From rich brown to almost translucent white, human skin colors span a remarkable spectrum.
The evolutionary story of how we came to be such a varied species skin color-wise began around 40,000 years ago when the human groups that had left Africa and spread out along the southern coast of Asia began to move north.
When people lived near the equator, greater concentrations of the pigment melanin in their skin, hair and eyes acted as a natural sunblock to protect them from high levels of cancer-causing ultraviolet radiation. But melanin also reduces the body’s production of vitamin D, which is stimulated by ultraviolet radiation. At higher latitudes, where vitamin D deficiency is more of a survival issue than skin cancer, genetic changes that reduced melanin production were favored by natural selection.
Although the overall theory of how non-African populations came to lose some of their color is pretty well accepted, there is still a lot to learn about the details.
Much of the research has focused on European populations. Now a new study, published recently in the journal PLoS Genetics, has identified a DNA variant involved in pigmentation that is specific to East Asian populations.
Scientists led by Esteban Parra of the University of Toronto focused their search for determinants of different shades of East Asian skin color on 10 SNPs in five genes already known to be involved in pigmentation. They analyzed the DNA of 122 people with East Asian ancestry living in Canada, and combined the genetic information with quantitative measurements of skin color.
The scientists found a variant associated with a 1.3 melanin unit reduction in skin pigmentation.
Although this is a small difference (variations associated with pigmentation identified in other populations have had effects of around 3 melanin units per copy), the researchers calculate that this SNP accounts for 9% of the variation in skin color seen in the study population.
The researchers replicated their finding of an association of with skin pigmentation in a group of 207 Han Chinese people living in China, although the effect of the variation, and the percent of the variability in skin color explained, was somewhat smaller.
Genetic evidence has previously suggested that the transition from melanin-rich to melanin-poor skin took place independently in the groups that would eventually become the populations we now call European and East Asian. The current study further supports this idea of “convergent evolution.” is in OCA2, a gene that has also been associated with pigmentation in European populations.
The variations associated with lighter skin in Europeans are not found in East Asians, however, and the C version of has not been found in Europeans.
Further research in diverse groups will be needed to understand exactly how human pigmentation has evolved around the world, and when in our history these changes took place.
