Shades of Sepia: Why scientists say you’re the color you are

According to Biological Anthropologist and Paleobiologist Nina Jablonski, the story behind the range in human skin color is a story of evolution … and it goes like this:

In theory, humans evolved from our primate roots in Africa — closely related to the chimpanzee. Before our ancestors shed their fur and walked completely upright, their skins hidden beneath all that fur was white. But once humans were … well … bare, our skins gradually turned black about 1.2 million years ago.

Shades of Sepia

To shield ourselves from deadly skin cancers caused by high levels of UV exposure, our bodies produced higher levels of melanin — the pigment-making chemical in our skins. The result was darker skin — our natural sunscreen that blocks cancer-causing UV rays … thus preserving the species.

About 60,000 years ago, some early human ancestors migrated out of Africa. As they settled farther from the equator and in colder climates closer to the poles, they’re skins produced less melanin. The northern-most regions didn’t have the same life-threatening UV intensity. Their dark pigment lightened. Their skins ceased to filter sunlight needed to produce vitamin D — essential for skeletal growth and health. Again, the species was saved.

Jablonski theorizes whatever color we are is due to natural selection in response to early human patterns of migration or … adaptation. Human skin tones, she asserts, are shades of sepia.

UV intensity and climate determines genetic variations in skin color

Below is a snapshot of NASA’s 7 Total Ozone Mapping Spectrometer (TOMS)taken on April 28, 2015. TOMS maps average daily and yearly ultraviolet radiation levels throughout the world.

Totalozonemapping

 

Map of UV radiation per year

Red and hot pink areas in the graphic below denote those regions with the most UV radiation per year. Then the color spectrum cools — purple, cyan, green, then gray — where gray represents the least amount of annual UV radiation.

Jablonski asserts all human skin pigment are variations of sepia. The range in tint and shade coincide with regional UV intensity.

Below is a colored map representing human skin color indigenous to each region. Sub-Sahara and Southern Africa — which are on or near the equator — are where deeper skin tones originate while Northern Europe — which is nearer to the poles — is home to those with much paler complexions.


Sources:

“Shedding Light on Skin Color,” Ann Gibbons, Science, 21 November 2014: Vol. 346 no. 6212 pp. 934-936 DOI: 10.1126/science.346.6212.934, http://www.sciencemag.org/content/346/6212/934.summary

“Natural Selection is Furthering Mutations that are Making Skin Paler,” Science Daily, December 5, 2014, http://www.sciencedaily.com/releases/2014/12/141205100058.htm

“Breaking the illusion of skin color — Nina Jablonski, TED-ed, YouTube, https://www.youtube.com/watch?v=tLsFl6QiFh4

“Skin color: Handy tool for teaching evolution?” Science Daily, http://www.sciencedaily.com/releases/2011/02/110220091826.htm

“Studies of a skin color gene across global populations reveal shared origins,” Penn State News, http://news.psu.edu/story/299166/2014/01/02/research/studies-skin-color-gene-across-global-populations-reveal-shared

“Evolutionary history is more than skin deep,” Understanding Evolution — Berkeley, http://evolution.berkeley.edu/evolibrary/news/140305_skincolor

“Skin Color Adaptation,” http://anthro.palomar.edu/adapt/adapt_4.htm

“How Skin Color is Determined,” American Society for Biotechnology and Molecular Biology, February 27, 2008, http://www.sciencedaily.com/releases/2008/02/080222155212.htm

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