Origins of the Human Rainbow

The conflicts and divisiveness over skin color stretches across recorded history. Yet, the irony is the variations in skin colors is a recent evolutionary development.

Humans didn't develop different skin tones until fifty to one hundred thousand years ago — when modern man migrated northward out of Africa. That is when skin color began to lighten.

For years, scientists believed evolutionary pressures produced lighter skin because in these higher latitudes the sun is less intense. Given the same amount of sun exposure, lighter skin will produce more vitamin D compared to darker skin.

That is super important since Vitamin D is vital to bone growth and maintenance. Plus the nutrient also protects us against a number of other diseases. But it is possible some other evolutionary pressures were at work.

One idea is sexual selection, which argues that males preferred women with pale skin — a sign of youth and fertility. Lighter skin is also a feature of the early infant stage which may have induced less aggression and more protection.

Of course there are no ancient statistics or health records to verify either of these hypotheses.

Another idea has to do with the dangers of cold weather. Data from soldiers of the Korean War suggest dark skin is more susceptible to frostbite than pale skin, since it emits more heat. So the cold may have negatively selected against dark skin, but again, there's little data to support this.

Though many ideas continue to be explored, the most likely explanation for the development of lighter skin tones is Vitamin D production. People with dark skin need sun exposure six times longer than light skinned people to make the same amount of vitamin D.

As for the rainbow of human skin colors we see today - it's likely many factors made that happen.