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Another confirmation of the theory that human skin color evolved to adapt to ultraviolet light

Posted on: July 26, 2014   by  tom.weishaar@gmail.com

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Vitamin D plays a fundamental role in the leading theory of the evolution of human skin color. The theory states that skin pigment changed in response to varying levels of UV radiation and is partially based on the observation that lighter skin tones require less ultraviolet B (UVB) radiation than darker skin tones to synthesize an equivalent amount of vitamin D.

As human populations moved away from their origins near the equator, individuals with lighter skin had higher vitamin D levels, which led to better health. Thus the lighter-skinned individuals in the population were better adapted to the context of low UV radiation availability. Driven by evolution over many generations, the average skin color of the populations exposed to less UV radiation gradually became lighter.

On the other hand, in populations that moved back toward the equator, average skin color became darker after many generations because the dark skin of our African ancestors is protective against the damaging health effects of high levels of UV radiation.

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4 Responses to Another confirmation of the theory that human skin color evolved to adapt to ultraviolet light

  1. PeterVermont

    “The melanin index, a reference guide that assigns a unique value to different skin colors, was about 1.4 times higher in Ghana than in the U.S., indicating that evolutionary pressure is already at work in a population group that was forced to migrate to the U.S. beginning in the early 1600’s.”

    Seriously?

    Let’s be real – the average lighter skins of African Americans relative to Africans is almost certainly due to mixed ancestry with non Africans.

    While I agree that skin color has been under selective pressure, probably due to vitamin D. My understanding is vitamin D deficiency probably exerts selective pressure through problems with inadequate development of the pelvis in females and subsequent troubles with childbirth.

  2. Stan Hingston

    Thanks Peter. That jumped out at me too.

  3. Tom Weishaar

    Peter – Understood, and I knew I was pushing it when I wrote that. But the point I wanted to make was that in the end, can you really tease apart “mixed ancestry” and “evolution”? – Tom

  4. PeterVermont

    I think this was a good article in general and don’t want to be too negative but sometimes it is better to just admit an error. Yes you really can tease apart mixed ancestry from evolution.

    Evolution would be change in frequency of alleles in a population due to differential survive related to (at least some) of the alleles that changed frequency.

    Mixed ancestry is measurable by modern DNA testing.

    Here are the genetic estimates from: http://www.theroot.com/articles/history/2013/02/how_mixed_are_african_americans.2.html

    * According to Ancestry.com, the average African American is 65 percent sub-Saharan African, 29 percent European and 2 percent Native American.

    * According to 23andme.com, the average African American is 75 percent sub-Saharan African, 22 percent European and only 0.6 percent Native American.

    * According to Family Tree DNA.com, the average African American is 72.95 percent sub-Saharan African, 22.83 percent European and 1.7 percent Native American.

    * According to National Geographic’s Genographic Project, the average African American is 80 percent sub-Saharan African, 19 percent European and 1 percent Native American.

    * According to AfricanDNA, in which I am a partner with Family Tree DNA, the average African American is 79 percent sub-Saharan African, 19 percent European and 2 percent Native American.

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