As people move more often and become more urbanised, skin colour may lose some of its evolutionary advantage, according to a Penn State anthropologist.
Approximately 2 million years ago, permanent dark skin colour imparted by the pigment melanin, began to evolve in humans to regulate the body’s reaction to UV rays from the sun, said Nina Jablonski, Distinguished Professor of Anthropology.
Melanin helped humans maintain the delicate balance between too much sunlight and not enough sunlight. The pigment allowed enough UV radiation to produce vitamin D, a vitamin that helps the body absorb calcium, while protecting the skin from the intense UV radiation in the equator. Too much sunlight can cause the destruction of folate, which is also critical to
As some humans moved away from the equator to places where the sun’s rays are not nearly as intense, they lost pigmentation, said Jablonski, who reported on her research at the annual meeting of the American Association for the Advancement of Science in Boston.
Unlike their ancestors, modern humans are more mobile. A person with darker skin may move to regions with less intense sunlight, and those with less pigmentation may move to areas that are closer to the equator.
In addition to moving regularly, most people now live in cities with limited exposure to the sun. Nearly 60% of the people in the world live in cities now, said Jablonski. Most people who live in cities also work indoors, further reducing their ability to make enough vitamin D in their skin. Health problems are compounded when people do not receive enough sunlight, or when they have a mismatch between their skin pigmentation and UV radiation.
In earlier studies, researchers found that early humans had pinkish skin that was covered with black fur, much like today’s chimpanzees. The fur acted as a sunscreen. However, following the loss of body hair — which helped the early humans stay active without overheating — permanent dark pigmentation became a crucial evolutionary tool to manage exposure to ultraviolet rays.
By studying patterns of pigmentation and the amount of ultraviolet rays, Jablonski found that skin colour was an example of natural selection at work to protect the skin from the sun.