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The Evolution of Skin


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Biological anthropologist Nina Jablonski reveals the unique history behind skin at May's SciCafe. © Heidi Lewis

Skin is the body’s largest organ, and one with a complex cultural and evolutionary past. At the upcoming SciCafe on Wednesday, May 2, biological anthropologist Nina Jablonskiwill discuss how human skin evolved, particularly as an adaptation to ultraviolet radiation. She recently answered a few questions about skin and its role in our lives.

When did you decide to study the history of human skin?

Nina Jablonski: By accident. About 23 years ago, a colleague asked me to give a lecture to his class about skin because he was going to be out of town for a conference. I obliged. In preparing for the lecture, I realized just how little had been written about the evolution and meaning of human skin.

Why is human skin unique?

Jablonski: The “primary uniqueness” of human skin is that it is mostly hairless. Because of this, the skin itself, rather than hair covering it, is the body’s main protection against physical assault. Many of the most important and distinctive attributes of skin are consequences of hairlessness. Our mostly hairless skin is tough, colorful, and available for deliberate decoration.

How do climate and geographical location affect skin color?

Jablonski: Skin color is closely related to intensity of ultraviolet radiation, or UVR. Higher concentrations of melanin pigment are protective against high levels of UVR. Lower levels of melanin are an adaptation to lower UVR. Modern humans evolved in equatorial Africa over 120,000 years ago, and our original skin color was dark. As humans dispersed outside of equatorial latitudes beginning around 80,000 years ago, populations entering the highest latitudes with the lowest UVR underwent genetic changes leading to loss of pigmentation.

Is human skin still evolving?

Jablonski: It may still be evolving, but not at the same rate it did earlier in our history. Modern humans use mostly cultural means like clothing and shelters to protect themselves from extremes of sunlight and temperature. Our skin is no longer under the environmental stress that it was, say, 50,000 years ago.

What effect are modern indoor lifestyles having on our skin?

Jablonski: The biggest effect that modern lifestyles have on us is the slowing or prevention of vitamin D production in the skin. Most people today live in cities and are protected from the UVR that starts the process of vitamin D production in skin. As a result, many people are deficient in this important vitamin.

What’s the most misunderstood thing about human skin?

Jablonski: People generally don’t appreciate just how much their skin does for them, in being a protective covering, a biochemical factory, and a canvas for self-expression.

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