Skin color is one of humankind’s most important physical traits, because it affects so many aspects of our health and social well-being. It is also one of the most interesting attributes to study because of its dynamic evolutionary history and its cultural transformation, in recent times, into a determinant of human interactions and destinies. So why don’t more people, especially scientists and educators, talk about it?
Skin color is one of the most actively avoided topics in polite conversation, and it effectively doesn’t exist as a topic of instruction or discussion in most classrooms. Recently, before I began a lecture to an audience of middle- and high-school teachers from a major urban public-school system, I asked the teachers how often each week they formally introduced issues related to race, including skin color, into classroom lessons. I also asked how many times per week kids in their classes raised questions...
Skin color is one of the best examples of evolution by natural selection acting on the human body. Thanks to research on the physiology of different skin-color phenotypes and on the genetic basis of skin pigmentation, we know two important facts; that the earliest Homo sapiens had dark skin, rich in protective melanin and that as small groups of modern humans dispersed out of the African tropics into less intensely sunny parts of Africa and Eurasia and into profoundly gloomy reaches of the Northern Hemisphere, they underwent genetic changes leading to the loss of melanin pigmentation.
Melanin-rich skin protects against the manifold harmful effects of ultraviolet radiation (UVR), and the African environments in which we evolved experienced high levels of UVR year-round. Among darkly pigmented African people today, little genetic variation occurs in MC1R, the primary pigmentation gene responsible for this protection, because a built-in defense against strong sun has been so important to health and normal reproduction. Lightly or moderately pigmented skin is actually depigmented skin, made so by genetic mutations which determine how much melanin is produced and packaged in skin cells. Depigmentation evolved at least twice in Homo sapiens’s history, as populations dispersed out of Africa. Repigmentation, including the evolution of enhanced tanning abilities, occurred at least as many times as populations spread into places with intense UVR, such as central India, Melanesia, and the Neotropics. Human skin pigmentation can be described as a marvelous demonstration of a labile trait.
But in the last few thousand years, and especially in the last few centuries, people have moved, voluntarily or otherwise, into places far removed from their ancestral homelands and solar regimes, and many are reaping the sad rewards of the mismatch.
People of northern European ancestry, for instance, living in Florida or Australia confront intense UVR conditions with pale, melanin-poor skin and suffer from sunburns, high rates of skin cancer, and accelerated skin aging. People of central African or southern Indian ancestry living in Wisconsin or Wales face low and highly seasonal UVR conditions with exquisitely sun-protected skin and suffer from vitamin D deficiencies as a result.
Fortunately, these problems are easy to understand and will be easy to treat once education about skin pigmentation and its relationship to health becomes more widespread. Social injustices that result from peoples of different colors meeting each other suddenly and on an unequal social footing are far more intractable. The association of skin color with human worth was probably humanity’s most perfidious myth and has proven to be its most persistent meme. It is now time to examine it and thoroughly overturn it.
Nina G. Jablonski is Distinguished Professor of Anthropology at Pennsylvania State University and spends most of her time thinking about human and primate evolution. She is the recipient of a 2012 Guggenheim Fellowship. Read an excerpt from Living Color: The Biological and Social Meaning of Skin Color.