"Everyone has skin, but nobody really talks about it," said Nina Jablonski. "Why do we have skin? What is unique about our skin? And why should we bother to take notice of it?"
These are just a few of the questions Jablonski answered at the Penn State Downtown Theatre on Wednesday at the first Research Unplugged event of the fall season.
Jablonski, professor and head of the department of anthropology at Penn State, led the conversation "More than skin deep: The culture and biology of the body's largest organ." She recently appeared on The Colbert Report and was featured in the New York Times for her book Skin: A Natural History. The attentive crowd of community members asked Jablonski about everything from the evolution of skin colors to the prevalence of skin cancer to why we get goosebumps.
"The basic structure of human skin is quite similar to the skin of cats and dogs and horses," Jablonski explained, "with the exception of a few key differences."
"While other animals have hair or fur, humans are functionally naked," said Jablonski. As it turns out, she noted, our nearly hairless skin has physiological significance. While our pets pant to lose body heat, we sweat. The evaporation of water from our skin's surface is essential to keeping us cool. "We come from a long lineage of efficient sweaters," she added.
"Over the course of human evolution, more sweat glands were needed to accommodate an increased range of activity," Jablonski said, noting that hairlessness became necessary for survival. "It's great if you can sweat, but it won't keep you cool to sweat into a blanket of matted, wet body hair."
Although losing body hair helped our equatorial African ancestors survive, it created another problem, noted Jablonski. Hairless skin without pigment—or color—is likely to burn. Ultraviolet light can destroy DNA that is essential for normal health and reproduction.
"It was at this time in our evolutionary history that we as a species became darkly pigmented," she explained. "Skin pigmentation not only protects against the dangerous effects of our environment, but it also regulates the amount of ultraviolet radiation absorbed into the body to produce Vitamin D." It's an interesting evolutionary equation, Jablonski noted, to filter the right amount of radiation.
Over the next million years, as our ancestors dispersed across the globe into Eastern Asia and eventually into Northern Europe—areas with less direct ultraviolet radiation—skin color underwent many changes.
"Vitamin D is an important part of the story," Jablonski reiterated. "We were forced to adapt to new environments and lose some pigmentation, which is why many of you in this room have lightly pigmented skin."
The discussion on hairlessness brought one audience member to question the invention of clothing and how human skin benefits from it. Jablonski said that clothing is our protection against the sun and "the normal bumps and grinds" that we encounter.
Jablonski noted that people who live in the tropics typically do not wear much clothing. "The presence of clothes inhibits sweat from evaporating," she said.
Another aspect of our skin is its exquisite sensitivity to touch, Jablonski remarked. "We use our skin to gather information about our environment through touch," she told the audience. "Touch is an essential part of physical development and physiological well-being." However, despite the fact that the human species innately loves to touch, we live in a touch-adverse society, she said, pointing out that many audience members were sitting with their arms folded across their chests. "If we were chimpanzees, we wouldn't be able to keep our hands off one another!" she joked.
Jablonski described another unique feature that sets human skin apart from that of other animals—our desire for decoration. "Your skin tells a lot about you," she said. "It immediately signals an observer about your age, how much sun exposure you've received, and what your likely ancestry is." Additionally, Jablonski continued, individuals use makeup, piercings, and tattoos as a form of expression. She said, "People think extremely carefully about these decorations because they want them to be symbols of themselves."
In response to a question about skin cancer, Jablonski explained that people descended from lightly-pigmented European ancestors "now go on vacations to Cabo San Lucas and northern Australia where they're exposed to more sunlight and sun damage," Jablonski warned. "We think we can avoid all these problems and fly around the world and just take a pill, and everything will be better. But we can't."
"Our skin absorbs a lot of environmental problems without us recognizing it consciously," Jablonski explained. "Skin cancer is just one reminder."
As she points out in her recent book, our skin is our most essential home: "Through our naked, sweaty, marked-up skin, we tell the world who we are."
Nina Jablonski, Ph. D., is professor and head of anthropology in the College of the Liberal Arts, firstname.lastname@example.org. Skin: A Natural History was published in October 2006 by University of California Press.