The Color of Our Skin from a Biologist’s Perspective

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Photograph by Sarah Leen from National Geographic http://science.nationalgeographic.com/science/enlarge/skin-colors.html                                 “Students from the Washington International Primary School in Washington, D.C., form a human rainbow of skin coloration. Melanin, a pigment, determines the color of skin and protects humans from the sun’s ultraviolet rays. “

Current Race Clashes

With clashes continuing in the United States between White supremacists and those fighting against racial inequality, I wanted to respond from a biologist’s point of view. The color of the skin is a result of biology, a difference in the amount of melanin in layers of epithelial tissue. We know some of the reasons for these differences and continue to learn more about the genetics of skin color. It is only very minor variances in the DNA between persons of light or dark skin that make them different. We share more similarities than we do differences.

The Biology of Brown

Darker skin is caused by high amounts of a pigment called melanin in the skin layers. Evidence indicates that our very first Homo sapiens ancestors were African and dark-skinned. The melanin protected them from the sun’s destruction of folate, a B vitamin, through the skin. Folate is required for embryo development and healthy sperm production. Those first ancestors were able to thrive because of their dark skin.

Foalte
The melanin in dark skin protects folate, a necessary B vitamin, from destruction by the sun’s UV rays.  Light skin does not have this protection.

As human populations increased and people migrated away from equatorial to temperate regions, the dark skin was a detriment. While too much sunlight destroys folate, on the other hand, it is required for vitamin D production by the skin. The lesser sunlight in temperate latitudes could not penetrate the protective melanin, and this would have caused vitamin D deficiencies. Vitamin D is required for proper calcium metabolism. Without it, a growing baby in the womb could not develop a skeleton, and a lactating mother would not be able to produce calcium-rich milk. So children born with lighter skin would have survived better than their darker skinned brothers. Over generations, light skin would become common in regions away from the equator.

Vitamin D
Vitamin D is made in the skin using the sun’s UV rays. Enough direct sunlight can penetrate dark skin to make required vitamin D. However, if the sunlight is indirect, as in temperate latitudes, then UV rays cannot penetrate the melanin and vitamin D is not produced. Light skin allows enough indirect sunlight through to make vitamin D.

A child born with lighter skin would be the result of mutations in genes responsible for making melanin. Our African ancestors would have functional genes to make melanin. Mutations, or minor changes, in the DNA would result in lighter skin. We know about several of these genes: MRCA1, KITLG, and SLC24A5. People with dark skin have these genes working and pumping out functional melanin. People with lighter skin have one or more mutant, non-functioning genes, so the amount of melanin is lower. Without these mutations, a person with white skin would be as ebony as his African cousin.

Mutations.jpg
Mutations are mistakes made in sections of DNA. A mutation can cause a gene to be non-functional. This is the case in several genes responsible for the production and distribution of melanin in the skin. If mutated, the genes are broken and cannot produce the pigment, resulting in lighter skin.

From a biologist’s point of view, skin color is just an adaptation that showed up long ago to help people survive in different environments. Biologically, skin color has little to do with survival in our modern age. A person of color can thrive in a temperate region like Oregon where his melanin inhibits vitamin D production just by taking a vitamin supplement. A person with fair skin can live just fine in Arizona where her skin has no protection from the UV rays by wearing clothes or sunscreen. When she wants to get pregnant, she can take folate supplements to over-come folate breakdown by the sun. We no longer depend on skin color to thrive in different environments.

Conclusion

So biologically, skin color no longer limits where we live and thrive. All of us, red or yellow or black or white, we came from the same ancestors, so are genetic cousins. A White supremacist’s hate is directed towards his own family. He is a mutant with broken genes. If these genes were repaired, he would be as dark as the one he hates. It is my hope that we can see that these genes are only a small difference between us, literally only skin deep. The vast similarities we share genetically, anatomically, and physiologically far outweigh the differences in these few genes.

One thought on “The Color of Our Skin from a Biologist’s Perspective

  1. Nice, also people with darker skin don’t look so ghastly under fluorescent light. Melanin synthesis is a tryrosinase pathway that’s still being explored, also the degradation pathways are not entirely clear.

    Like

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