Melanin refers a broad group of pigments that determines skin color in human beings. It ranges from dark to light where each shade also has its variations. Therefore, it is difficult to accurately map the number of skin colors there are found among the human race. Melanin is produced by specialized cells on the skin called melanocytes, and its primary purpose is to protect the skin from harmful UV sun rays (Barsh, 2013). This is why people from tropical and template geographical areas are darker than those in colder regions. It is important to demystify the science behind skin color variations since the concept has been wrongfully used in the past to socially, physically, intellectually, and economically differentiate groups of people.
Scientists theorize that before modern man evolved, the physical structure resembled that of a chimpanzee with soft light-colored skin covered with hair (Jabolonski & Chaplin, 2010). The hair protected man from the sun and cold and covered the delicate skin underneath. However, as the continental drift and other changes in the environment pushed man into warmer climates in search of food and water, some of these features became unnecessary. Therefore, to adapt to this new hot climate, early man lost the hair and developed pores to enable cooling through perspiration.
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However, this left the skin exposed and vulnerable to radiation from Ultraviolet sun rays. Dark pigmentation, therefore, developed due to excess melanin to protect man from harmful radiation. Dark skin contains so much melanin that very little UV radiation, and specifically very little of the shorter-wavelength UVB radiation, can penetrate the skin (Deng & Xu, 2017). Although most of the effects of UVB, ultraviolet shortwave rays, are harmful, they perform one vital function: initiating the formation of vitamin D in the skin. Furthermore, it is proven that UVB in excess breaks down folic acid in the body. The deficiency of folic acid results in reproduction problems in both males and females. It can also cause congenital disabilities such as neural tube defects where the arches of the spinal vertebrae fail to wrap around the spinal code (Jabolonski & Chaplin, 2010). This nutrient also helps in generating DNA during rapid cell division such as the production of sperm cells. The skin got darker to prevent folic acid breakdown and ensure reproductive success.
Although most scientists agree on the theory of darker pigmentation origination from the equator, most disagree on the specific mechanisms that led to current variation. Modern man evolved in Africa then spread to the rest of the world (Parra, 2007). Migration is one of the selective mechanisms that explain why skin pigmentation changed in different human populations. As man migrated to lower and higher latitudes where the UV radiation was less concentrated, another problem arose. UV rays help in the formation of Vitamin D and the absorption of calcium and in places with low sunlight, dark skin would prevent the acquisition of these important nutrients (Barsh, 2013). Therefore to allow more UV rays, the skin lost some of its pigmentations.
Since the higher latitudes receive less sun than the lower ones, people from northern Europe lost the most melanin and look white while those from places like Chile and South Africa, although darker are still lighter than people native from the equator. Similarly, since man migrated to Asia, Austro-Melanesia, then to Europe, darker to lighter skin pigmentations can be traced among the original inhabitants of these areas (Jabolonski & Chaplin, 2010). Even among indigenous people, the distribution of skin pigmentation varies. It may be surprising that Africa has the highest variation of skin color despite the fact that Africans are often all labeled as “blacks.”
Natural selection also caused variation in skin pigmentation. The term refers to a process through which strongest traits are passed on to future generations while weak ones die out to ensure the survival of a species. In people living near the equator where sun rays were most concentrated, natural selection chose dark pigmentation over light skin and passed it through generations for reproductive purposes. If folic acid were destroyed thus producing future generations with neural tube defects, this would have doomed humanity. Similarly, those that got lighter pigmentation did so to ensure that future generations could access vitamin D and calcium necessary for bone development and a healthy immune system (Norton, 2008).
An exception to natural selection and migration appears where groups in latitudes with low UV radiation maintained dark pigmentation. The theory that explains this is that when there is an alternative source of Vitamin D, there is no need to develop a lighter pigmentation to allow more sun absorption. For instance, tribes like the Inuit and Lapp supplement the nutrient in their diets with seafood and fruits, and they also have darker skin despite their geographical location in Alaska and Northern Canada. They are also relatively new to the areas they inhabit and thus have not given natural selection a chance to change their skin color (Parra, 2007; Jabolonski & Chaplin, 2010). Despite the evidence, it is important to note that it is difficult to tell how patterns of radiation have changed over time or when exactly skin pigmentation evolved since there were multiple waves of migration out of Africa as well as the extensive genetic interchange between different groups
Sexual selection has also been pointed out by many scientists, notably Charles Darwin. It is the tendency for women in all populations to be light-skinned in comparison to men by 3 to 4 percent. One speculation to explain this is that men are more attracted to light-skinned women, so natural selection prefers to advance genes that account for less melanin to ensure reproductive success (Deng & Xu, 2017). Although this could be a reality today, a more probable explanation is that women need more Vitamin D and Calcium during pregnancy, birth, and Lactation so they can heal fast and pass valuable nutrients to their offspring. Having lighter pigmentation must have developed to allow women to absorb more UV rays for Vitamin D synthesis. However, it is curious how this plays out for women in equatorial communities because too much UV radiation would cause skin damage or destroy folic acid which they also need for reproductive success.
The skin color of the indigenous people of Africa has had the longest time to adapt because anatomically modern humans first evolved there (Barsh, 2013). Even though people continued to move from one continent to another over the years, their pigmentation did not change because unlike early man, they had clothing, shelter, and improved diets to protect them from developing any deficiencies. These facts draw attention to culture as a selection mechanism in the evolution of skin color. For instance, people who originate near the Red Sea have different pigmentation due to culture.
On the western shore, there are Nilotes such as the Dinka of Sudan who have been there for at least six millennia. They are very tall and lean and have incredibly dark skins which can be explained as adaptations to stay safe from UV radiation and heat respectively. However, modern groups on the Eastern shore of the Red Sea and the Arabian Peninsula have lived there for two millennia and originated from Europe. They remain light-skinned despite similar conditions because they have used cultural items such as heavy clothing and artificial shade to adapt to the same environment (Jabolonski & Chaplin, 2010). Without these protective clothing, their skins would have ideally darkened. Therefore, the less time a group has spent in the area, the more their adaptations are likely to be cultural rather than biological.
Migration today has affected the natural order of things. While during the era of skin color evolution it was more likely to find rickets in light-skinned people and skin cancer on dark-skinned people, this has changed. People move freely to areas their pigment has not adapted to so, a light-skinned person who is exposed to too much sun in the tropics risks getting skin cancer whereas a dark-skinned person who moves to low UV latitudes can get rickets due to poor Vitamin D formation.
Genetics is a viable selection mechanism for skin color, but due to various variations in pigmentation, it has been difficult to isolate which specific genes are responsible for pigmentation. Significant strides that have been made are in identifying genes that cause albinism which is a lack of melanin. The melanocortin 1 receptor gene (MC1R) has also been studied exhaustively as pigmentation allele responsible for characteristics such as red hair and fair skin. These results could be instrumental in unlocking the genetic alleles for skin color but so far little is known on the topic (Deng & Xu, 2017).
Despite what most people would believe about skin color, it is merely a survival adaptation, and it should not be used as a tool to discriminate against some groups of people. The differences are only skin-deep and deep inside, our genetic make-up as a species is the same. People should realize that the black man is not inferior but a reminder of how far evolution has taken the human race in a bid to make it adaptable to varying environmental conditions to ensure its continuity.
References
Barsh, G. S. (2003). What Controls Variation in Human Skin Color? PLoS Biology , 1 (1), e27. doi:10.1371/journal.pbio.0000027
Deng, L., & Xu, S. (2017). Adaptation of human skin color in various populations. Hereditas , 155 (1). doi:10.1186/s41065-017-0036-2
Jablonski, N. G., & Chaplin, G. (2010). Human skin pigmentation as an adaptation to UV radiation. In J. C. Avise & F. J. Ayala (Eds.), In the light of evolution: Volume IV: The human condition (4th ed., pp. 167-183). Retrieved from https://books.google.co.ke/books
Norton, H. L. (2008). Evolution of Skin Pigmentation Differences in Humans. Encyclopedia of Life Sciences . doi:10.1002/9780470015902.a0021001
Parra, E. J. (2007). Human pigmentation variation: Evolution, genetic basis, and implications for public health. American Journal of Physical Anthropology , 134 (S45), 85-105. doi:10.1002/ajpa.20727
