Scientists Don't Yet Know What Causes White Skin

Humans come in a variety of colors, from the darkest brown and black to the most translucent white, but evolutionary biologists don't know yet why these hues appeared, between 100,000 and 50,000 years ago. Their evolution is relatively short-lived, in that, for the largest part of human history, people were of only one color. Numerous theories have appeared over the years, attempting to explain these differences, but they've all come up short on covering all aspects of the problem, LiveScience reports.

One of the theories that is more widely tolerated states that vitamin D was the main driver of the color change. People living at higher latitudes experienced a lot less sunlight than those living near the Equator and the Tropics, so their skin became of a lighter shade. The original human had a darker, browner skin color, anthropologists say. However, a new scientific study seems to suggest that other factors may have been at work in dictating this shift. Other ideas hold that even mating habits of early humans may have had a saying in this evolution.

“In our opinion the vitamin D hypothesis is one of the most likely hypotheses responsible for skin lightening, although there still is no consensus about it,” Asta Juzeniene, an expert at the Oslo University Hospital, in Oslo, Norway, says. The scientist is also the author of the new study, published in the August issue of the respected Journal of Photochemistry and Photobiology B: Biology. According to the paper, several evolutionary factors contributed to skin-hue change, as latitudes increased.

Mating rituals may have been important, Juzeniene says. “One of the hypotheses is that men seem to prefer women with a light skin color, which can be regarded as a sign of youth and fertility. Because light skin characterizes the early infant stage of primates, it may have become a visual cue that triggers appropriate adult behavior toward infants, i.e. decreased aggressiveness and increased desire to provide care and protection,” she reveals. This may have been especially true at higher latitudes.

“Development of agriculture has occurred in several places, and did not necessarily lead to skin lightening if the ambient UVB [ultraviolet light from the sun] level was sufficiently high to allow adequate vitamin D synthesis. Cold climates and high latitudes would speed up the need for skin lightening,” the expert concludes, adding that even this occupation, which is not very old in human history, may have also contributed to specific skin colors.