding paint color, or maybe the colors really aren’t that different and it’s simply a trick presented by paint advertisers. However, looking closer, I can see the vague tinges of shade difference. Observing this array of color all with their own name, I realize that we humans have a deep understanding of color variation. And, this ability to see color has allowed us to note the vast diversity of skin color among our own species.
Skin is 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, our skin is more than just a walking advertisement. It is the knight of our bodies, protecting our delicate innards from physical, chemical, or microbial harm. But it is more than that. Skin also provides critical information about the ambient environment and objects we interact within our environment. So, let’s dive in and find out why the human color swatch is so variable!
What Is Skin Made Of?
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, which holds the connective tissue, blood vessels, oil, sweat glands, nerves, and hair follicles. The dermis is the foundational block of your skin. It is what supports the epidermis and enables your skin to thrive. That healthy glow or occasional angry pimple you see come from the dermis. The epidermis, however, is the skin we see every day and the one that defines our color. While the dermis is the supporting actress that obviously does the most work, the epidermis is who we will be focusing on for today.
Why Does The Epidermis Determine Color?
Within the Epidermis there layers known as the melanocytes layers. These layers determine skin color since they host melanin, the primary pigment found in the body. 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. How do these affect skin color? If an individual has more eumelanin they will exhibit darker skin color compared to someone with more pheomelanin. Additionally, there are also two skin types that react differently. The first is constitutive skin color which consists of your genetically predetermined skin color in the absence of any external stimuli, like sunlight. 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!
Why The Difference?
Generally, individuals with more eumelanin will exhibit a higher degree of facultative skin color and are descendants of individuals who resided in environments with high exposure to sunlight. Individuals with more pheomelanin will exhibit less facultative skin color and are descendants of individuals who resided in environments with less exposure to sunlight. This difference is strongly associated with a latitudinal signal, with darker skin being present around the poles and equator and lighter skin being present bellow the poles and equator. This latitudinal signal is directly associated with exposure to high degrees of sunlight. Both the poles and the equator have 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 catnap in the sun?
Why Is Sunlight Important?
Like all good tetrapod’s our skin is made to protect us from the big bad world and help us synthesize vitamin D. Vitamin D is critical in maintaining overall body function and maintenance. It manages calcium in the blood, gut, and brain and helps to provide communication between cells. Unfortunately, vitamin D is not produced within the body but instead primarily absorbed from sunlight. However, we also absorb UV light from sunlight and too much of it can cause sunburns and cancers can form. So, a balance must be made between the amount of UV penetration and vitamin D synthesis.
So what Does This All Mean?
Individuals with darker skin color have increased protection against UV radiation, but can’t absorb vitamin D as effectively as individuals with lighter skin color and vice versa. Darker-skinned individuals are able to obtain enough vitamin D if they reside in environments with adequate sunlight like in the poles and equator. However, lighter skin-colored individuals have an increased risk of obtaining diseases like skin cancer from areas with increased UV absorption, like in the poles and equator. But, lighter-skinned individuals living in areas with little to no sunlight are better adapted to that specific environment compared to darker-skinned individuals since they are able to better absorb sunlight.
As society continues to develop, 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, like milk, multivitamins, or vitamin D tablets. Lighter skinned individuals in environments with high exposure to sunlight can overcome high absorption of UV radiation by wearing sunscreen or clothing, reducing the surface area exposed directly to sunlight. Regardless, it’s important to note that while an environment may not be “best suited” to your evolutionary biology, many many people of different skin colors are able to live in “nonideal” environments without needing outside help. You’re just a little less adapted to that specific environmental pressure. Humans are incredibly general in our biology. it’s what has allowed us to become so prolific. 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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