Written by: Jasmine Biju
Charles Darwin, a pioneer in biology known for his breakthrough contributions to theories on evolution, explained the diversity of various organisms and documented his synthesized research in his book, “On the Origin of Species.” This book contained valuable insight into the diversity of many species but had minimal information on the extent of variability between humans. Darwin recognized the most conspicuous marker of human diversity to be the variety of human skin pigmentation; however, he went on to say, “These differences do not coincide with corresponding differences in climate.” With the research and knowledge we have today, we now understand that Darwin’s understanding of skin color was actually wrong.
What Darwin did not realize at the time was that the evolution of skin pigmentation is indeed a result of UV intensity at different geographical locations. Today, what we witness is a beautiful gradient of darker pigmentation close to the equator and lighter pigmentation close to the poles. The first humans had darker skin colors, as our species evolved in areas that received high ultraviolet radiation.
UVC, UVB, and UVA are different forms of ultraviolet light. UVC has the shortest wavelength, making it the most dangerous; however, the incoming light is impeded by the Earth’s ozone layer. UVB is the second shortest wavelength and causes skin burning if exposed for prolonged periods of time or in short periods of time with high intensity. UVA is the longest of the three types of UV radiation, and it is understood as the main contributor to skin aging. Though UV radiation has harmful effects, sunlight is important for the production of vitamin D and overall well-being. Vitamin D is an important molecule that the body needs in order to maintain strong bones and a healthy immune system. Current research tells us that sunscreen does not interfere with the production of vitamin D.
The equator has high amounts of ultraviolet light as it is the geographical location on Earth in which the Sun’s rays hit the most directly. Melanin, a polymer compound in our skin, serves as a biological defense mechanism against harmful sunlight exposure. As the first humans lived close to the equator, melanin was critical in the prevention of DNA and folate, an important molecule that helps to fuel cell production and reproduction, harm.
As humans dispersed and moved away from the equator, conditions grew colder and the need for melanin dissipated. This had its own ramifications, as individuals further away from their equatorial homeland did not receive sufficient UV radiation to produce vitamin D. Ultimately, highly melanated skin paired with lower levels of sunlight in these non-equatorial regions led to less vitamin D production in individuals with deeper skin tones. Lighter skin tones in less sunny locations are able to produce more melanin than their highly melanated counterparts, so it became favorable to have a lighter skin color. This explains the development of different skin complexions around the world.
Evolution induced by geographic distribution has created the beautiful, diverse population that we see today. People of all pigments live next to each other and are evidence of this fascinating biological process. Skin color is the product of human evolution, and for that, it must be celebrated.
References:
“Human Skin Color Variation.” Smithsonian National Museum of Natural History. https://humanorigins.si.edu/evidence/genetics/human-skin-color-variation
Jaffe, Mia. “If humans have a common ancestor, why do we have different skin colors?” The Tech Interactive, 2015, https://www.thetech.org/ask-a-geneticist/skin-color-and-natural-selection
Jablonski, Nina. “The Evolution of Skin Color.” PennState, https://www.psu.edu/impact/story/the-evolution-of-skin-color/
Neale, R E et al. “The effect of sunscreen on vitamin D: a review.” The British journal of dermatology vol. 181,5 (2019): 907-915. doi:10.1111/bjd.17980.
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