These changes in skin colour were due to mutations in genes controlling the skin’s production of melanin, a group of pigments that are widespread among animals. Generally, the more melanin a person produces, the darker the skin colour. Some mutations in skin colour genes became common because they helped people adapt to new environments through a process called natural selection.

Change in skin colour is one of the best examples of natural selection in humans. Skin colour is an adaptation to the intensity of ultra-violet radiation (UVR) from sunlight in different parts of the world.

Darker skin colour protects against the strong UVR of equatorial regions. Specifically, darker skin protects the body’s supply of folate, a substance essential to the normal embryonic development of the brain and spinal cord, among other body processes.

Progressively lighter skin colours are found in people who live further away from the equator because they need some UVR for their body to produce Vitamin D, a nutrient that is essential for strong bones. Without enough Vitamin D, a person can develop osteoporosis and rickets.

So, we can see that skin colour balances the body’s need to protect folate with its need to synthesise Vitamin D. Today, of course, we have other ways to meet these needs, including the use of sun-screening skin lotions or Vitamin D supplements in the diet.

Most importantly, skin colour is an adaptation to different levels of UV radiation. Because the geographic distribution of UV radiation generally forms a continuum without sharp breaks, so too does skin colour. This means that it is not possible to meaningfully divide people into categories or “races” based on skin colour. And, of course, the genes controlling skin colour have nothing to do with a person’s capabilities or character.

Dig Deeper

Skin Colour and Ultraviolet Radiation

Skin colour differences reflect adaptations to the intensity of ultraviolet radiation (UVR), which is effected mainly by latitude, but also cloud cover, altitude and other factors. Below are two maps showing the global distributions of UVR and predicted skin colours, based on research published by Dr. George Chaplin in 2004 entitled “Geographic distribution of environmental factors influencing human skin coloration.”

American Journal of Physical Anthropology, 125(3), 292-302. doi:10.1002/ajpa.10263

More About Human Skin Colour

Prof. Nina Jablonski, an anthropologist and world expert on skin colour, aptly states that “perhaps no other feature of the human body has more meaning” than skin colour. Nina has written two must-read books describing cultural and biological perspectives on skin colour. These are:

Skin: A Natural History, Berkeley: University of California Press (2006),

Living Color: The Biological and Social Meaning of Skin Color, Berkeley: University of California Press (2012).

Map of the intensity of autumnal ultraviolet radiation (UVR), which is highly correlated with skin colour. The most intense UVR (red and purple) is found near the Equator. Image courtesy of George Chaplin.

Predicted distribution of human skin colors based primarily on the intensity of ultraviolet radiation from sunlight. The actual skin colors of indigenous peoples matches predicted colors extremely well. Image courtesy of George Chaplin.