The Skinny on Skin
Aaron Dalton on the body's largest, and perhaps most mysterious, organ
A Natural History.
By Nina G. Jablonski.
Univ. of California Press. 266 pp. $24.95
If pleasure is the absence of pain, as Epicurus proposed, I might add that it is also the absence of itch. Such was my frame of mind as I approached Nina G. Jablonski’s treatise on skin while in the midst of a flare-up of seborrheic dermatitis. Dermatologists aren’t sure what causes this chronic skin condition or how to cure it, and so, since my teenage years, I have applied one cream and then another whenever my skin blooms with red, itchy patches.
The condition is an uncomfortable reminder of how mysterious a thing is the flexible body wrapper we call “skin,” which is, in fact, our largest organ. In this exhaustive treatment, Jablonski, an anthropology professor at Pennsylvania State University, traces skin’s evolution from a simple epidermis on early multicellular organisms to the complex layers that cover modern humans, composed of keratin proteins and melanocytes in our outer layer, the epidermis, and collagen fibers, nerves, blood vessels, and hair follicles in the dermis layer beneath. Along the way we also learn why snakes shed their skin (the individual scales cannot grow), why crocodile skin is so tough (it contains bones called ossifications), and why hippopotamuses have pink sweat (it acts as a sunscreen).
But Jablonski’s focus is the human animal and the link between our skin and our behavior. For example, she makes a strong case that after we evolved into bipedal creatures who moved around under the African sun, we lost most of our body hair to make our sweat-based cooling process more efficient. The hair that remains on the tops of our heads, she suggests, protects the scalp from ultraviolet radiation.
Indeed, the sun, in Jablonski’s estimation, has played an important role in our skin’s development. Human skin must protect the body from the harmful effects of ultraviolet radiation even as it uses that radiation to produce beneficial vitamin D. Darker-skinned peoples living in tropical areas that receive high amounts of ultraviolet radiation find an evolutionary advantage to having lots of melanin to protect them from solar radiation, despite the fact that melanin greatly slows vitamin D production. By contrast, lighter-skinned peoples in cooler climates, such as Scandinavia, where solar exposure is limited, run the sun-damage risks attendant upon their lower levels of melanin in order to produce as much vitamin D as possible.
Jablonski concludes with a look at what’s ahead for skin, exploring how gene therapy and collagen scaffolding may help treat psoriasis sufferers and burn patients, how people may bleach or tan their skin by deactivating or activating melanin production, and how pollution sensors and identification chips embedded beneath the skin could make us physically safer—though more vulnerable to invasions of privacy.
Jablonski is sometimes perfunctory, as in the too-few pages she devotes to our sense of touch and to the wear and tear that skin endures. She’s at her best when she plays to her strengths as an anthropologist, for example, in her persuasive later chapters on the various ways humans have modified their skin to express themselves—piercing it, tattooing it, scarring it, painting it, and injecting it with Botox.
I grew up listening to my chemist father chide my sister for applying eye shadow because it contained suspected carcinogens that could be easily absorbed through the skin. And he opposed piercing and tattooing less for aesthetic reasons than because such epidermal embellishments compromise the body’s natural barrier against the hostile outside world. Like many fathers before him, however, he was railing against ancient, powerful desires. The frozen body of a late-Neolithic man, recovered from a glacier in 1991, shows that the practice of tattooing dates back at least 5,000 years.