The History of Skin

NYTimes
January 9, 2007
A Conversation With Nina G. Jablonski
Always Revealing, Human Skin Is an Anthropologist’s Map
By CLAUDIA DREIFUS

In an era of academic hyper-specialization, Dr. Nina G. Jablonski has an amazingly broad résumé. At 53, she heads the anthropology department at Pennsylvania State University. She’s also a primatologist, an evolutionary biologist and a paleontologist.

Last year, Dr. Jablonski led an expedition to China, where she dug for human fossils in an attempt to learn how early man coped with climate change. This month, she’s in Kenya, where she and Meave Leakey are putting together a study on prehistoric monkeys.

For more than a decade, Dr. Jablonski has been trying to get her arms around a ubiquitous and yet mysterious topic: the biology, evolution and social function of human skin. The results of her studies have been published by the University of California Press as “Skin: A Natural History.”

“Skin has been studied to absolute death by dermatologists,” Dr. Jablonski said jokingly during a recent visit to New York City. “They know it inside and out from the point of view of diseases that afflict it. What we wanted to learn was how human skin came to be as it is and what that meant for humanity.”

Q. What set you off on writing a natural history of human skin?

A. I had an insight in 1981, when I was teaching gross anatomy to medical students at the University of Hong Kong. The students had been presented with a cadaver to dissect, and they were tremendously frightened of it. However, their attitude changed the very moment they cut through the skin. With the skin gone, they began seeing it as a mere body devoid of a personal history, and they could get on with their work.

That moment showed me how much of what we consider our humanity is imbued in our skin. It stayed with me for a long time. Then about 15 years ago, I joined a project studying the natural history of skin color. The topic was so engrossing that I began looking into the larger question of what our skin does and is.

Q. And what have you found?

A. That skin is the most underappreciated of our organs. Unless we’re having the sort of problem that brings us to a dermatologist, we take our skin for granted. We never think of it as working very hard for our body or doing valuable things for us socially.

But when you really start thinking about it, it’s a factory that produces vitamin D, sweat, hormones, oils, wax, pigments — substances we need. Skin is a raincoat in that it protects us from water, bugs and noxious chemicals. It’s also a billboard which we adorn with powder, tattoos, piercing and scars to give off instant messages about our history, health, values and availability for mating.

On an evolutionary level, there are three remarkable facts about skin. It comes in colors, of course. Compared to other mammals, our skin is relatively hairless. And it’s sweaty. In the last few million years, humans became the sweatiest of mammals.

Q. Is that important?

A. Absolutely. It’s often said that our large brains are what made it possible for us to evolve from ape to human. But those big brains could never have developed if we didn’t have exceptionally sweaty skin.

It happened this way. There was a tremendous takeoff in human evolution about two million years ago when primates who could no longer be called apes appeared in the savannahs of East Africa. These early humans ran long distances in open areas. In order to survive in the equatorial sun, they needed to cool their brains. Early humans evolved an increased number of sweat glands for that purpose, which in turn permitted their brain size to expand. As soon as we developed larger brains, our planning capacity increased, and this allowed people to disperse out of Africa. There’s fossil evidence of humans appearing in Central Asia around this time.

Q. In a nutshell, what has your research shown about why humans have varying skin colors?

A. That it’s not about race — it’s about sun and about how close our ancestors lived to the Equator. Skin color is what regulates our body’s reaction to the sun and its rays. Dark skin evolved to protect the body from excessive sun rays. Light skin evolved when people migrated away from the Equator and needed to make vitamin D in their skin. To do that, they had to lose pigment. Repeatedly over history, many people moved dark to light and light to dark. That shows that color is not a permanent trait.

Q. Did early humans decorate their skin?

A. We don’t know. There’s no human skin in the fossil record. The oldest preserved skin we have is that of Ötzi, the Neolithic iceman whose mummified body was found in the Alps in 1991. Ötzi lived about 5,000 years ago. Interestingly, he has tattoos. But we can only guess what they mean.

Modern humans, we love to alter our skin. You’ll find very few people walking around today with unadorned skin. They might make permanent changes — piercing, scarring, tattooing — to memorialize events and announce their identity. Or they might use cosmetics for temporary alterations to announce their attractiveness, mood or sexual availability. The bottom line: humans are the self-decorating ape.

Q. I get the feeling that you think cosmetic use is some kind of ancient evolutionary behavior. Are we reading you correctly?

A. Evolution is all about attracting a mate and getting a chance to reproduce, so yes, makeup helps with that. When a woman uses eyeliner to make her eyes appear larger, she’s giving off a message: “I want you to see me as attractive.” Large eyes in a woman are almost universally seen as appealing. This is not just a girl thing. Male body paint in East Africa emphasizes forbidding facial expressions. They announce a man’s prowess as a warrior and as a mate.

Q. How do you feel about your own skin?

A. I like it. It is my unwritten biography. My skin reminds me that I’m a 53-year-old woman who has smiled and furrowed her brow and, on occasion, worked in the desert sun too long. I enjoy watching my skin change because it’s one of the few parts of my body that I can watch. We can’t view our livers or heart, but this we can. And yes, I use cosmetics. Like other humans, I have a penchant for changing my appearance easily and quickly. It also helps me feel more confident. That may seem silly, but I still do it.

Q. You made news in 2004 when you discovered the world’s oldest chimpanzee fossil. These were chimp teeth about a half-million years old. Where did you find them?

A. In a drawer at the National Museum of Kenya in Nairobi. I was rummaging through this bag labeled “fossil monkeys” and I saw it. “This doesn’t look like monkey,” I thought. It turned out they were from an early chimp. That find proved important because there had been no chimpanzee this old in the fossil record. By analyzing it, we’ve learned that chimpanzees in their current form have probably existed for longer than previously thought. (Laughs) Since my find, people have been rummaging through dusty museum drawers everywhere!