I recall overhearing a conversation from my teenage years that stands out when reflecting on the subject of skin color. A young, lightly-complected girl asked her mother why the woman sitting across from them had dark skin. The lady across from them responded, “It’s because god likes many flavors. Not just chocolate or just vanilla.” I see much beauty in diversity and so liked this answer much more than the beliefs I had grown up with.
Growing up, I was always told by the people of my Mormon religious community that people with darker skin were descendants of those cursed by God. I suppose some of this was borrowed from the early protestant interpretations of “the curse of Cain” and “the curse of Ham” that were used to justify slavery. However, some of it was also written right in the doctrine: “Wherefore, as [the ancient Americans] were white, and exceedingly fair and delightsome, that they might not be enticing unto my people the Lord God did cause a skin of blackness to come upon them.”1
Anyway, now that I have grown up, I have done away with childish and potentially harmful myths that explain away the world in which we live. I thought it time to find the real answer.
So why different skin color? Not surprisingly, the answer had to do with where our ancestors lived in relation to the sun and the evolution of our species.2A If your ancestors lived primarily in the North, since the migration out of Africa 60 thousand years ago, you are likely to have lighter skin, hair, and eyes. If they lived more around the equator where there is more UV exposure, you are likely to have darker features. This is because of how our ancestors’ bodies had developed the right balance of melanin to allow for the right amount of production of vitamin D and protection from the decay of folate.2B
World map of annual UVB exposure: http://www.ufz.de/gluv/index.php?en=32435
Melanin is the chemical that changes the color of our hair, eyes, and skin and it works as a natural sunscreen. The more you produce, the darker your skin, hair, and eyes are. Melanin acts very efficiently at blocking out UV rays, but UV rays are needed, specifically UVB, to produce vitamin D in the skin. So, a person who has larger amount of melanin in their skin living in an area of the world that doesn’t receive much UVB is likely to suffer the effects of a vitamin D deficiency.2C
Why is Vitamin D so important? Vitamin D is needed for our bodies to absorb calcium, to make strong bones, and it also very important in maintaining a strong immune system that protects us from disease and infection. A deficiency in vitamin D can lead to more diseases, infections, scoliosis, cancer, and rickets.2D
On the other side of the spectrum, if you were living in the bush thousands of years ago in an area on earth that receives a high level of UV radiation, like the equator, and you have a lighter pigment of skin, you also have a disadvantage.2E This is because UV radiation breaks down folate.3A
Why is folate so important? It is needed for cell division and is also particularly important in fetal development. Deficiencies in folate leads to birth defects, miscarriage, and maternal mortality.3B It also has a negative impact on sperm development.2F
So, where people lived in relation to the equator and the color of your skin played a large role in the survival of their descendants. Luckily, in this day and age it is easy for us to get our vitamin D through nutrition and protect ourselves from the sun with sunscreen, clothes, and shelter. This allows us to live pretty much anywhere in our diverse global community.
What about exceptions? You may have noticed a couple of exceptions; most notably the Native people in the Americas. From the explanation thus far, you would think that the people who live in the arctic would have the lightest features. Also, you may have noticed on the UVB exposure map above that the place with the most exposure to UVB radiation, Chile and Peru, are not the places with the people who have the darkest features.
Obviously, a lot of the exceptions have to do with the influence of European colonization that only happened over the past 500 years or so. This is definitely the case with Chileans, who have a highly Spaniard and Native mixed ancestry.6 However, there are some factors that fall outside of European influence.
Take a quick look at migration before the Agricultural revolution….
Animation Depicting the History of Migration | Video Credit: BI Science
Native Americans migrated to the Americas from Asia only 15 thousand years ago.4 This is the most recent of the major migrations and followed by the agricultural revolution 3 or 4 thousand years after.5 So, the circumstances and time frame are hardly conducive to significant change in features. The agricultural revolution allowed people to take residence in a certain area, build homes that protect them from the sun, develop technologies, and have better nutrition.2G As agriculture and means of protection from the sun spread and developed, how much melanin we produced became less of a factor in the natural selection of our species.
Finally, there are the Inuit who live in the arctic and have a darker skin than we would expect. On top of there being very little UVB in the arctic, it is sometimes dark for days in the winter. It is easy to come to the conclusion that, because of the Inuit features that block UVB and the lack of UVB in the arctic, they would be suffering a serious Vitamin D deficiency. However, we know that their diet consisted of narwhal and other vitamin D enriched animals, which helped ensure that they didn’t suffer from the ill effects of vitamin D deficiencies that might lead to them dying out.2H Also, the arctic experiences many long hours of sunlight during the summer and the sunlight is intensified by the reflection off the snow. So, protection from UV radiation is still a necessity.
- Smith, J., Jr. (2006). 2 Nephi 5:21. In The book of Mormon: Another testament of Jesus Christ. New York, NY: Doubleday.
- Jablonski, N. (April 10, 2015). PSW2345 Human Skin Color. Retrieved from https://youtu.be/wlB3m9Zl12E
- Branda, RF & Eaton, JW (18 August 1978) Skin Color and Nutrient Photolysis: An Evolutionary Hypothesis. Science201 no. 4356 pp. 625-626
- Goebel, T. (2008) The Late Pleistocene Dispersal of Modern Humans in the Americas. Science, Vol 319, no.5869 pp.1497-1502
- Barker, G (25 March 2009). The Agricultural Revolution in Prehistory: Why did Foragers become Farmers? Oxford University Press.
- Valenzuela, C. and Harb Z. (1977).Socioeconomic Assortive Mating in Santiago, Chile: A Demonstration Using Stochaistic Matrices of Mother-Child Relationships Applied to ABO Blood Groups. The Society for the Study of Social Biology, Volume 24, PP. 225-233